On the feasibility of using industrial urea to mitigate thermal and shrinkage cracking in concrete

Abstract

Industrial urea is an organic compound that is widely used for various physiological processes and for producing nitrogen fertilizers. This study hypothesized that mixing urea with concrete would decrease the temperature and expansion of the cement microstructure abruptly due to the reaction with water and a cement hydration product. This study tested the hypothesis by experiments. The performance of concrete was evaluated after setting the mixing ratio of industrial urea was to 0%, 5%, 10%, and 15%. The results showed that temperature decreased drastically immediately after mixing and the decrease in temperature increased with a higher mixing ratio. Consequently, condensation was delayed, and heat of hydration decreased. It was found that when considering workability and compressive strength development performance, the proper mixing ratio of urea was around 10%. This study proposed the mixing design technique of concrete mixed with urea. Additionally, this study reported better carbonation resistance and mitigated shrinkage strain of concrete mixed with urea compared to existing low-heat mixing ratios.