Search Results (865)

The recycling of construction and demolition waste and the reduction of carbon emissions are important issues in sustainable construction. Recycled aggregate concrete (RAC) is promising for structural use, but the weak old mortar and multiple interfacial transition zones in recycled coarse aggregate (RCA) may reduce the load-transfer capacity at the steel–concrete interface. To address this problem, this study developed carbonated recycled aggregate concrete-filled flat steel tube (FST-CRAC) members and investigated their interfacial bond–slip behavior through material strength tests and push-out tests on nine specimens. The effects of RCA replacement ratio, carbonation treatment, section aspect ratio, and width-to-thickness ratio were examined. RCA was carbonated at 0.5 MPa for 24 h. The 28-day compressive strength increased from 32.6 to 44.3 MPa in the uncarbonated P series and from 36.2 to 46.2 MPa in the carbonated T series. However, because the two series were developed through separate preliminary mix-design trials, these differences should be interpreted as being jointly associated with carbonation treatment and mix-proportion adjustments rather than as evidence of an isolated causal effect of carbonation. Push-out failure was governed by interfacial debonding, local crushing near the corners, and post-peak frictional slip, with damage consistently concentrated at the short sides and corners of the flat section. Carbonation treatment increased the peak bond load by 2.85–26.23%, with the largest benefit observed at a moderate replacement ratio, while increasing the RCA replacement ratio from 50% to 100% increased the peak load by 27.90% for uncarbonated specimens but only 4.21% for carbonated specimens, indicating that carbonation reduces the sensitivity of bond capacity to replacement ratio. A moderate increase in section aspect ratio increased the peak load by 22.30–25.86%, and reducing the width-to-thickness ratio increased the peak load by 5.95–40.92%. A four-linear bond–slip constitutive model was proposed to describe the full interfacial response, from initial bonding through peak degradation to residual friction. These findings provide experimental support for the use of carbonated recycled aggregates in steel tube-confined composite members and a basis for subsequent nonlinear analysis. Full article

Growing environmental concerns associated with Portland cement production, along with the continuous accumulation of construction and demolition waste, have intensified the need for sustainable construction materials and effective recycling strategies. This study experimentally investigates the performance of fly ash-based geopolymer concrete (GPC) incorporating recycled concrete aggregate (RCA) as a partial replacement for natural coarse aggregate, compared to conventional ordinary Portland cement concrete (OPC), with a particular focus on integrated durability performance. Ten mixtures were prepared, including five GPC and five OPC mixes with RCA replacement levels of 0–100% by volume. Mechanical properties were evaluated through compressive, splitting tensile, and flexural strength tests, while durability performance was assessed using water permeability, chloride penetration, acid resistance, elevated temperature exposure up to 1000 °C, and accelerated corrosion tests, supported by SEM–EDX analysis. Results show that GPC outperforms OPC across all replacement levels. Optimal performance was achieved at 20–40% RCA, while at 60% RCA a slight reduction in strength was observed; however, the values remained relatively high, particularly for GPC mixtures, indicating stable performance. A significant reduction occurred only at full replacement. GPC also exhibited lower permeability, enhanced corrosion resistance, improved thermal stability, and better resistance to acid attack. This study provides strong evidence that GPC can effectively compensate for the inherent limitations of RCA, offering a durable and eco-efficient alternative for structural and infrastructure applications. Full article

The construction sector generates over one-third of all waste in Europe, yet the reuse of building components remains marginal compared to recycling, and circular strategies are rarely aligned on the territorial scale at which materials, stakeholders and infrastructure operate. This paper investigates the regulatory, institutional, infrastructural and operational conditions under which reuse to become a systemic practice. A desk-based comparative analysis of six European contexts (Belgium, the Netherlands, Switzerland, Germany, France, Denmark) was conducted on 282 documents, using a framework of seven dimensions grouped into three macro-families drawn from the literature on territorial circular ecosystems. The findings show that these conditions form a dependency chain of five ordered links: legal recognition of the non-waste status; a standardized pre-demolition audit; preparation and storage physical hubs, in parallel with research infrastructures, absorbing technical uncertainty; a guarantee system covering performance, liability and insurability; and a demand-side activation. The guarantee link is a constraint and a key element in demand activation. Regulation is necessary but not sufficient, since binding instruments target recycling or auditing while reuse remains voluntary in all six contexts. The chain yields a typology of ecosystem configurations and a replicable diagnostic instrument, whose transferability is assessed on the Italian case. Full article

