Materials

2024

Jump to: 2023, 2022, 2021, 2020

22 pages, 10976 KiB

Open AccessArticle

Concrete Defect Localization Based on Multilevel Convolutional Neural Networks

by Yameng Wang, Lihua Wang, Wenjing Ye, Fengyi Zhang, Yongdong Pan and Yan Li

Materials 2024, 17(15), 3685; https://doi.org/10.3390/ma17153685 - 25 Jul 2024

Viewed by 601

Abstract

Concrete structures frequently manifest diverse defects throughout their manufacturing and usage processes due to factors such as design, construction, environmental conditions and distress mechanisms. In this paper, a multilevel convolutional neural network (CNN) combined with array ultrasonic testing (AUT) is proposed for identifying [...] Read more.

Concrete structures frequently manifest diverse defects throughout their manufacturing and usage processes due to factors such as design, construction, environmental conditions and distress mechanisms. In this paper, a multilevel convolutional neural network (CNN) combined with array ultrasonic testing (AUT) is proposed for identifying the locations of hole defects in concrete structures. By refining the detection area layer by layer, AUT is used to collect ultrasonic signals containing hole defect information, and the original echo signal is input to CNN for the classification of hole locations. The advantage of the proposed method is that the corresponding defect location information can be obtained directly from the input ultrasonic signal without manual discrimination. It effectively addresses the issue of traditional methods being insufficiently accurate when dealing with complex structures or hidden defects. The analysis process is as follows. First, COMSOL-Multiphysics finite element software is utilized to simulate the AUT detection process and generate a large amount of ultrasonic echo data. Next, the extracted signal data are trained and learned using the proposed multilevel CNN approach to achieve progressive localization of internal structural defects. Afterwards, a comparative analysis is conducted between the proposed multilevel CNN method and traditional CNN approaches. The results show that the defect localization accuracy of the proposed multilevel CNN approach improved from 85.38% to 95.27% compared to traditional CNN methods. Furthermore, the computation time required for this process is reduced, indicating that the method not only achieves higher recognition precision but also operates with greater efficiency. Finally, a simple experimental verification is conducted; the results show that this method has strong robustness in recognizing noisy ultrasonic signals, provides effective solutions, and can be used as a reference for future defect detection. Full article

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17 pages, 6297 KiB

Open AccessArticle

Investigation of Physical-Mechanical Properties and Microstructure of Mortars with Perlite and Thermal-Treated Materials

by Nastasia Saca, Lidia Radu, Stefania Stoleriu, Daniela Dobre, Răzvan Calotă and Roxana Truşcă

Materials 2024, 17(14), 3412; https://doi.org/10.3390/ma17143412 - 10 Jul 2024

Viewed by 637

Abstract

This study aimed to obtain and characterize a mortar with perlite aggregate and thermal-treated materials that could substitute for Portland cement. First, the thermally treated materials were obtained by calcinating old Portland cement (OC-tt) and concrete demolition waste (CC-tt) at 550 °C, for [...] Read more.

This study aimed to obtain and characterize a mortar with perlite aggregate and thermal-treated materials that could substitute for Portland cement. First, the thermally treated materials were obtained by calcinating old Portland cement (OC-tt) and concrete demolition waste (CC-tt) at 550 °C, for 3 h. Second, plastic mortars with a perlite: cement volume ratio of 3:1 were prepared and tested for water absorption, mechanical strength, and thermal conductivity. The microstructure was also analyzed. Portland cement (R) was partially substituted with 10%, 30%, and 50% OC-tt. Thermal-treated materials negatively influenced the compressive and flexural strengths at 7 and 28 days. With an increase in the substitution percentage to 50%, the decrease in the compressive strength was 40% for OC-tt and 62.5% for CC-tt. The presence of 10% OC-tt/CC-tt positively influenced the water absorption. The thermal conductivity of the tested mortars was in the range of 0.37–0.48 W/m·K. SEM analysis shows the expanded perlite pores remained unbroken. Full article

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27 pages, 13596 KiB

Open AccessArticle

Reinforcement Effects on Tensile Behavior of Ultra-High-Performance Concrete (UHPC) with Low Steel Fiber Volume Fractions

by Xianzhi Luo, Sumei Zhang, Aidong Li, Chenming Zhang and Yuchen Zhang

Materials 2024, 17(10), 2418; https://doi.org/10.3390/ma17102418 - 17 May 2024

Viewed by 708

Abstract

Ultra-high-performance concrete (UHPC) with a low steel fiber volume fraction offers lower material costs than UHPC with typical steel fiber volume fractions, and has the potential to mitigate the ductility degradation of rebar-reinforced UHPC (R-UHPC). This study explores the reinforcement effect on the [...] Read more.

Ultra-high-performance concrete (UHPC) with a low steel fiber volume fraction offers lower material costs than UHPC with typical steel fiber volume fractions, and has the potential to mitigate the ductility degradation of rebar-reinforced UHPC (R-UHPC). This study explores the reinforcement effect on the tensile behavior of UHPC with a low fiber volume fraction with the aim of facilitating more cost-efficient UHPC applications. The axial tensile behavior of 30 UHPC specimens with low fiber volume fractions at different reinforcement ratios was tested through direct tensile tests. The findings indicate that adopting UHPC with a low fiber volume fraction can significantly mitigate the ductility deterioration of rebar-reinforced UHPC (R-UHPC), and both increasing the reinforcement ratio and decreasing the fiber volume fraction contribute to the improvement in ductility. The failure modes of R-UHPC are determined by the ratio of reinforcement ratio and fiber volume fraction, rather than a single parameter, which also means that R-UHPC with different parameters may correspond to different methods to predict tensile load-bearing capacity. For UHPC with a fiber volume fraction low to 0.5%, incorporating steel rebars gives superior multi-crack cracking behavior and excellent capacity to restrict the maximum crack width. Increasing the fiber volume fraction from 0.5% to 1.0% at the same reinforcement ratio will yield little benefit other than an increase in tensile load-bearing capacity. Full article

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18 pages, 9946 KiB

Open AccessArticle

Seismic Damage and Behavior Assessment of Drift-Hardening Concrete Walls Reinforced by LBUHS Bars

by Jiayu Che, Bunka Son and Yuping Sun

Materials 2024, 17(9), 2070; https://doi.org/10.3390/ma17092070 - 28 Apr 2024

Viewed by 668

Abstract

This paper experimentally and analytically investigated the damage and seismic behavior of concrete walls reinforced by low-bond ultra-high-strength (LBUHS) bars. To this end, four half-scale rectangular concrete walls were fabricated and tested under reversed cyclic loading and constant axial compression. The test variables [...] Read more.

This paper experimentally and analytically investigated the damage and seismic behavior of concrete walls reinforced by low-bond ultra-high-strength (LBUHS) bars. To this end, four half-scale rectangular concrete walls were fabricated and tested under reversed cyclic loading and constant axial compression. The test variables were the shear span ratio and the axial load ratio. Based on the test results, the propagation of cracks on the wall surface, the maximum strain capacity of concrete, the hysteresis loops and envelope curves, the residual drifts, and the strain distributions of LBUHS rebars were presented and discussed. The experimental results showed that all the test walls could exhibit drift-hardening capability until at least a 2.0% drift ratio if LBUHS rebars were anchored by nuts at their ends. The test results also indicated that the maximum strain capacity of concrete was above 0.86%, much larger than the currently recommended 0.4%. After unloading from the transient drift ratios of 2.0% and 2.5% for the walls with shear span ratios of 1.5 and 2.0, respectively, the measured residual drift ratios were controlled below 0.4%, which is less than the critical drift ratio (0.5%) having 98% repairable probability recommended in the FEMA document (P-58) for general concrete structures. Furthermore, a numerical method was presented to evaluate the cyclic response of the test walls, and a comparison between the experimental and the calculated results verified the reliability and accuracy of the proposed numerical method. Full article

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18 pages, 19766 KiB

Open AccessArticle

Effect of Mineral Powders on the Properties of Foam Concrete Prepared by Cationic and Anionic Surfactants as Foaming Agents

by Qi Liu, Huanghua Chen, Shiyu Fang and Jin Luo

Materials 2024, 17(3), 606; https://doi.org/10.3390/ma17030606 - 26 Jan 2024

Cited by 1 | Viewed by 1035

Abstract

Foam concrete is a type of cement mortar in which air bubbles are introduced using an appropriate foaming agent. The complex conditions for the preparation of solid particle stabilized foams limit their wide application in construction. In this study, a method of adding [...] Read more.

Foam concrete is a type of cement mortar in which air bubbles are introduced using an appropriate foaming agent. The complex conditions for the preparation of solid particle stabilized foams limit their wide application in construction. In this study, a method of adding small amounts of calcite (Cal) and muscovite (Mus) to the cement paste matrix is proposed to improve the properties of foam concrete prepared with cationic and anionic surfactants as foaming agents. The effects of mineral powders on the flowability, compressive strength, water absorption, pore characteristics, thermal conductivity and frost resistance of foam concrete were investigated and the enhancement mechanism was revealed by the results of XRD, low-field nuclear magnetic resonance (LF-NMR), Fourier transform infrared spectroscopy (FTIR) and SEM. The results showed that the mineral powders interacted with anionic and cationic surfactants through physical adsorption. Whether anionic or cationic surfactants were used as foaming agents, the addition of mineral powders promoted the formation of shell-like structures around the foam, thus enhancing the performance of foam concrete. As a result, the fluidity, compressive strength and frost resistance of the foam concrete increased, the water absorption and thermal conductivity decreased, and the average size of the pores decreased. Full article

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20 pages, 11018 KiB

Open AccessArticle

Influence of Service Conditions and Mix Design on the Physical–Mechanical Properties of Roller-Compacted Concrete for Pavement

by Julián Pulecio-Díaz, Miguel Sol-Sánchez and Fernando Moreno-Navarro

Materials 2024, 17(3), 552; https://doi.org/10.3390/ma17030552 - 23 Jan 2024

Viewed by 1365

Abstract

This research focuses on the behavior of roller-compacted concrete (RCC) used in pavements, which are prone to deterioration affecting their performance. These deteriorations result from various causes, including traffic load, errors during construction, mix design, and ambient conditions. Among these, ambient conditions could [...] Read more.

This research focuses on the behavior of roller-compacted concrete (RCC) used in pavements, which are prone to deterioration affecting their performance. These deteriorations result from various causes, including traffic load, errors during construction, mix design, and ambient conditions. Among these, ambient conditions could lead to a marked variable impact on material behavior and durability depending on the conditions associated with each region. Accordingly, this study aims to deepen the understanding of the effect, which a broader range of ambient conditions and different mix designs have on the physical and mechanical properties of RCC. Measurements such as the amount of water vapor per kilogram of air were used to apply the findings comprehensively. The RCC analysis encompassed experimentation with different compositions, altering the cement water ratio amount, and adding a superplasticizer. The impact of curing on the materials was evaluated before subjecting them to various humidity and temperature conditions. Laboratory tests were conducted to measure performance, including moisture, shrinkage, compressive strength, and the progression of flexural fracture resistance over curing periods of up to 90 days. The results revealed a logarithmic correlation between shrinkage and ambient humidity, which is the most determining factor in performance. Mix optimization through increased cement and reduced water enhanced the tensile strength of the material. Furthermore, the curing process was confirmed to increase resistance to shrinkage, especially in the long term, establishing it as a crucial element for the structural stability of RCC, which is relatively insensitive to variations in ambient conditions. Full article

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19 pages, 5810 KiB

Open AccessArticle

Prediction of the Physical-Mechanical Properties of Roller-Compacted Concrete Pavements under Different Service and Mix Conditions Based on Cement and Water Content

by Julián Pulecio-Díaz, Miguel Sol-Sánchez and Fernando Moreno-Navarro

Materials 2024, 17(3), 549; https://doi.org/10.3390/ma17030549 - 23 Jan 2024

Viewed by 897

Abstract

Roller-compacted concrete (RCC) for pavements has experienced problems with its physical-mechanical performance over extended periods due to ambient and in situ curing conditions. Accordingly, this study aimed to present multiple regression equations for calculating the physical-mechanical properties of RCC for pavements under different [...] Read more.

