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The construction industry’s pursuit of sustainable and high-performance materials has led to the exploration of alternative aggregates and innovative additives. This paper investigates the combined influence of recycled aggregates (RA) and nano TiO₂ particles on M20 and M30 concretes, addressing ecological concerns and seeking to improve material properties. RA, sourced from construction and demolition waste, presents a sustainable solution to alleviate the environmental impact associated with traditional virgin aggregates (VA). However, challenges related to the mechanical strength and durability often hinder the widespread use of RA in concrete. This study aims to bridge this gap by exploring the reinforcing potential of nano TiO₂ particles.

Nanomaterial such as TiO₂ is known for its photocatalytic properties and reinforcement capabilities and has emerged as a promising additive in construction materials. The investigation herein involves the incorporation of nano TiO₂ at percentages of 0.5% and 1% in both VA- and RA-based M20 and M30 concretes. Comprehensive series of tests on mechanical, durability and microstructural properties are conducted for each concrete mix.

Results unequivocally indicate that the addition of TiO₂ significantly improves the properties of concrete, with RA-based concrete exhibiting performance comparable to that of VA-based counterparts. This breakthrough suggests a viable application of RA with TiO₂ in construction projects, promoting sustainability without compromising performance. Following experimental analyses, linear regression and multiple linear regression analyses are used to establish predictive equations correlating interfacial transition zone (ITZ) thickness with TiO₂ percentage, compressive strength, tensile strength, flexural strength and chloride penetration.

These equations serve as valuable tools for predicting ITZ thickness in future concrete formulations based on specified parameter quantities, thereby contributing to informed decision-making in sustainable construction practices. The findings of this study have the potential to contribute to the improvement of environmentally conscious construction methods while also improving the performance and durability of concrete structures.

This study aims to characterize the behavior of blended concrete, including metakaolin (MK) and quarry dust (QD), as supplementary cementing materials. The study focuses on evaluating the effects of these materials on the fresh and hardened properties of concrete.

MK, a pozzolanic material, and QD, a fine aggregate by-product, are potentially sustainable alternatives for enhancing concrete performance and reducing environmental impact. The addition of different percentages of MK enhances the pozzolanic reaction, resulting in improved strength development. Furthermore, the optimum dosage of MK, mixed with QD, and mechanical properties like compressive, flexural and split tensile strength of concrete were evaluated to investigate the synergetic effect of MK and quarry dust for M20-grade concrete.

The results reveal the influence of metakaolin and QD on the overall performance of blended concrete. Cost analysis showed that the optimum mix can reduce the 7%–8% overall cost of the materials for M20-grade concrete. Energy analysis showed that the optimum mix can reduce 7%–8% energy consumption.

The effective utilization is determined with the help of the analytical hierarchy process method to find an optimal solution among the selected criteria. According to the AHP analysis, the optimum content of MK and quarry dust is 12% and 16%, respectively, performing best among all other trial mixes.