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3 pages, 170 KiB

Open AccessEditor’s ChoiceEditorial

Special Issue: “Microstructures and Durability of Cement-Based Materials”

by Jeong Gook Jang and Solmoi Park

Materials 2021, 14(4), 866; https://doi.org/10.3390/ma14040866 - 11 Feb 2021

Cited by 3 | Viewed by 1792

Abstract

Cement-based materials play an irreplaceable role in building and sustaining our society by meeting the performance demand imposed on structures and sustainability. Cement-based materials are no longer limited to derivatives of Portland cement, and appreciate a wider range of binders that come from [...] Read more.

Cement-based materials play an irreplaceable role in building and sustaining our society by meeting the performance demand imposed on structures and sustainability. Cement-based materials are no longer limited to derivatives of Portland cement, and appreciate a wider range of binders that come from various origins. It is therefore of utmost importance for understanding and expanding the relevant knowledge on their microstructure and likely durability performance. This Special Issue “Microstructures and Durability of Cement-Based Materials” presents recent studies reporting microstructural and durability investigation revealing the characteristics of cement-based materials. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

Research

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16 pages, 8360 KiB

Open AccessArticle

Durability and Strength Characteristics of Casein-Cemented Sand with Slag

by Sung-Sik Park, Seung-Wook Woo, Sueng-Won Jeong and Dong-Eun Lee

Materials 2020, 13(14), 3182; https://doi.org/10.3390/ma13143182 - 16 Jul 2020

Cited by 10 | Viewed by 2318

Abstract

Casein is often used as an eco-friendly wood adhesive. In this study, we used casein for soil cementation by mixing it with Jumunjin sand, sodium hydroxide (SH), and calcium hydroxide (CH) as a standard casein formula. The modified casein binder with different proportions [...] Read more.

Casein is often used as an eco-friendly wood adhesive. In this study, we used casein for soil cementation by mixing it with Jumunjin sand, sodium hydroxide (SH), and calcium hydroxide (CH) as a standard casein formula. The modified casein binder with different proportions of SH and CH was applied to improve water resistance. Furthermore, a blast furnace slag (BFS) was additionally mixed and reacted with alkalinity of modified casein binder. Thus, three types (standard, modified, and modified + BFS, referred to as STD, MOD, and MBS, hereafter) of casein binders were tested for durability and strength of casein-cemented sand. A piezoelectric sensor was installed within each sample to determine the curing time of the casein-cemented samples. The samples were air-cured at room temperature for seven days and some were repeatedly immersed in water thrice. Unconfined compression and jar slake tests were carried out to evaluate the strength and durability of the casein-cemented sand. Also, the microstructure was analyzed using a scanning electron microscope (SEM). We observed variations of peak conductance and corresponding frequency converged as the curing time increased. It was most significant for the MBS samples, which developed strength early. The unconfined compressive strength (UCS) of the air-cured samples was higher than those repeatedly immersed in water due to wash-off of the casein binder. The UCS of the dry MBS sample was 9900 kPa while that of the immersed sample was 430 kPa, which gradually decreased to 60 kPa upon repeated immersion. The samples with STD and MOD had no resistance to durability and showed cracks on the surface, while the MBS sample exhibited significantly improved durability and no cracks. We found that the MBS binder had a positively significant effect on the durability and strength of casein-cemented sand. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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14 pages, 5625 KiB

Open AccessArticle

Effect of Carbon Nanotube and Styrene-Acrylic Emulsion Additives on Microstructure and Mechanical Characteristics of Cement Paste

by Jie Fan, Gengying Li, Sijie Deng, Chengwei Deng, Zhongkun Wang and Zhijun Zhang

Materials 2020, 13(12), 2807; https://doi.org/10.3390/ma13122807 - 22 Jun 2020

Cited by 15 | Viewed by 2782

Abstract

Carbon nanotubes (CNTs) are considered as one of the ideal modifiers of cement materials, since CNTs can improve the mechanical properties of cement paste effectively. However, the interfacial interaction between CNTs and the cement matrix is weak. Moreover, it is difficult to disperse [...] Read more.