European circular construction policies, including the EU Construction and Demolition Waste Protocol and the Level(s) framework, provide strategic guidance for improving material recovery from buildings. However, limited research documents how these frameworks operate under real project conditions, characterised by incomplete information, evolving inventories and market-dependent recovery pathways. This paper documents a pre-demolition audit carried out in the Czech context and maps the observed process onto the EU CDW Protocol and Level(s) Indicator 2.2 framework. A structured implementation approach is applied to an in-depth case study of the selective deconstruction and deep refurbishment of an office building in the Czech Republic. The results show both the circular recovery potential and operational feasibility of the audit process, illustrating how audit recommendations evolved through documentation review, field verification and engagement with potential material outlets. The findings demonstrate that feasible recovery routes depended not only on material identification and technical recyclability but also on market verification, stakeholder coordination and legal or organisational enablement. The case further highlights the importance of auditor expertise and brokerage in enabling reuse and recycling routes under real project constraints. Insights from the case study are discussed in relation to experiences reported in other European countries. This study contributes empirical evidence documented in relation to European circular-construction frameworks and suggests that PDA reporting should combine mass-based indicators with the transparent documentation of recommendation maturity, implementation constraints and reporting-boundary assumptions. Full article

To promote construction waste recycling and develop sustainable pavement materials, this study utilized recycled aggregates (crushing value 7.8%) obtained from bridge demolition as a 100% replacement for natural aggregates in recycled pervious concrete. The research focused on investigating the influence of different aggregate gradations (single-sized 4.75–9.5 mm and binary-graded combinations: 4.75–9.5 + 16–31.5 mm, 2–5 + 13–26.5 mm) and different water-to-cement ratios (0.26, 0.27, 0.30) on the concrete properties. Tests on compressive strength, splitting tensile strength, and connected porosity revealed the following results: The strength of recycled pervious concrete was comparable to that of natural aggregate concrete, and strength decreased with increasing aggregate size. The optimal water-to-cement ratio varied with gradation: 0.27 for the single-sized 4.75–9.5 mm aggregate and 0.30 for the binary-graded combinations. Splitting tensile strength was generally low, showed insignificant growth from 7 d to 28 d, was sensitive to interfacial defects, and exhibited high data variability. Connected porosity was inversely proportional to compressive strength and decreased with increasing water-to-cement ratio. This study provides experimental evidence for optimizing the preparation of high-performance recycled pervious concrete using recycled aggregates. In addition, the influence of fiber type, dosage, and length was preliminarily examined through an orthogonal design. Full article

The construction sector has a significant impact on natural resources consumption and waste generation. In accordance with circular economy principles, the adoption of secondary materials, encompassing both reused and recycled components, by construction companies is of increasing strategic importance, especially in cities and their surrounding areas. However, enterprises in this sector continue to face substantial challenges related to implementation of these materials. The article aims to investigate the opinions of representatives of companies operating in the construction sector in the West Pomeranian Voivodeship of Poland regarding the benefits and obstacles associated with the implementation of secondary materials, as well as to identify measures that could contribute to the wider use of these materials in practice. The study was conducted using a diagnostic survey method based on computer-assisted web interviews. The sample comprised 46 respondents from the West Pomeranian Voivodeship of Poland. The analysis of the collected opinions emphasized that waste reduction, protection of the environment and natural resources are perceived as the most significant benefits. Among the main obstacles to implement these materials, respondents highlighted the lack of specialized platforms for secondary materials trading, difficulties in materials sorting, including construction and demolition waste, as well as complex bureaucratic procedures. In the respondents’ opinion, the measures crucial for facilitating the use of secondary materials include the development of legislation enabling the reclassification of waste as secondary construction materials, ensuring reliable access to these materials, and providing government support. It was revealed that despite broad recognition of environmental benefits, the primary obstacle is the absence of an effective marketplace for secondary materials, pointing to a crucial role for institutional intervention. Recommendations for companies’ managers from the construction sector, designers and local policymakers were proposed. Full article

