Search Results (287)

Effective management and handling of construction and demolition waste (CDW) can yield significant technical and environmental benefits for road pavement construction. This article aims to provide a comprehensive and up-to-date chronological review of studies on the mechanical performance of asphalt mixtures—primarily hot mix asphalt (HMA)—incorporating recycled concrete aggregate (RCA). Since the main limitation of RCA is the presence of residual adhered mortar, the review also includes studies that applied various surface treatments (mechanical, chemical, and thermal, among others) to enhance mixture performance. The article summarizes the experimental procedures used and highlights the key findings and conclusions of the reviewed research. Although the results are varied and sometimes contradictory—mainly due to the source variability and heterogeneity of RCA—the use of these materials is technically viable. Moreover, their application can provide environmental, social, and economic advantages, particularly in the construction of low-traffic roadways. Finally, the article identifies research gaps and offers recommendations for future researches. Full article

The aviation industry is under increasing pressure to reduce its environmental impact while maintaining safety and performance standards. One promising area for improvement lies in the use of sustainable materials in airport infrastructure. One of the issues preventing uptake of emerging sustainable technologies is the lack of guidance relating to the opportunities, potential benefits, associated risks and an implementation plan specific to airport pavements. This research reviewed opportunities to incorporate waste materials into rigid airport pavements, focusing on concrete base slabs. Commonly used supplementary cementitious materials (SCMs), such as fly ash and ground granulated blast furnace slag (GGBFS) were considered, as well as recycled aggregates, including recycled concrete aggregate (RCA), recycled crushed glass (RCG), and blast furnace slag (BFS). Environmental Product Declarations (EPDs) were also used to quantify the potential for environmental benefit associated with various concrete mixtures, with findings showing 23% to 50% reductions in embodied carbon are possible for selected theoretical concrete mixtures that incorporate waste materials. With considered evaluation and structured implementation, the integration of waste materials into rigid airport pavements offers a practical and effective route to improve environmental outcomes in aviation infrastructure. It was concluded that a Triple Bottom Line (TBL) framework—assessing financial, environmental, and social factors—guides material selection and can support sustainable decision-making, as does performance-based specifications that enable sustainable technologies to be incorporated into airport pavement. The study also proposed a consequence-based implementation hierarchy to facilitate responsible adoption of waste materials in airside pavements. The outcomes of this review will assist airport managers and pavement designers to implement practical changes to achieve more sustainable rigid airport pavements in the future. 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 study aimed to optimize the performance of pervious concrete (PC) while promoting sustainability using recycled concrete aggregates (RCAs), styrene butadiene rubber (SBR) waste, and silica fume (SF). The mixtures were developed using the Taguchi approach with four mix design factors, each at three levels: the water-to-binder ratio (w/b), RCA replacement percentage by weight of natural aggregates, the cement substitution rate with SF, and the SBR addition rate by binder mass. Thus, a total of nine mixes were prepared and tested for density, porosity, permeability, compressive strength, splitting tensile strength, abrasion resistance, and resistance to freezing and thawing. The results revealed that incorporating RCA and SBR decreased density and compressive strength but increased porosity and permeability. The performance of PC enhanced with SF addition and reduced w/b. TOPSIS was then employed to find the optimum mixture design proportions by considering multiple performance criteria. The results indicated that a high-performing sustainable PC mixture, with enhanced strength and durability characteristics, was formulated with a w/b ratio of 0.30, 25% RCA, 5% SF replacement, and 4% SBR addition. 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

Recycled concrete aggregates (RCAs) have the potential to be used as a sustainable, cost-effective, and environmentally friendly material in pavement base construction. However, there is a lack of information on the durability, strength, and hydraulic properties of RCA. The primary purpose of this study was to evaluate the properties and performances of commonly available RCAs in Oklahoma as pavement bases through laboratory testing and AASHTOWare Pavement ME simulations. For this purpose, three RCAs (RCA-1, RCA-2, and RCA-3) and a virgin limestone aggregate (VLA-1) were collected from local sources. RCA-1 and RCA-3 were produced in the field by crushing the existing concrete pavement of Interstate 40 and US 69 sections, respectively. RCA-2 was produced by crushing concrete and rubble collected in a local recycling plant. Laboratory testing for this study included particle size distribution, wash loss, optimum moisture content and maximum dry density (OMC-MDD), Los Angeles (LA) abrasion, durability indices (D_c and D_f), permeability (k), and resilient modulus (M_r). The properties of aggregates were compared and the service life (performance) of aggregate bases was studied through mechanistic analysis using the AASHTOWare Pavement ME design software (version 2.6, AASHTO, USA). The results indicated that the properties of RCAs can differ greatly based on the origin of the source materials and the methods used in their processing. Recycled aggregates from concrete pavements of interstate and state highways exhibited similar or improved performance as virgin aggregates. RCA produced in a recycling plant was found to show durability and strength issues due to the presence of inferior quality materials and contaminants. Also, the results indicated that the fine aggregate durability test is a useful tool for screening recycled aggregates to ensure quality during production and construction. Bottom-up fatigue cracking was identified as the most affected performance criterion for flexible pavements when using RCA as the base layer. The findings will help increase the use of RCA as pavement base to promote environmental sustainability. 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