Carbon nanotubes (CNTs) are considered as one of the ideal modifiers of cement materials, since CNTs can improve the mechanical properties of cement paste effectively. However, the interfacial interaction between CNTs and the cement matrix is weak. Moreover, it is difficult to disperse CNTs within cement paste. To overcome these shortages, in this study, CNTs were firstly dispersed into a styrene-acrylic emulsion (SAE). Then the homo-dispersion CNT/SAE emulsion was incorporated into cement paste. The effect of the CNT/SAE hybrid-system on the mechanical properties and microstructure of cement paste was studied. For purposes of comparison, the properties of cement paste mono incorporating CNTs or SAE are also investigated. The results show that CNT/SAE network films could be observed in cement paste by using a field emission scanning electron microscope (FESEM). These network films could bridge the cracks and refine the pores of a cement matrix. Infrared analysis and Raman spectroscopy show that the CNT/SAE hybrid modifier has stronger interfacial adhesion and better load transfer ability over the mono adding of CNTs and SAE emulsion. As a result, the hybrid addition of CNT/SAE significantly improved the flexural strength of cement paste. Especially, the addition of 0.1% CNTs and 15% SAE by mass of cement improved the 28-day flexural strength of cement paste by 21% and 25% as compared to the mono addition of CNTs or SAE, respectively. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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15 pages, 6225 KiB

Open AccessArticle

Effects of Temperature on Fluidity and Early Expansion Characteristics of Cement Asphalt Mortar

by Xiaohui Zeng, Huasheng Zhu, Xuli Lan, Haichuan Liu, H.A Umar, Youjun Xie, Guangcheng Long and Cong Ma

Materials 2020, 13(7), 1655; https://doi.org/10.3390/ma13071655 - 3 Apr 2020

Cited by 5 | Viewed by 2513

Abstract

In order to solve the problems of the sudden loss of fluidity and low expansion rate of CAM I (cement asphalt mortar type I) in a construction site with high environmental temperature, this paper studies the effect of temperature on the fluidity, expansion [...] Read more.

In order to solve the problems of the sudden loss of fluidity and low expansion rate of CAM I (cement asphalt mortar type I) in a construction site with high environmental temperature, this paper studies the effect of temperature on the fluidity, expansion ratio and pH value of CAM I. The mechanism of action was analyzed by IR (infrared spectrometry), SEM (scanning electron microscopy) and other test methods. The results showed that a high temperature accelerates aluminate formation in cement paste. Aluminate adsorbs emulsifiers leading to demulsification of emulsified asphalt, and wrapped on the surface of cement particles, this causes CAM I to lose its fluidity rapidly. The aluminum powder gasification reaction is inhibited, resulting in an abnormal change in the expansion ratio. Based on findings, the application of an appropriate amount of superplasticizers can effectively improve the workability and expansion characteristics of CAM I at a high temperature. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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13 pages, 3119 KiB

Open AccessArticle

Mechanical Properties, Microstructure, and Chloride Content of Alkali-Activated Fly Ash Paste Made with Sea Water

by Salman Siddique and Jeong Gook Jang

Materials 2020, 13(6), 1467; https://doi.org/10.3390/ma13061467 - 23 Mar 2020

Cited by 16 | Viewed by 3106

Abstract

The aim of the present study is to investigate the potential of sea water as a feasible alternative to produce alkali-activated fly ash material. The alkali-activated fly ash binder was fabricated by employing conventional pure water, tap water, and sea water based alkali [...] Read more.

The aim of the present study is to investigate the potential of sea water as a feasible alternative to produce alkali-activated fly ash material. The alkali-activated fly ash binder was fabricated by employing conventional pure water, tap water, and sea water based alkali activating solution. The characteristics of alkali-activated materials were examined by employing compressive strength, mercury intrusion porosimetry, XRD, FT-IR, and ²⁹Si NMR along with ion chromatography for chloride immobilization. The results provided new insights demonstrating that sea water can be effectively used to produce alkali activated fly ash material. The presence of chloride in sea water contributed to increase compressive strength, refine microstructure, and mineralogical characteristics. Furthermore, a higher degree of polymerization on the sea water-based sample was observed by FT-IR and ²⁹Si NMR analysis. However, the higher amount of free chloride ion even after immobilization in sea water-based alkali-activated material, should be considered before application in reinforced structural elements. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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19 pages, 7939 KiB

