Search Results (1,436)

The increasing demand for sustainable construction materials has driven research into the reuse of plastic waste for renewable building applications. This study introduces a new lightweight insulating mortar for floor and roof systems, utilizing recycled rigid polyurethane (PU) foam as the primary aggregate. The binder mainly consists of Portland cement, with no added sand, and includes minor additives to enhance mechanical, physical, and thermal properties. Initial tests demonstrated that key performance metrics—density, compressive strength, and thermal conductivity—are significantly influenced by the PU content. As the proportion of PU increased, all three parameters decreased. The optimized formulation, comprising 92.25 vol.% PU foam, 6.75 vol.% cement, and 1 vol.% additives, achieved a low bulk density of 420 kg/m³, a compressive strength of 1 MPa, and a thermal conductivity of 0.07 W/m·K. A pilot-scale production system with a capacity of 1500 L/h (equivalent to 20 bags of 75 L) was subsequently designed, implemented, and validated. These findings underscore the potential of PU-based lightweight insulating mortars to reduce environmental impact and support the development of sustainable construction practices globally. Full article

The United States of America could build 20,000 bases for the Statue of Liberty every year using its construction and demolition waste, and 456 bases using waste glass from jars and bottles. However, some sectors of the population still face a shortage of affordable housing. The challenges of disposing of such large amounts of waste and solving the housing shortage could be addressed together if these materials, considered part of a closed-loop system, were integrated into new building blocks. This research studies compressed earth blocks that incorporate soils and gravels excavated in situ, river sand, crushed concrete from demolition waste, and recycled glass sand. To stabilize the blocks, cement is used at 5, 10, and 15% (by weight). The properties studied include the following: density, apparent porosity, initial water absorption, simple compression, modulus of elasticity, and thermal conductivity. Optical image analysis proved to be a tool for predicting the values of these properties as the stabilizer changed. To assist in decision making regarding the best overall performance of the total 12 mix designs, a ranking system is proposed. The best blocks, which incorporate the otherwise waste materials, exhibited simple compression values up to 7.3 MPa, initial water absorption of 8 g/(cm² × min^0.5) and thermal conductivity of 0.684 W/m·K. Full article

Recycled Concrete Aggregate (RCA), made of construction and demolition waste, provides a sustainable alternative to natural aggregates. Experimental research using locally available RCA is necessary due to the differences in properties between the original concrete. This study examined four full-scale reinforced concrete beams (two with 100% RCA and two with natural aggregates (NA)) to compare deflections, cracking, and flexural capacity. The experimental results reveal that beams made with RCA exhibited larger deflections, earlier and more extensive cracking, and lower peak loads than those made with NA concrete. This behavior is primarily attributed to the reduced tensile strength of RCA concrete. The results indicate that RCA concrete exhibits distinct behavior compared to NA concrete, particularly in crack development and strain progression. Therefore, additional experiments should be conducted to update the design calculations, particularly in the serviceability limit state, to account for the unique behavior of concrete with RCA. Full article

The construction industry is a major source of environmental degradation as it is responsible for a significant share of global CO₂ emissions, especially from cement and aggregate consumption. This study fills the need for sustainable construction materials by developing and evaluating a low-carbon fiber-reinforced concrete (FRC) made of steel slag powder (SSP), processed recycled concrete aggregates (PRCAs), and waste steel rivet fibers (WSRFs) derived from industrial waste. The research seeks to reduce dependency on virgin materials while maintaining high values of mechanical performance and durability in structural applications. Sixteen concrete mixes were used in the experimental investigations with control, SSP, SSP+RCA, and RCA, reinforced with various fiber dosages (0%, 0.2%, 0.8%, 1.4%) by concrete volume. Workability, density, compressive strength, tensile strength, and water absorption were measured according to the appropriate standards. Compressive and tensile strength increased in all mixes and the 1.4% WSRF mix had the best performance. However, it was found that a fiber content of 0.8% was optimal, which balanced the improvement in strength, durability, and workability by sustainable reuse of recycled materials and demolition waste. It was found by failure mode analysis that the transition was from brittle to ductile behavior as the fiber content increased. The relationship between compressive, tensile strength, and fiber content was visualized as a 3D response surface in order to support these mechanical trends. It is concluded in this study that 15% SSP, 40% PRCA, and 0.8% WSRF are feasible, specific solutions to improve concrete performance and advance the circular economy. Full article