The construction sector relies heavily on virgin mineral resources and produces significant quantities of construction and demolition waste. This study examines crushed brick aggregate (CBA) as a volumetric substitute for natural river sand in micro-concrete at replacement levels of 0%, 25%, 50%, 75%, and 100%. Results show that increasing CBA content decreases consistency and flexural strength while increasing water absorption. However, compressive strength is maintained even at full replacement. One-way ANOVA demonstrated significant overall effects of CBA replacement level on all investigated properties. However, Tukey’s HSD comparisons indicated that not all adjacent replacement levels exhibited significant differences. Specifically, compressive strength at 25% and 50% replacement did not differ significantly from the reference mixture. A nominal resource-efficiency assessment based on the absolute-volume method and literature-derived density values indicates that, at 25% volumetric replacement, the mixture incorporates approximately 286.7 kg/m³ of CBA and saves 362.4 kg/m³ of natural sand while retaining 94.3% of the reference compressive strength. For Croatia’s estimated 8882 t of waste bricks in 2024, a maximum yield scenario suggests production of about 30,985 m³ of this mixture and natural sand savings of approximately 11,231 t. The 25% replacement level offers the most balanced outcome in terms of secondary resource utilisation, consistency, mechanical performance, and water absorption. Full article

Although low-carbon geopolymers incorporating construction and demolition waste (CDW) offer a promising circular economy pathway, the synergistic mechanisms between pretreated recycled fine aggregates (RFA) and geopolymer binders have not been systematically elucidated. This study investigated the comprehensive performance of geopolymer mortar containing recycled powder (RP) incorporating RFA; 50% Fly ash, 25% slag, and 25% RP were incorporated as precursor for the production of geopolymer binders, while the replacement ratios (0%, 20%, 40%, 60%, 80%, 100%) and the pretreatment methods (carbonation and prewetting) of RFA were taken as experimental parameters. The effect of these parameters on the fluidity, setting time, water absorption, compressive strength, and microstructure of recycled geopolymer mortar (RGM) and recycled cement mortar (RCM) was analyzed. Results showed that as the RFA replacement ratio increases, the measured properties generally decline. However, pretreating the RFA, particularly through carbonation, effectively mitigates these drawbacks. The use of 60% carbonated RFA enhanced the compressive strength of RGM by 12% compared to untreated RFA at equivalent replacement ratio. A comparative evaluation of the performance variations between RGM and RCM revealed that geopolymer mortar exhibited lower fluidity, faster setting time, and higher compressive strength. The microstructure analysis by SEM showed that the geopolymerization reaction between adherent cement paste in RFA and geopolymer binders significantly enhanced the microstructural compactness compared to RCM. Furthermore, carbonation and prewetting treatments can mitigate cracks and pores in the mortar. The results demonstrate that RGM prepared with carbonated RFA offer an estimated 76% reduction in net CO₂ emission and 14.3% reduction in total cost relative to conventional cement mortar. This study established a framework that compares the mechanisms of RFA pretreatment and equip engineers with validated pretreatment strategies for upcycling CDW into construction materials. Full article

This study investigated the underwater abrasion resistance of recycled aggregate concrete according to ASTM C1138 using recycled aggregates obtained from demolished concrete as a 100% replacement of natural aggregates. The objective was to reduce the consumption of natural resources and minimize construction and demolition waste. In addition, ground granulated blast furnace slag (BFS) was used as a supplementary cementitious material at replacement ratios of 25% and 50%. Three BFS products with Blaine fineness values of 3000, 4000, and 6000 cm²/g were used to investigate their effects on the compressive strength and underwater abrasion resistance of recycled aggregate concrete. The experimental results showed that the compressive strength of recycled aggregate concrete was approximately 7% lower than that of natural aggregate concrete. However, the underwater abrasion test according to ASTM C1138 showed that the abrasion depth of recycled aggregate concrete was comparable to that of natural aggregate concrete. After 72 h of testing, the abrasion depth of recycled aggregate concrete was only slightly higher than that of natural aggregate concrete. In contrast, recycled aggregate concrete exhibited a higher weight loss, with an average value of 2.10% compared with 1.77% for natural aggregate concrete. Among the BFS mixtures, increasing the Blaine fineness of BFS resulted in lower abrasion depth and lower mass loss. Concrete containing BFS6000 exhibited the best underwater abrasion resistance within the BFS mixtures, although all BFS mixtures showed higher abrasion depth and mass loss than recycled aggregate concrete without BFS. At the 25% replacement ratio, concrete containing BFS6000 exhibited the lowest abrasion depth (3.11 mm) and weight loss (3.37%), whereas concrete containing BFS3000 showed higher values. A similar trend was observed at the 50% replacement ratio, although both abrasion depth and weight loss slightly increased compared with the corresponding 25% mixtures. The results demonstrate that recycled aggregate concrete combined with BFS has good potential for hydraulic structures and other concrete structures exposed to underwater abrasion. Although a slight reduction in compressive strength was observed, the underwater abrasion resistance can be improved by using BFS with higher Blaine fineness together with quality-controlled recycled aggregates. These findings provide useful information for the development of sustainable recycled aggregate concrete and support the efficient utilization of recycled materials in hydraulic engineering applications. Full article

