Search Results (442)

The increasing demand for sustainable construction materials has driven research into low-carbon geopolymers that mitigate both cement-related emissions and plastic and glass waste accumulation. This study explores the development of geopolymer concrete incorporating fly ash (FA), slag (S), and FA + S blends, with 10% recycled crushed glass (RCG) and recycled plastic waste (RPW) as partial coarse aggregate replacements. Compressive strength testing revealed that FA + S-based geopolymers (25FA + S) with 100% ordinary Portland cement (OPC) replacement achieved a 7-day strength of 24.6 MPa, representing a 98% improvement over control specimens. Slag-based geopolymers demonstrated water absorption properties comparable to OPC, indicating enhanced durability. Microstructural analyses using SEM, XRD, and EDS confirmed the formation of a dense aluminosilicate matrix, with slag promoting FA reactivity and reinforcing interfacial transition zone (ITZ). These effects contributed to superior mechanical performance and water resistance. Despite minor shrinkage-induced cracking, full OPC replacement with S or FA + S geopolymers outperformed control specimens, consistently exceeding the target strength of 15 MPa required for low-impact, single-story housing applications within seven days. These findings underscore the potential of geopolymer systems for rapid and sustainable construction, offering an effective solution for reducing carbon footprints and repurposing industrial waste. Full article

Sustainability in the construction sector has become a fundamental objective for mitigating escalating environmental challenges; given that concrete is the most widely used man-made material, extending its service life is therefore critical. Among durability concerns, magnesium sulfate (MgSO₄) attack is particularly deleterious to concrete structures. Therefore, this study investigates the short- and long-term performance of concrete produced with copper slag (CS)—a massive waste generated by copper mining activities worldwide—employed as a supplementary cementitious material (SCM), together with recycled coarse aggregate (RCA), obtained from concrete construction and demolition waste, when exposed to MgSO₄. CS was used as a 15 vol% cement replacement, while RCA was incorporated at 0%, 20%, 50%, and 100 vol%. Compressive strength, bulk density, water absorption, and porosity were measured after water curing (7–388 days) and following immersion in a 5 wt.% MgSO₄ solution for 180 and 360 days. Microstructural characteristics were assessed using scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis with its differential thermogravimetric derivative (TG-DTG), and Fourier transform infrared spectroscopy (FTIR) techniques. The results indicated that replacing 15% cement with CS reduced 7-day strength by ≤10%, yet parity with the reference mix was reached at 90 days. Strength losses increased monotonically with RCA content. Under MgSO₄ exposure, all mixtures experienced an initial compressive strength gain during the short-term exposures (28–100 days), attributed to the pore-filling effect of expansive sulfate phases. However, at long-term exposure (180–360 days), a clear strength decline was observed, mainly due to internal cracking, brucite formation, and the transformation of C–S–H into non-cementitious M–S–H gel. Based on these findings, the combined use of CS and RCA at low replacement levels shows potential for producing environmentally friendly concrete with mechanical and durability performance comparable to those of concrete made entirely with virgin materials. Full article

This research focuses on improving the characteristics of recycled concrete and utilizing solid waste resources through the combination of industrial waste pre-impregnation and the carbonation process. A novel pre-impregnation–carbonation aggregate method is proposed to increase the content of carbonatable components in the surface-bonded mortar of recycled coarse aggregate by pre-impregnating it with carbide slag slurry (CSS). This approach enhances the subsequent carbonation effect and thus the properties of recycled aggregates. The experimental results showed that the method significantly improved the water absorption, crushing value, and apparent density of the recycled aggregate. Additionally, it enhanced the compressive strength, split tensile strength, and flexural strength of the recycled concrete produced using the aggregate improved by this method. Microanalysis revealed that CO₂ reacts with calcium hydroxide and hydrated calcium silicate (C-S-H) to produce calcite-type calcium carbonate and amorphous silica gel. These reaction products fill microcracks and pores on the aggregate and densify the aggregate–paste interfacial transition zone (ITZ), thereby improving the properties of recycled concrete. This study presents a practical approach for the high-value utilization of construction waste and the production of low-carbon building materials by enhancing the quality of recycled concrete. Additionally, carbon sequestration demonstrates broad promise for engineering applications. Full article