The growing demand for sustainable and energy-efficient construction has driven significant interest in the development of advanced insulation materials that reduce energy usage while minimizing environmental impact. Although conventional insulation materials such as polyurethane, polystyrene, and mineral wools offer excellent thermal and acoustic performance, they are derived from non-renewable sources, have high embodied carbon (EC) (up to 7.3 kg CO₂-eq/kg), and pose end-of-life disposal challenges. Thus, this review critically examines the emergence of insulation materials derived from natural and recycled sources, which align with circular economy principles by minimizing waste, promoting material reuse, and extending product life cycles. Sustainable alternatives such as sheep wool, hemp, flax, and jute not only exhibit competitive thermal conductivity (as low as 0.031–0.046 W/m·K) and very good sound absorption but also offer low EC, biodegradability, and regional availability. Despite some limitations, including variable fire resistance and thickness requirements, these bio-based insulators present a viable path toward greener building solutions. The review highlights that waste-based insulation materials are essential for sustainable construction due to their low EC, renewability, and contribution to waste reduction, making them a necessary alternative even when conventional materials demonstrate superior short-term performance. Full article

The construction industry is responsible for 50% of mineral resource extraction and 35% of greenhouse gas (GHG) emissions. In this context, concrete stands out as one of the most consumed materials in the world. More than 30 billion tons of this material are produced annually, resulting in the extraction of around 19.4 billion tons of aggregates (mainly sand and gravel) per year. Therefore, it is urgent to develop strategies that aim to minimize the environmental impacts arising from this production chain. Currently, one of the most widely adopted solutions is the production of concrete through the reuse of construction and demolition waste. Thus, the objective of this research is to conduct a systematic literature review (SLR) on the use of recycled aggregates in concrete production, aiming to increase urban resilience by reducing the consumption of natural aggregates. An extensive search was performed in one of the most respected scientific databases (Scopus), and after a careful selection process, the main articles related to the topic were considered eligible through the PRISMA protocol. The selected manuscripts were then subjected to bibliographic and bibliometric analyses, allowing us to reach the state-of-the-art on the subject. The results obtained on the replacement rates of natural aggregate by recycled aggregate indicate that the recommendations vary from 20 to 60%, and these rates may be higher as long as the recycled aggregate is characterized, and may reach up to 100% as long as the matric concrete has a minimum compressive strength of 60 MPa. The specific gravity of most recycled aggregates ranges from 1.91 to 2.70, maintaining an average density of 2.32 g/cm³. Residual mortar adhered to recycled aggregates ranges from 20 to 56%. The water absorption process of recycled aggregate can vary from 2 to 15%. The mechanical strength of mixtures with recycled aggregates is significantly reduced due to the amount of mortar adhered to the aggregates. The use of recycled aggregates results in a compressive strength approximately 2.6 to 43% lower than that of concrete with natural aggregates, depending on the replacement rate. The same behavior was identified in relation to tensile strength. The modulus of elasticity showed a reduction of 25%, and the flexural strength was reduced by up to 15%. Full article

The global pursuit of a sustainable and decarbonized energy landscape requires the development of novel materials capable of supporting lightweight construction, advanced energy conversion, storage, and thermal management technologies. Among these, metal foams have emerged as a versatile class of porous materials, offering a unique combination of low density, high surface area, three-dimensional (3D) interconnected porosity, and favorable thermal and electrical conductivities. These attributes make them highly suitable for a broad range of applications critical to the ongoing energy transition, assuming an increasingly central role in enabling clean, efficient, and resilient energy infrastructures. From this key perspective, the present review highlights the relevance of the adoption of metal foams in several fields crucial for the energy transition. By presenting methodologies and outcomes of research results, mainly from the last five years, the paper underscores the potential of low-weight, high-surface, and high-performance porous materials in contemporary and future industry, supporting sustainable development and, more generally, energy transition and circular economy. The approach also aims to minimize negative impacts and promote sustainability, for example, by recycling and transforming waste materials. Full article