Roller-compacted concrete (RCC) for pavements has experienced problems with its physical-mechanical performance over extended periods due to ambient and in situ curing conditions. Accordingly, this study aimed to present multiple regression equations for calculating the physical-mechanical properties of RCC for pavements under different service and mix conditions. For this purpose, the research included two cement and two water contents, one reduced with admixture, and four combinations of temperature and relative humidity. For model calibration and definition of the equations, cubic and beam samples were fabricated to carry out physical-mechanical tests, such as moisture content, shrinkage, and modulus of rupture. Laboratory-obtained data were studied with the Response Surface Methodology (RSM) to determine the best regression equations. The main findings determined that the behavior of a mixture of RCC at a prolonged ambient exposure time is possible because the surface models and the RSM were consistent with the different service and mix conditions. The models showed an accuracy of 98.99% in detecting shrinkage changes from 12 to 16% cement with 5.65% water in dry to wet ambient conditions. Similarly, moisture content and modulus of rupture had a 98.27 to 98.88% fit. Finally, the drying shrinkage, with mixes of 12% cement and water content variations with water-reducing admixture and superplasticizer effects, had an adjustment of 94.87%. Full article

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2023

Jump to: 2024, 2022, 2021, 2020

18 pages, 6128 KiB

Open AccessArticle

Study on Influencing Factors of Hydraulic Engineered Cementitious Composites Layer Bonding Performance

by Yupu Wang, Jiazheng Li and Yan Shi

Materials 2023, 16(20), 6693; https://doi.org/10.3390/ma16206693 - 14 Oct 2023

Viewed by 1050

Abstract

The layer bonding performance of hydraulic engineered cementitious composites (HECCs) plays an important role in their application in hydraulic buildings. This performance encompasses the bonding between layers of HECCs, as well as between HECCs and normal mortar (NM) layers. The influence of various [...] Read more.

The layer bonding performance of hydraulic engineered cementitious composites (HECCs) plays an important role in their application in hydraulic buildings. This performance encompasses the bonding between layers of HECCs, as well as between HECCs and normal mortar (NM) layers. The influence of various factors on the layer bonding performance of HECCs was investigated. These factors included different pouring intervals (0 min, 20 min, 40 min, 60 min, 2.5 h, 7 days, 14 days, and 28 days), pouring directions (horizontal and vertical), degree of saturation (100%, 70%, 50%, 30%, and 0%), and surface roughness (varying sand-pour roughness). It was found that longer pouring interval times led to a decrease in the layer bonding performance, and the strength of the layer bonding fell below 50% compared to concrete without layers, with the lowest recorded strength being only 1.12 MPa. The layer’s horizontal flexural strength surpassed the vertical flexural strength, but the horizontal compressive strength fell below the vertical compressive strength. Additionally, the bonding performance of the substrate at 0% saturation was 15–20% lower compared to other saturation levels. Notably, roughness significantly enhanced the performance of HECC layers, with improvements reaching a maximum of 180–200%. Furthermore, the layer performance of HECCs and NM experienced an improvement of 20.5–37.5%. Full article

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12 pages, 5349 KiB

Open AccessArticle

Experimental Study of Dynamic Tensile Strength of Steel-Fiber-Reinforced Self-Compacting Concrete Using Modified Hopkinson Bar

by Jian Ma, Yifei Huo, Ning Wang, Zhang Sun, Liang Bian and Ruiyuan Huang

Materials 2023, 16(16), 5707; https://doi.org/10.3390/ma16165707 - 20 Aug 2023

Cited by 3 | Viewed by 1111

Abstract

As a typical brittle material, the tensile strength of concrete is much lower than its compressive strength. The main failure mode of concrete buildings under explosive and impact loading is spalling, so it is crucial to understand the dynamic tensile performance of concrete. [...] Read more.

As a typical brittle material, the tensile strength of concrete is much lower than its compressive strength. The main failure mode of concrete buildings under explosive and impact loading is spalling, so it is crucial to understand the dynamic tensile performance of concrete. This paper presents an experimental study on the dynamic tensile strength of steel-fiber-reinforced self-compacting concrete (SFRSCC). Specimens of two different self-compacting concrete (SCC) mixes (C40 and C60) and four different fiber volume fractions (0.5%, 1.0%, 1.5%, and 2.0%) are fabricated. Dynamic tensile strengths of SFRSCC are obtained using a modified Hopkinson bar system. The relationships between the dynamic tensile strength of the corresponding SCC mix, the quasi-static compressive strength, and the fiber volume fraction are discussed. An empirical equation is proposed. It is shown that SFRSCC with high compressive strength has higher dynamic tensile strength than low-strength SFRSCC for the same fiber content, and the dynamic tensile strength of SFRSCC possesses an approximately linear relation with the fiber volume fraction. The mechanism underlying this fiber-reinforcement effect is investigated. Full article

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13 pages, 1258 KiB

Open AccessEditor’s ChoiceArticle

Understanding Chloride Diffusion Coefficient in Cementitious Materials

by Zhiyuan Xu and Guang Ye

Materials 2023, 16(9), 3464; https://doi.org/10.3390/ma16093464 - 29 Apr 2023

Cited by 3 | Viewed by 2176

Abstract

One of the key problems that affect the durability of reinforced concrete structures is the corrosion of rebar induced by chloride. Despite the complicated transport mechanism of chloride ions in cementitious materials, diffusion is still the key mechanism of chloride ingress. The determination [...] Read more.

One of the key problems that affect the durability of reinforced concrete structures is the corrosion of rebar induced by chloride. Despite the complicated transport mechanism of chloride ions in cementitious materials, diffusion is still the key mechanism of chloride ingress. The determination of the chloride diffusion coefficient will help to predict the chloride profile inside the cementitious materials and estimate the service life with regard to chloride-induced corrosion. However, this paper shows that the chloride diffusion coefficient in the literature is sometimes misunderstood. Such a misunderstanding results in the overestimation of the chloride resistance of cementitious materials. To clarify the chloride diffusion coefficient, this paper first presents the steady- and non-steady-state diffusion equations in cementitious materials. The factors that influence the diffusive flux are identified. The effective and apparent diffusion coefficients are then clearly explained and properly defined. We also point out the obscure definitions of the effective diffusion coefficient in the literature. The varied definitions of the effective diffusion coefficient are the result of the consideration of different factors affecting the diffusion process. Subsequently, this paper discusses two natural diffusion test methods that are frequently employed in cementitious materials to measure the chloride diffusion coefficient. The influencing factors considered by the measured diffusion coefficients are analyzed in detail. Then, the diffusion coefficients determined in some of the studies are reviewed. It is shown that three typical errors could occur when numerically determining the diffusion coefficients. Full article

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25 pages, 4432 KiB

Open AccessArticle

Modeling the Thermoelastic Bending of Ferric Oxide (Fe₂O₃) Nanoparticles-Enhanced RC Slabs

by Zouaoui R. Harrat, Mohammed Chatbi, Baghdad Krour, Marijana Hadzima-Nyarko, Dorin Radu, Sofiane Amziane and Mohamed Bachir Bouiadjra

Materials 2023, 16(8), 3043; https://doi.org/10.3390/ma16083043 - 12 Apr 2023

Cited by 3 | Viewed by 1413

Abstract

Nanoparticles, by virtue of their amorphous nature and high specific surface area, exhibit ideal pozzolanic activity which leads to the formation of additional C-S-H gel by reacting with calcium hydroxide, resulting in a denser matrix. The proportions of ferric oxide (Fe₂O [...] Read more.

Nanoparticles, by virtue of their amorphous nature and high specific surface area, exhibit ideal pozzolanic activity which leads to the formation of additional C-S-H gel by reacting with calcium hydroxide, resulting in a denser matrix. The proportions of ferric oxide (Fe₂O₃), silicon dioxide (SiO₂), and aluminum oxide (Al₂O₃) in the clay, which interact chemically with the calcium oxide (CaO) during the clinkering reactions, influence the final properties of the cement and, therefore, of the concrete. Through the phases of this article, a refined trigonometric shear deformation theory (RTSDT), taking into account transverse shear deformation effects, is presented for the thermoelastic bending analysis of concrete slabs reinforced with ferric oxide (Fe₂O₃) nanoparticles. Thermoelastic properties are generated using Eshelby’s model in order to determine the equivalent Young’s modulus and thermal expansion of the nano-reinforced concrete slab. For an extended use of this study, the concrete plate is subjected to various mechanical and thermal loads. The governing equations of equilibrium are obtained using the principle of virtual work and solved using Navier’s technique for simply supported plates. Numerical results are presented considering the effect of different variations such as volume percent of Fe₂O₃ nanoparticles, mechanical loads, thermal loads, and geometrical parameters on the thermoelastic bending of the plate. According to the results, the transverse displacement of concrete slabs subjected to mechanical loading and containing 30% nano-Fe₂O₃ was almost 45% lower than that of a slab without reinforcement, while the transverse displacement under thermal loadings increased by 10%. Full article

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11 pages, 1749 KiB

Open AccessArticle

Investigation into the Time-Dependent Crack Propagation Rate of Concrete

by Jingxiang Song, Hongbo Gao and Ran Zhu

Materials 2023, 16(6), 2337; https://doi.org/10.3390/ma16062337 - 14 Mar 2023

Viewed by 1508

Abstract

Mass concrete structures under long-term loads are susceptible to time-dependent fractures, which pose a threat to their structural integrity and safety. In order to study the crack growth rate of concrete materials under long-term constant load, the data were processed according to the [...] Read more.

Mass concrete structures under long-term loads are susceptible to time-dependent fractures, which pose a threat to their structural integrity and safety. In order to study the crack growth rate of concrete materials under long-term constant load, the data were processed according to the calculation method of fatigue crack growth rate. The relationship between the crack growth rate and strength factor in the stable growth stage was obtained using the Paris formula. The experimental data and theoretical analysis show that the time-dependent fracture curve CMOR(t)-t of the standard three-point bending beam specimens could be divided into three stages. The relationship between the crack propagation rate da/dt(t) in the second stage and the intensity factor K(t) could be well described by the Paris formula. The life of crack growth of a standard three-point curved beam is inversely proportional to the level of constant load. These conclusions can provide data support for further studies on crack extension life under long-term constant load. Full article

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16 pages, 7381 KiB

Open AccessArticle

Influence of Basalt/Polypropylene Fiber on Permeability and Uniaxial Compressive Properties of Waste Tire Rubberized Concrete

by Dan-yang Su, Jian-yong Pang, Chen-yue Han, Jian-yu Huang, Xiu-yue Hu and Wei Shi

Materials 2023, 16(2), 481; https://doi.org/10.3390/ma16020481 - 4 Jan 2023

Cited by 3 | Viewed by 1440

Abstract

The rubber particles obtained from the grinding of waste tires can replace a portion of the fine aggregates in concrete, thus effectively reducing the level of environmental damage and saving resources. However, when concrete is mixed with rubber, it greatly reduces its strength. [...] Read more.

The rubber particles obtained from the grinding of waste tires can replace a portion of the fine aggregates in concrete, thus effectively reducing the level of environmental damage and saving resources. However, when concrete is mixed with rubber, it greatly reduces its strength. In this study, by introducing basalt fiber (BF) and polypropylene fiber (PF) as modified materials in rubberized concrete, the influence of the fiber type/volume ratio on the slump, water absorption, static uniaxial compression, and permeability of the rubberized concrete was tested. The axial compression stress–strain relationship was analyzed, the effect of the fiber type/volume ratio on the energy dissipation of the rubberized concrete during uniaxial compression was expounded, and a stress–strain constitutive model under uniaxial compression was established. The test results showed that the fiber reduces the fluidity and water absorption of the rubberized concrete. Compared with the polypropylene fiber, the basalt fiber increased the strength of the rubberized concrete, while the polypropylene fiber mainly inhibited the expansion and penetration of the macroscopic crack of the rubberized concrete. The mixing of the basalt fiber and polypropylene fiber significantly decreased the release rate of the elastic strain energy of the rubberized concrete, increased the dissipation energy, and thus improved its ductility and toughness. During a loading process under confining pressure, the permeability of the tested specimen decayed exponentially, and the fiber greatly enhanced the anti-permeability of the rubber concrete. Full article

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2022

Jump to: 2024, 2023, 2021, 2020

15 pages, 2270 KiB

Open AccessArticle

Effect of Super-Absorbent Polymer (SAP) Incorporation Method on Mechanical and Shrinkage Properties of Internally Cured Concrete

by Xingliang Huang, Xiaoyu Liu, Hongliu Rong, Xiaolong Yang, Yunsheng Duan and Tingting Ren

Materials 2022, 15(21), 7854; https://doi.org/10.3390/ma15217854 - 7 Nov 2022

Cited by 10 | Viewed by 2670

Abstract

To study the effect of SAP incorporation on the early shrinkage of SAP internally cured concrete with the aim to solve the problems of early shrinkage and cracking of bridge leveling-layer concrete, using the SAP incorporation method as a parameter, the mechanical properties [...] Read more.

