Abstract

     This paper studies the fresh and mechanical properties of high-strength concrete (HSC) by incorporating recycled concrete aggregates (RCA) of varying sizes and concentrations. The recycled aggregate concrete (RAC) was prepared by partially replacing RCA with natural coarse aggregate (NCA) at 0%, 15%, 30%, and 45%, with aggregate sizes ranging from 5 to 12 and 12–۲۰-mm. Fresh concrete properties, such as slump, Kelly ball, compacting factor, K-slump, and fresh density, were tested to determine the influence of RCA size and concentration. In addition, the mechanical properties were studied through the execution of compressive, split-tensile, and stress-strain tests. The test results revealed that increasing the RCA concentration declines the fresh and hardened properties of HSC. In the fresh concrete experimentation, the 12–۲۰ mm aggregate size RAC mixes exhibited greater workability than the 5–۱۲ mm aggregate mixes. On the contrary, 5–۱۲ mm aggregate mixes RAC had higher compressive and split-tensile strength and a higher modulus of elasticity than 12–۲۰ mm aggregate mixes concrete. When it comes to sustainability, the study found that the smaller size range of RAC produces inferior embodied CO2 (eCO2) and provides a cost-effective and sustainable solution for the construction industry.

Introduction

     Over the last decades, the construction community has faced several challenges, including a scarcity of natural resources and excessive energy consumption that directly impacts environmental pollution. These challenges include using natural resources and energy, the generation of greenhouse gases (CO2), and the growth of building and demolition waste (Datta et al., 2022, Vo et al., 2021). Recycling the demolition waste is the most promising option for reducing the building industry’s adverse environmental effects in the construction sector. This attention is increasingly growing since it was projected that the world has to reckon with the problems of disposing of 3 billion tons of demolished concrete waste annually until 2012 (Akhtar et al., 2018). In recent years, Zhang et al. (2020) reported that the global accumulative carbonation of concrete waste might produce roughly 3.0 Bt CO2 between 2018 and 2035. As a result, using recycled concrete aggregate (RCA) made from waste concrete in engineering construction can help protect the environment while increasing the residual value of waste concrete. In addition, these RCAs have gained widespread acceptance from the construction research community as alternative building structure materials in recent decades.

Conclusions

     In this paper, the size and concentration effect of RCA on the production of HSC has been studied. Eight concrete mixes with different RCA concentration levels with an interval of 15% were considered. The obtained experimental results of the rheological and mechanical properties are concluded as follows:

• All the mixes had a satisfactory slump result greater than 150 mm, which led to the high workability of concrete. Concrete mixtures of the 12–۲۰ mm aggregate size range have a larger slump, compacting factor, ball penetration, and K-slump value than the 5–۱۲ mm size range concrete. In addition, the high density and workability of mixes decrease with an increasing concentration of RCA replacement level.

• The decrease in the split-tensile strength of RAC with the increase of the RCA concentration is relatively smaller than compressive strength and MOE. The 5–۱۲ mm coarse aggregate size enhances the strength and MOE of the mixes compared to the 12–۲۰ mm aggregate size. In terms of sustainability assessment, the cost and eCO2 emission decrease with RCA incorporation, leading to a low-cost and environment-friendly concrete production with better strength.