The dramatic increase in global construction and demolition waste (CDW) is a considerable environmental challenge, but recycled building materials face serious marketing bottlenecks. Although existing studies have focused on the technological path and policy regulation of CDW management, they have not yet considered the impact of sales effort level under the dual-channel sales model. Considering the coexistence of price competition and bidirectional free-riding behavior, this paper constructs a Stackelberg game model, which includes a construction waste remanufacturer with both online and offline sales channels and a building materials retailer, to reveal the pricing decision-making mechanism under bidirectional free-riding behavior. The results of the study show that (1) in the decentralized decision-making model, offline free-riding has a negative effect on the online channel, and when the effort cost coefficient is high, it increases the retail price of recycled building materials in the offline channel; at the same time, under high cross-price sensitivity, both the manufacturer and the retailer are negatively affected by online free-riding behaviors; (2) in contrast to decentralized decision-making, centralized decision-making motivates the supply chain as a whole to significantly increase sales effort investment and develop a better pricing strategy under the condition of satisfying the threshold cross-price sensitivity, which ultimately improves the overall efficiency of the supply chain. The findings provide an important theoretical basis and management insights for the coordination of dual-channel supply chains, the governance of free-riding behavior, and the promotion of recycled building materials in the recycling economy. Full article

This study investigated a 100% waste-derived material system, using bottom ash (BA) and recycled concrete aggregate (RCA) for sustainable pavement base applications. This innovative approach diverts both construction and power plant waste from landfills while replacing conventional natural aggregates and cement-based binders. Five RCA:BA replacement ratios (90:10 to 50:50) were evaluated with three Na₂SiO₃:NaOH alkaline activator ratios (1:1, 1:1.5, and 1:2) through unconfined compressive strength (UCS) testing, scanning electron microscopy, energy dispersive X-ray spectroscopy (SEM-EDX), and X-ray diffraction (XRD) analysis. The RCA90BA10 composition with a G/N ratio of 1:2 achieved exceptional performance, reaching 9.14 MPa UCS at 7 days while exceeding the Department of Highways, Thailand, requirement of 2.413 MPa. All geopolymer-stabilized mixtures substantially surpassed minimum specifications, validating the technology for high-traffic pavement applications. Toughness evaluation confirmed superior energy absorption capacity of 107.89 N·m for the optimal formulation. Microstructural characterization revealed that higher G/N ratios promoted extensive sodium aluminosilicate hydrate and calcium silicate hydrate gel formation, creating dense, well-integrated matrices. XRD patterns confirmed successful geopolymerization through pronounced amorphous gel development between 20° and 35° 2θ, correlating directly with mechanical performance improvements. The RCA90BA10 formulation demonstrated optimal balance between reactive aluminosilicate content and structural aggregate framework. This technology offers significant environmental benefits by diverting construction and power plant waste from landfills while achieving mechanical properties superior to conventional materials, providing a scalable solution for sustainable infrastructure development. Full article