Open AccessArticle

Inventive Microstructural and Durability Investigation of Cementitious Composites Involving Crystalline Waterproofing Admixtures and Portland Limestone Cement

by Pejman Azarsa, Rishi Gupta and Alireza Biparva

Materials 2020, 13(6), 1425; https://doi.org/10.3390/ma13061425 - 20 Mar 2020

Cited by 38 | Viewed by 5741

Abstract

The durability of a cement-based material is mainly dependent on its permeability. Modifications of porosity, pore-structure and pore-connectivity could have significant impacts on permeability improvement, which eventually leads to more durable materials. One of the most efficient solutions in this regard is to [...] Read more.

The durability of a cement-based material is mainly dependent on its permeability. Modifications of porosity, pore-structure and pore-connectivity could have significant impacts on permeability improvement, which eventually leads to more durable materials. One of the most efficient solutions in this regard is to use permeability reducing admixtures (PRA). Among these admixtures for those structures exposed to hydro-static pressure, crystalline waterproofing admixtures (CWA) have been serving in the construction industries for decades and according to ACI 212—chemical admixtures’ report, it has proven its capability in permeability reduction and durability-enhancement. However, there is substantial research being done on its durability properties at the macro level but very limited information available regarding its microstructural features and chemical characteristics at the micro level. Hence, this paper presents one of the first reported attempts to characterize microstructural and chemical elements of hydration products for cementitious composites with CWA called K, P and X using Scanning Electron Microscopy (SEM). Backscattered SEM images taken from a polished-section of one CWA type—K—admixture were analyzed in ImageJ to obtain paste matrix porosity, indicating a lower value for the CWA-K mixture. X-ray analysis and SEM micrographs of polished sections were examined to identify chemical compositions based on atomic ratio plots and brightness differences in backscatter-SEM images. To detect chemical elements and the nature of formed crystals, the fractured surfaces of three different CWA mixtures were examined. Cementitious composites with K admixture indicated needle-like crystal formation—though different from ettringite; X and P admixtures showed sulfur peaks in Energy Dispersive Spectrum (EDS) spectra, like ettringite. SEM images and X-ray analyses of mixtures incorporating Portland Limestone Cement (PLC) indicated lower-than-average porosity but showed different Si/Ca and Al/Ca atomic ratios. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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19 pages, 5166 KiB

Open AccessArticle

Field Validation of Concrete Transport Property Measurement Methods

by Ahmed Abd El Fattah, Ibrahim Al-Duais, Kyle Riding, Michael Thomas, Salah Al-Dulaijan and Mesfer Al-Zahrani

Materials 2020, 13(5), 1166; https://doi.org/10.3390/ma13051166 - 5 Mar 2020

Cited by 15 | Viewed by 2561

Abstract

Reinforcing steel corrosion, caused by chloride ingress into concrete, is the leading cause of reinforced concrete deterioration. One of the main findings in the literature for reducing chloride ingress is the improvement of the durability characteristics of concrete by the addition of supplementary [...] Read more.

Reinforcing steel corrosion, caused by chloride ingress into concrete, is the leading cause of reinforced concrete deterioration. One of the main findings in the literature for reducing chloride ingress is the improvement of the durability characteristics of concrete by the addition of supplementary cementitious materials (SCMs) and/or chemical agents to concrete mixtures. In this study, standard ASTM tests—such as rapid chloride permeability (RCPT), bulk diffusion and sorptivity tests—were used to measure concrete properties such as porosity, sorptivity, salt diffusion, and permeability. Eight different mixtures, prepared with different SCMs and corrosion inhibitors, were tested. Apparent and effective chloride diffusion coefficients were calculated using bound chloride isotherms and time-dependent decrease in diffusion. Diffusion coefficients decreased with time, especially with the addition of SCMs and corrosion inhibitors. The apparent diffusion coefficient calculated using the error function was slightly lower than the effective diffusion coefficient; however, there was a linear trend between the two. The formation factor was found to correlate with the effective diffusion coefficient. The results of the laboratory tests were compared and benchmarked to their counterparts in the marine exposure site in the Arabian Gulf in order to identify laboratory key tests to predict concrete durability. The overall performance of concrete containing SCMs, especially fly ash, were the best among the other mixtures in the laboratory and the field. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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12 pages, 1768 KiB