This study investigated the fracture behavior of concrete beams with recycled coarse aggregate (RCA) and recycled fine aggregate (RFA) using the box-counting method to measure crack fractal dimensions under load. Beams with RCA showed higher fractal dimensions due to RCA’s lower elastic moduli and compressive strengths, resulting in reduced deformation resistance, ductility, and more late-stage crack propagation. A direct proportional relationship existed between RCA/RFA replacement ratios and crack fractal dimensions. Second-order and third-order polynomial trend surface-fitting techniques were applied to examine the complex relationships among RFA/RCA dosage, applied load, and crack fractal dimension. The results indicated that the RFA dosage had a negative quadratic influence, while load had a positive linear effect, with dosage impact increasing with load. A second-order functional relationship was found between mid-span deflection and crack fractal dimension, reflecting nonlinear behavior consistent with concrete mechanics. This study enhances the understanding of recycled aggregate concrete beam fracture behavior, with the crack fractal dimension serving as a valuable quantitative indicator for damage state and crack complexity assessment. These findings are crucial for engineering design and application, enabling better evaluation of structural performance under various conditions. Full article

Ceramic tiles classified as non-biodegradable are made from fired clay, silica, and other natural materials for several construction applications. Waste ceramic tiles (WCTs) are produced from several sources, including manufacturing defects; surplus, broken, or damaged tiles resulting from handling; and construction and demolition debris. WCTs do not decompose easily, leading to long-term accumulation in landfills and occupying a significant amount of landfill space, which has substantial environmental impacts. Recycling WCTs offers several critical ecological benefits, including reducing landfill waste and pollution, conserving natural resources, lowering energy consumption, and supporting the circular economy, which in turn contributes to sustainable construction and waste management practices. In green concrete manufacturing, WCTs are widely utilized as replacements for cement, fine, and coarse aggregates, and the recycling level in the concrete industry is an increasingly explored practice aimed at promoting sustainability and reducing construction waste. From this view, this paper reports the innovative technologies, advancements in green concrete performance, and development trends in the reuse of WCTs in the production of systems. The effects of WCTs on fresh, engineering, microstructural, and durable properties, as well as their environmental performance, are reviewed. In conclusion, the use of technologies for recycling WCTs has demonstrated potential in promoting sustainability and supporting the transition toward a more environmentally friendly construction industry. This approach offers a practical contribution to sustainable development and represents significant progress in closing the recycling loop within the construction sector. Full article

In order to address a challenging issue in the recycling of construction debris, the impact of carbonization treatment on the characteristics of recycled aggregates (RCAs) was experimentally examined in this work. Both direct carbonization and carbonization following calcium hydroxide pretreatment were used in the study to assess the impact of carbonization on the physical characteristics of recycled aggregates. According to the findings, carbonization raised the recycled aggregates’ apparent density while drastically lowering their porosity and water absorption (by as much as 20–30%). Although the recycled aggregate’s crushing index marginally increased with age, its overall physical qualities remained excellent. Pretreatment with calcium hydroxide can improve the physical characteristics of recycled aggregates, further optimize their pore structure, and efficiently encourage the carbonation process. Furthermore, recycled aggregate’s crushing index can be considerably decreased and its quality much enhanced by the ultrasonic cavitation treatment. According to the study, the carbonation-treated recycled aggregate’s microstructure was denser in the interfacial transition zone and had a stronger link with the cement paste, improving the recycled aggregate concrete’s overall performance. XRD, infrared spectral analysis, and SEM scanning were used to determine the increased calcium carbonate content in the recycled aggregate following carbonation treatment as well as its microstructure improvement process. The findings offer fresh concepts for achieving resource efficiency and environmental preservation through the use of recycled aggregates in concrete, as well as theoretical backing for their use. Full article

This study proposes a method for separating asphalt and aggregates in recycled asphalt pavement (RAP) materials using surfactants as solvents. This method utilizes surfactants to soften the asphalt by reducing its surface tension, separating the RAP clusters, and washing away the asphalt from the RAP. The wastewater is recycled during the emulsification–separation process without discharge. Factors affecting the separation effect of RAP, including the type of anionic surfactants, the surfactant concentration, the emulsion-to-RAP ratio, temperature, the rotation rate and time, and the RAP’s particle size, were investigated in depth, and the separation effect and its influence on the aggregate properties were evaluated. The experimental results indicate that when using the optimal process to mix and treat 13.2 mm and 9.5 mm RAP clusters, it is possible to achieve 100% separation of the coarse RAP above 4.75 mm, with a 64.58% reduction in the asphalt content. The angularity of the aggregate remained unchanged after separation. It was observed from scanning electron microscopy (SEM) images that the asphalt on the surface of the coarse aggregate had been eluted, and the morphology of the aggregate surface was completely exposed. This environmentally friendly separation method provides new possibilities for high-content RAP recycling in pavement engineering. Full article

