Effect of Different Cooling Methods on Mechanical Properties of Brick Aggregate Reed Straw Concrete after Exposure to High Temperature

In this paper, the mechanical properties of concrete containing recycled brick aggregate with reed straw (RS) were investigated after exposure to high temperatures. The concrete was heated to 300°C, 500°C, 700°C, and 900°C and cooled to room temperature by both natural cooling and water flushing. The compressive strength, split tensile strength, and axial compressive strength of brick aggregate reed straw concrete (BARSC) after the heating-cooling treatment were obtained, and the effects of different cooling methods and RS dosage on the mechanical properties of BARSC after elevated temperatures were analyzed. The results show that compared with natural cooling, the color of the water-cooled sample is darker, and the cracks and shedding are more obvious. The hydration products in BARSC will decompose after being subjected to high temperature, resulting in the structure becoming loose, which seriously affects the mechanical properties of BARSC. Regardless of the cooling method used, the mechanical properties of concrete with different RS content decreased with the increase of heating temperature and decreased with the increase of RS content. The incorporation of RS is beneficial to improve the flexural performance of concrete. Compared with the reference concrete specimen, the flexural strength of RS-4% is increased by 64.7%. From 300°C to 900°C, the difference of compressive strength and axial compressive strength of BARSC-4% treated by the two cooling methods increased from 10.26% to 65.9% and from 5.75% to 68.78%, respectively. Comparing the two cooling methods, the thermal shock induced by water cooling causes more serious damage to BARSC and greater loss of strength. At room temperature, the splitting tensile strength of BARSC-2% is the largest, which is 13% higher than that of the reference sample, and the stress-strain curves tended to flatten out depending on the cooling method and heating temperature.