Search Results (59)

Urban development increases impervious surfaces and stormwater runoff, while the construction sector generates large volumes of construction and demolition waste (CDW). Pervious concrete can mitigate runoff through infiltration and may also valorize CDW, yet its production and testing procedures remain heterogeneous, particularly with recycled aggregates. This study experimentally screens practical processing parameters for pervious concrete produced with basalt and CDW coarse aggregates. The influence of chemical admixture, consolidation method, and end-surface preparation was first assessed to define suitable production conditions: adequate cohesion without admixture required raising the water-to-cement ratio from 0.30 to 0.65; high-energy Proctor compaction crushed the CDW aggregates, favoring standard tamping-rod consolidation; and end-surface preparation had only a minor effect on compressive strength. The selected procedures were then applied to an ACI 522R-based basalt mixture designed for a target void content of 25%, which achieved a fresh density of 1985 kg/m³, a void ratio of 16.88%, and a mean permeability coefficient of 12.18 × 10⁻³ m/s, about twelve times the minimum required by ABNT NBR 16416. Its 28-day compressive strength (12.75 MPa) remained below the 20 MPa pavement-surfacing requirements, although within the typical range reported by ACI 522R for pervious concrete (2.8 to 28 MPa). Overall, aggregate gradation, compaction procedure, and admixture-enabled paste cohesion emerged as the dominant factors governing the strength–porosity–permeability trade-off, guiding subsequent mix optimization. Full article

While construction and demolition waste (CDW) remains one of the largest waste streams and a major source of environmental impacts worldwide, strategies based on circular economy principles, selective deconstruction, and pre-demolition audits (PDAs) have been increasingly promoted to mitigate these impacts. This study presents a comparative life cycle assessment (LCA) of high material recovery deconstruction and conventional demolition of an administrative building in Czechia. Two end-of-life (EoL) scenarios were evaluated: a Circular scenario derived from detailed PDA data and real material flows, and a Business-as-usual (BAU) demolition scenario representing conventional demolition practice. The system boundary included EoL stage (modules C2–C4) and module D in accordance with EN 15804+A2. Environmental modelling was conducted in SimaPro software V.9.2. using the ecoinvent 3.7 database and covered nine environmental impact categories. Results show that circular deconstruction consistently yielded higher environmental benefits, with improvements ranging from 1% to almost 15% across the assessed categories. Recycling of aluminium, steel, and glass contributed most significantly to avoided impacts, while concrete recycling provided benefits mainly under high-quality recovery pathways. The study demonstrates the value of PDA as an effective decision-support tool to improve material recovery and support more sustainable CDW management. Full article

Recycled aggregates (RAs) from construction and demolition waste (CDW) provide substantial circular-economy benefits, yet their elevated porosity, adhered mortar, and heterogeneity typically impair the mechanical performance and durability of recycled aggregate concrete (RAC). This PRISMA 2020-compliant systematic review synthesises 2180 records (2015–2026) to evaluate advanced strategies for enhancing RA quality prior to structural use. This paper critically compares removal-based treatments (mechanical, thermal, acid cleaning) with strengthening and densification approaches, including accelerated carbonation, pozzolanic and nano-silica coatings, polymer impregnation, microbial-induced calcium carbonate precipitation (MICP), and modified mixing methods such as triple-stage mixing (TSMA). Evidence shows that while all RA types (including recycled fine aggregate (RFA), recycled coarse aggregate (RCA), and their combination (RFCA)) can slightly reduce compressive strength and 30% replacement serves as a critical threshold, beyond this, strength loss accelerates, particularly in RCA and RFCA mixes. However, accelerated carbonation and TSMA consistently refine the interfacial transition zone, reduce water absorption by 17–30%, and recover 85–94% of natural aggregate concrete strength. Bio-deposition reduces water absorption by 13–21%, while acid/silica fume treatments improve late-age strength but carry environmental trade-offs. This review formulates a practice-oriented implementation framework for structural-grade RAC. Sustainability analyses indicate that carbonated RA can achieve net-positive CO₂ abatement when under low-carbon energy supply. A mechanistic schematic is presented to synthesise treatment-to-pore-structure/durability pathways across the four principal treatment routes, and a quantitative synthesis plot compares water absorption reductions across all treatment types using 13 data points drawn from included studies. A structured treatment comparison evaluates the energy intensity, industrial scalability, CO₂ footprint, and technology readiness level for each strategy. The remaining challenges include a lack of hybrid treatment studies, limited real-scale durability data, and insufficient mechanistic models linking treatment to pore structure evolution. This review recommends harmonised durability-based criteria and updates to standards (e.g., BS 8500, EN 12620) to support the scalable deployment of treated RA. Full article