Open AccessArticle

Prediction on Compressive and Split Tensile Strengths of GGBFS/FA Based GPC

by Songhee Lee and Sangmin Shin

Materials 2019, 12(24), 4198; https://doi.org/10.3390/ma12244198 - 13 Dec 2019

Cited by 8 | Viewed by 2908

Abstract

Based on rate constant concept, empirical models were presented for the predictions of age-dependent development of compressive and split tensile strengths of geopolymer concrete composite (GPCC) with fly ash (FA) blended with ground granulated blast furnace slag (GGBFS). The models were empirically developed [...] Read more.

Based on rate constant concept, empirical models were presented for the predictions of age-dependent development of compressive and split tensile strengths of geopolymer concrete composite (GPCC) with fly ash (FA) blended with ground granulated blast furnace slag (GGBFS). The models were empirically developed based on a total of 180 cylindrical test results of GPCC. Six different independent factors comprising of curing temperature, the weight ratios of GGBFS/binder, the aggregate/binder, the alkali solution/binder, the Na₂SiO₃/NaOH, and the NaOH concentration were considered as the variables. The ANOVA analyses performed on Taguchi orthogonal arrays with six factors in three levels showed that the curing temperature and ratio of GGBFS to binder were the main contributing factors to the development of compressive strength. The models, functionalized with these contributing factors and equivalent age, reflect the level of activation energy of GPCC similar to that of ordinary Portland cement concrete (OPC) and a higher frequency of molecular collisions during the curing period at elevated temperature. The model predictions for compressive and split tensile strength showed good agreements with tested results. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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25 pages, 11120 KiB

Open AccessArticle

The Effects of Multi-Walled Carbon Nanotubes and Steel Fibers on the AC Impedance and Electromagnetic Shielding Effectiveness of High-Performance, Fiber-Reinforced Cementitious Composites

by Namkon Lee, Sungwook Kim and Gijoon Park

Materials 2019, 12(21), 3591; https://doi.org/10.3390/ma12213591 - 31 Oct 2019

Cited by 18 | Viewed by 2843

Abstract

This study aimed to investigate the effect of multi-walled carbon nanotubes (MWCNTs) and steel fibers on the AC impedance and electromagnetic shielding effectiveness (SE) of a high-performance, fiber-reinforced cementitious composite (HPFRCC). The electrical conductivity of the 100 MPa HPFRCC with 0.30% MWCNT was [...] Read more.

This study aimed to investigate the effect of multi-walled carbon nanotubes (MWCNTs) and steel fibers on the AC impedance and electromagnetic shielding effectiveness (SE) of a high-performance, fiber-reinforced cementitious composite (HPFRCC). The electrical conductivity of the 100 MPa HPFRCC with 0.30% MWCNT was 0.093 S/cm and that of the 180 MPa HPFRCC with 0.4% MWCNT and 2.0% steel fiber was 0.10 S/cm. At 2.0% steel fiber and 0.3% MWCNT contents, the electromagnetic SE values of the HPFRCC were 45.8 dB (horizontal) and 42.1 dB (vertical), which are slightly higher than that (37.9 dB (horizontal)) of 2.0% steel fiber content and that (39.2 dB (horizontal)) of 0.3% MWCNT content. The incorporation of steel fibers did not result in any electrical percolation path in the HPFRCC at the micro level; therefore, a high electrical conductivity could not be achieved. At the macro level, the proper dispersion of the steel fibers into the HPFRCC helped reflect and absorb the electromagnetic waves, increasing the electromagnetic SE. The incorporation of steel fibers helped improve the electromagnetic SE regardless of the formation of percolation paths, whereas the incorporation of MWCNTs helped improve the electromagnetic SE only when percolation paths were formed in the cement matrix. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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14 pages, 2203 KiB