With the ongoing acceleration in urban development, the volume of construction and demolition waste continues to rise, while the availability of natural aggregates is steadily declining. Utilizing recycled aggregates in concrete has become a vital approach to fostering sustainability within the construction sector. This research develops a life cycle-based environmental impact evaluation model for recycled aggregate concrete, applying the Life Cycle Assessment (LCA) framework. Through the eFootprint platform, a quantitative evaluation is carried out for C30-grade concrete containing varying levels of recycled aggregate replacement. Four replacement ratios of recycled coarse aggregate (30%, 50%, 70%, and 100%) were evaluated. The assessment includes six key environmental indicators: Global Warming Potential (GWP), Primary Energy Demand (PED), Abiotic Depletion Potential (ADP), Acidification Potential (AP), Eutrophication Potential (EP), and Respiratory Inorganics (RI). The findings reveal that higher substitution rates of recycled aggregate lead to noticeable reductions in RI, EP, and AP, indicating improved environmental performance. Conversely, slight increases are observed in GWP and PED, especially under long transport distances. Analysis of contributing factors and sensitivity indicates that cement manufacturing is the principal driver of these increases, contributing over 80% of the total GWP, PED, and ADP impacts, with aggregate transport as the next major contributor. This study offers methodological insights into the environmental evaluation of recycled aggregate concrete and supports the green design and development of low-carbon strategies in construction. Full article

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

As a highly active mineral admixture, metakaolin is often used as an efficient performance-enhancing material for concrete, but its performance in long-term complex service environments still needs to be verified. This article presents a composite green concrete with a substitution rate of 30% for recycled coarse aggregates (RCAs) and iron tailings (IOTs) and a waste polypropylene fiber (WPF) content of 0.6%. Concrete with different mixing conditions of metakaolin was prepared, and its carbonization resistance was studied with macro- and micro-experimental methods. The results indicated that when the content of metakaolin was less than 10%, its mechanical and deformation properties gradually improved, resulting in a maximum increase of 70% in its cubic compressive strength. Overall, carbonization improved the corresponding mechanical properties. For example, when carbonized for 14 days, the compressive strength growth rate increased by nearly 30%, and the elastic modulus did not change significantly. Through microscopic testing, it could be seen that when the content of metakaolin reached 10%, an appropriate amount of metakaolin (10%) promoted the hydration of cement, with the least number of pores and the best compaction performance, resulting in the best overall performance. But when added excessively, the coupling effect of secondary hydration and carbonization reactions could lead to the emergence of new harmful pores in the matrix structure. In future engineering applications of metakaolin, it is recommended that its mixing ratio be less than 10% to achieve better concrete performance. Full article

The concrete industry increasingly seeks sustainable alternatives to conventional materials to reduce the environmental impact while maintaining structural performance. This study evaluates the use of locally sourced rhyolite as a coarse aggregate combined with recycled supplementary cementitious materials (SCMs) to address the sustainability and durability. Due to its high silica content, rhyolite is prone to the alkali–silica reaction (ASR), which may affect concrete durability. Concrete mixtures incorporating rhyolite with silica fume (SF), Class F fly ash (FA), and slag cement (SC) were tested for compressive strength, porosity, density, absorption, mortar bar expansion, electrical resistivity, and rapid chloride permeability. All rhyolite-based mixtures—regardless of SCM incorporation—achieved higher 90-day compressive strengths than the conventional control mixture, with 10% SF reaching the highest value. Additionally, each recycled SCM effectively reduced ASR-induced expansion, with 20% FA showing the most significant reduction and superior durability, including the greatest decrease in chloride permeability and the highest electrical resistivity, indicating enhanced corrosion resistance. These results confirm that rhyolite aggregates, when combined with SCMs, can improve durability and reduce ASR. Therefore, rhyolite shows potential for use in structural concrete under standard exposure conditions. This strategy supports circular economy goals by incorporating regional and recycled materials to develop concrete with improved durability characteristics. Full article