Rapid urban expansion and industrial development have significantly increased waste generation while simultaneously intensifying the demand for construction materials. This dual pressure has accelerated the depletion of natural resources and raised serious environmental concerns. To address these challenges, considerable research efforts have focused on developing sustainable cementitious materials with reduced environmental impact and improved durability performance. One promising approach involves partially substituting Portland cement (PC) with supplementary cementitious materials (SCMs), which can enhance material performance while reducing environmental footprint and production costs. Recently, recycled powder (RP) derived from construction and demolition waste (CDW) has attracted growing attention as a sustainable alternative binder component. This review provides a comprehensive evaluation of the durability performance of Portland cement mortars incorporating RP obtained from concrete waste. Key durability indicators, including water absorption, capillary transport, chloride penetration resistance, freeze–thaw behavior, carbonation resistance, sulfate attack resistance, and drying shrinkage, are critically examined under various activation methods. In addition, the environmental and economic implications associated with RP utilization, including cost efficiency and CO₂ emission reduction potential, are analyzed. The findings provide a structured understanding of RP activation strategies and their effectiveness in improving the durability and sustainability of cement-based materials. Full article

The production route for cement clinker, including the clinkerization protocol and temperature, is highly dependent on the selection of raw materials. Natural resource reserves used in cement manufacturing are steadily declining due to rapid urbanization and the growing demand for building materials. Consequently, there is an urgent need to identify alternative resources, potentially from cost-effective primary raw materials or waste products. This study aims to evaluate the feasibility of incorporating recycled concrete as construction and demolition waste (C&DW) with unconventional clayey materials (bentonite and zeolite) into clinker synthesis at a reduced temperature of 1300 °C. The effect of mechanical pretreatment of the clinker raw meal, applied for durations of 10 to 30 min, was investigated. Mix designs combining traditional and alternative raw materials, along with different mechanical pretreatment durations, were systematically tested to assess their impact on raw meal clinkerization and the resulting cement mechanical properties. Despite variations in raw meal composition, the produced clinkers consistently exhibited phase compositions comprising C₃S, C₂S, C₃A, and C₄AF, as confirmed by XRD, FTIR, and SEM/EDS analyses. Among the studied raw materials, clayey components played a dominant role in controlling the formation of the main cement minerals, demonstrating that zeolite and bentonite can effectively substitute standard clays. Additionally, C&DW did not impede clinkerization; rather, it functioned as a silica source, replacing quartz sand. Short mechanical pretreatments (10 min) enhanced the content of cement minerals, whereas longer treatments adversely affected clinkerization. This study offers new insights into cement clinker production at reduced temperatures through the use of C&DW combined with unconventional clayey materials. The clinkerization temperature was reduced by approximately 100 °C from the conventional 1400–1450 °C, while still producing cements with mechanical performance comparable to ordinary Portland cement (OPC). The resulting zeolite- and bentonite-based cements, either mechanically untreated or subjected to short pretreatment, are potentially suitable for structural concrete applications, while cements produced with longer mechanical pretreatments may be more appropriate for lower-demand or non-structural uses. Full article