Open AccessArticle

Importance of Cation Species during Sulfate Resistance Tests for Alkali-Activated FA/GGBFS Blended Mortars

by Youngkeun Cho, Joo Hyung Kim, Sanghwa Jung, Yoonseok Chung and Yeonung Jeong

Materials 2019, 12(21), 3547; https://doi.org/10.3390/ma12213547 - 29 Oct 2019

Cited by 7 | Viewed by 2373

Abstract

In this study, the changes in mass, compressive strength, and length of blended mortars were analyzed to investigate their sulfate resistance according to the ground granulated blast furnace slag (GGBFS) blending ratio and type of sulfate solution applied. All alkali-activated mortars showed an [...] Read more.

In this study, the changes in mass, compressive strength, and length of blended mortars were analyzed to investigate their sulfate resistance according to the ground granulated blast furnace slag (GGBFS) blending ratio and type of sulfate solution applied. All alkali-activated mortars showed an excellent sulfate resistance when immersed in a sodium sulfate (Na₂SO₄) solution. However, when immersed in a magnesium sulfate (MgSO₄) solution, different sulfate resistance results were obtained depending on the presence of GGBFS. The alkali-activated GGBFS blended mortars showed a tendency to increase in mass and length and decrease in compressive strength when immersed in a magnesium sulfate solution, whereas the alkali-activated FA mortars did not show any significant difference depending on the types of sulfate solution applied. The deterioration of alkali-activated GGBFS blended mortars in the immersion of a magnesium sulfate solution was confirmed through the decomposition of C–S–H, which is the reaction product from magnesium ions, and the formation of gypsum (CaSO₄·2H₂O) and brucite (Mg(OH)₂). Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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10 pages, 2472 KiB

Open AccessArticle

Utilization of Calcium Carbide Residue Using Granulated Blast Furnace Slag

by Joonho Seo, Solmoi Park, Hyun No Yoon, Jeong Gook Jang, Seon Hyeok Kim and H. K. Lee

Materials 2019, 12(21), 3511; https://doi.org/10.3390/ma12213511 - 26 Oct 2019

Cited by 26 | Viewed by 3679

Abstract

The solidification and stabilization of calcium carbide residue (CCR) using granulated blast furnace slag was investigated in this study. CCR binding in hydrated slag was explored by X-ray diffraction, ²⁹Si and ²⁷Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, [...] Read more.

The solidification and stabilization of calcium carbide residue (CCR) using granulated blast furnace slag was investigated in this study. CCR binding in hydrated slag was explored by X-ray diffraction, ²⁹Si and ²⁷Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, and thermodynamic calculations. Mercury intrusion porosimetry and and compressive strength tests assessed the microstructure and mechanical properties of the mixtures of slag and CCR. C-A-S-H gel, ettringite, hemicarbonate, and hydrotalcite were identified as the main phases in the mixture of slag and CCR. The maximum CCR uptake by slag and the highest volume of precipitated solid phases were reached when CCR loading in slag is 7.5% by mass of slag, according to the thermodynamic prediction. This feature is also experimentally observed in the microstructure, which showed an increase in the pore volume at higher CCR loading. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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18 pages, 6088 KiB

Open AccessArticle

Compression Characteristics and Microscopic Mechanism of Coastal Soil Modified with Cement and Fly Ash

by Na Li, Qianying Zhu, Wei Wang, Fei Song, Dongliang An and Haoran Yan

Materials 2019, 12(19), 3182; https://doi.org/10.3390/ma12193182 - 28 Sep 2019

Cited by 29 | Viewed by 3201

Abstract

It is of great significance to study the consolidation characteristics of modified coastal cement-soil. A one-dimensional consolidation test and microscopic test were carried out. In the tests, the cement content was 20%, fly ash content was 0%, 5%, 10%, 20%, and 30%, and [...] Read more.

