Effect of Mixed Recycled Aggregate on the Mechanical Strength and Microstructure of Concrete under Different Water Cement Ratios.

Tao Meng,Bo Zhang,Huadong Wei,Cungui Zhang,Xiufen Yang,Yuncai Zhang

doi:10.3390/ma14102631

Abstract

Mixed recycled aggregate (MRA) is a kind of recycled aggregate containing discarded bricks and other impurities that is inferior to ordinary recycled concrete aggregate. To study the effect of MRA in concrete, specimens with 100% MRA under different water–cement ratios (W/C) of 0.50, 0.42, 0.36 and 0.30 were prepared, and the mechanical properties and microstructure were tested. Results show that compared with ordinary concrete, the compressive strength of mixed recycled aggregate concrete (MRAC) with the same W/C was reduced by more than 50% at 28 days, but the axial compression ratio was relatively high, reaching over 0.87. Affected by the high water absorption of MRA, the hydration rate of cement slowed, which was beneficial to the long-term development of the properties of MRAC. An appropriate increase in cement content could strengthen MRA and densify the pore structure of MRAC. The research results of this article prove that MRA has high utilization value and could be used to prepare MRAC with application potential using optimal gradation, which is of positive significance for promoting the consumption of construction waste.

Highlights

As a widely used building material, concrete consumes many natural resources, which has a negative impact on the environment
The compressive strength of group mixed recycled aggregate concrete (MRAC)-0.30 increased significantly, the 7 d compressive strength increased by 35.5% compared to the 3-d compressive strength, and the 28 d compressive strength increased by 41.9% compared to the 7-d compressive strength
Taking the group MRAC-0.36 as an example, the proportion of less harmful holes increased by 15%, and the proportion of harmless holes increased by 14%

Summary

Introduction

As a widely used building material, concrete consumes many natural resources, which has a negative impact on the environment. Some scholars considered crushing the industrial byproducts and construction solid waste from which impurities have been removed into recycled aggregate (RA), replacing natural aggregate partially or completely to prepare recycled aggregate concrete (RAC), holding that this can relieve resource pressure and effectively eliminate construction waste [2,3,4,5]. Compared with natural aggregate, the water absorption of RA is more significant, and the porosity, shape, specific surface area, etc. The workability of the concrete mixture deteriorates due to the high water absorption of the RA, and the density of the mixture will be reduced by 5–15% compared with natural aggregate concrete [8,13,14]. The compressive strength could be reduced by 30% at a 100%

Methods

Results

Conclusion