Search Results (27)

Recycled materials have gained extensive recognition in many industrial sectors for enhancing sustainability and reducing environmental impacts. Combining ceramic tile waste (CTW) in concrete mixes with recycled aggregate will help lower natural aggregate demand and reduce the amount sent to landfill. This paper aims to study the mechanical properties of CTW in concrete mixes as a brick aggregate replacement and its impact on concrete strength and durability. To evaluate and assess their strength and durability, three types of concrete cubes were prepared using 20%, 40%, and 70% of waste ceramic tiles as a replacement for coarse aggregate. Two kinds of concrete samples were also prepared with conventional coarse aggregate as the control specimen (CC). A 1:2:4 concrete mixed ratio was used in this research with a 0.50 water–cement ratio. The samples were tested after 14 days and 28 days to assess their mechanical properties, including strength and durability. When CTW was added to concrete mixtures instead of brick chips, the mechanical strength rose considerably, and the water absorption performance increased. Moreover, replacing brick chips with ceramic waste in concrete could have significant environmental benefits. Full article

Limestone-calcined clay (LC3) cement has emerged as a promising low-carbon alternative to ordinary Portland cement (OPC), offering significant potential to reduce carbon emissions while maintaining comparable mechanical performance. However, the absence of a prediction model for the formulation of the LC3 system presents challenges for optimisation within the evolving concrete industry. This study introduces a multi-objective optimisation (MOO) framework to design the optimal LC3 system, aiming to maximise compressive strength while minimising environmental and economic costs, simultaneously. The MOO framework integrates a regularised multivariate polynomial regression (MPR) model, achieving an R² of 0.927 and MSE of 3.445 for mechanical performance prediction. Additionally, life cycle assessment quantifies the environmental impact, and collected market prices contribute to financial considerations of the LC3 system. Utilising a dataset of 366 LC3 mortar mixtures, the optimisation challenges the conventional 2:1 calcined clay-to-limestone ratio (CC:LS). For high strength (≥65 MPa), target a CC:LS ratio of 1:1 to 1.6:1; for lower strength (<65 MPa), increase calcined clay content, resulting in a CC:LS ratio of 1.6:1 to 2:1. The proposed framework serves as a valuable starting point to enhance the efficiency of LC3 system design and help decision-making to achieve desired mechanical, economic, and environmental objectives. Full article

Recycling solid waste is one of the most important ways to reduce carbon footprints and put sustainability into practice. This research aims to bridge the gap between the results of previous studies and the effectiveness and sustainability benefits of using plastic waste (PW) in concrete mixes by partially replacing coarse aggregate with PW. Furthermore, we examine the suitability of the concrete produced for use as a construction material. The research methodology is based on studying the physical and mechanical behavior of concrete produced by partially replacing coarse aggregate with 0%, 2.5%, 5%, 7.5%, 10%, and 12.5% PW. For the conventional concrete–CC mix of 0% PW, the design strength, f_cu, was 35 MP, with a slump of 100 mm, using a water–cement ratio of 0.5, a M.A.S of coarse aggregate of 20 mm, and a sand F.M. of 2.2. According to British standards, BS, slump and density tests were carried out for concrete samples produced in their fresh state and strength tests, ultrasonic testing, etc. for concrete samples after hardening. The results indicated that there is no significant difference between the dry density and bulk density of concrete produced at all its age stages, regardless of the percentage of PW that replaces the aggregate. It also indicated that the compressive strength, the flexural strength, and the splitting tensile strength of the produced concrete decrease steadily and significantly when aggregates are replaced by PW by more than 2.5%. It was found that the decrease in compressive strength does not exceed 1% for concrete with 2.5% PW compared to the strength of CC, while the compressive strength of concrete with 5% PW decreases by 24%. The maximum reduction rate of the flexural strength and splitting tensile strength was 40% and 32%, respectively, for concrete at 12.5% PW compared to the strength of CC. Therefore, PW concrete can retain its strength when used in small quantities of up to 2.5% and can be applied in structural works. Full article