To promote the high-value utilization of construction and demolition waste in cementitious materials, this study proposed an integrated strengthening strategy combining recycled coarse aggregate modification with cementitious matrix optimization. Recycled coarse aggregates with particle sizes of 4.75–31.5 mm were prepared from demolished concrete waste collected in Aksu, Xinjiang, China, and treated by particle shaping, alkaline solutions, and polyvinyl alcohol (PVA). Silica fume and a polycarboxylate superplasticizer were used to optimize the cementitious matrix. The physical properties of recycled aggregates, the mechanical performance of recycled aggregate concrete, and the mechanical and durability performance of high-content recycled aggregate cement-stabilized materials were evaluated. Particle shaping reduced water absorption and the crushing index from 6.8% and 14.4% to 5.6% and 12.6%, respectively. After treatment with 5% NaOH and 10% PVA, the apparent density increased to 2779 kg/m³, whereas water absorption and the crushing index decreased to 3.3% and 8.3%, meeting Class II recycled coarse aggregate requirements. With 10% silica fume and 0.2% superplasticizer, the 28-day compressive strength of recycled aggregate concrete prepared with the optimized aggregate and matrix reached 27.6 MPa, corresponding to 97.5% of that of natural aggregate concrete. The combined modification approach improved mechanical performance and reduced drying shrinkage, but the replacement ratio should be limited to 60% to satisfy the F50 freeze–thaw requirement under the tested conditions. Full article

This study assesses the technical performance and environmental impact of traditional and eco-efficient materials used in civil construction in Colombia through a structured synthesis of scientific, technical, and regulatory evidence covering the period 2010–2025. The analysis integrates mechanical performance indicators, environmental footprint metrics, and the national regulatory framework supporting sustainable material adoption. Results show that conventional materials—Portland cement, structural steel, ceramic bricks, and timber—remain essential due to their proven structural reliability but are also responsible for the highest contributions to CO₂ emissions, energy consumption, and resource depletion. In contrast, eco-efficient alternatives, including blended concretes with mineral additions, geopolymers, rammed earth, Guadua angustifolia, and natural biocomposites, achieve carbon emission reductions between 40% and 85% while maintaining comparable mechanical performance for specific applications. Colombian policies—notably Resolutions 1257 of 2021 and 0194 of 2025—promote waste valorization and low-impact materials, yet their implementation remains limited by technical, economic, and knowledge barriers. The findings support a decision-oriented framework for material selection that balances structural efficiency with environmental responsibility. Full article

The reuse of the finest fraction derived from recycled aggregate washing has been investigated for the manufacture of mortars. This practice contributes to the circular economy and lowers CO₂ emissions in the manufacturing of construction materials. A distinction was made between concrete-rich residues (RH) and mixed concrete–ceramic wastes (RHM). Chemical and mineralogical analyses of samples collected over a two-year period revealed consistent homogeneity over time. The RH residues are richer in CaO, primarily as calcite. Conversely, higher ceramic content in the waste correlates with increased SiO₂, Al₂O₃, and K₂O concentrations, predominantly as phyllosilicates and feldspars. Ettringite and portlandite occur in trace amounts. DTA-TG analysis reveals the presence of minor contents of portlandite and C-S-H gel. Mortars were prepared by replacing 10%, 20%, and 30% of Portland cement (OPC) with concrete-derived (RH) and mixed concrete–ceramic (RHM) wastes. At 10% and 20% substitution, both wastes yielded similar strengths, confirming their high potential for masonry mortars without prior treatment. However, at 30% replacement, RH provided markedly higher compressive and flexural strengths than RHM, likely due to a greater presence of the C-S-H gel phase in concrete waste. While 10% and 20% replacements successfully meet the 70% Strength Activity Index (SAI) threshold, a 30% limit severely reduces strength. Consequently, substitutions of 30% or higher require mechanical or thermal activation to enhance CDW reactivity. Given the minimal performance gap between RH and RHM, processing mixed CDW streams uniformly is recommended to maximize economic viability and ensure batch homogeneity in industrial washing plants. Full article