Valorizing construction and demolition waste (CDW) via alkaline activation enables low-carbon binders. This study assesses binary geopolymers formulated with recycled brick powder (PLR) and recycled concrete powder (PCR) in seven precursor ratios (0–100% PCR), activated with a ternary NaOH/Na₂SiO₃/KOH solution (silicate modulus M_s ≈ 3.2) at L/B = 0.15, and cured for 7, 14, and 28 days. Compressive strength (fc), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) were used to link microstructure–phases–properties. A local maximum in fc at ~30% PCR (16.2 MPa at 28 d) was observed versus 0% PCR (14.2 MPa) and ≥50% PCR (13.8 → 10.1 MPa at 28 d). XRD indicated a reduction in inherited crystalline phases and an increased amorphous fraction at ~30% PCR; FTIR (normalized peak position and FWHM of the T–O–Si band, not absolute intensity) suggested higher network extension; SEM-EDS (local/semiquantitative) showed a moderate rise in Ca that supports C-A-S-H domains bridging the N-A-S-H network. At a high PCR, excess Ca simplified mineralogy (quartz/portlandite dominance), promoted competitive routes (C-S-H/carbonation), reintroduced microdefects, and reduced fc. A theoretical oxide balance per mix identified a compositional window where Ca/(Si + Al) ≈ 0.35–0.45 coincides with the mechanical optimum and with XRD/FTIR tracers. Overall, a ~30% PCR window maximizes co-reticulation of N-A-S-H/C-A-S-H and densification without compromising aluminosilicate continuity, providing transferrable design and process-control criteria for CDW-based geopolymer binders. Full article

Recycled powder (RP), a by-product with a particle size smaller than 150 μm, is generated during the processing of construction and demolition waste (CDW) for recycled aggregate production. RP mainly consists of recycled concrete powder and recycled brick powder. Previous studies have demonstrated that RP can serve as a supplementary cementitious material (SCM) in concrete production. Due to the heterogeneity of parent materials with different ages, service environments, and compositions, the physicochemical properties and reactivity of RP vary significantly, which largely accounts for the inconsistent results reported in the literature. This paper presents a critical review of the application of RP as an SCM in construction. The preparation technologies, chemical and physical properties, microstructural characteristics, and activation methods of RP are systematically examined. Owing to its irregular and rough surface morphology, RP tends to reduce workability and increase water demand when incorporated as an SCM. Nevertheless, when the replacement level and median particle size are limited (typically below 30% and 20 μm, respectively), RP can contribute through micro-filling, nucleation, and limited pozzolanic effects, thereby mitigating adverse impacts on mechanical and durability properties. The mechanisms and effectiveness of mechanical grinding, thermal activation, chemical activation, and CO₂ treatment are comparatively evaluated. Moreover, the incorporation of RP in cement-based materials offers significant economic and environmental benefits. Full article

To meet 2050 climate targets, the construction sector must reduce CO₂ emissions and transition toward circular material flows. Recycled aggregates (RA) derived from construction and demolition waste (CDW) and industrial byproducts such as oil shale ash (OSA) show potential for use in concrete, although their application remains limited by standardisation and performance limitations, particularly in structural uses. This study aims to develop and evaluate low-strength, resource-efficient concrete mixtures with full replacement of natural aggregates (NA) by CDW-derived aggregates, and partial or full replacement of cement CEM II by OSA–metakaolin (MK) binder, targeting non-structural 3D-printing applications. Mechanical performance, printability, cradle-to-gate life cycle assessment, eco-intensity index, and transport-distance sensitivity for RA were assessed to quantify the trade-offs between structural performance and global warming potential (GWP) reduction. Replacing NA with RA reduced compressive strength by ~11–13% in cement-based mixes, while the aggregate type had a negligible effect in cement-free mixtures. In contrast, full cement replacement by OSA-MK binder nearly halved compressive strength. Despite the strength reductions associated with the use of waste-derived materials, RA-based cement-free 3D-printed specimens achieved ~30 MPa in compression and ~5 MPa in flexure. Replacing CEM II with OSA-MK and NA with RA lowered GWP by up to 48%, with trade-offs in the air-emission, toxicity, water and resource categories driven by the OSA supply chain. The cement-free RA mix achieved the lowest GWP and best eco-intensity, whereas the CEM II mix with RA offered the most balanced multi-impact profile. The results show that regionally available OSA and RA can enable eco-efficient, structurally adequate 3D-printed concrete for construction applications. Full article