This paper presents experimental and theoretical assessments of the structural behavior of circular steel fiber-reinforced concrete (SFRC) columns reinforced with glass fiber-reinforced polymer (GFRP) bars subjected to a concentric axial compressive load. Laboratory experiments were planned to evaluate and compare the effect of different design parameters on the structural behavior of column specimens based on experiments and finite element (FE) analysis. The experimental variables were (i) concrete types, i.e., conventional concrete (CC) and fiber-reinforced concrete (FC), (ii) longitudinal reinforcement types, i.e., steel and GFRP bars, and (iii) transverse rebar configurations, i.e., tied and spiral with different pitches. Sixteen column specimens were fabricated and categorized into four groups with respect to rebar configurations and concrete types. The results showed that the failure modes and cracking patterns of those four column groups were comparable, particularly in the pre-peak branches of load-deflection curves. Even though the average ultimate load of the columns with longitudinal GFRP bars was 17.9% less than that with longitudinal steel bars, the ductility index (DI) was 10.2% greater than their counterpart on average. The addition of steel fibers (SF) to concrete increased the axial peak load by up to 3.1% and the DI by up to 6.6% compared to their counterpart CC columns without SFs. The DI of specimens was increased by higher volumetric ratios (up to 12%) and spiral types (up to 5.5%). The concrete damage plastic (CDP) model for FC columns was updated in the finite element software ABAQUS 6.14. Finally, a new simple equation was theoretically proposed to predict the axial capacity of specimens by considering the inclusion of longitudinal GFRP rebars, volumetric ratio, and steel spiral/hoop ties. Good agreement between the proposed model predictions and the experimental/numerical results was observed. Full article

India generates 759.02 million metric tons of coal ash annually. Part of that quantity is successfully utilized, and the remaining portion of the ash is discarded into a landfill. There also is a need to address pollution. Cement industries are responsible for 7% of global warming. Cement has been replaced entirely by thermal power plant waste, and bottom ash is used as a binder to overcome those issues. A few researchers have carried out strength characterization, but an extensive study needs to be carried out under different environmental exposures. Therefore, the present study investigated macro and micro properties of bottom ash geopolymer concrete (BAGPC) subjected to aggressive ecological exposure conditions such as acid, salt, and sulfate attack. Sodium silicate (Na₂SiO₃) and sodium hydroxide (NaOH) of eight molarities were used as activators for the bottom ash geopolymer concrete (BAGPC) binder. Further bonding between steel and conventional concrete BAGPC mixes was investigated. The durability of conventional concrete (CC) was taken as the control mix to compare the durability of the optimized mix (B4) of bottom ash geopolymer. The test samples were cured for 28 days under ambient temperature and tested for the effect of MgSO₄, NaCl, and HCl. The strength loss and weight loss of the BAGPC B4 mix after 7, 28, 56, 90, and 180 days under aggressive conditions showed better performance than CC. It has been observed that geopolymer concrete has good bonding in nature, and the bond strength results indicate excellent bonding between steel and concrete. Microstructure studies revealed that the BAGPC B4 mix had a strong microstructure and not as much of a porous structure. It is concluded that BAGPC has potential value in the construction industry based on all aspects of the experiment. Full article

