Mechanical and durability performance of 100% recycled aggregate concrete pavers made by compression casting

Abstract

Sustainable infrastructure developments require optimal use of natural resources and the recycling of the materials generated at the end of the service life of concrete structures. Construction and Demolition (C&D) waste in the form of Recycled Concrete Aggregates (RCA) has been used to manufacture structural and non-structural concrete which is known as Recycled Aggregate Concrete (RAC). However, not all the C&D waste could be incorporated into the structural concrete and the development of innovative construction products for the efficient and economic utilization of RCA is still under investigation. This study aimed to produce concrete pavers with 100% recycled aggregates and a minimum amount of cement through Compression Casting Technique (CCT). A comprehensive experimental investigation was carried out to find out the optimum values of fine to coarse aggregate ratio, cement contents, and casting pressure for the concrete pavers so that a minimum target compressive strength of 35 MPa at 7-days is achieved. The concrete mixes with fine and coarse aggregate contents of 60% and 40%, respectively, cement contents of 15% and 20%, and casting pressure of 20 MPa were found to be the most economical and feasible to produce concrete pavers exhibiting the target compressive strength. The mechanical (i.e., compressive and flexural strength) as well as durability (i.e., drying shrinkage, water absorption, cyclic ponding in sulfuric acid and sodium chloride salt solution) properties were investigated in detail for the pavers made from the selected optimum concrete mixes. The compressive and flexural strength of RAC pavers satisfied the minimum required strength values specified in international standards [GB – 28 635–2012, IS 15658:2021, A231.2–14, ASTM C936, ASTM C 1272, ASTM C902] and local [NHA & AJK] specification. The durability tests showed that the RAC pavers are resilient against salt and acid attack. The porous nature of RAC positively affected the pavers’ compressive strength, especially under a saline environment. The maximum water absorption of the RAC pavers was 6.34% which was found to be in the acceptable range, however, their drying shrinkage was higher than Natural Aggregate Concrete (NAC) pavers. As for the impact of casting technique, the properties of the RAC pavers were improved by employing CCT. To predict compressive strength based on the parameters of this study, an equation is proposed by regression analysis of the obtained compressive strength results which showed reasonable accuracy in predicting the strength of pavers. Finally, this study concluded that it is feasible and reliable to manufacture concrete pavers of 35 MPa compressive strength at 7-days (or 55 MPa at 28-days) by replacing 100% natural aggregates with recycled aggregates (both fine and coarse), using 20% cement content, and employing compression casting.