The behavior of the bond between thermally shocked recycled asphalt pavement concrete and steel bars

Abstract

This study evaluates the bond behavior between thermally shocked recycled asphalt pavement (RAP) concrete and steel bars. The effects of elevated temperatures, RAP replacement percentages, cooling regime, and steel bar diameter on bond performance were investigated. In addition, the mechanical properties of RAP concrete were also studied, before and after thermal shock damage. According to test results, mechanical properties involving compressive, splitting, and flexural strengths decreased with increasing temperature under thermal shock, while the residual strengths improved after exposure. The compressive strength of specimens at 400 °C decreased by 29.54 %, 28.71 %, 23.47 %, and 18.57 % for replacement ratios of 0 %, 25 %, 50 %, and 75 % of RAP, respectively. Additionally, at 600°C, there was a noticeable decrease in the bond strength for all concrete mixtures with a reduction percentage of 65.92 %, 49.46 %, 44.28 %, and 38.73 % for concrete with a 0 %, 25 %, 50 %, and 75 % replacement ratio, respectively. The extent of the increase in the residual strength correlated with the percentage of RAP aggregate replacement, showing lesser reductions with higher RAP content. Notably, rapid cooling after exposure to elevated temperatures resulted in a more significant strength reduction compared to natural cooling, attributed to thermal shock-induced cracks. Additionally, the bond strength between concrete and steel bars decreased with elevated temperatures, regardless of the RAP aggregate replacement ratio. However, an increase in RAP content showed an increase in residual bond strength. Moreover, the diameter of the steel bars played a crucial role in bond strength, with larger diameters exhibiting consistently lower bond strengths across various temperatures. Compared to 14-mm steel bar embedment, specimens with a 20-mm steel bar embedment exhibited a lower bond strength, ranging from 26 % to 40 %, 38–45 %, and 53–61 % at exposure temperatures of 23 °C, 400 °C, and 600 °C, respectively.