The present study was conducted to clarify the flexural behaviors of the Composite Girders of a Prestressed Segmental Ultra-High-Performance Concrete (UHPC) Channel and a Reinforced Conventional Concrete Deck (PSUC-RCCD). The girders can be used as bridge superstructures with the advantages of structural efficiency, cost-effectiveness, and easy construction. A total of five specimens were tested. Three of them were PSUC-RCCD specimens, including two semi-segmental girders (the channel beams were composed of five segments with dry-joints) and one integral girder (the channel beams were integral ones without dry-joints). The two other specimens were P-UHPC girders composed of PSUC and UHPC deck slabs; one was semi-segmental and the other was integral. The flexural behaviors of the specimens were investigated, including the load-displacement curves, crack distribution, cracking moments, and ultimate flexural capacity. The study compared the influence of the segment number and deck material on the flexural behaviors of semi-segmental girders and introduced and validated methods for calculating the cracking moment and flexural capacity of both semi-segmental and integral sections in PSUC-RCCD and P-UHPC girders. The results show that the entire loading process of all the specimens can be classified into the elastic phase, the cracks development phase, and the failure phase. Compared to the integral girders, the number of segments has little effect on the flexural behavior of the semi-segmental girders, but it has a significant effect on the cracking moments. The cracking moments of the semi-segmental girders is only 0.58~0.60 of the integral girders. Reducing the strength of the deck slab by changing the material from UHPC to CC does not significantly affect their flexural behaviors. Based on the test results, this work proposes a method for predicting the cracking moment and flexural capacity of the semi-segmental girders, the results of which fit well with the test results, and it is applicable in the structural design of such members. Full article

Large engineering structures made of various materials, including concrete (e.g., bridges, dams, buildings, and multilevel car parks), steel (e.g., power towers, ships, and wind turbines), or others, are often subjected to severe vibration, dynamic, and cyclic loads, which lead to crack initiation, crack growth, and finally structural failure. One of the effective techniques to increase the fatigue life of such structures is the use of reinforced materials. In the meantime, environmental factors, such as corrosion caused by corrosive environments, also affect the fatigue behavior of materials. Therefore, the main purpose of this paper is to study the influence of corrosive environment on the high-cycle fatigue (HCF) behavior of concrete reinforced by epoxy resin. For this purpose, five corrosive environments with different intensities, including fresh air, water: W, sea water: SW, acidic: AC, and alkaline: AL, were considered and the laboratory samples of conventional concrete (CC) and polymer concrete (PC) were immersed in them for one month. Next, axial fatigue tests were performed under compressive–compressive loading with a frequency of 3 Hz on cylindrical specimens. Moreover, to achieve reliable results, for each stress amplitude, the fatigue test was repeated three times, and the average number of cycles to failure was reported as the fatigue lifetime. Finally, the stress–life cycle (S-N) curves of different states were compared. The results showed that polymer concrete can resist well in corrosive environments and under cyclic loads compared to the conventional concrete, and in other words, the epoxy resin has performed its task well as a reinforcer. The results of fatigue tests show that the load bearing range of 10 tons by CC has reached about 18 tons for PC, which indicates an 80% increase in fatigue strength. Meanwhile, the static strength of samples in the vicinity of fresh air has only improved by 12%. Full article

Geopolymer concrete (GPC) has been the subject of ongoing research as a suitable substitute for conventional concrete production because of its benefits for the environment. However, there is little research regarding retrofitting the structural part if a GPC member fails. The current study thus concentrates on the damaged GPC structural members/columns. For this purpose, twelve columns which include four CC columns, four GPC Columns, and four FRGPC columns, were retrofitted with CFRP sheets and tested in the electrohydraulic testing apparatus (5000 kN). The results showed significant improvement in the ultimate load value of all 12 columns. Axial strain in all 12 columns also increased significantly. The ductility index of the columns was also calculated using axial strain values. The axial load–displacement behavior, ductility, and loading capacity of the evaluated columns are all significantly improved by the addition of steel fibers. Full article

In composite structures, interface shear resistance is a critical design criterion for transferring forces between interconnected elements at the contact surface. Recently, Ultra-High-Performance Concrete (UHPC) applications in construction have been growing rapidly due to superior mechanical and durability properties; however, there is no guidance on how to predict the interface shear resistance of UHPC cast on hardened conventional concrete (CC). This paper presents the experimental and analytical investigations conducted to develop friction and cohesion factors of the shear friction theory for UHPC cast on hardened CC in composite sections. Push-off shear tests and slant shear tests were conducted to evaluate and validate the effect of interface surface texture, interface reinforcement ratio, CC and UHPC compressive strength, and fiber presence. A friction factor of 1.0 was adopted—as in the current code provisions—while a cohesion factor of 3.45 MPa (0.5 ksi) between UHPC cast on intentionally roughened hardened CC was proposed, which is significantly higher than that in the current code provisions of CC. Also, increasing the interface shear reinforcement ratio increased the interface shear resistance significantly and resulted in a more ductile failure. Neither UHPC compressive strength nor the presence of steel fibers had a significant effect on the interface shear resistance of UHPC cast on hardened CC. Full article

