Erhan Güneyisi

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 influence of using crumb rubber (CR) obtained from the second scraping of used tires as fine aggregate in manufacturing self-compacting mortar (SCM) was investigated experimentally in this study. To explore this, natural fine aggregate in SCM mixes was partially replaced with CR at levels ranging from 5% to 25% by total fine aggregate volume. Two mix series, one with a total binder of 500 kg/m3 and the other with a 540 kg/m3 binder, were designed at water-to-binder ratios of 0.40 and 0.33. Ordinary Portland cement (80% by weight) and fly ash (20% by weight) were used to manufacture mortars. Twelve SCM mixes were cast and tested to evaluate their fresh-state properties, including setting times, flow diameter, and flow time. Moreover, the compressive strengths at 3, 7, 28, 56, and 90 days were determined for each mix to investigate their strength development. The test results indicated that the incorporation of CR adversely affected the fresh properties of the SCM mixes, and an increase in the CR replacement level systematically diminished their strength characteristics. Nevertheless, it was observed that it could be used in a controlled manner to achieve the desired properties.

The common wisdom in the literature about clinker aggregate (CA) is that it improves the performance properties of mortar or concrete to some extent. The current study, in this context, investigated the physical characteristics and mechanical performances of alkali-activated composites (AACs) made entirely with CA. The CA was used in three particle sizes of 0–2 mm (named No.10), 2–4 mm (named No.5), and 4–8 mm (named medium). To examine the impact of the fine CA-size fraction on the characteristics of AAC, No.10 CA was partially replaced by No.5 CA up to 50%, while the content of the medium CA was kept constant in all AAC mixtures. Moreover, to evaluate the influence of the 8-h curing temperature on the performance of the AACs, different temperature-based curing strategies (ambient, 45, and 75 °C) were applied to the AACs. In the production of AACs, granulated blast furnace slag was employed as an aluminosilicate-rich raw material, and a sodium silicate and sodium hydroxide combination was used as an alkaline activator. Physical properties (flowability, water absorption, capillary water absorption, and dry unit weight), and 8-h strength performances (flexural and compressive) were determined. Furthermore, to monitor the influence of high temperatures on the characteristics of the AAC, the mixtures were exposed to elevated temperatures (200, 500, and 800 °C). In SEM image analysis, it was determined that spherical CSH gels were formed in the heat-cured AACs. It has been observed that the geopolymerization products decompose in AACs exposed to 800 °C. To evaluate statistically the experimental results, a multi-factor analysis of variance (ANOVA) was also applied. The results revealed that increasing the coarser fine aggregate fraction led to higher water absorption and apparent porosity capacities and lower unit weight. Besides, strength performance was improved by applying a heat-curing strategy to the AAC, whereas a decrease was observed by increasing the No.5 CA fraction. There was a remarkable reduction in compressive strength and considerable loss of mass when the AAC mixes were exposed to high temperatures.