Investigation on the effects of recycled coarse aggregates from concrete waste on compressive strength of c-25 concrete

Abstract

The recycled construction materials derived from the wastage materials during construction and wastage due to demolition, rehabilitation, natural and technological disasters are becoming of great interest in most project implementation. The driving force for recycling concrete is three-fold: preserving natural resources, utilizing the growing waste, and saving energy and money. The utilization of recycled aggregate is also an effective solution to the problem of possessing excess waste materials while simultaneously maintaining satisfactory concrete quality; indeed, it may also be a breakthrough towards sustainable development. It is known that the strength of concrete depends on the quality of ingredients used. Among those elements, the major portion is taken by coarse aggregate. This study utilizes demolished concrete (waste laboratory test cubes for this purpose) by crushing as coarse aggregate often termed as the recycled coarse aggregate (RCA) for investigating the effects on compressive strength and producing industry quality concrete. Large-scale recycling can substantially reduce the consumption of natural aggregate. This research investigated the fresh and mechanical properties of 25 MPa recycled aggregate concrete (RAC) made with different RCA replacement levels (i.e., 100%NA+0%RA; 0%NA+100%RA; 50%NA+50%RA; 75%NA+25%RA; 25%NA+75%RA). Concrete mix design (ACI mix design method) having five mix proportions for both natural and recycled aggregate were prepared using a water-cement ratio and cement contents of 0.62, 288.71kg/m3 respectively. Total of forty-five concrete cubes (150mm*150mm*150mm) was produced and tested at the age of 7, 14 and 28 days. Also, physical properties of all the materials before and after replacement have been assessed. This study reveals that, concrete produced with 75%NA+25%RA replacement level had the highest average compressive strength with 28.1MPa. However, the performance of RAC is decreasing with increasing RCA replacement levels, but their overall performance is comparable to natural aggregate concrete (NAC). It can therefore, be concluded from the findings of this research that use of recycled coarse aggregate in the construction industry helps to prevent unnecessary damages to the environment and provide optimum exploitation of the resources and also offers important economic advantages.