Currently, the partial substitution of mineral aggregates with rubber particles in the preparation of rubber concrete (RC) is an effective method for recycling waste rubber materials. However, the mechanism of interfacial interactions in RC at high temperatures is not well understood. This study aims to explore the effect of high temperature on intermolecular interactions at the RC interface and its relationship with macroscopic mechanical properties. Molecular dynamics (MD) simulation technology was employed to construct an RC interface model. The temperature is controlled at room temperature (300 K), medium low temperature (320 K, 340 K, 360 K), and high temperature (500 K, 700 K). The interface model was analyzed from multiple dimensions such as binding energy, turning radius, and interface structure. The results show that the higher the temperature, the more easily water molecules aggregate at the interface of the two phases. As the temperature increases, the proportion of water molecules at the interface increases from 6% to 16%. Since rubber and water molecules cannot form hydrogen bonds, the formation of chemical bonds at the interface between the two phases is affected, leading to a decrease in RC binding energy. The interface bonding energy decreases by 12.6% at a temperature of 700 K. In addition, the radius of gyration of rubber is proportional to temperature. As the temperature increases, the average radius of gyration increases from 5.8 Å to 6.15 Å, and the numerical fluctuation amplitude is greater, resulting in a relatively loose and unstable rubber structure. Furthermore, the bonding strength in RC mainly comes from non-hydrogen bond interactions, and high temperatures cause an increase in bond length while reducing the strength and stability of chemical bonds. Finally, high temperatures increase the atomic movement speed in natural rubber (NR). As the temperature increases, the diffusion coefficients of H_NR and C_NR increase from 0.08 and 0.04 to 1.835 and 1.473, respectively, preventing good connections between atoms at the interface. The study provides nanoscale insights for optimizing RC. Full article

The replacement of natural aggregates with recycled aggregates in concrete production has gained attention as a sustainable approach for valorizing construction and demolition waste (CDW). Although regulatory frameworks in this area remain underdeveloped, extensive research has demonstrated that acceptable mechanical and durability properties can be achieved. However, the elevated water absorption associated with recycled materials—mainly due to residual attached mortar and increased porosity—continues to pose a challenge. When used without prior treatment, these particles absorb part of the mixing water intended for cement hydration, potentially compromising both fresh and hardened concrete performance. This study explores the use of graphene oxide (GO) nanocoating as a surface modification strategy to mitigate water absorption. Absorption test were performed to evaluate the effectiveness of the treatment, followed by the preparation of multiple concrete mixes incorporating varying substitution rates of natural aggregate with untreated and GO-treated recycled material. The mixtures were assessed for workability and compressive strength. Results indicate that GO nanocoating substantially reduces water (up to 30%) uptake and improves the overall performance of concrete containing recycled constituents, increasing its compressive strength by up to 32%, highlighting its potential as a viable pretreatment for sustainable concrete production. Full article

The blended system of solid waste micro-powders is of great significance for the efficient utilization of recycled micro-powder. In this study, a ternary blended cementitious system composed of fly ash, slag, and recycled micro-powder was constructed, and its effects on the workability, mechanical properties, shrinkage performance, and microstructure of recycled mortar were systematically investigated. The experimental results show that with the increasing dosage of slag and recycled micro-powder (partially replacing cement and fly ash), the standard consistency water demand of the cementitious system decreases and the setting time is prolonged. When the replacement levels of recycled micro-powder and slag are both 10%, the 3-day, 7-day, and 28-day mechanical strengths of the mortar specimens are comparable to those of the reference group, with an increased flexural-to-compressive strength ratio and improved brittleness. SEM and mercury intrusion porosimetry (MIP) analyses revealed that systems incorporating low addition levels of recycled micro powder and slag powder exhibit calcium silicate hydrate (C-S-H) gel, acicular ettringite crystals, and a denser pore structure. However, at higher dosages (>10%), the porosity increases significantly and the pore structure deteriorates, resulting in reduced shrinkage performance. Overall, when the replacement rate of cement–fly ash by recycled micro-powder and slag is 10%, the ternary blended system exhibits optimal macroscopic performance and microstructure, providing a scientific basis for the resource utilization of solid waste. Full article