To study the effect of SAP incorporation on the early shrinkage of SAP internally cured concrete with the aim to solve the problems of early shrinkage and cracking of bridge leveling-layer concrete, using the SAP incorporation method as a parameter, the mechanical properties test of internally cured concrete, the shrinkage performance test of ring restraint and the scanning electron microscope observation test were carried out. The effects of the SAP content and incorporation method on the flowability, mechanical properties, shrinkage performance and microstructure of internally cured concrete were analyzed. The experimental results show that when the content of the SAP in concrete is 0.2% of the mass of cementitious materials, it has the least influence on the compressive strength of concrete. The addition of preabsorbed water to the SAP can delay early cement hydration, increase the later cement hydration rate and final hydration degree, and improve the concrete strength. Preabsorbed water mixed with an SAP can effectively improve the shrinkage of concrete, and the shrinkage reduction effect is more obvious than that from the dry addition of the SAP; the early cracking risk of concrete without an SAP is high, and it will crack before day 28. The addition of an SAP can strengthen the microstructure of concrete and improve its density and crack resistance, effectively avoiding concrete cracking. It is recommended that the water-absorbent resin be incorporated in a preabsorbent manner, and the SAP preabsorbent ratio is equal to the maximum water storage rate of the SAP. Full article

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18 pages, 4732 KiB

Open AccessArticle

Relationship between Fractal Dimension and Properties of Engineered Cementitious Composites with Different Aggregates

by Duotian Xia, Ruilin Chen, Duo Zhang and Jianjun Cheng

Materials 2022, 15(21), 7666; https://doi.org/10.3390/ma15217666 - 31 Oct 2022

Cited by 9 | Viewed by 1753

Abstract

In this study, the effects of different fine aggregates on the properties of polyethylene fiber engineered cementitious composite (PE-ECC) were systematically investigated. The PE-ECCs were prepared with four fine aggregates, respectively. Furthermore, their flowability, compressive strength, and uniaxial tensile properties were studied experimentally [...] Read more.

In this study, the effects of different fine aggregates on the properties of polyethylene fiber engineered cementitious composite (PE-ECC) were systematically investigated. The PE-ECCs were prepared with four fine aggregates, respectively. Furthermore, their flowability, compressive strength, and uniaxial tensile properties were studied experimentally and comparatively analyzed by microscopic techniques including X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), and mercury intrusion porosimetry (MIP). The results showed that all the different types of fine aggregates exhibited little effect on the flowability of PE-ECC, but a greater effect on the compressive strength, uniaxial tensile strength, and ultimate tensile strain. PE-ECC prepared from untreated desert sand showed the best comprehensive performance, with compressive strength, uniaxial tensile strength, and ultimate tensile strain of 47.92 MPa, 6.26 MPa, and 3.638%, respectively. Moreover, it was found that the ultra-fine particles in the desert sand promoted the hydration reaction of cement and produced more C–S–H gels. The pore structures of ECC prepared with different aggregates exhibited obvious fractal characteristics, and the fractal dimension ranged from 2.8 to 2.9. The fractal dimension showed a strong correlation with parameters including ultimate tensile strain and pore structure, and the larger the fractal dimension, the smaller the ultimate tensile strain, porosity, and average pore size of ECC. Full article

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28 pages, 15894 KiB

Open AccessArticle

Uniaxial Compression Failure and Size Effect of Recycled Aggregate Concrete Based on Meso-Simulation Analysis

by Jingbo Zhuo, Yamin Zhang, Mei Ma, Yu Zhang and Yuanxun Zheng

Materials 2022, 15(16), 5710; https://doi.org/10.3390/ma15165710 - 18 Aug 2022

Cited by 7 | Viewed by 2081

Abstract

Recycled aggregate concrete (RAC) is a kind of five-phase composite material at the meso-level. It has a more complex interfacial transition zone (ITZ) than ordinary aggregate concrete (NAC), which is an important factor affecting the meso-failure of RAC. In addition, the maximum aggregate [...] Read more.

Recycled aggregate concrete (RAC) is a kind of five-phase composite material at the meso-level. It has a more complex interfacial transition zone (ITZ) than ordinary aggregate concrete (NAC), which is an important factor affecting the meso-failure of RAC. In addition, the maximum aggregate size plays an important role in the nonlinear mechanical behavior of concrete, which is closely related to the size effect. In this paper, a 2D random aggregate model of RAC is established based on meso-mechanics. The mechanical properties and failure modes of RAC under uniaxial compression are simulated using a plastic damage constitutive model. Through variable parameter analysis, the effects of the properties and thickness of ITZ on the elastic modulus and peak stress of RAC are studied, and the effect of the maximum aggregate size on the size effect of the compressive strength of RAC is discussed. The results show that the ITZ strength has a positive linear correlation with the peak stress and elastic modulus of RAC, while the ITZ thickness has a negative linear correlation with the peak stress and elastic modulus of RAC. Under the same specimen size (D = 100 mm, 150 mm, 200 mm, 300 mm), with an increase in the maximum aggregate size (d_max =20 mm, 25 mm, 30 mm, 35 mm), the nominal compressive strength of RAC increases by 6–10%, and the size effect is gradually weakened. When the maximum aggregate size reaches 30 mm, a decrease in the size effect tends to slow down compared with the maximum aggregate size of 20 mm. The classical Bažant size effect law is applicable to describe the compressive properties of RAC under different maximum aggregate sizes, and has a certain guiding significance for the prediction of the size effect of RAC in practical engineering. Full article

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19 pages, 6459 KiB

Open AccessArticle

Mechanical and Pore Properties of Concrete Using Basalt-Based Recycled Aggregates According to Mixture Conditions

by Hong-Beom Choi, Jin-O Park, Hyung-Do Lee and Kyeo-Re Lee

Materials 2022, 15(16), 5677; https://doi.org/10.3390/ma15165677 - 18 Aug 2022

Cited by 2 | Viewed by 1432

Abstract

This study investigated recycled aggregates of Jeju Island—where porous basalt exists as a natural aggregate—and is a study aimed at verifying the applicability of the basalt-based recycled aggregate in the field. To this end, the application properties of concrete were analyzed using the [...] Read more.

This study investigated recycled aggregates of Jeju Island—where porous basalt exists as a natural aggregate—and is a study aimed at verifying the applicability of the basalt-based recycled aggregate in the field. To this end, the application properties of concrete were analyzed using the quality improvement of the recycled aggregate (PRA), the type of fine aggregate received in the region, and the cement content as variables. In an experiment using concrete in which 50% of the PRA was replaced with basalt (BA), the air content of the fresh concrete decreased due to the increasing solid content of the aggregate when PRA and fine aggregates (with an even particle size distribution) were used. Regarding the properties of the hardened concrete, when the PRA and fine aggregate (with a high fineness modulus) were used, the compressive strength was 33.6 MPa and the modulus of elasticity was 23.1 GPa, which are higher than those of the BA specimen. The resistance to carbonation increased due to the improved quality of the PRA specimen. Pores that are 0.3 mm in size or larger decreased when the PRA and fine aggregates of even particle sizes were used. This form of pore reduction was found to have a direct correlation with the improvement of mechanical properties. Full article

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15 pages, 5437 KiB

Open AccessArticle

Influence of the Addition of Dispersible Color Powder and Polyacrylic Emulsion on the Durability of Cement Mortar

by Chih-Ming Huang, Her-Yung Wang, Wein-Duo Yang, Tien-Chun Kao and Sing-Yuan Fang

Materials 2022, 15(15), 5305; https://doi.org/10.3390/ma15155305 - 2 Aug 2022

Cited by 2 | Viewed by 1632

Abstract

Cement mortar can be colored using color additive technology to give colorful facades to the surfaces of buildings, and to beautify the environment. In this study, weight ratios of color powder/cement at 1:80, 1:40, and 1:27, and polyacrylic emulsion/cement at a ratio of [...] Read more.

Cement mortar can be colored using color additive technology to give colorful facades to the surfaces of buildings, and to beautify the environment. In this study, weight ratios of color powder/cement at 1:80, 1:40, and 1:27, and polyacrylic emulsion/cement at a ratio of 1:5 were added as pigments to cement mortar; the fresh properties, slump, slump flow, hardened properties, compressive strength, flexural strength, ultrasonic pulse velocity, durability, surface electrical resistivity and thermal conductivity of the colored cement mortar were then examined. The results showed that adding color powder/cement at 1:80 and polyacrylic emulsion/cement at 1:5 gives the best water/cement (W/C) ratio, which equals 0.5; this can effectively improve the hardness and durability of colored cement mortar. At 28 days of aging, the strength of the various colored cement mortars was maintained at 33.1–36.8 MPa. The acrylic-based emulsion significantly improved the flexural strength of the specimen. At 91 days of aging, all of the cement mortars exceeded the control group, with an anti-bay strength of 19.9–21.7 MPa, and the strength increased with aging. Adding appropriate amounts of inorganic color powder and mixing water can effectively enhance the fresh and hardened properties and durability of the colored cement mortar, while polyacrylic emulsion may significantly improve the test pieces and flexural strength, which increases with age. Moreover, natural α-Fe₂O₃ (rust layer) is formed on the surface of the colored cement mortar samples through the addition of inorganic color powder that contains Fe(III) ion; this prevents the intrusion of noxious ions and thus increases the durability. All of the test pieces of colored cement mortar in this study had a surface resistance of over 20 kΩ-cm on the seventh day of the test period, meaning good surface compactness. In addition, because the thermal conductivity of the added inorganic color powder was higher than that of cement, the thermal conductivity was significantly improved. Full article

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20 pages, 5454 KiB

Open AccessArticle

Particle Characterization of Manufactured Sand and Its Influence on Concrete Properties

by Jiale Wu, Weiguo Shen, Deqiang Zhao, Miaomiao Wu, Zhen Yu, Zhicheng Zhao, Zhitang Li, Dinglve Wu and Jiangtao Sun

Materials 2022, 15(13), 4593; https://doi.org/10.3390/ma15134593 - 30 Jun 2022

Cited by 7 | Viewed by 2598

Abstract

With the rapid development of infrastructure construction, it is an inevitable trend to replace natural sand in short supply with manufactured sand to meet sustainable development. In this paper, the relationship between the particle shape characteristics of manufactured sand and concrete performance is [...] Read more.

With the rapid development of infrastructure construction, it is an inevitable trend to replace natural sand in short supply with manufactured sand to meet sustainable development. In this paper, the relationship between the particle shape characteristics of manufactured sand and concrete performance is discussed using a morphological analysis and concrete experiments. The particle shape parameters of five types of manufactured sand were obtained by using the aggregate image measurement system (AIMS) and digital image processing (DIP) techniques, and the correlations between different parameters were analyzed. Moreover, the properties of concrete with the five kinds of manufactured sand were tested. The results show that particle size and type have a significant impact on particle shape parameters. Particle shape parameters, especially angularity, correlate well with the workability and compressive strength of concrete while having little effect on the durability of concrete. An accurate understanding of the morphological characteristics of manufactured sand is conducive to the optimization of concrete mix designs. Therefore, it is suggested that a manufactured-sand shape test be included in aggregate specification. Full article

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21 pages, 5513 KiB

Open AccessReview

Microbiologically Induced Concrete Corrosion: A Concise Review of Assessment Methods, Effects, and Corrosion-Resistant Coating Materials

by Bhavesh Chaudhari, Biranchi Panda, Branko Šavija and Suvash Chandra Paul

Materials 2022, 15(12), 4279; https://doi.org/10.3390/ma15124279 - 16 Jun 2022

Cited by 17 | Viewed by 3487

Abstract

Microbiologically induced concrete corrosion (in wastewater pipes) occurs mainly because of the diffusion of aggressive solutions and in situ production of sulfuric acid by microorganisms. The prevention of concrete biocorrosion usually requires modification of the mix design or the application of corrosion-resistant coatings, [...] Read more.