This study systematically investigates the influence of grain refinement on the microstructural evolution and mechanical properties of recycled Al-7Si-0.3Mg-1Fe alloy through the addition of varying concentrations (0–1.25 wt.%) of Al-5Ti-2B master alloy. The synergistic effects of Al-5Ti-2B on the α-Al phase, eutectic Si, and Fe-rich intermetallics were characterized using metallographic analysis, XRD, SEM-BSE imaging, and EDS. In the unrefined alloy, the microstructure consisted of an α-Al solid solution with coarse plate-like eutectic Si, while Fe primarily formed needle-like β-Al₅FeSi phases that either surrounded or penetrated the eutectic Si. Increasing the Al-5Ti-2B addition refined both the α-Al dendrites and eutectic Si, while the β-Al₅FeSi phase transitioned from coarse to fine needles. The optimal refinement was achieved at a 1% Al-5Ti-2B addition, yielding a tensile strength of 149.4 MPa and elongation of 4.3%. However, excessive addition (1.25%) led to eutectic Si aggregation and β-Al₅FeSi coarsening, resulting in mechanical property deterioration and brittle fracture behavior. These findings provide insights into optimizing grain refinement for enhancing the performance of recycled Al-Si-Mg-Fe alloys. Full article

This study focuses on improving the recycled coarse aggregate (RCA) replacement ratio in recycled aggregate concrete products. First, the mix design and compressive performance of recycled aggregate concrete (RAC, RCA replacement percentages of 20%, 35%, and 50%) were evaluated using the monofactor analysis method and response surface methodology under three different conditions: single addition of nano-calcium carbonate (NC, dosages of 0.1%, 0.2%, and 0.3%), single addition of basalt fibre (BF, volume content of 0.1%, 0.2%, and 0.3%), and combined addition of both. The results show that the compressive strength of RAC at 7 and 28 days rises as the BF or NC content increases and then falls as the NC content increases. According to the sensitivity analysis, RAC’s compressive strength is significantly impacted by the replacement ratio of RCA, with NC having a more considerable effect on RAC’s 7-day compressive strength than BF, while BF affects the 28-day compressive strength more than NC does. Based on the desirability function, the ideal BF and NC content in RAC was optimised and confirmed by the compressive strength test. It demonstrates that the best compressive performance is achieved by RAC with 1% NC and 0.3% BF. Finally, concrete pavement brick models were created using the ideal mix proportion provided by the compressive strength test. The model compression test results show that RAC pavement bricks (RCA replacement ratio of 60%) with 1% NC and 0.3% BF had a 28d compressive strength of 5.7% and 15.8% higher than NAC and RAC pavement bricks, respectively. Full article

Recycling in the construction industry is a necessity, not just a fashionable trend in scientific research. The use of coal slag aggregates in concrete means a significant reduction in environmental footprint and should be a priority. For these reasons, this study presents tests of the physical and mechanical properties of high-performance concrete (HPC) with coal slag (CS) used as a replacement for natural coarse aggregate in the amounts of 10%, 20%, and 30% after a long curing time. The investigation determined the porosity, water absorption, density, compressive strength, flexural strength, tensile splitting strength, modulus of elasticity, and ultrasonic pulse velocity (UPV), and analyzed HPC microstructure at 28, 56 days, as well as 2 years of maturation. The use of coal slag resulted in significant increases in compressive strength, flexural strength, and tensile splitting strength compared to reference concrete. However, for HPC with CS, a slight decrease in the elastic modulus and UPV was obtained. The SEM analysis showed a very good adhesion of the cement paste to the slag aggregate. In general, research shows that it is possible to obtain durable high-performance concrete with a 30% replacement of natural aggregate by coal slag. Full article

In this study, the mechanical properties and failure characteristics of concrete with 10–20 mm recycled coarse aggregate at 0%, 25%, 50%, 75%, and 100% substitution rates were studied. In addition, the influence of coal gangue powder (CGP) on the mechanical properties of concrete was studied under the dosages of 5%, 10%, 15%, and 20%. The research results show that the peak strength of recycled concrete decreases with the increase in the replacement rate of 10–20 mm recycled coarse aggregate. When the replacement rate is 25%, the decrease in strength is the smallest. When the content of CGP increases from 0 to 20%, the peak strength of recycled concrete increases first and then decreases. When the content of CGP is 15%, the peak strength reaches the maximum value. The peak strength increases slightly. The density of pores and cracks in recycled concrete increases with the increase of 10–20 mm recycled coarse aggregate replacement rate. When the substitution rate exceeds 25%, the proportion of cracks increases by nearly 1.7 times. After adding CGP to recycled concrete, the pore density and crack ratio inside a specimen are significantly reduced. When the CGP content exceeds 15%, the crack ratio tends to be stable. When the CGP content is 15%, the crack ratio is 0.519%, which is 23.5% lower than that of the RAC-25 specimen. When the content exceeds 15%, the crack ratio tends to be stable. Full article