Impact of compaction on the mechanical property of circular concrete

Abstract

Circular concrete is one of the main focuses of current research in the construction industry. This is due to the fact that the construction sector is facing several pressures from society and policymakers. In an attempt to assure the sustainability of the sector, different research options have been put in place. Among them, the use of recycled aggregates and recycled cement is a subject of current research.

The objective of this study is to optimize the particle size distribution of aggregates and understand the compaction of concrete made of recycled aggregates and recycled cement, so as to reduce the amount of cement used in the new concrete mix. Particle size optimization is aimed at improving the density of concrete made of regularly packed aggregates and the distribution of voids, thereby improving its sustainability and strength. This could be achieved by optimizing the amount of water, the size of aggregates and fillers, and adjusting the amount of cement in the mix design.

In this specific study, recycled aggregates (<12mm) are used along with natural aggregates of different sizes (<12mm and <16 mm). The role of maximum aggregate size and the effect of the complete substitution of natural aggregates with recycled aggregates have been studied. Furthermore, the effects of compaction, the role of internal pores, and aggregate size distribution on the mechanical properties of hardened recycled concrete are also investigated. Three recipes have been designed to employ different types of aggregates. The water-to-cement ratio of the recipes was adjusted based on the magnitude of the slump. The recipes were cast in various procedures associated with different durations of vibration to understand the role of vibration on their compressive strength after 7, 28, and 91 days.

After optimizing the duration of vibration and casting concrete samples, the selected specimens with natural aggregates and recycled aggregates were scanned by a macro-CT scanner to comprehend the spatial distribution of aggregates and air bubbles inside the hardened concrete. Results indicate that the duration of vibration was observed to be critical depending on the type and size of aggregate. Despite the direct relationship between vibration and internal pores, the impact seems to be negative beyond a certain time. The compaction and mechanical properties of concrete made of recycled aggregates need more vibration compared to natural aggregates.