Microbiologically induced concrete corrosion (in wastewater pipes) occurs mainly because of the diffusion of aggressive solutions and in situ production of sulfuric acid by microorganisms. The prevention of concrete biocorrosion usually requires modification of the mix design or the application of corrosion-resistant coatings, which requires a fundamental understanding of the corrosion process. In this regard, a state-of-the-art review on the subject is presented in this paper, which firstly details the mechanism of microbial deterioration, followed by assessment methods to characterize biocorrosion and its effects on concrete properties. Different types of corrosion-resistant coatings are also reviewed to prevent biocorrosion in concrete sewer and waste-water pipes. At the end, concluding remarks, research gaps, and future needs are discussed, which will help to overcome the challenges and possible environmental risks associated with biocorrosion. Full article

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32 pages, 9932 KiB

Open AccessArticle

Application of Artificial Intelligence Methods for Predicting the Compressive Strength of Self-Compacting Concrete with Class F Fly Ash

by Miljan Kovačević, Silva Lozančić, Emmanuel Karlo Nyarko and Marijana Hadzima-Nyarko

Materials 2022, 15(12), 4191; https://doi.org/10.3390/ma15124191 - 13 Jun 2022

Cited by 13 | Viewed by 2240

Abstract

Replacing a specified quantity of cement with Class F fly ash contributes to sustainable development and reducing the greenhouse effect. In order to use Class F fly ash in self-compacting concrete (SCC), a prediction model that will give a satisfactory accuracy value for [...] Read more.

Replacing a specified quantity of cement with Class F fly ash contributes to sustainable development and reducing the greenhouse effect. In order to use Class F fly ash in self-compacting concrete (SCC), a prediction model that will give a satisfactory accuracy value for the compressive strength of such concrete is required. This paper considers a number of machine learning models created on a dataset of 327 experimentally tested samples in order to create an optimal predictive model. The set of input variables for all models consists of seven input variables, among which six are constituent components of SCC, and the seventh model variable represents the age of the sample. Models based on regression trees (RTs), Gaussian process regression (GPR), support vector regression (SVR) and artificial neural networks (ANNs) are considered. The accuracy of individual models and ensemble models are analyzed. The research shows that the model with the highest accuracy is an ensemble of ANNs. This accuracy expressed through the mean absolute error (MAE) and correlation coefficient (R) criteria is 4.37 MPa and 0.96, respectively. This paper also compares the accuracy of individual prediction models and determines their accuracy. Compared to theindividual ANN model, the more transparent multi-gene genetic programming (MGPP) model and the individual regression tree (RT) model have comparable or better prediction accuracy. The accuracy of the MGGP and RT models expressed through the MAE and R criteria is 5.70 MPa and 0.93, and 6.64 MPa and 0.89, respectively. Full article

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20 pages, 3856 KiB

Open AccessArticle

Compressive Strength Prediction of Rubber Concrete Based on Artificial Neural Network Model with Hybrid Particle Swarm Optimization Algorithm

by Xiao-Yu Huang, Ke-Yang Wu, Shuai Wang, Tong Lu, Ying-Fa Lu, Wei-Chao Deng and Hou-Min Li

Materials 2022, 15(11), 3934; https://doi.org/10.3390/ma15113934 - 31 May 2022

Cited by 11 | Viewed by 1965

Abstract

Conventional neural networks tend to fall into local extremum on large datasets, while the research on the strength of rubber concrete using intelligent algorithms to optimize artificial neural networks is limited. Therefore, to improve the prediction accuracy of rubber concrete strength, an artificial [...] Read more.

Conventional neural networks tend to fall into local extremum on large datasets, while the research on the strength of rubber concrete using intelligent algorithms to optimize artificial neural networks is limited. Therefore, to improve the prediction accuracy of rubber concrete strength, an artificial neural network model with hybrid algorithm optimization was developed in this study. The main strategy is to mix the simulated annealing (SA) algorithm with the particle swarm optimization (PSO) algorithm, using the SA algorithm to compensate for the weak global search capability of the PSO algorithm at a later stage while changing the inertia factor of the PSO algorithm to an adaptive state. For this purpose, data were first collected from the published literature to create a database. Next, ANN and PSO-ANN models are also built for comparison while four evaluation metrics, MSE, RMSE, MAE, and

R^{2}

, were used to assess the model performance. Finally, compared with empirical formulations and other neural network models, the result shows that the proposed optimized artificial neural network model successfully improves the accuracy of predicting the strength of rubber concrete. This provides a new option for predicting the strength of rubber concrete. Full article

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21 pages, 8655 KiB

Open AccessArticle

Additive Digital Casting: From Lab to Industry

by Ena Lloret-Fritschi, Elia Quadranti, Fabio Scotto, Lukas Fuhrimann, Thibault Demoulin, Sara Mantellato, Lukas Unteregger, Joris Burger, Rafael G. Pileggi, Fabio Gramazio, Matthias Kohler and Robert J. Flatt

Materials 2022, 15(10), 3468; https://doi.org/10.3390/ma15103468 - 11 May 2022

Cited by 14 | Viewed by 2400

Abstract

Concrete construction harms our environment, making it urgent to develop new methods for building with less materials. Structurally efficient shapes are, however, often expensive to produce, because they require non-standard formworks, thus, standard structures, which use more material than is often needed, remain [...] Read more.

Concrete construction harms our environment, making it urgent to develop new methods for building with less materials. Structurally efficient shapes are, however, often expensive to produce, because they require non-standard formworks, thus, standard structures, which use more material than is often needed, remain cheaper. Digital fabrication has the potential to change this paradigm. One method is Digital Casting Systems (DCS), where the hydration of self-compacting concrete is controlled on the fly during production, shortening the required setting time and reducing hydrostatic pressure on the formwork to a minimum. This enables a productivity increase for standard concrete production. More importantly, though, it enables a rethinking of formworks, as the process requires only cheap thin formworks, thus, unlocking the possibility to produce optimised structural members with less bulk material and lower environmental cost. While DCS has already proven effective in building structural members, this process faces the challenge of moving into industry. This paper covers the next steps in doing so. First, we present the benchmark and expectations set by the industry. Second, we consider how we comply with these requirements and convert our fast-setting self-compacting mortar mix into a coarser one. Third, we present the next generation of our digital processing system, which moves closer to the industrial requirements in terms of size and the control system. Finally, two prototypes demonstrate how DSC: (a) increases standard bulk production by 50% and (b) can be cast into ultra-thin formworks. We discuss the results and the short-term industrial concerns for efficiency and robustness, which must be addressed for such a system to be fully implemented in industry. Full article

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20 pages, 11535 KiB

Open AccessArticle

Influence of Sugarcane Bagasse Ash and Silica Fume on the Mechanical and Durability Properties of Concrete

by William Earl Farrant, Adewumi John Babafemi, John Temitope Kolawole and Biranchi Panda

Materials 2022, 15(9), 3018; https://doi.org/10.3390/ma15093018 - 21 Apr 2022

Cited by 28 | Viewed by 3028

Abstract

Cement production is environmentally unsustainable due to the high anthropogenic carbon emissions produced. Supplementary cementitious materials (SCMs), derived from the by-products of different industries, have been deemed an effective way to reduce carbon emissions. The reduction in carbon emissions is achieved by lowering [...] Read more.

Cement production is environmentally unsustainable due to the high anthropogenic carbon emissions produced. Supplementary cementitious materials (SCMs), derived from the by-products of different industries, have been deemed an effective way to reduce carbon emissions. The reduction in carbon emissions is achieved by lowering the clinker factor of cement, through a partial replacement with an SCM. Sugarcane Bagasse Ash (SCBA) is produced as an agricultural waste from the sugarcane industry and has gained a lot of attention for being a feasible and readily available pozzolanic material, underutilised as an SCM. This study evaluates alkali-activated sugarcane bagasse ash’s mechanical and durability performance, at varied contents, in binary blended cement concrete and ternary blended cement concrete containing silica fume (SF). Potassium Hydroxide (KOH), used as the alkali activator, is intended to enhance the reactivity of the ash, with the possibility of a high-volume SCBA content. The mechanical performance was investigated by compressive and split tensile strength tests, and durability performance was investigated using the Oxygen Permeability Index (OPI) test. In addition, a micro-CT porosity test was conducted to assess how the microstructure and porosity of the concrete affect the mechanical and durability performance. The results indicated that using SCBA in a ternary blend with SF can significantly improve the overall performance and create less porous concrete. At 30% SCBA and 10% SF replacement, the performance tests revealed the highest mechanical strength and the lowest permeability, outperforming the control concrete and the binary blended cement concrete containing only SCBA. Full article

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16 pages, 5939 KiB

Open AccessArticle

Colour Change of Sustainable Concrete Containing Waste Ceramic and Hybrid Fibre: Effect of Temperature

by Hadee Mohammed Najm, Ominda Nanayakkara, Mahmood Ahmad and Mohanad Muayad Sabri Sabri

Materials 2022, 15(6), 2174; https://doi.org/10.3390/ma15062174 - 15 Mar 2022

Cited by 12 | Viewed by 2581

Abstract

Construction and demolition (C&D) waste was considered as zero value materials and, as a result, most C&D waste materials ended up in landfills, eventually constituting environmental issues. Therefore, it is important to explore the potential of such C&D waste materials for concrete production. [...] Read more.

Construction and demolition (C&D) waste was considered as zero value materials and, as a result, most C&D waste materials ended up in landfills, eventually constituting environmental issues. Therefore, it is important to explore the potential of such C&D waste materials for concrete production. Thus, this research effort aims to find a new method to improve sustainable concrete properties exposed to elevated temperatures at the lowest costs and identify the relationship between temperature change and a change in colour in a heat-exposed concrete structure. Therefore, this study explored the behaviour of three types of concrete: plain concrete (PC), waste ceramic optimal concrete (WOC), and waste ceramic optimal concrete reinforced by hybrid fibre (WOC-Hybrid) in ambient and elevated temperature. The study shows that colour change in a concrete structure exposed to high temperature has a consistent relationship, where it has been found that the colour alteration is of great interest because its appearance usually coincides with the onset of a significant loss of concrete strength as a result of elected temperatures. Overall, it can be considered that waste ceramic materials reinforced by hybrid fibres can be used for concrete production, and by doing so, the negative impact of these wastes on the environment can be controlled as well as fortify the mechanical properties. Full article

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17 pages, 3554 KiB

Open AccessArticle

Mechanical, Thermal, and Fire Properties of Composite Materials Based on Gypsum and PCM

by Kateřina Stejskalová, David Bujdoš, Lukáš Procházka, Bedřich Smetana, Simona Zlá and Jiří Teslík

Materials 2022, 15(3), 1253; https://doi.org/10.3390/ma15031253 - 8 Feb 2022

Cited by 15 | Viewed by 2225

Abstract

One of the solutions for overheating the interior in the summer without increasing energy consumption is the integration of phase change material (PCM) into interior plasters. However, adding PCM to plasters deteriorates their properties and thus their usability. The aim of this paper [...] Read more.