Decarbonising the construction industry’s substantial ecological footprint demands credible substitutes that preserve structural performance while valorising waste. Although construction and demolition waste (CD&W) has been widely studied, the vast potential of agricultural residues (e.g., corncob, rice husk) and, crucially, their synergy remains underexplored. This study couples a systematic literature review with mathematical modelling to evaluate binary CD&W–agro-waste binders. A modified Andreasen–Andersen packing framework and pozzolanic activity indices inform multi-objective optimisation and Pareto analysis. The optimum identified is a 70:30 CD&W-to-agricultural ratio at 20% total cement replacement, predicted to retain 86.0% of OPC compressive strength versus a 79.4% average for single-waste systems (8.3% non-additive uplift). Life-cycle assessment (cradle-to-gate) shows a 20.3% carbon reduction for the synergistic blend (vs. 19.6% CD&W-only; 19.3% agro-only); when normalised by strength (kg CO₂-eq/MPa·m³), the blend delivers 6.3% better carbon efficiency than OPC (5.63 vs. 6.01), outperforming agro-only (5.79) and CD&W-only (6.61). Global diversion arithmetic indicates feasible redirection of 0.246 Gt y⁻¹ of wastes (5.7% of CD&W and 1.8% of agricultural residues) at 30% market penetration. Mechanistically, synergy arises from particle size complementarity, complementary Ca–Si reactivity generating additional C–S–H, and improved rheology at equivalent flow. Monte Carlo analysis yields a 91.2% probability of ≥40 MPa and 78.3% probability of ≥80% strength retention for the optimum; the 95% interval is 39.5–55.3 MPa. Variance-based sensitivity attributes 38.9% of output variance to the Bolomey constant and 44% to pozzolanic indices; interactions contribute 19.5%, justifying global (not local) uncertainty propagation. While promising, claims are bounded by cradle-to-gate scope and the absence of empirical durability and end-of-life evidence. The results nevertheless outline a tractable pathway to circular, lower-carbon concretes using co-processed waste. The approach directly supports circular economy goals and scalable regional deployment. Full article

Sustainable management of Construction and Demolition Waste (CDW) is key to the Circular Economy. Reusing crushed concrete as recycled concrete aggregates (RCAs) in hot-mix asphalt (HMA) is a viable CDW solution, although RCA’s high absorption can affect performance. This study evaluates the effect of partially replacing 0%, 10%, and 30% of virgin aggregate with RCA in a dense-graded HMA, assessing its moisture susceptibility and cracking resistance. Specimens were subjected to long-term water-immersion aging (3 and 6 months at 25 °C) and tested for Indirect Tensile Strength (ITS), Tensile Strength Ratio (TSR), and Cracking Tolerance Index (CT-index). RCA incorporation consistently increased ITS at all aging levels. In particular, the 30% RCA mixtures exhibited the highest strength, exceeding the absolute ITS thresholds required by various U.S. transportation agencies to ensure structural capacity. While TSR values remained below the 80% AASHTO T 283 threshold, 10% and 30% RCA mixes had higher TSR than the control, indicating a comparative improvement in moisture resistance. Conversely, the CT-index decreased with more RCA and longer immersion, particularly at 30% RCA, revealing a trade-off between strength gain and cracking tolerance under prolonged wet exposure. Overall, a 10% RCA replacement level provided the most balanced performance, supporting its technical feasibility for sustainable, performance-based mixture design. Full article

Construction and demolition waste (CDW) was successfully utilized as an aggregate with 100% replacement of natural aggregates and mineral admixtures, with up to 60% replacement of ordinary Portland cement (OPC) in the production of recycled concrete. The effects of ratios of concrete-based CDW (concrete-CDW)/brick-based CDW (brick-CDW) in both aggregates and CDW mineral admixture contents in the binder on recycled concrete were investigated in terms of their workability and compressive strength, microstructure, and sustainability. The results showed that with an increase in the ratios of brick-CDW/concrete-CDW aggregates, the concrete workability continuously deteriorated, while the compressive strength firstly increased and then decreased. Compared to the 100% dosage of concrete-CDW aggregates, the 28-day compressive strength of the recycled concrete was 37.4 MPa; the optimized relative proportions of brick-CDW and concrete-CDW aggregates were 20% and 80%, respectively; and the 28-day compressive strength was the highest, reaching to 46.7 MPa, and increasing by 24.9%. In a binder study, the microstructure of the paste was found to be improved, with the dosage of brick-CDW and concrete-CDW admixtures at up to 20%. In this range, the workability changed slightly when the relative proportion of brick-CDW admixture increased, the 28-day compressive strength of the recycled concrete increased, and the pore structure was refined. Furthermore, the utilization of a large amount of CDW as a mineral admixture and aggregate in concrete significantly reduced costs and CO₂ emissions in different regions. Full article

