Search Results (5)

Construction and demolition waste residue soil (CDWRS) recycled foamed concretes were prepared by introducing the original CDWRS into modified binders. Pore structure, hardened performance, and sandwich wallboard application were also investigated. The results indicated that 51 kg/m³ of water glass and 7.5 kg/m³ of gypsum could significantly increase the strength and generate a slight influence on the thermal insulation performance of CDWRS recycled foamed concrete. The largest enhancing rate of 28-day compressive strength at a density of 600 kg/m³ could reach 205.5%. Foamed concrete with 1126 kg/m³ of CDWRS, modified with water glass and gypsum, showed a low thermal conductivity of 0.11 W/(m·K) and a dry density of 626 kg/m³. In total, 988 kg/m³ of CDWRS in foamed concrete led to a compressive strength of 7.76 MPa, a thermal conductivity of 0.14 W/(m·K), and a dry density of 948 kg/m³. Utilization of the foamed concrete in the sandwich structure could fabricate energy-saving wallboards with a minimum heat transfer coefficient of 0.75 W/(m²·K) and a relatively high compressive strength of 16.5 MPa, providing great confidence of CDWRS consumption in the building energy-saving field. Full article

In several countries, brick and ceramic tile are the most important construction materials; therefore, associated waste generation is common in construction and demolitions. An alternative use for waste is to incorporate it into road construction. However, the biggest limitation to use it as structural pavement layers is that strength and durability regulatory requirements are not met for highways when it is used. As an alternative, construction and demolition waste (CDW) soil mixtures are proposed as subgrade improvements which require less of a thickness increase of pavement structures to meet highway standards. The results of this article present the behavior of silty soil, brick residues, and ceramic tile mixtures in different added material ratios. Laboratory evaluations were conducted and included material characterization, compaction tests, obtaining CBR values, and obtaining resilient moduli. A parametric thicknesses evaluation was performed on flexible pavement structures with different traffic conditions and CDW ratios. It was concluded that CDW material addition increases strength and the resilient modulus similarly to granular subbase (AASHTO M147-65). Therefore, the pavement thickness can be reduced, and costs can be decreased by more than 7%. Full article

Waste cement is a construction and demolition waste produced from old buildings’ demolition and transformation. In recent years, the recycling of recycled concrete is limited to the use of recycled aggregate, and the research on the utilization of waste cement in waste concrete is scarce. This study explored the effective application of waste cement for the adsorption of cadmium (Cd²⁺) from an aqueous solution and the bioavailability and immobility of Cd²⁺ in soil. Results showed that the maximum adsorption capacities of ordinary Portland cement(OPC) paste, fly ash cement (FAC) paste, and zeolite cement (ZEC) paste for Cd²⁺ were calculated to be 10.97, 9.47, 4.63 mg·g⁻¹, respectively. The possible mechanisms for Cd²⁺ adsorption in the solution by waste cement mainly involve precipitation by forming insoluble Cd²⁺ compounds in alkaline conditions, and ion exchange for Cd²⁺ with the exchangeable calcium ions in waste cement, which were confirmed by XRD and SEM. Results from diethylene triaminepentaacetic acid (DTPA) extraction and toxicity characteristic leaching procedure (TCLP) implied reduction of the Cd²⁺ mobility. DTPA-extractable Cd²⁺ decreased by 52, 48 and 46%, respectively, by adding 1% OPC, FAC and ZEC. TCLP-extractable Cd²⁺ decreased by 89.0, 80.3, and 56.0% after 1% OPC, FAC, and ZEC treatment, respectively. BCR analyses indicate that OPC, FAC, and ZEC applications increased the percentage of Cd²⁺ in residual fraction and induced a high reduction in the acid-soluble Cd²⁺ proportion. The leaching column test further confirmed a reduction in Cd²⁺ mobility by waste cement treated under continuous leaching of simulated acid rain (SAR). Therefore, waste cement exhibited a significant enhancement in the immobilization of Cd²⁺ under simulated acid rain (SAR) leaching. In summary, the application of alkaline waste cement could substantially remove Cd²⁺ from wastewater and reduce Cd²⁺ mobility and bioavailability in contaminated soil. Full article

Geosynthetic-reinforced soil structures have been used extensively in recent decades due to their significant advantages over more conventional earth retaining structures, including the cost-effectiveness, reduced construction time, and possibility of using locally-available lower quality soils and/or waste materials, such as recycled construction and demolition (C&D) wastes. The time-dependent shear behaviour at the interfaces between the geosynthetic and the backfill is an important factor affecting the overall long-term performance of such structures, and thereby should be properly understood. In this study, an innovative multistage direct shear test procedure is introduced to characterise the time-dependent response of the interface between a high-strength geotextile and a recycled C&D material. After a prescribed shear displacement is reached, the shear box is kept stationary for a specific period of time, after which the test proceeds again, at a constant displacement rate, until the peak and large-displacement shear strengths are mobilised. The shear stress-shear displacement curves from the proposed multistage tests exhibited a progressive decrease in shear stress with time (stress relaxation) during the period in which the shear box was restrained from any movement, which was more pronounced under lower normal stress values. Regardless of the prior interface shear displacement and duration of the stress relaxation stage, the peak and residual shear strength parameters of the C&D material-geotextile interface remained similar to those obtained from the conventional (benchmark) tests carried out under constant displacement rate. Full article

Brick is one of the most common building materials, and it is also one of the largest components of waste generated from both construction and demolition. Reuse of this waste would reduce the environmental and social impacts of construction. One potential bulk use of such waste is as a cementing agent for soil stabilization. However, this is currently limited by the need to mill the residue to a particle size below 0.035 mm. In this study, the behavior of two soil types stabilized using alkali-activated brick dust was investigated. The unconfined compression strength at different curing temperatures and moistures and the use of different types and concentrations of alkaline activators were investigated. It was found that the addition of brick dust resulted in an increase in the soil strength between 1.7–2.3 times with respect to the non-stabilized material, suggesting that the resulting materials will find practical applications in construction. Full article