One of the solutions for overheating the interior in the summer without increasing energy consumption is the integration of phase change material (PCM) into interior plasters. However, adding PCM to plasters deteriorates their properties and thus their usability. The aim of this paper is to determine how the microencapsulated PCM affects the mechanical, thermal, and fire properties of plasters and how much PCM can be added to the plaster. Two sets of samples were prepared: in set S, part of the aggregate was replaced by PCM; and in set R, only PCM was added. The bulk density, flexural strength, compressive strength, tensile strength perpendicular to the surface, thermal conductivity coefficient, specific heat capacity, melting, and solidification temperatures and enthalpy were measured. A single-flame source fire test and a gross heat of combustion fire test were performed to determine the reaction to the fire class. The results show that with an increasing proportion of PCM, the strength of the samples of set R decreased more significantly than it did with the samples of set S. It was found that only up to about 10% PCM could be added to set R, while up to 30% PCM could be added to set S. Full article

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2021

Jump to: 2024, 2023, 2022, 2020

18 pages, 4544 KiB

Open AccessArticle

X-ray CT Investigation of Bond Mechanism in Reinforced SCC Elements of Different Placement Technology

by Piotr Dybeł and Milena Kucharska

Materials 2021, 14(21), 6236; https://doi.org/10.3390/ma14216236 - 20 Oct 2021

Cited by 5 | Viewed by 1803

Abstract

The effect of different placing methods of the self-compacting concrete (SCC) mix—from the top and from the bottom of the form—on the bond failure mechanism was investigated within the scope of this paper. Existing studies regarding the known mechanisms of bond failure do [...] Read more.

The effect of different placing methods of the self-compacting concrete (SCC) mix—from the top and from the bottom of the form—on the bond failure mechanism was investigated within the scope of this paper. Existing studies regarding the known mechanisms of bond failure do not consider the bottom-up method of concrete placing, which improves the quality of the concrete microstructure around reinforcing bars. Background tests were performed on panel elements with dimensions of 800 × 480 × 160 mm. Ribbed steel reinforcing bars with a diameter of 16 mm were used in the tests, which were placed horizontally in the forms. A pull-out method was used to investigate the bond strength. X-ray computed tomography (CT) was used as a novel and non-destructive technique that allowed a 3D insight into the bond between the rebar and the concrete after the ultimate bond stress had been reached. The results provided a clear description of the phenomena occurring during the fresh state of concrete in the vicinity of rebars (bleeding, plastic settlement, vertical density variation) and showed their significance for bond mechanisms. Finally, it was demonstrated that placing the mix from the bottom of the form resulted in the same bond failure mechanism for both bars located at the top and the bottom of the panel elements. This was translated into identical bond properties throughout the element with regard to bond stiffness and bond strength. It was found that the described and known mechanisms of bond failure are only an idealized description of the performance of the reinforcing bar-concrete joint. The analysis of the steel–concrete interface (SCI) imaging indicated that, in reality, the forming bond failure mechanisms were a complex process that could be affected by many factors. Full article

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16 pages, 4468 KiB

Open AccessArticle

Effect of Internal Pores Formed by a Superabsorbent Polymer on Durability and Drying Shrinkage of Concrete Specimens

by Il-Sun Kim, So-Yeong Choi, Yoon-Suk Choi and Eun-Ik Yang

Materials 2021, 14(18), 5199; https://doi.org/10.3390/ma14185199 - 10 Sep 2021

Cited by 14 | Viewed by 1919

Abstract

In this study, the effect of internal pores formed by a superabsorbent polymer (SAP) was analyzed by evaluating the compressive strength, chloride penetration depth, drying shrinkage, and pore size distribution of SAP-containing concrete, while securing workability using a water-reducing agent (WRA). The experimental [...] Read more.

In this study, the effect of internal pores formed by a superabsorbent polymer (SAP) was analyzed by evaluating the compressive strength, chloride penetration depth, drying shrinkage, and pore size distribution of SAP-containing concrete, while securing workability using a water-reducing agent (WRA). The experimental results showed that the amount of WRA necessary increased as the amount of SAP added increased, and that the compressive strength was the highest when the SAP content was 1.5% of the concrete mix. Drying shrinkage tended to decrease as the SAP content increased, and it decreased by approximately 31–41% when the SAP content was 2.0% compared to that of the reference mix. The SAP expanded by approximately three times inside concrete, and it was distributed within the internal pores of air-entrained concrete. The optimal SAP content in concrete mix was 1.5%, and an SAP content of 2.0% or higher adversely affected the workability and compressive strength. Full article

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17 pages, 5145 KiB

Open AccessArticle

Research on Interlayer Bonding Quality Control Method of Dam Concrete Based on Equivalent Age

by Wei-Jia Liu, You-Bo Wang, Qing-Bin Li, Xiao-Feng Gao, Yao-Shen Tan, Chun-Feng Liu, Yu Hu and Xu-Jing Niu

Materials 2021, 14(18), 5192; https://doi.org/10.3390/ma14185192 - 9 Sep 2021

Cited by 6 | Viewed by 1969

Abstract

Interlayer bonding quality is the key to the stability and durability of dam concrete. In this study, interlayer splitting tensile strength, relative permeability coefficient, and electric flux of dam concrete at different temperatures were tested. The relationships between equivalent age and strength coefficient, [...] Read more.

Interlayer bonding quality is the key to the stability and durability of dam concrete. In this study, interlayer splitting tensile strength, relative permeability coefficient, and electric flux of dam concrete at different temperatures were tested. The relationships between equivalent age and strength coefficient, relative permeability coefficient ratio, and electric flux ratio were established. Meanwhile, a comprehensive early-warning and control system of dam interlayer bonding quality based on the above relationships was proposed. The results showed that the interlayer mechanical properties, impermeability, and anti-chloride ion permeability of dam concrete decreased with the increase of temperature. Moreover, the equivalent age was linearly correlated with strength coefficient, relative permeability coefficient ratio, and electric flux ratio of concrete. The correlation coefficients were 0.986, 0.973, and 0.924, respectively. In addition, the interlayer bonding quality of dam concrete can be effectively controlled by the early-warning system established according to the relationship between equivalent age and interlayer properties parameters. Full article

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14 pages, 3090 KiB

Open AccessEditor’s ChoiceArticle

Study on the Frost Resistance of Concrete Modified with Steel Balls Containing Phase Change Material (PCM)

by Xiaosa Yuan, Baomin Wang, Peng Chen and Tao Luo

Materials 2021, 14(16), 4497; https://doi.org/10.3390/ma14164497 - 11 Aug 2021

Cited by 8 | Viewed by 2566

Abstract

In order to investigate the effect of phase change materials on the frost resistance of concrete in cold regions, hollow steel balls were used in this paper for the macroscopic encapsulation of the phase change material to replace some of the coarse aggregates [...] Read more.

In order to investigate the effect of phase change materials on the frost resistance of concrete in cold regions, hollow steel balls were used in this paper for the macroscopic encapsulation of the phase change material to replace some of the coarse aggregates in the preparation of phase change concrete. On the premise of ensuring reasonable mechanical properties, concrete mixed with different contents and different surface treatments of grouting steel balls were tested for the compressive strength and splitting tensile strength to determine the optimum content of phase change steel balls and investigate the frost resistance of phase change concrete. At the same time, industrial CT was used to explore the internal pore evolution pattern of concrete during the freeze–thaw period. The test results show that the optimum content of steel balls is 75%; during the freeze–thaw process, the mass loss, relative dynamic elastic modulus loss, and strength loss of phase change concrete are all lower than those of ordinary concrete, and the increase in porosity of phase change concrete is also significantly lower than that of ordinary concrete; the addition of phase change materials can optimise the distribution of the internal pore in concrete, improve its internal pore structure, and enhance its frost resistance. Full article

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19 pages, 3518 KiB

Open AccessEditor’s ChoiceArticle

Experimental Evaluation of Shrinkage, Creep and Prestress Losses in Lightweight Aggregate Concrete with Sintered Fly Ash

by Rafał Stanisław Szydłowski and Barbara Łabuzek

Materials 2021, 14(14), 3895; https://doi.org/10.3390/ma14143895 - 13 Jul 2021

Cited by 14 | Viewed by 2527

Abstract

The paper presents the experimental results of shrinkage, creep, and prestress loss in concrete with lightweight aggregate obtained by sintering of fly ash. Two concrete mixtures with different proportions of components were tested. Concrete with a density of 1810 and 1820 kg/m³ [...] Read more.

The paper presents the experimental results of shrinkage, creep, and prestress loss in concrete with lightweight aggregate obtained by sintering of fly ash. Two concrete mixtures with different proportions of components were tested. Concrete with a density of 1810 and 1820 kg/m³, and a 28-day strength of 56.9 and 58.4 MPa was obtained. Shrinkage and creep were tested on 150 × 250 × 1000 mm³ beams. Creep was tested under prestressing load for 539 days and concrete shrinkage for 900 days. The measurement results were compared with the calculations carried out according to the Eurocode 2 as well as with the results of other research. A very low creep coefficient and lower shrinkage in relation to the calculation results and the results of other research were found. It was also revealed that there is a clear correlation between shrinkage and creep, and the amount of water in the concrete. The value of the creep coefficient during the load holding period was 0.610 and 0.537, which is 56.0 and 49.3% of the value determined from the standard. The prestressing losses in the analyzed period amounted to an average of 13.0%. Based on the obtained test results, it was found that the tested lightweight aggregate concrete is well suited for prestressed concrete structures. Shrinkage was not greater than that calculated for normal weight concrete of a similar strength class, which will not result in increased loss of prestress. Low creep guarantees low deflection increments over time. Full article

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18 pages, 9164 KiB

Open AccessArticle

Lightweight Reactive Powder Concrete Containing Expanded Perlite

by Stefania Grzeszczyk and Grzegorz Janus

Materials 2021, 14(12), 3341; https://doi.org/10.3390/ma14123341 - 17 Jun 2021

Cited by 11 | Viewed by 2762

Abstract

This paper presents the test results of the lightweight concrete properties obtained by adding expanded perlite (EP) to an RPC mix in quantities from 30% to 60% by volume of the concrete mix. It has been shown that in these cases it is [...] Read more.

This paper presents the test results of the lightweight concrete properties obtained by adding expanded perlite (EP) to an RPC mix in quantities from 30% to 60% by volume of the concrete mix. It has been shown that in these cases it is possible to obtain concrete containing 30% by volume with density of approximately 1900 kg/m³ and the compressive strength > 70 MPa, with a very low water absorption value (3.3%), equal to the water absorption value of RPC without lightweight aggregate (3.3%). However, with the increased quantity of perlite (from 45% to 60%), the concrete density reduction is not observed, as the expanded perlite demonstrates very low resistance to crushing. With the increased amount of perlite, the longer periods of mixing time for all the mix components are required to obtain the homogeneous and fluid concrete mix, what causes grounding down EP. Therefore, using larger quantities of this aggregate in RPC is not recommended. The lightweight RPC shows very good freeze-thaw resistance in the presence of de-icing salt (the scaling mass is lower than 0.1 kg/m²). The above is explained by the compact microstructure of this concrete and the RPC mix location in open pores on the perlite aggregate surface, which consequently affects the strengthening of the aggregate-matrix contact without an interfacial transition zone (ITZ) visible. It has been demonstrated that pozzolanic activity of expanded perlite is much lower than the activity of silica fume and quartz powder, and its impact on increasing the RPC strength is minimal. Full article

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15 pages, 5651 KiB

Open AccessEditor’s ChoiceArticle

Deterioration of Portland Cement Pervious Concrete in Sponge Cities Subjected to Acid Rain

by Longxin Gao, Yong Lai, Mohammad Rashadul Islam Pramanic and Wuman Zhang

Materials 2021, 14(10), 2670; https://doi.org/10.3390/ma14102670 - 20 May 2021

Cited by 13 | Viewed by 3038

Abstract

The deterioration of Portland cement pervious concrete (PCPC) subjected to wet-dry cycles in the simulated acid rain solution was investigated; 4% silica fume (SF) and 8% fine aggregate (FAG) were used to replace part of cement and the coarse aggregates (weight by weight), [...] Read more.

