Mohammed Layth Abbas

The recycling of construction and demolition waste in concrete composites is becoming increasingly significant for mitigating environmental impacts and enhancing resource efficiency while also providing accessible, cost-effective, and beneficial materials for sustainable construction. This study examines the synergistic effects of composite waste powders on the microstructural, mechanical, thermodurability, and sustainability characteristics of the concrete utilizing multibinder systems, which include portland cement (PC), ceramic waste powder (CWP), marble waste powder (MWP) and red brick waste powder (RBWP). Twenty-seven concrete mixtures were formulated, adhering to a consistent water-to-binder ratio of 0.38 and a total binder content of 450    kg / m 3 . The control contained only PC as the binder, whereas the other mixtures included binary, ternary, and quaternary cementitious waste blends of PC–CWP–MWP–RBWP to assess their collective impact on the concrete performance. Additionally, the multicriteria decision-making (MCDM) and desirability function optimization were employed to ascertain the ideal concrete mixture, guaranteeing a balance among the mechanical performance, durability, and sustainability. The findings of the experimental study indicated that incorporating up to 10% CWP or MWP enhanced the compressive and flexural strengths owing to the pozzolanic and filler effects; however, elevated RBWP concentration markedly diminished the strength. The thermal conductivity improved by as much as 36.9% in quaternary mixtures, signifying improved insulation. The sorptivity index decreased by 11.9% with CWP and MWP, but it increased by 31.7% with RBWP due to its higher porosity. The carbon footprint ( CO 2 emissions) decreased about 13.9% in binary mixtures and up to 33.1% in quaternary systems, with CWP demonstrating the most significant effect. The MCDM suggests that a concrete mixture with 20% CWP is the best concrete mix since it provides the highest overall score with 0.621 based on their strength, durability, thermal conductivity, and sustainability properties.

The application of lightweight aggregate concrete as a core material for concrete-filled steel tube (CFST) composite columns offer various advantages such as lower self-weight and thermal conductivity, higher fire resistance and durability as well as more resistance against the earthquake loading. In this study, the axial strength of steel tubes filled with normal weight concrete (NWC) and lightweight concrete (LWC) were evaluated by applying two widely used design codes, American Concrete Institute (ACI) and Eurocode 4 (EC4). The assessment included circular steel tubes with variable diameter-to-thickness (D/t) ratios of 30, 60, and 90, coupled with steel yielding strengths of 185, 275, and 450 MPa, while keeping constant wall thickness and length-to-diameter (L/D) ratio. Twelve distinct LWC combinations from the literature, each having verified compressive strength, were employed as infill materials for the steel tubes. A total of 108 results of the ultimate axial strengths predicted by the ACI and EC4 were then investigated and compared to assess their accuracy and applicability to tubes filled with NWC and LWC. A statistical analysis was also conducted to determine the effectiveness of the investigated variables. The findings showed that variations in the D/t ratio had a substantial effect on the ultimate strength of circular steel tube columns filled with NWC and LWC with a contribution rate about 85% according to the statistical evaluation of the ACI and EC4 equations, which is slightly higher in the former. Moreover, the strength predictions by using the EC4 formula gave greater as compared to those obtained by the ACI, ranging from 29 to 54%.

This study aimed to develop an eco-friendly, lightweight, and synthetic aggregate (SLA) based on clay suitable for use in structural lightweight concrete. The researchers utilized the cold-bonded pelletization process to agglomerate pozzolanic materials, specifically attapulgite extracted from a quarry, and crushed into a fine filler. The appropriate calcination temperature for manufacturing this clay as a pozzolanic material is 750°C. A total of 22 mixes were created using a combination of high reactive attapulgite (HRA) and cement (PC), with the attapulgite replacement rate varying from 100-50% by a 10% decrement. Different types of curing methods, including oven-dry, oven-water, room-water, and room-room, were applied. The aggregate properties were evaluated to determine density, specific gravity, water absorption, aggregate impact value, crushing strength, and compressive strength. The results revealed that it could produce lightweight synthetic aggregate from clay-based materials with a bulk density of 793kg/m3 with suitable physical and mechanical properties. As the percentage of cement in the mixture increased, the specific gravity and density were increased to 18.12% and 36.61%, whereas impact and crushing values of aggregate improved by 81.83%. This, in turn, leads to a significant boost in compressive strength up to 100.94%. Furthermore, there is a noticeable decrease in absorption. Moreover, the aggregate held under oven water positively impacts the strength development of cement-based composites.

Physico-durability aspects of partial substitution via pelletized fly ash lightweight nano-silica concrete