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

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

The integration of Recycled Concrete Aggregate (RCA) and Reclaimed Asphalt Pavement (RAP) into Hot Mix Asphalt (HMA) presents a sustainable solution to mitigate environmental impacts and reduce reliance on virgin materials. This study investigates the influence of RCA and RAP as partial replacements for natural limestone aggregates on the volumetric, mechanical, and performance properties of asphalt mixtures. Replacement levels of 11%, 33%, and 66% (by total aggregate weight) were evaluated through comprehensive testing, including dynamic modulus, flow number, stiffness factor, and loss modulus assessments under varying temperatures and loading frequencies. Findings indicate that recycled aggregate incorporation results in a progressive reduction in optimum asphalt binder content, voids in mineral aggregates (VMAs), and voids filled with asphalt (VFAs). While all mixtures demonstrated acceptable stiffness-frequency behavior, the 33% replacement mix provided the best balance of rutting resistance and fatigue performance, satisfying Superpave volumetric criteria. The 11% mix exhibited enhanced fatigue resistance, whereas the 66% mix, despite showing the highest rutting stiffness, failed to meet minimum volumetric thresholds and is therefore unsuitable for structural applications. Statistical analysis (one-way ANOVA) confirmed the significant effect of RCA and RAP content on the mechanical response across performance zones. The results highlight the potential of using moderate recycled aggregate levels (particularly 33%) to produce durable, sustainable, and cost-efficient asphalt mixtures. For regions with mixed distress conditions, a 33% replacement is recommended, while 11% may be preferable in fatigue-critical environments. Further research incorporating viscoelastic continuum damage models and life cycle cost analysis is suggested to optimize design strategies and quantify long-term benefits. Full article

Pavement structures are one of the most critical civil infrastructures for the socio-economic development of communities. However, pavement construction demands an elevated financial budget and generates large amounts of environmental impacts. Accordingly, the new trends in daily engineering practices have integrated sustainability criteria verification into traditional pavement design procedures. Thus, this research explores the sustainability implications of asphalt pavement incorporating a Cement-Treated Base (CTB) and Recycled Concrete Aggregate (RCA) within the local context of a Global South country. The environmental and economic performances of four different types of asphalt structures were assessed, each differing in how the CTB is employed. These structures include conventional flexible pavement, semi-rigid pavement, inverted base pavement, and simple composite pavement. Furthermore, each structure is evaluated under four varying contents of coarse RCA (i.e., 0%, 15%, 30%, and 45%) in their asphalt mixtures. This approach results in a comprehensive analysis spanning 16 unique scenarios, providing valuable insights into the interplay between RCA content and CTB inclusion for sustainable infrastructure development. It is important to highlight that the Life-Cycle Assessment and Life-Cycle Cost Analysis methodologies were implemented to perform the environmental and economic inspections, respectively. Overall, this investigation demonstrates that although pavement structures comply with mechanistic design standards, they can yield significantly different cost effectiveness and environmental burdens from each other. Therefore, executing a sustainability-related appraisal is essential for accomplishing definitive infrastructure designs. Consequently, this research effort is expected to be used by stakeholders (e.g., civil engineers, designers, and governmental agencies) to support data-driven decision making in the road infrastructure industry. Full article

This research presents a sensitivity analysis of various parameters that affect the carbonation of recycled aggregates (RAs), namely CO₂ concentration, temperature, and relative humidity. The range of parameter values is close to that found in cement plant chimneys with regard to the forced carbonation of RAs. With this purpose, the main characteristics of flue gas streams (CO₂ concentration, temperature, and relative humidity) from two Portuguese cement plants were identified and used in this research. The results indicated that temperatures around 60 °C and CO₂ concentrations around 25% accelerate the carbonation reaction and increase CO₂ absorption in mixed recycled aggregates (MRAs). CO₂ absorption consistently decreased as the relative humidity was reduced from 60% to 40%. The highest amount of CO₂ captured was by a recycled concrete aggregate (RCA) in the conditions of 23 °C, 60% RH, and 25% CO₂. Overall, the RAs were able to capture a significant amount of CO₂, ranging from 52 to 348 kg of CO₂ per tonne of cement paste, depending on the nature of the RA. These findings drawn from a parametric campaign provide valuable insights into the potential enforcement of carbonation for recycled aggregates under conditions that closely reflect those found in cement plants. Full article