Recycled aggregate concrete (RAC) offers an effective approach to reducing the environmental burden associated with construction and demolition waste. In this study, a fiber-reinforced RAC was developed by replacing part of the cement with fly ash and ground granulated blast-furnace slag, while glass fibers or basalt fibers were incorporated as reinforcing materials. A systematic experimental program was conducted to evaluate the mechanical behavior of the proposed concrete under different saturation conditions. The results show that the best toughness performance was achieved in the natural moisture state. In comparison, compressive and flexural strengths reached their maximum values under dry conditions, whereas splitting tensile strength peaked in the natural state. Based on the experimental data, prediction equations were established for the splitting tensile and flexural strengths by considering both saturation degree and fiber content. A stress–strain model under uniaxial compression was also developed. In addition, scanning electron microscopy (SEM) was employed to examine the fiber–matrix interface and hydration products, thereby clarifying the microstructural characteristics of the concrete at different saturation levels. Full article

Construction and demolition waste remains a major sustainability challenge, while the use of mixed recycled aggregates in structural concrete is still limited due to concerns over variability, water absorption, and durability. This study investigates whether washed mixed recycled coarse aggregate can partially or fully replace natural coarse aggregate in concrete for seawall block applications. The recycled aggregate was characterized and then upgraded through simple washing and grading to remove fines and contaminants. Concrete mixes incorporating 0%, 5%, 1780, 20%, 50%, and 100% recycled aggregate replacement were produced and tested for workability, compressive strength, flexural strength, density, and water absorption under both tap-water and saline curing conditions. The results demonstrate that washing significantly improves aggregate quality, enabling compressive strength comparable to the reference mix at replacement levels up to approximately 20%. Higher replacement levels led to reductions in workability, flexural strength, and density; however, performance remained within technically acceptable limits. Overall, the findings indicate that washed mixed recycled coarse aggregate is a viable material for seawall concrete, supporting more circular and sustainable use of construction and demolition waste in marine infrastructure. Full article

Recycled brick aggregate (RBA) and old mortar (OM) account for a large proportion of construction and demolition waste. To date, few systematic studies have addressed how their coupling interaction governs the performance of recycled concrete (RC). In this study, a two-factor experimental design was carried out, where RBA content (0–15%) and OM content (0–15%) were set as independent variables. The physical properties of recycled aggregates (RAs) and mechanical behaviors of RC were measured, and the underlying mechanisms were elaborated from both macroscopic and microscopic perspectives. Experimental results reveal that increasing RBA and OM contents raise the water absorption and crushing value of RA while reducing their apparent density. OM exerts a more substantial impact on water absorption and apparent density, whereas RBA predominantly controls the fluctuation of crushing value. When RBA dosage rises from 0% to 15%, the maximum reductions in compressive strength and flexural strength reach 20.7% and 23.4%, respectively. When OM dosage increases from 5% to 15%, the corresponding strength reductions are 24.8% and 20.3%. Scanning electron microscopy (SEM) characterizations prove that internal pores and microcracks within RBA, along with loose zones at the interface between OM and fresh mortar, act as vulnerable paths for crack initiation and propagation, which deteriorates the bulk macroscopic mechanical properties. Range analysis and analysis of variance confirm that RBA serves as the dominant influential factor. The contribution proportions of RBA to compressive strength and flexural strength are 68.3% and 72.5%, which exceed those of OM (31.7% and 27.5%). The combined action of RBA and OM produces an evident negative superposition effect, with no detectable performance compensation effect observed. This research lays a solid foundation for optimizing the mixing proportion of RA derived from construction waste and promoting the engineering application of RC. Full article