It is of great significance to study the consolidation characteristics of modified coastal cement-soil. A one-dimensional consolidation test and microscopic test were carried out. In the tests, the cement content was 20%, fly ash content was 0%, 5%, 10%, 20%, and 30%, and the water content was 80%. The consolidation test results showed that: (1) Compared with coastal cement soil, the deformation of coastal cement soil modified with a 20% fly ash content was reduced from 4.31 to 2.70 mm, and the vertical compression deformation was reduced by 1.61 mm. (2) During consolidation and compression, the e–p curve (pore ratio-pressure curve) of fly ash-modified coastal cement soil was slower than that of coastal cement soil and the rate of change of pore ratio. (3) The compression coefficient of fly ash-modified coastal cement soil was reduced from 0.780 to 0.598 MPa-1 compared with that of coastal cement soil. The microscopic test results indicate that after adding the proper amount of fly ash, a skeleton was formed between the microscopic particles of the sample, which improved its resistance to compression and deformation. The results of this study indicate that it is feasible to modify coastal cement soil with an appropriate amount of fly ash to improve its compression resistance. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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15 pages, 2367 KiB

Open AccessArticle

The Effect of Changing Fly Ash Content on the Modulus of Compression of Stabilized Soil

by Shuai Yang and Wenbai Liu

Materials 2019, 12(18), 2925; https://doi.org/10.3390/ma12182925 - 10 Sep 2019

Cited by 15 | Viewed by 2330

Abstract

Adding a curing agent can enhance the mechanical properties of soil including its compressive strength. However, few studies have quantitatively analyzed the compressive strength and microstructure of soils to explore the impact of changes in the microstructure on compressive strength. In addition, the [...] Read more.

Adding a curing agent can enhance the mechanical properties of soil including its compressive strength. However, few studies have quantitatively analyzed the compressive strength and microstructure of soils to explore the impact of changes in the microstructure on compressive strength. In addition, the cost of curing agents is too high to be widely used. In this study, curing agents with different proportions of fly ash were added to dredger fill to reduce the amount of curing agents needed. The quantitative analysis of the relationships between the modulus of compression Es and microstructures of stabilized soil samples is presented. The modulus of compression Es was gauged from compression tests. Microscopic images acquired using a scanning electron microscope were processed using the Image-Pro Plus (IPP) image processing software. The microscopic parameters, obtained using IPP, included the average equivalent particle size Dp, the average equivalent aperture size Db, and the plane pore ratio e. This research demonstrated that the fly ash added to the curing agent achieved the same effect as the curing agent, and the amount of curing agent required was reduced. Therefore, the modulus of compression for stabilized soil can be improved. This is due to the hydration products (i.e., calcium silicate hydrate, calcium hydroxide, and ettringite), produced by the hydration reaction, and which adhere to the surface of the particles and fill the spaces among them. Thus, the change in the pore structure and the compactness of the particles helps to increase the modulus of compression. In addition, there was a good linear relationship between the modulus of compression and the microscopic parameters. Using the mathematical relationships between the macroscopic and microscopic parameters, correlations can be built for macro–microscopic research. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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10 pages, 2346 KiB

Open AccessArticle

Effect of Carbonation on Abrasion Resistance of Alkali-Activated Slag with Various Activators

by Hyeong-Ki Kim, Keum-Il Song, Jin-Kyu Song and Jeong Gook Jang

Materials 2019, 12(17), 2812; https://doi.org/10.3390/ma12172812 - 2 Sep 2019

Cited by 5 | Viewed by 2874

Abstract

The effect of carbonation on the abrasion resistance of alkali-activated slag (AAS) was investigated. Various activator sets were selected for synthesizing AAS specimens, and the compressive strength was measured before and after carbonation. The abrasion resistance of the specimens was measured in accordance [...] Read more.

