Influence of parent concrete on the properties of recycled aggregate concrete

Abstract

This paper discusses first the properties of recycled aggregates derived from parent concrete (PC) of three strengths, each of them made with three maximum sizes of aggregates. The relative physical and mechanical properties of fresh granite aggregate are discussed. Using these nine recycled aggregates, three strengths of recycled aggregate concrete (RAC) were made and studied. Typical relationship between water–cement ratio, compressive strength, aggregate-cement ratio and cement content have been formulated for RAC and compared with those of PC. RAC requires relatively lower water–cement ratio as compared to PC to achieve a particular compressive strength. The difference in strength between PC and RAC increases with strength of concrete. The relative evaluation of tensile and flexural strengths and modulus of elasticity has also been made.

Introduction

As the rate of demolition is increasing day-by-day, it is essential to effectively reuse demolition waste in order to conserve the non-renewable natural resources. Recycling of concrete demolition waste as coarse aggregate for new concrete would facilitate, its large-scale utilisation. A classification of earlier studies on recycled aggregate concrete (RAC) is presented in Table 1. Salient observations drawn from these studies [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [23], [24], [25] are (i) method of crushing of parent concrete has significant effect on recycled aggregate, (ii) particle shape of recycled aggregate is more irregular than natural aggregate and presents a coarser surface, (iii) RAC requires more water for the same workability than normal concrete [11], [16], (iv) density, compressive strength and modulus of elasticity of RAC are relatively lower than that of parent concrete, and (v) for a given water–cement ratio, permeability, rate of carbonation and risk of reinforcement corrosion are higher [2].

Most of the studies on recycled aggregate concrete have adopted nominal mixes while some have given importance to partial replacement of recycled aggregate [8]. Direct use of recycled aggregates by many researchers lead to the adoption of different maximum size of aggregate in RAC as compared to the parent concrete. For a rational comparison, maximum size of aggregate in parent and RAC should be kept the same. The review further indicates that the characteristics of recycled aggregates produced from different strengths of parent concrete require a systematic investigation. This paper reports the properties of recycled aggregate concrete made with different maximum sizes of aggregates derived from different strengths of parent concrete.