In recent decades, corrosion in steel reinforcement has been one of the fundamental risks in steel-reinforced concrete (RC) structures. Geosynthetics can be an alternative approach to solve corrosion problems. The current experimental research work investigates the structural performance of geogrid-reinforced concrete (GRC) elements. Initially, five different geotextiles and biaxial geogrid materials were selected and embedded in the concrete specimens separately to study their mechanical properties. The results of the testing showed that the geogrid embedded specimen behaved more mechanically than the conventional concrete (CC) specimens due to increased bonding characteristics. The limiting moment and load-carrying capacities of the RC and GRC beams were determined with reference to limit state design principles. In order to compare the structural performance of the beams, two RC beams and two GRC beams with the size of 150 mm × 300 mm × 2100 mm were cast. The structural performances in terms of the load-carrying capacity, energy absorption, stiffness degradation, and ductility were examined. The results of the tests indicated that even though the load-carrying capacity of the GRC beams was slightly lower, they demonstrated enhanced performance by 42%, 40%, and 68% higher in the energy absorption, stiffness degradation, and ductility, respectively, than those of the RC beams on average. The augmented inelastic performance and better bonding properties of the GRC beams aid in noticeable structural performance. Full article

In this research work, two types of recycled aggregates were used: (1) the recycled concrete aggregate, RCA, obtained by crushing the parent concrete produced using limestone cement and (2) the recycled concrete aggregate RCA-FA produced by crushing parent concrete made with FA blended cement. After the carbonation treatment process, the carbonated RCA-C and RCA-FA-C recycled aggregates were produced. The recycled concrete mixtures were prepared using the four types of recycled aggregates (RCA, RCA-FA, RCA-C, and RCA-FA-C) in 50% (by volume) to replace natural coarse aggregates. The physical and mechanical properties and durability (sorptivity, chloride ion penetration, and carbonation resistance) were determined and analysed. The obtained results were also compared with those of conventional concrete (CC). It was concluded that the physical and mechanical properties of recycled concrete improved when RCA-C were employed in concrete production. In contrast, the recycled concrete produced with RCA-FA-C was found to have the worst property values. According to durability properties, the concrete made with RCA-C and RCA-FA aggregates achieved the highest chloride resistance, similar to CC concrete. Nevertheless, the concrete produced with uncarbonated RCA acquired carbonation resistance equivalent to CC concrete. Full article

The utilization of waste materials in concrete lowers its cost, and this method of dealing with the problem of trash disposal is viewed as the most environmentally friendly. Fly Ash Cenospheres (FAC) are one of the principal wastes produced by coal power stations. The huge volume of FAC produced worldwide has created a sustainability challenge, owing to the potential implications of inappropriate disposal. Using cenospheres in concrete materials would make effective and efficient use of these waste products while also supplementing what the present raw material, such as river sand, can supply for concrete material production. Though the application of FAC in concrete is currently carried out by the construction industry, there is still a lack of understanding about its performance in concrete with Manufactured Sand (M Sand) as fine aggregate. Therefore, in this paper, a comprehensive study explores the concept of adding FAC to M Sand concrete. The properties of fresh and hardened concrete, such as density, workability, compression, split tensile, flexure, and impact resistance after the addition of FAC in volume replacement (0–100% with a difference of 5% at thirteen different ratios) is represented, followed by microstructural analysis. From the results, it can be concluded that strength reduction takes place as FAC content increases from 0–100%, however, the strength is within the target limit of 31.2 N/mm² of conventional concrete (CC) of grade M25 when the percentage replacement is below 35% of volume. Therefore, reducing the volume of fine aggregate does not negatively affect the strength properties, but also impacts the environmental concern positively with optimum recommendation of 35% of fine aggregate as FAC. Full article