The effect of carbonation on the abrasion resistance of alkali-activated slag (AAS) was investigated. Various activator sets were selected for synthesizing AAS specimens, and the compressive strength was measured before and after carbonation. The abrasion resistance of the specimens was measured in accordance with the ASTM C944 test method. The relationship between the mass loss caused by abrasion and compressive strength was analyzed to understand the effect of matrix strength on abrasion resistance. Test results showed that the decrease in compressive strength of AAS specimens by carbonation reduced their abrasion resistance. In addition, the abrasion resistance of AAS before and after carbonation was sensitively influenced by activator type. It can be concluded that additional caution is required when using AAS where abrasion may have occurred. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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21 pages, 11978 KiB

Open AccessArticle

Fractal Analysis of the Fracture Evolution of Freeze-Thaw Damage to Asphalt Concrete

by Jun Li, Fengchi Wang, Fu Yi, Jie Ma and Zhenhuan Lin

Materials 2019, 12(14), 2288; https://doi.org/10.3390/ma12142288 - 17 Jul 2019

Cited by 21 | Viewed by 3123

Abstract

AC (asphalt concrete)-13, as the main material used in pavement construction, has been applied widely in seasonal frozen areas. In order to understand the fracture mechanism in the freeze-thaw (F-T) damage process, the mesoscale structure of AC-13 is obtained by computed tomography (CT). [...] Read more.

AC (asphalt concrete)-13, as the main material used in pavement construction, has been applied widely in seasonal frozen areas. In order to understand the fracture mechanism in the freeze-thaw (F-T) damage process, the mesoscale structure of AC-13 is obtained by computed tomography (CT). The fractal dimension of cracks is used as a damage evaluation index. Most previous studies have only focused on the fractal dimensions of whole cracks, while ignoring the fractal tectonic process and the self-similarity degree of a single fracture. Therefore, in this study, the intrinsic mechanism of fractures and damage were investigated. In addition, the critical crack stress and fracture toughness models of a single fracture in a freeze-thaw damage process are established for AC-13. The results indicate that in terms of the critical crack stress and fracture toughness, with the increase of F-T times, there is an obvious decreasing trend. The fracture model can effectively describe the fracture toughness calculated by ABAQUS in the process of freeze-thaw cycles. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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12 pages, 3016 KiB

Open AccessArticle

Effect of CaSO₄ Incorporation on Pore Structure and Drying Shrinkage of Alkali-Activated Binders

by Hyeongmin Son, Sol Moi Park, Joon Ho Seo and Haeng Ki Lee

Materials 2019, 12(10), 1673; https://doi.org/10.3390/ma12101673 - 23 May 2019

Cited by 19 | Viewed by 3086

Abstract

This present study investigates the effects of CaSO₄ incorporation on the pore structure and drying shrinkage of alkali-activated slag and fly ash. The slag and fly ash were activated at a 5:5 ratio by weighing with a sodium silicate. Thereafter, 0%, 5%, [...] Read more.

This present study investigates the effects of CaSO₄ incorporation on the pore structure and drying shrinkage of alkali-activated slag and fly ash. The slag and fly ash were activated at a 5:5 ratio by weighing with a sodium silicate. Thereafter, 0%, 5%, 10%, and 15% of CaSO₄ were incorporated to investigate the changes in phase formation and internal pore structure. X-Ray Diffraction (XRD), thermogravimetry (TG)/derivative thermogravimetry (DTG), mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), and drying shrinkage tests were carried out to find the correlation between the pore structure and drying shrinkage of the specimens. The results showed that CaSO₄ incorporation increased the formation of thenardite, and these phase changes affected the pore structure of the activated fly ash and slag. The increase in the CaSO₄ content increased the pore distribution in the mesopore. As a result, the capillary tension and drying shrinkage decreased. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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8 pages, 3258 KiB

Open AccessArticle

Revealing the Microstructure Evolution and Carbonation Hardening Mechanism of β-C₂S Pastes by Backscattered Electron Images

by Songhui Liu, Xuemao Guan, Haibo Zhang, Yuli Wang and Mifeng Gou

Materials 2019, 12(9), 1561; https://doi.org/10.3390/ma12091561 - 13 May 2019

Cited by 17 | Viewed by 3691

Abstract

β-dicalcium silicate (β-C₂S) minerals were prepared. The compositions, microstructures, and distributions of the carbonation products of hardened β-C₂S paste were revealed by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, and backscattered electron (BSE) image analysis. The results show that [...] Read more.