The deterioration of Portland cement pervious concrete (PCPC) subjected to wet-dry cycles in the simulated acid rain solution was investigated; 4% silica fume (SF) and 8% fine aggregate (FAG) were used to replace part of cement and the coarse aggregates (weight by weight), respectively. The wear resistance, the compressive, and flexural strength of PCPC were measured. The results show that after 12 wet-dry cycles in acid rain solution the compressive strength and the flexural strength of control PCPC are decreased by 30.7% and 40.8%. The final compressive strength of PCPC with 4% SF and PCPC with 8% FAG is increased by 6.9% and 30.3%, and the final flexural strength is increased by 25.4% and 72.3%, respectively. The wear loss of PCPC is decreased by 58.8% and 81.9% when 4% SF and 8% FAG is added to PCPC, respectively. The microstructures of PCPC with wet-dry cycles are also discussed. Full article

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19 pages, 6725 KiB

Open AccessArticle

Dynamic Properties of Pretreated Rubberized Concrete under Incremental Loading

by Aijiu Chen, Xiaoyan Han, Zhihao Wang and Tengteng Guo

Materials 2021, 14(9), 2183; https://doi.org/10.3390/ma14092183 - 24 Apr 2021

Cited by 7 | Viewed by 1759

Abstract

Recycling scrap tyres as alternative aggregates of concrete is an innovative option. To clarify the dynamic properties of the pretreated rubberized concrete with some cumulative damage, the natural frequency, flexural dynamic stiffness, and damping ratio of the specimens under incremental stress level were [...] Read more.

Recycling scrap tyres as alternative aggregates of concrete is an innovative option. To clarify the dynamic properties of the pretreated rubberized concrete with some cumulative damage, the natural frequency, flexural dynamic stiffness, and damping ratio of the specimens under incremental stress level were investigated in this paper. The results indicated that the pretreatment of rubber particles improved the strength, ductility, and crack resistance of the rubberized concrete. The reduction of the flexural dynamic stiffness was clarified with the increase of concrete stress level. The addition of the pretreated rubber particles enhanced the concrete energy dissipation capacity during the destruction, and the specimen dissipated more energy with the increase of rubber content before its failure. Full article

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19 pages, 11022 KiB

Open AccessArticle

Supervised Learning Methods for Modeling Concrete Compressive Strength Prediction at High Temperature

by Mahmood Ahmad, Ji-Lei Hu, Feezan Ahmad, Xiao-Wei Tang, Maaz Amjad, Muhammad Junaid Iqbal, Muhammad Asim and Asim Farooq

Materials 2021, 14(8), 1983; https://doi.org/10.3390/ma14081983 - 15 Apr 2021

Cited by 48 | Viewed by 3606

Abstract

Supervised learning algorithms are a recent trend for the prediction of mechanical properties of concrete. This paper presents AdaBoost, random forest (RF), and decision tree (DT) models for predicting the compressive strength of concrete at high temperature, based on the experimental data of [...] Read more.

Supervised learning algorithms are a recent trend for the prediction of mechanical properties of concrete. This paper presents AdaBoost, random forest (RF), and decision tree (DT) models for predicting the compressive strength of concrete at high temperature, based on the experimental data of 207 tests. The cement content, water, fine and coarse aggregates, silica fume, nano silica, fly ash, super plasticizer, and temperature were used as inputs for the models’ development. The performance of the AdaBoost, RF, and DT models are assessed using statistical indices, including the coefficient of determination (R²), root mean squared error-observations standard deviation ratio (RSR), mean absolute percentage error, and relative root mean square error. The applications of the above-mentioned approach for predicting the compressive strength of concrete at high temperature are compared with each other, and also to the artificial neural network and adaptive neuro-fuzzy inference system models described in the literature, to demonstrate the suitability of using the supervised learning methods for modeling to predict the compressive strength at high temperature. The results indicated a strong correlation between experimental and predicted values, with R² above 0.9 and RSR lower than 0.5 during the learning and testing phases for the AdaBoost model. Moreover, the cement content in the mix was revealed as the most sensitive parameter by sensitivity analysis. Full article

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18 pages, 5195 KiB

Open AccessArticle

Mechanical and Durability Properties of Portland Limestone Cement (PLC) Incorporated with Nano Calcium Carbonate (CaCO₃)

by Lochana Poudyal, Kushal Adhikari and Moon Won

Materials 2021, 14(4), 905; https://doi.org/10.3390/ma14040905 - 14 Feb 2021

Cited by 30 | Viewed by 4825

Abstract

Despite lower environmental impacts, the use of Portland Limestone Cement (PLC) concrete has been limited due to its reduced later age strength and compromised durability properties. This research evaluates the effects of nano calcium carbonate (CaCO₃) on the performance of PLC [...] Read more.

Despite lower environmental impacts, the use of Portland Limestone Cement (PLC) concrete has been limited due to its reduced later age strength and compromised durability properties. This research evaluates the effects of nano calcium carbonate (CaCO₃) on the performance of PLC concrete. The study follows a series of experiments on the fresh, hardened, and durability properties of PLC concrete with different replacement rates of nano CaCO₃. Incorporation of 1% nano CaCO₃ into PLC concrete provided the optimal performance, where the 56 days compressive strength was increased by approximately 7%, and the permeability was reduced by approximately 13% as compared to Ordinary Portland Cement (OPC) concrete. Further, improvements were observed in other durability aspects such as Alkali-Silica Reaction (ASR) and scaling resistance. Additionally, nano CaCO₃ has the potential to be produced within the cement plant while utilizing the CO₂ emissions from the cement industries. The integration of nanotechnology in PLC concrete thus will help produce a more environment-friendly concrete with enhanced performance. More in-depth study on commercial production of nano CaCO₃ thus has the potential to offer a new generation cement—sustainable, economical, and durable cement—leading towards green infrastructure and global environmental sustainability. Full article

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Graphical abstract

14 pages, 23404 KiB

Open AccessArticle

Fly Ash with Ammonia: Properties and Emission of Ammonia from Cement Composites

by Filip Chyliński, Anna Goljan and Agnieszka Michalik

Materials 2021, 14(4), 707; https://doi.org/10.3390/ma14040707 - 3 Feb 2021

Cited by 5 | Viewed by 2130

Abstract

The article presents the results of tests performed on fly ash with a high content of ammonium (up to 400 ppm) from the NOx reduction process. The main properties of fly ash were tested according to EN 450-1 and the results were compared [...] Read more.

The article presents the results of tests performed on fly ash with a high content of ammonium (up to 400 ppm) from the NOx reduction process. The main properties of fly ash were tested according to EN 450-1 and the results were compared with fly ash without ammonium. The comparison showed that fly ash with high concentration of ammonium suits the requirements of the European standard. Although the requirements do not limit the ammonium content, using such material as an additive for cement composites causes the emission of gaseous ammonium during mixing and from the final product. For this reason, the emission of ammonium from mortars containing fly ash were tested. The results have shown that using high ammonium fly ash might pollute indoor air and affect the health of users. Full article

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14 pages, 6828 KiB

Open AccessArticle

Long-Term Compressive Strength Development of Steel Fiber Shotcrete from Cores Based on Accelerator Types at Tunnel Site

by Kyong Ku Yun, Seunghak Choi, Taeho Ha, Seong Kwon Kim, Mohammad Shakhawat Hossain and Seungyeon Han

Materials 2021, 14(3), 580; https://doi.org/10.3390/ma14030580 - 26 Jan 2021

Cited by 4 | Viewed by 2019

Abstract

In this study, cement minerals, aluminates, and alkali-free accelerators incorporated with steel fiber were used to scrutinize the influence of accelerating agents on the long-term performance of tunneling shotcrete. Performance tests were identified based on the core compressive strength of mix shotcrete specimens [...] Read more.

In this study, cement minerals, aluminates, and alkali-free accelerators incorporated with steel fiber were used to scrutinize the influence of accelerating agents on the long-term performance of tunneling shotcrete. Performance tests were identified based on the core compressive strength of mix shotcrete specimens with different types of accelerating agents throughout timeframes of 1, 3, 6, and 12 months. Here, 37 kg of steel fiber was incorporated into the cement mineral and aluminate mixes, and 40 kg of steel fiber was incorporated in an alkali-free mix for the shotcrete mix design. The KSF 2784 and ASTM 214 standards were followed for specimen fabrication and core cutting. For all specimens, shotcrete test panels of 250 × 600 × 500 mm were manufactured for core compressive strength tests conducted using 100, 75 and 55 mm diameter cylindrical molds and a length-to-diameter ratio of 2. The 1-month compressive strength of all test variables satisfied the Korea Expressway Co. standard of 21 MPa. The core compressive strength of the shotcrete specimens showed a tendency to increase with age, but a strength reduction occurred in 6 months and increased again at 12 months. Moreover, the impact of the diameter changes in the shotcrete core specimens was analyzed based on the mixing. For 12 months, a large increase in the core compressive strength occurred, particularly in the alkali-free specimens. The comparison also focused on the relative strength compared with a cast concrete mold and shotcrete core specimens. It is necessary to use alkali-free accelerators considering the long-term performance of tunnels and worker safety. Full article

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16 pages, 5251 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Preliminary Evaluation of Cement Mortars Containing Waste Silt Optimized with the Design of Experiments Method

by Abbas Solouki, Giovanni Viscomi, Piergiorgio Tataranni and Cesare Sangiorgi

Materials 2021, 14(3), 528; https://doi.org/10.3390/ma14030528 - 22 Jan 2021

Cited by 11 | Viewed by 2516

Abstract

Every year, up to 3 billion tons of non-renewable natural aggregates are demanded by the construction sector and approximately 623 million tons of waste (mining and quarrying) was produced in 2018. Global efforts have been made to reduce the number of virgin aggregates [...] Read more.

Every year, up to 3 billion tons of non-renewable natural aggregates are demanded by the construction sector and approximately 623 million tons of waste (mining and quarrying) was produced in 2018. Global efforts have been made to reduce the number of virgin aggregates used for construction and infrastructure sectors. According to the revised waste framework directive in Europe, recycling at least 70% of construction and demolition waste materials by 2020 was obligatory for all member states. Nonetheless, quarries must work at full capacity to keep up with the demands, which has made quarry/mining waste management an important aspect during the past decades. Amongst the various recycling methods, quarry waste can be included in cement mortar mixtures. Thus, the current research focuses on producing cement mortars by partially substituting natural sand with the waste silt obtained from the limestone aggregate production in S.A.P.A.B.A. s.r.l. (Italy). A Design of Experiments (DOE) method is proposed to define the optimum mix design, aiming to include waste silt in cement mortar mixtures without affecting the final performance. Three cement mortar beams were produced and tested for each of the 49 randomized mixtures defined by the DOE method. The obtained results validate the design approach and suggest the possibility of substituting up to 20% of natural sand with waste silt in cement mortar mixtures. Full article

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32 pages, 7428 KiB

Open AccessEditor’s ChoiceReview

Palm Oil Fuel Ash-Based Eco-Efficient Concrete: A Critical Review of the Short-Term Properties

by Mugahed Amran, Gunasekaran Murali, Roman Fediuk, Nikolai Vatin, Yuriy Vasilev and Hakim Abdelgader

Materials 2021, 14(2), 332; https://doi.org/10.3390/ma14020332 - 11 Jan 2021

Cited by 64 | Viewed by 5410

Abstract

The huge demand for concrete is predicted to upsurge due to rapid construction developments. Environmental worries regarding the large amounts of carbon dioxide emanations from cement production have resulted in new ideas to develop supplemental cementing materials, aiming to decrease the cement volume [...] Read more.

The huge demand for concrete is predicted to upsurge due to rapid construction developments. Environmental worries regarding the large amounts of carbon dioxide emanations from cement production have resulted in new ideas to develop supplemental cementing materials, aiming to decrease the cement volume required for making concrete. Palm-oil-fuel-ash (POFA) is an industrial byproduct derived from palm oil waste’s incineration in power plants’ electricity generation. POFA has high pozzolanic characteristics. It is highly reactive and exhibits satisfactory micro-filling ability and unique properties. POFA is commonly used as a partially-alternated binder to Portland cement materials to make POFA-based eco-efficient concrete to build building using a green material. This paper presents a review of the material source, chemical composition, clean production and short-term properties of POFA. A review of related literature provides comprehensive insights into the potential application of POFA-based eco-efficient concrete in the construction industry today. Full article

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14 pages, 2975 KiB

Open AccessArticle

Utilization of Treated Agricultural Residue Ash as Sodium Silicate in Alkali Activated Slag Systems

by Feraidon F. Ataie

Materials 2021, 14(2), 329; https://doi.org/10.3390/ma14020329 - 11 Jan 2021

Cited by 2 | Viewed by 1800

Abstract

This study investigated the influence of rice straw ash (RSA), rice husk ash (RHA), and silica fume (SF) on alkali activated slag (AAS) systems. RSA, RHA, and SF were treated with sodium hydroxide to improve their reactivity in AAS systems. Although addition of [...] Read more.