With the rise in cement production required by conventional concrete, CO₂ emissions increase, causing pollution to the atmosphere. Geopolymer concrete (GPC) is investigated in the literature as an eco-efficient alternative to conventional concrete (CC). However, most geopolymer studies focus on studying the mechanical properties of GPC, with only limited investigations on the structural performances of structural elements using GPC. The structural behaviors of GPC elements are yet to be completely understood, and there are no current studies on investigating the structural behaviors of geopolymer slag concrete. Thus, this paper investigates the flexural performances of reinforced geopolymer slag concrete beams, focusing on the effects of different beam depths and reinforcement ratios. Five full-scale ambient-cured reinforced geopolymer slag concrete beams were tested under four-point flexure, in addition to one control conventional concrete (CC) beam. The structural performances are evaluated, including the cracking moment, flexural capacity, load–deflection relationship, and crack distribution. The results indicate that the flexural behaviors of GPC beams are comparable to that of the CC beams. Compared to the CC beams, the GPC beams have 7.4% higher flexural moment capacity, 60% lower stiffness, 28% lower ductility, and 18.3% higher toughness. Finally, the Egyptian code of practice ECP 203 and ACI 318 are found to be applicable to safely design under-reinforced GPC flexural beam elements. Full article

Increasing the rate of construction material consumption has caused significant environmental problems in recent decades, especially the production of ordinary Portland cement (OPC), which has been associated with 8% of the world’s human CO₂ emissions and is considered the leading binder of concrete. This study aims to investigate the effects of substituting conventional concrete (CC) material with green concrete (GC) in the non-structural concrete works of a residential building in New Borg El-Arab City, Egypt. It attempts to establish what the effects are of using GC on cement, natural aggregates, and CO₂ emissions in the design phase. By using a design-based solution (DBS), we began with redesign, reduce, reselect, reuse, and recycle strategies to find an optimal solution for applying recycle aggregate concrete (RAC) as a replacement material in selected building parts, such as the internal floor, external sidewalk, entrance steps, and wall boundary. AutoCAD software and 3Dmax were used to modify the original design and obtain two design references with four different scenarios. Comparative analyses were applied to investigate the effects of different concrete materials. The results show a reduction of about 19.4% in cement consumption in terms of the total concrete of the building and a 44.5% reduction in CO₂ emissions due to the reduction of cement in specific building parts. In addition, this solution decreased natural coarse aggregate (NCA) consumption by 23.7% in the final concrete. This study recommends that GC materials close the loop of cementitious material consumption to reduce environmental impacts and achieve sustainability in the Egyptian building sector. Full article

The linear economy paradigm in place to date has to be seriously challenged to give way to a new school of thought known as the circular economy. In this research work, precast kerbs and paving blocks made with recycled concrete (RACC-mixture) bearing 50 wt% mixed recycled aggregate (masonry content of 33%) and an eco-efficient cementitious material as 25 wt% conventional binder replacement were evaluated to assess their intrinsic potential to replace traditional raw materials, in keeping with circular economy criteria. Therefore, precast products were subjected to mechanical strength, durability and microstructure tests and were compared to conventional concrete units (CC-mixture and commercially available precast elements). Although a class demotion was observed for water absorption and some decreases in flexural strength (26%), splitting tensile strength (12.8%) and electrical resistivity (45%) and a lower class water absorption were registered, and the recycled mixture also exhibited a greater performance in terms of compressive strength (6%), a better abrasion resistance classification and a comparable porosity and microstructure, which ensures a good concrete durability. In any case, the results showed that precast pieces were European standard-compliant, thus supporting the viability of the mixed recycled aggregates and eco-efficient cementitious replacement in footways. Full article