β-dicalcium silicate (β-C₂S) minerals were prepared. The compositions, microstructures, and distributions of the carbonation products of hardened β-C₂S paste were revealed by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, and backscattered electron (BSE) image analysis. The results show that a dense hardened paste of β-C₂S can be obtained after 24 h of carbonation curing. The hardened pastes are composed of pores, silica gel, calcium carbonate, and unreacted dicalcium silicate, with relative volume fractions of 1.3%, 42.1%, 44.9%, and 11.7%, respectively. The unreacted dicalcium silicate is encapsulated with a silica gel rim, and the pores between the original dicalcium silicate particles are filled with calcium carbonate. The sufficient carbonation products that rapidly formed during the carbonation curing process, forming a dense microstructure, are responsible for the carbonation hardening of the β-C₂S mineral. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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12 pages, 5916 KiB

Open AccessFeature PaperArticle

Calcined Oyster Shell Powder as an Expansive Additive in Cement Mortar

by Joon Ho Seo, Sol Moi Park, Beom Joo Yang and Jeong Gook Jang

Materials 2019, 12(8), 1322; https://doi.org/10.3390/ma12081322 - 23 Apr 2019

Cited by 64 | Viewed by 8976

Abstract

The present study prepared calcined oyster shell powder having chemical composition and crystal structure of calcium oxide and lime, respectively, and investigated the fresh and hardened properties of cement mortar incorporating calcined oyster shell powder as an additive. The test results indicated that [...] Read more.

The present study prepared calcined oyster shell powder having chemical composition and crystal structure of calcium oxide and lime, respectively, and investigated the fresh and hardened properties of cement mortar incorporating calcined oyster shell powder as an additive. The test results indicated that the hydration of calcined oyster shell powder promoted the additional formation of Ca(OH)₂ at the initial reaction stage, thereby increasing the heat of hydration. In particular, the volumetric increase of calcined oyster shell powder during hydration compensated the autogenous shrinkage of mortar at early ages, ultimately leading to a clear difference in the shrinkage values at final readings. However, an excessive incorporation of calcined oyster shell powder affected the rate of C–S–H formation in the acceleratory period of hydration, resulting in a decrease in the compressive strength development. Meanwhile, the degree of flow loss was inconsequential and rapid flow loss was not observed in the specimens with calcined oyster shell powder. Therefore, considering the fresh and hardened properties of cement mortar, the incorporation of calcined oyster shell powder of approximately 3% by weight of cement is recommended to enhance the properties of cement mortar in terms of compressive strength and autogenous shrinkage. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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Effect of Graphene Oxide on the Crystallization of Calcium Carbonate by C₃S Carbonation

by Dapeng Zheng, Haibin Yang, Feng Yu, Bo Zhang and Hongzhi Cui

Materials 2019, 12(13), 2045; https://doi.org/10.3390/ma12132045 - 26 Jun 2019

Cited by 12 | Viewed by 3703

Abstract

The effect of graphene oxide (GO) on the crystallization of calcium carbonate (CaCO₃) is explored in this paper. Precipitation of CaCO₃ was carried out by bubbling carbon dioxide (CO₂) through tricalcium silicate (C₃S) hydration solution with [...] Read more.

The effect of graphene oxide (GO) on the crystallization of calcium carbonate (CaCO₃) is explored in this paper. Precipitation of CaCO₃ was carried out by bubbling carbon dioxide (CO₂) through tricalcium silicate (C₃S) hydration solution with different graphene oxide admixture contents (0.2%, 1% and 2% mass ratios based on C₃S). The polymorph, morphology, crystal size and particle size of CaCO₃ were evaluated using X-ray diffraction (XRD), an environmental scanning electronic microscope (ESEM), and laser particle size analysis. The results showed that addition of GO was able to promote the conversion of CaCO₃ to a calcite crystal phase with higher thermal stability and crystallinity than the control. However, as the dosage of GO increased, the growth of the calcite crystal particles was somewhat suppressed, resulting in a decrease in the crystal particle size and a narrow particle size distribution. When the amount of GO was 0.2%, 1% and 2%, the crystal size of the calcite was 5.49%, 12.38%, and 24.61% lower than that of the sample without GO, respectively, while the particle size of the calcite also decreased by 17.21%, 39.26%, 58.03%, respectively. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

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