This study evaluates the viability of water jig for removing the impurities from CDW and the concentration of concrete aggregates from mixtures containing 10%, 20%, and 30% impurities (brick and gypsum), simulating the materials commonly found in CDW. Laboratory-scale jigging tests were conducted in single-stage jigging, and the products were characterized based on density > 2.6 g/cm³, water absorption, shape factor, and bulk density to evaluate the separation performance. It was noted that dense fractions consistently achieved high purity with less than 1% impurities and a concrete content of more than 99% and that more than 80% of dense material was recovered. These results demonstrate that water jigging is a technically viable method for producing recycled aggregates of sufficient quality for reuse in concrete while also reducing CDW disposal by more than 40% and contributing to the sector’s carbon footprint reduction. The findings confirm that even a single-stage jigging process can provide high-quality recycled aggregates, offering a simple and effective route for CDW beneficiation. Full article

Construction and demolition waste (CDW) is the most significant portion of solid waste generated throughout the European Union (EU). CDW represents more than a third of the waste generated, considering the waste generated by all economic activities and household waste. The central reuse of CDW is as a base for roads, and in specific cases, it can be reused as recycled coarse aggregates (RA) in the manufacture of precast concrete, new building blocks, bricks, and as RA on new concrete formulations, among other activities. This work aims to enable the concentration of the aggregates mixed in the CDW with the jigging process. The recovered RA was replaced in the concrete, and four different replacement levels (25%, 50%, 75%, and 100%) were analyzed for reuse in new C30/40 concretes. Physical characterization of the material was performed, and compressive strength tests were conducted to verify the RA replacement’s influence on the concrete. The work tests allowed us to observe the positive variation of the material’s physical properties according to the jigging processing and the efficiency of recovering the aggregates. After analyzing the results obtained in the strength force tests, it is possible to conclude that the RA generated can be a substitute for natural aggregates (NA) in new C30/40 concrete formulations. When 100% RJA is used as a replacement, the 28-day compressive strength reaches 33.2 MPa, which is only 6% lower than that of the NA group, reducing the environmental liabilities inherent in the aggregate mining process and generating an economically viable material. Full article

This study investigates the mechanical performance of concrete paving stones manufactured with recycled aggregates derived from TransMilenio slab demolition waste (CDW-A-TS) as a sustainable alternative to conventional natural coarse aggregates (river gravel) and fine aggregates (river sand). Construction and demolition waste from Bogotá’s mass transit system slabs was processed to produce recycled aggregates, which were replaced at substitution levels of 0%, 30%, 50%, and 100% by volume of natural aggregates. The mechanical properties evaluated included compressive strength, flexural strength, abrasion resistance, and water absorption, following Colombian Technical Standards (NTC) and international protocols. Results demonstrate that all CDW-A-TS mixtures exhibit enhanced compressive strength, with improvements ranging from 14.71% to 32.82% compared to the control mix. Flexural strength also increased by 1.34% to 6.13%. However, water absorption increased proportionally with CDW-A-TS content (10.66% to 25.24%). The optimal substitution level was identified at 30% CDW-A-TS based on a composite evaluation of mechanical performance (compressive and flexural strength), durability indicators (water absorption and abrasion resistance), This research demonstrates the technical viability of incorporating TransMilenio demolition waste in paving stone production, contributing to circular economy principles and sustainable urban infrastructure development. This finding aligns with prior research affirming the viability of incorporating recycled coarse aggregates in concrete prefabricates, such as paving stones, for various construction applications. Full article

The waste management and recycling industry in Saudi Arabia is facing ongoing challenges in reducing the negative impact resulting from the recycling process. Different types of waste lack an efficient and accurate method for classification, especially in cases that require the rapid processing of materials. A deep learning prediction model based on a convolutional neural network algorithm was developed to classify and predict the types of construction and demolition waste (CDW). The CDW image dataset used contained 9273 images, including concrete, asphalt, ceramics, and autoclaved aerated concrete. The model obtained an overall accuracy of 97.12%. The Green Ground image prediction model is extremely useful in the construction and demolition industry for automating sorting processes. The model improves recycling rates by ensuring that materials are sorted correctly, thus reducing waste sent to landfills, by accurately identifying different types of materials in CDW images. As part of Saudi Arabia’s 2030 sustainability objectives, these steps contribute to achieving a greener future, complying with environmental regulations, and promoting sustainability. Full article