This study investigated the influence of rice straw ash (RSA), rice husk ash (RHA), and silica fume (SF) on alkali activated slag (AAS) systems. RSA, RHA, and SF were treated with sodium hydroxide to improve their reactivity in AAS systems. Although addition of SF in AAS systems increased compressive strength, samples containing RSA or RHA had higher compressive strength than those having SF. Treated RSA or RHA further increased compressive strength of AAS samples. It was shown that samples containing treated ash samples had similar compressive strength to those made with sodium silica activator. Therefore, it is suggested that treated ash samples could be used as alternative sources of silica for AAS. Drying shrinkage of AAS samples increased considerably when treated RSA or RHA were used as partial replacement of slag. This could be attributed to higher silica modulus (SiO₂/Na₂O) ratio of samples containing treated ash, which in turn would lead to a finer pore size structure compared to control samples. However, SF significantly reduced drying shrinkage of AAS. This could be because SF reduces the permeability and porosity of AAS samples. Full article

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21 pages, 12860 KiB

Open AccessArticle

A Comparative Study on Skid Resistance of Concrete Pavements Differing in Texturing Technique

by Pawel Gierasimiuk, Marta Wasilewska and Wladyslaw Gardziejczyk

Materials 2021, 14(1), 178; https://doi.org/10.3390/ma14010178 - 1 Jan 2021

Cited by 11 | Viewed by 2803

Abstract

The paper presents a comparison of the skid resistance of concrete pavements textured with different techniques in the process of simulating phenomena occurring in actual road conditions. Tests were carried out on five different texturing methods for concrete pavements: burlap drag (BuD), brush [...] Read more.

The paper presents a comparison of the skid resistance of concrete pavements textured with different techniques in the process of simulating phenomena occurring in actual road conditions. Tests were carried out on five different texturing methods for concrete pavements: burlap drag (BuD), brush drag (BrD), transverse tining (TT), longitudinal tining (LT) and exposed aggregate concrete (EAC). Changes in the skid resistance were recorded by measurements with a British pendulum tester and a circular texture meter before and during the simulation of the abrasion (1st phase of test) and polishing (2nd phase of test) of specimens using a slab polisher. The results of BPN (British pendulum number) and MPD (mean profile depth) allowed us to determine the influence of microtexture and macrotexture on skid resistance. Analysis of variance showed that the method of texturing concrete pavements has a significant influence on the mean BPN values as well as the MPD parameter at each stage of the test. In order to distinguish homogeneous groups in terms of BPN and MPD levels at the particular stages of the process, the Tukey’s HSD (honest significant difference) post-hoc test was performed. It was found that EAC obtained the most favorable results of all the tested pavement types. Due to the high value of the MPD coefficient after the test and the appropriate values of the friction coefficient, it was confirmed that the EAC pavement will be a durable solution due to the guarantee of skid resistance on high-speed roads during its service life. Full article

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2020

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16 pages, 2372 KiB

Open AccessArticle

Influence of Redispersible Powder on Properties of Self-Leveling Mortar of Ternary Cementitious System

by Wenyan Dong, Congqi Fang and Ran Hu

Materials 2020, 13(24), 5703; https://doi.org/10.3390/ma13245703 - 14 Dec 2020

Cited by 8 | Viewed by 1972

Abstract

The self-leveling mortar (SLM) of a ternary cementitious system with different dosages of redispersible powder (RP) with ordinary Portland cement (OPC), sulfoaluminate cement (SAC), and calcium sulfate (CS) as cementitious materials was investigated with regard to fluidity, bond strength, shrinkage rate, abrasion resistance, [...] Read more.

The self-leveling mortar (SLM) of a ternary cementitious system with different dosages of redispersible powder (RP) with ordinary Portland cement (OPC), sulfoaluminate cement (SAC), and calcium sulfate (CS) as cementitious materials was investigated with regard to fluidity, bond strength, shrinkage rate, abrasion resistance, flexural strength, and compressive strength. The performance parameters obtained from the experimental test for SLM were weighted values calculated with an analytic hierarchy process (AHP). The comprehensive index of performance was evaluated on the basis of a weighted-sum method, and the optimal dosage of RP was determined according to the comprehensive index. The experimental results demonstrated that the fluidity of SLM decreased with the increase in RP dosage at the beginning but then increased thereafter and decreased rapidly as the dosage went beyond 3.0%. The addition of RP resulted in a significant improvement in bond strength (of SLM), reduction in the shrinkage rate, abrasion loss, early flexural strength and compressive strength, and resistance to cracking. The properties of SLM with 3.0% RP can meet the requirements of the industrial standard for cementitious self-leveling floor mortar. Compared with the SLM without RP, the bond strength of SLM with 3.0% RP was increased by 46.7%, while the shrinkage rate and abrasion loss were reduced by 50% and 71.9% respectively. The weighted values of fluidity, compressive strength, flexural strength, stability, cohesiveness, and abrasion resistance were 0.422, 0.196, 0.196, 0.089, 0.058, and 0.039, respectively. A higher value of the comprehensive index generally denotes a better performance. The comprehensive index of SLM with 3.0% RP was the highest. Full article

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13 pages, 3711 KiB

Open AccessArticle

Production of Greener High-Strength Concrete Using Russian Quartz Sandstone Mine Waste Aggregates

by Aleksandr Tolstoy, Valery Lesovik, Roman Fediuk, Mugahed Amran, Murali Gunasekaran, Nikolai Vatin and Yuriy Vasilev

Materials 2020, 13(23), 5575; https://doi.org/10.3390/ma13235575 - 7 Dec 2020

Cited by 49 | Viewed by 3524

Abstract

Quartz sandstone (QS) is a mine waste; therefore, its use in construction allows for both reducing the cost of the concrete and contributing to the utilization of waste. The scientific originality of this study is the identification of models of the effect of [...] Read more.

Quartz sandstone (QS) is a mine waste; therefore, its use in construction allows for both reducing the cost of the concrete and contributing to the utilization of waste. The scientific originality of this study is the identification of models of the effect of QS aggregate on the physicomechanical, durability characteristics, and eco-safety of greener high-strength concrete. The study used an energy-efficient method of non-thermal effects of electromagnetic pulses on the destruction mechanisms of quartz-containing raw materials. The characteristics of quartzite sandstone aggregates, including the natural activity of radionuclides, were comprehensively studied. The features of concrete hardening, including the formation of an interfacial transition zone between the aggregate and the cement matrix, were studied, taking into account the chemical and morphological features of quartzite sandstone. In addition, the microstructural and morphological properties of concrete were determined after a 28 day curing. In this study, the behaviors of the concrete with QS aggregate were investigated, bearing in mind the provisions of geomimetics science on the affinity of structures. The results obtained showed that the QS aggregate had the activity of natural radionuclides 3–4 times lower compared to traditional aggregates. Efficient greener concrete with a 46.3 MPa compressive strength, water permeability grade W14, and freeze–thaw resistance of 300 cycles were also obtained, demonstrating that the performance of this greener concrete was comparable to that of traditional concrete with more expensive granite or gabbro diabase aggregates. Full article

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16 pages, 4892 KiB

Open AccessArticle

Influence of Hydrated Lime on the Chloride-Induced Reinforcement Corrosion in Eco-Efficient Concretes Made with High-Volume Fly Ash

by Manuel Valcuende, Rafael Calabuig, Ana Martínez-Ibernón and Juan Soto

Materials 2020, 13(22), 5135; https://doi.org/10.3390/ma13225135 - 14 Nov 2020

Cited by 7 | Viewed by 1681

Abstract

The main objective of this study was to analyze the influence that the addition of finely ground hydrated lime has on chloride-induced reinforcement corrosion in eco-efficient concrete made with 50% cement replacement by fly ash. Six tests were carried out: mercury intrusion porosimetry, [...] Read more.

The main objective of this study was to analyze the influence that the addition of finely ground hydrated lime has on chloride-induced reinforcement corrosion in eco-efficient concrete made with 50% cement replacement by fly ash. Six tests were carried out: mercury intrusion porosimetry, chloride migration, accelerated chloride penetration, electrical resistivity, and corrosion rate. The results show that the addition of 10–20% of lime to fly ash concrete did not affect its resistance to chloride penetration. However, the cementitious matrix density is increased by the pozzolanic reaction between the fly ash and added lime. As a result, the porosity and the electrical resistivity improved (of the order of 10% and 40%, respectively), giving rise to a lower corrosion rate (i_CORR) of the rebars and, therefore, an increase in durability. In fact, after subjecting specimens to wetting–drying cycles in a 0.5 M sodium chloride solution for 630 days, corrosion is considered negligible in fly ash concrete with 10% or 20% lime (i_CORR less than 0.2 µA/cm²), while in fly ash concrete without lime, corrosion was low (i_CORR of the order of 0.3 µA/cm²) and in the reference concrete made with Portland cement, only the corrosion was high (i_CORR between 2 and 3 µA/cm²). Full article

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15 pages, 2226 KiB

Open AccessArticle

Comparison of Drying Shrinkage of Concrete Specimens Recycled Heavyweight Waste Glass and Steel Slag as Aggregate

by So Yeong Choi, Il Sun Kim and Eun Ik Yang

Materials 2020, 13(22), 5084; https://doi.org/10.3390/ma13225084 - 11 Nov 2020

Cited by 22 | Viewed by 2473

Abstract

This study analyzed the fundamental properties of concrete using steel slag, to test its viability as an aggregate material. An experimental investigation into the effect of steel slag as a coarse aggregate, and heavyweight waste glass as a fine aggregate, on the drying [...] Read more.

This study analyzed the fundamental properties of concrete using steel slag, to test its viability as an aggregate material. An experimental investigation into the effect of steel slag as a coarse aggregate, and heavyweight waste glass as a fine aggregate, on the drying shrinkage of concrete was performed. The calculated shrinkage strain was compared to five different shrinkage prediction models, namely, the ACI 209, B3, KCI 2012, EC 2 and GL 2000 model codes, to evaluate their ability to accurately predict shrinkage behavior. From the results, the elastic modulus of concrete increased with the increase in steel slag substitution ratio, however drying shrinkage decreased. The predictive value of the existing prediction model of drying shrinkage differed from the experimental values, and requires correction to improve its accuracy. The B3 model code showed the best prediction results of drying shrinkage. Full article

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14 pages, 2713 KiB

Open AccessArticle

Concrete Compressive Strength under Changing Environmental Conditions during Placement Processes

by Andrzej Ambroziak and Patryk Ziolkowski

Materials 2020, 13(20), 4577; https://doi.org/10.3390/ma13204577 - 14 Oct 2020

Cited by 17 | Viewed by 4324

Abstract

The technological process of concrete production consists of several parts, including concrete mix design, concrete mix production, transportation of fresh concrete mix to a construction site, placement in concrete framework, and curing. Proper execution of these steps provides good quality concrete. Some factors [...] Read more.

The technological process of concrete production consists of several parts, including concrete mix design, concrete mix production, transportation of fresh concrete mix to a construction site, placement in concrete framework, and curing. Proper execution of these steps provides good quality concrete. Some factors can disturb the technological process, mainly temperature and excessive precipitation. Changing daily temperature and rainfall during fabrication, transportation, and placement can shape not only the properties of the concrete mix but also the compressive strength of hardened concrete. In this paper, we tried to answer the question of how temperature and precipitation affect concrete production. The scope of this study was to determine the change of compressive strength of the hardened concrete in a specific period for selected concrete mix recipes, taking into account changing daily temperature and precipitation magnitude. The investigated concrete mixes concrete compressive strength beyond that of the concrete grade, termed “concrete superstrength”. This concrete post limiting behaviour of concrete is also discussed. Full article

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18 pages, 6073 KiB

Open AccessArticle

Effects of Groove and Steel Fiber on Shear Properties of Concrete with Recycled Coarse Aggregate

by Danying Gao, Yongming Yan, Yuyang Pang, Jiyu Tang, Lin Yang and Zhiqiang Gu

Materials 2020, 13(20), 4537; https://doi.org/10.3390/ma13204537 - 13 Oct 2020

Cited by 6 | Viewed by 1870

Abstract

In this paper, a series of shear specimens with or without groove were manufactured to mainly analyze the effects of grooves (or shear section height) and steel fibers on the shear properties of concrete with recycled coarse aggregate through double-side direct shear test. [...] Read more.