This study presents a comparison of the mechanical properties of selected high-performance concrete mixtures, some of which contained a proportion of recycled concrete aggregate (15% or 30%) as a substitute for natural aggregate. A reference mixture without recycled concrete aggregate was used for comparison. Initially, the properties of concrete containing both the natural and recycled aggregate types were characterized. This was followed by a series of mechanical tests investigating the compressive strength, flexural strength, and chemical resistance (including resistance to de-icing agents and sulfuric acid). The structural performance of reinforced concrete (RC) beams produced from the mixtures was assessed, and surface morphology was evaluated using a digital microscope. The results confirmed that the use of recycled aggregate had a measurable yet limited effect on the properties of hardened concrete. While the compressive strength tended to decrease slightly with an increasing degree of replacement, the flexural strength remained stable in all the mixtures. The tested mixtures demonstrated adequate resistance to de-icing agents and sulfuric acid. Interestingly, specimens subjected to a frost-resistance test showed improved flexural strength, potentially due to ongoing hydration or microcrack healing. In addition, the RC beams with partial aggregate replacement achieved a higher load-bearing capacity compared to the reference beams. The optical surface evaluation method proved to be a valuable tool, complementary to conventional strength testing. This research enhances the current understanding of recycled aggregate concrete and supports its potential for structural applications. Full article

Nowadays, the circular economy is driving the construction industry towards greater sustainability for both environmental and financial purposes. One prominent area of research with significant contributions to circular economy is the reuse of steel from decommissioned structures in new construction projects. This approach is deemed far more efficient than ordinary steel recycling, due to the fact that it contributes towards reducing both the cost of the new project and the associated carbon emissions. Along these lines, the feasibility of utilizing steel wind turbine towers (WTTs) as part of a new structure is investigated herein, considering that wind turbines are decommissioned after a nominal life of approximately 25 years due to fatigue limitations. General principles of structural steel reuse are first presented in a systematic manner, followed by two case studies. Realistic data about the geometry and cross-sections of previous generation models of WTTs were obtained from the Greek Center for Renewable Energy Sources and Savings (CRES), including drawings and photographic material from their demonstrative wind farm in the area of Keratea. A specific wind turbine was selected that is about to exceed its life expectancy and will soon be decommissioned. Two alternative applications for the reuse of the tower were proposed and analyzed, with emphasis on the structural aspects. One deals with the use of parts of the tower as a small-span pedestrian bridge, while the second addresses the transformation of a tower section into a water storage tank. Several decision factors have contributed to the selection of these two reuse scenarios, including, amongst others, the geometric compatibility of the decommissioned wind turbine tower with the proposed applications, engineering intuition about the tower having adequate strength for its new role, the potential to minimize fatigue loads in the reused state, the minimization of cutting and joining processes as much as possible to restrain further CO₂ emissions, reduction in waste material, the societal contribution of the potential reuse applications, etc. The two examples are briefly presented, aiming to demonstrate the concept and feasibility at the preliminary design level, highlighting the potential of decommissioned WTTs to find proper use for their future life. Full article

The growing need to improve the management of end-of-life vehicle (ELV) waste and mitigate its environmental impact is a global concern. One promising approach to enhancing the recyclability of these vehicles is leveraging synergies between the automotive and construction industries as part of a circular economy strategy. In this context, ELV waste emerges as a valuable source of secondary raw materials, enabling the development of sustainable innovations that capitalize on its physical and mechanical properties. This paper aims to develop and evaluate construction industry composites incorporating waste from ELV carpets, with a focus on maintaining or enhancing performance compared to conventional materials. To achieve this, an experimental program was designed to assess cementitious composites, specifically subfloor mortars, incorporating automotive carpet waste (ACW). The results demonstrate that, beyond the physical and mechanical properties of the developed composites, the dynamic stiffness significantly improved across all tested waste incorporation levels. This finding highlights the potential of these composites as an alternative material for impact noise insulation in flooring systems. From an academic perspective, this research advances knowledge on the application of ACW in cement-based composites for construction. In terms of managerial contributions, two key market opportunities emerge: (1) the commercial exploitation of composites produced with ELV carpet waste and (2) the development of a network of environmental service providers to ensure a stable waste supply chain for innovative and sustainable products. Both strategies contribute to reducing landfill disposal and mitigating the environmental impact of ELV waste, reinforcing the principles of the circular economy. Full article