This research investigates the structural behavior of high-strength concrete beams reinforced with carbon fiber-reinforced polymer (CFRP) bars and varying percentages of recycled concrete aggregate (RCA). The study examined 15 reinforced concrete beams (200 × 250 × 2000 mm) constructed with different RCA proportions (0%, 25%, 50%, 75%, and 100%) and tested at three shear span-to-depth ratios ($a/d$ = 1.5, 2.5, and 3.5), addressing a critical knowledge gap in sustainable structural engineering. Specimens exhibited compressive strengths of 55–67 MPa and reached ultimate load capacities of up to 198.4 kN. Notably, beams with 75% RCA achieved 35.7% higher capacity than control specimens at $a/d$ = 1.5, challenging conventional expectations about RCA performance. Failure modes transitioned from shear-dominated at $a/d$ = 1.5 to flexure-dominated at $a/d$= 3.5, with optimal ductility indices (up to 2.75) observed at $a/d$ = 2.5. Statistical analysis revealed significant correlations between $a/d$ ratio and performance metrics, with a perfect parabolic relationship for the ductility index (R² = 1.0, $p<0.001$). Comparison with ACI 440.1R15 predictions showed generally conservative estimates (mean experimental-to-predicted ratio = 1.02, COV = 16.9%). The findings demonstrate that high-strength concrete can successfully incorporate substantial RCA quantities (up to 75%) without compromising performance when using CFRP reinforcement, potentially reducing virgin material consumption by approximately 33% for sustainable construction applications. Full article

In the context of sustainable construction, recycled concrete aggregates (RCAs), including both fine and coarse fractions derived from construction and demolition waste (CDW), are gaining traction due to their potential to mitigate environmental impacts by reducing reliance on natural aggregates and minimizing waste. This paper provides a comprehensive review of the effects of RCAs on the mechanical and durability properties of concrete, including compressive and tensile strengths, modulus of elasticity, and resistance to environmental degradation. The review highlights that the presence of adhered mortar and higher porosity in RCAs generally leads to reduced mechanical performance and durability. However, pretreatment methods—mechanical, chemical, and thermal—along with optimized mix designs and the use of supplementary cementitious materials (SCMs) have shown to significantly improve the concrete properties of RCAs. Additionally, recent studies on carbon dioxide (CO₂) capture through the accelerated carbonation of RCAs offer promising environmental benefits. Life cycle assessment (LCA) analyses reveal reductions in energy use, CO₂ emissions, and material costs when RCAs are properly processed and locally sourced. Despite challenges related to RCA quality variability, the review identifies pathways for the effective use of RCAs in structural applications. Full article

With the increasing rate of urbanization and the annual rise in municipal domestic waste, the use of harmless municipal solid waste incineration fly ash (HMSWIFA) as a construction material has been gradually adopted and promoted. However, significant differences exist in how various characteristics of HMSWIFA affect the performance of recycled aggregate concrete (RCA). To analyze the effects of HMSWIFA content and particle size on the macroscopic properties and microstructure of RCA, this paper conducts compressive, flexural, frost resistance, and Scanning Electron Microscope (SEM) characterization on RCA with varying dosages and particle sizes of HMSWIFA as a cement replacement. The results indicate that HMSWIFA enhances the compressive strength (CS) and frost resistance of RCA. Experimental data reveal that HMSWIFA with a particle size of 600–900 μm exhibits the best modification effect at an admixture level of 10–15%: the 28-day CS increased by 1.90–3.60%, the mass loss after freezing and thawing decreased by 0.37–0.45%, and the increase in dynamic elastic modulus reached 16.09–16.44%. Notably, the flexural strength (FS) experienced a reduction of 1.81% at a high dosage of the optimal particle size. This study elucidates the coupling relationship of “particle size-admixture-performance” in HMSWIFA-modified recycled concrete, demonstrating that reasonable control of the particle size distribution of HMSWIFA can achieve a synergistic effect of mechanical enhancement and durability improvement. The research findings provide a valuable reference for the application of municipal waste incineration HMSWIFA in RCA, facilitating the recycling of waste resources to mitigate pollution and enhance energy efficiency. Full article