In this paper, a series of shear specimens with or without groove were manufactured to mainly analyze the effects of grooves (or shear section height) and steel fibers on the shear properties of concrete with recycled coarse aggregate through double-side direct shear test. In addition, the relationship between the shear strength and the compressive strength and splitting tensile strength of steel fiber reinforced concrete with recycled coarse aggregate (SFRCAC) was also discussed. The experimental results showed that the peak load, deformation corresponding to the peak load and calculated shear strength of the specimens with grooves were lower than those of the specimens without grooves. The steel fiber and recycled coarse aggregate (RCA) had a significant effect on the shear properties of SFRCAC. As the volume content of steel fibers increased, the shear strength of SFRCAC and the corresponding deformation increased gradually. With the replacement ratio of RCA increasing, the shear strength of SFRCAC decreased but the corresponding deformation increased gradually. Finally, the formula for calculating the shear strength of SFRCAC was proposed by analyzing and fitting the test results and the data of related literature. Full article

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13 pages, 3646 KiB

Open AccessArticle

Study on the Deterioration of Concrete under Dry–Wet Cycle and Sulfate Attack

by Fang Liu, Tonghuan Zhang, Tao Luo, Mengzhen Zhou, Kunkun Zhang and Weiwei Ma

Materials 2020, 13(18), 4095; https://doi.org/10.3390/ma13184095 - 15 Sep 2020

Cited by 41 | Viewed by 2882

Abstract

In order to study the deterioration and mechanism of dry–wet cycles and sulfate attack on the performance of concrete in seaside and saline areas, the deterioration of compressive strength of concrete with different water cement ratios under different erosion environments (sodium sulfate soaking [...] Read more.

In order to study the deterioration and mechanism of dry–wet cycles and sulfate attack on the performance of concrete in seaside and saline areas, the deterioration of compressive strength of concrete with different water cement ratios under different erosion environments (sodium sulfate soaking at room temperature and coupling of dry–wet cycling and sodium sulfate) was studied here. At the same time, ICT (industrial computed tomography) and NMR (nuclear magnetic resonance) techniques were used to analyze the internal pore structure of concrete under different erosion environments. The results show that the compressive strength under different erosion environments increases first and then decreases, and the dry–wet cycle accelerates the sulfate erosion. With the increase of dry and wet cycles, larger pores are filled with erosion products and developed into small pores in the early stage of erosion; in the later stage of erosion, the proportion of larger pores increases, and cracks occur inside the sample. In the process of sulfate soaking and erosion, the smaller pores in the concrete account for the majority. As the sulfate erosion continues, the T₂ spectrum distribution curve gradually moves right, and the signal intensity of the larger pores increases. Full article

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15 pages, 931 KiB

Open AccessArticle

Effect of Low Atmospheric Pressure on Air Entrainment in Cement-Based Materials: An On-Site Experimental Study at Different Elevations

by Xin Chen, Xu Liu, Bo Tian, Yong Ge and Lihui Li

Materials 2020, 13(18), 3975; https://doi.org/10.3390/ma13183975 - 8 Sep 2020

Cited by 20 | Viewed by 2297

Abstract

The efficiency and stability of air entrainment in concrete are sometimes found to be weaker at higher elevation. This phenomenon was attributed to the low atmospheric pressure by many researchers, however, the level of influence of atmospheric pressure on concrete air content dramatically [...] Read more.

The efficiency and stability of air entrainment in concrete are sometimes found to be weaker at higher elevation. This phenomenon was attributed to the low atmospheric pressure by many researchers, however, the level of influence of atmospheric pressure on concrete air content dramatically varied among different studies. In order to clarify the effect of low atmospheric pressure on air entrainment in cement-based materials, an on-site experimental study was conducted with a rigorous control of irrelevant variables. The study focused on the air-entraining efficiency in cement paste, mortar, and concrete prepared in both low and standard atmospheric pressures. The air bubble stability in fresh mortar and air void characteristics of hardened mortar in different atmospheric pressures were also included. In the study, little effect of low atmospheric pressure on the air-entraining efficiency and air bubble stability in mortar with studied air-entraining agents (AEAs) was found. The air void characteristics were found to be similar between mortar with SJ-2 or 303R type AEAs prepared in different atmospheric pressures. Concrete with either SJ-2 or 303R type AEA prepared in low atmospheric pressure presented a satisfactory air content. These conclusions indicate that it is not necessary to worry excessively about the potentially adverse effect of atmospheric pressure on the frost resistance of concrete if a suitable AEA is applied. Additionally, a supplementary mortar study found that the low temperature of raw materials stored at high elevation would significantly weaken the air entrainment, reminding that potential causes in addition to low atmospheric pressure should also be taken seriously. Full article

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12 pages, 4109 KiB

Open AccessFeature PaperArticle

Influence of the Size and Type of Pores on Brick Resistance to Freeze-Thaw Cycles

by Ivanka Netinger Grubeša, Martina Vračević, Vilma Ducman, Berislav Marković, Imre Szenti and Ákos Kukovecz

Materials 2020, 13(17), 3717; https://doi.org/10.3390/ma13173717 - 22 Aug 2020

Cited by 18 | Viewed by 3002

Abstract

This paper estimates the frost resistance of bricks using the ratio of compressive strength before freezing to compressive strength after freezing to describe the damage degree of bricks being exposed to freeze-thaw cycles. In an effort to find the ratio that clearly distinguishes [...] Read more.

This paper estimates the frost resistance of bricks using the ratio of compressive strength before freezing to compressive strength after freezing to describe the damage degree of bricks being exposed to freeze-thaw cycles. In an effort to find the ratio that clearly distinguishes resistant bricks from non-resistant bricks, the authors attempted to establish the correlation between the ratio and Maage factor as a recognized model for assessing brick resistance. To clarify the degree of damage of individual bricks, the pore size distribution has been investigated by means of mercury porosimetry. Additionally, micro computed X-ray tomography (micro-CT) has been employed to define the influence of the type of pores (open or closed) and their connectivity on the frost resistance of bricks. According to the results, it can be concluded that there is a good correlation between the Maage factor and the ratio of pre- to post-freeze-thaw cycle compressive strengths, and that the latter ratio strongly correlates with the percentage of large pores (≥3 mm) in the brick. If such a correlation could be confirmed in a larger sample, then the ratio of pre- to post-freeze-thaw cycle compressive strengths could be used as a new method for assessing brick resistance to freeze-thaw cycles and it would be possible to determine the minimum percentage of large pores required to ensure the overall resistance of brick to freeze-thaw conditions. The complexity of the problem is, however, evidenced by the fact that no clear connection between the type (open versus closed) or connectivity of pores and the frost resistance of bricks could be revealed by micro-CT. Full article

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15 pages, 7046 KiB

Open AccessArticle

Undissolved Ilmenite Mud from TiO₂ Production—Waste or a Valuable Addition to Portland Cement Composites?

by Filip Chyliński, Jan Bobrowicz and Paweł Łukowski

Materials 2020, 13(16), 3555; https://doi.org/10.3390/ma13163555 - 12 Aug 2020

Cited by 9 | Viewed by 3098

Abstract

This paper presents a method of utilising ilmenite MUD created during the production of titanium dioxide (TiO₂) according to the sulphate method as an additive for Portland cement composites. After the production process, undissolved MUD was additionally rinsed with water and [...] Read more.

This paper presents a method of utilising ilmenite MUD created during the production of titanium dioxide (TiO₂) according to the sulphate method as an additive for Portland cement composites. After the production process, undissolved MUD was additionally rinsed with water and filtrated in the factory to make it more useful (R-MUD) for implementation and also to turn back some of the by-products of the production of TiO₂. R-MUD is less hazardous waste than MUD. It has a lower concentration of sulphuric acid and some heavy metals. The rinsing process raised the concentration of SiO₂, which is a valuable part of R-MUD because of its potential pozzolanic activity. This means that the R-MUD might be a reactive substitute of part of Portland cement in building composites. The article presents the results of research on the pozzolanic activity of R-MUD and other materials with proved pozzolanic activity, such as silica fume, fly ash and natural pozzolana (trass). Tests were performed using thermal analysis techniques. The tests showed that the pozzolanic activity or R-MUD after three days is at the same level as silica fume and after 28 days it is twice as high as the activity of fly ash. Beyond the 180th day of curing, R-MUD had the same level of activity as fly ash. The summary is supplemented by calorimetric tests, which confirm the high reactivity of R-MUD compared to other commonly used concrete additives, already in the initial hydration period. In summary, heat of hydration after 72 h of Portland cement with R-MUD is at the same level as the heat of hydration of Portland cement with silica fume and also pure Portland cement grout. The results confirm that the process of formation of micro-silica contained in R-MUD react with calcium hydroxide to form the C-S-H phase, which is responsible for the microstructure of cement composites. Full article

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11 pages, 3608 KiB

Open AccessArticle

Effect of Mineral Admixtures on the Sulfate Resistance of High-Strength Piles Mortar

by Yanyan Hu, Linlin Ma and Tingshu He

Materials 2020, 13(16), 3500; https://doi.org/10.3390/ma13163500 - 8 Aug 2020

Cited by 6 | Viewed by 2516

Abstract

Pre-stressed high-strength concrete piles (PHCP) are widely used in the building industry in China. The main aim of our research was to investigate the utilization of quartz powder, fly ash, and blast furnace slag as mineral additives to prepare PHCP mortar. The samples [...] Read more.

Pre-stressed high-strength concrete piles (PHCP) are widely used in the building industry in China. The main aim of our research was to investigate the utilization of quartz powder, fly ash, and blast furnace slag as mineral additives to prepare PHCP mortar. The samples were prepared using steam and autoclaving steaming. The influence of minerals on the sulfate resistance of mortar was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests. The results showed that when compared to single doped quartz powder samples, samples prepared using fly ash or blast furnace slag improved the sulfate resistance of the PHCP mortar. Furthermore, the resistance to sulfate attack of samples with dual doped quartz powder, fly ash, and blast furnace slag also improved. MIP tests showed that mineral additives can change the pore size distribution after autoclave curing. However, the number of aching holes increased after mixing with 20% quartz powder and caused a decrease in the sulfate resistance. Full article

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17 pages, 14156 KiB

Open AccessArticle

Characteristics of Lightweight Cellular Concrete and Effects on Mechanical Properties

by Wei Yu, Xu Liang, Frank Mi-Way Ni, Abimbola Grace Oyeyi and Susan Tighe

Materials 2020, 13(12), 2678; https://doi.org/10.3390/ma13122678 - 12 Jun 2020

Cited by 13 | Viewed by 3031

Abstract

This study investigated the pore structure and its effects on mechanical properties of lightweight cellular concrete (LCC) in order to understand more and detailed characteristics of such structure. As part of investigation, environment scanning electron microscopes (ESEM) and industrial high-definition (HD) macro photography [...] Read more.

This study investigated the pore structure and its effects on mechanical properties of lightweight cellular concrete (LCC) in order to understand more and detailed characteristics of such structure. As part of investigation, environment scanning electron microscopes (ESEM) and industrial high-definition (HD) macro photography camera were separately used to capture and compare images of specimens. Physical properties of the pore structure, including pore area, size, perimeter, fit ellipse, and shape descriptors, were studied based on the image processing technology and software applications. Specimens with three different densities (400, 475, and 600 kg/m³) were prepared in the laboratory. Firstly, the effects of density on the characteristics of pore structure were investigated; furthermore, mechanical properties (compressive strength, modulus of elasticity and Poisson’s ratio, flexural strength and splitting tensile strength of LCC) were tested. The relationships among pore characteristics, density, and mechanical properties were analyzed. Based on the results obtained from the lab test—comparisons made between specimens with high-densities and those with low-densities—it was found significant variability in bubble size, thickness, and irregularity of pores. Furthermore, the increase of density is accompanied by better mechanical properties, and the main influencing factors are the thickness of the solid part and the shape of the bubble. The thicker of solid part and more regular pores of LCC has, the better mechanical properties are. Full article

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