# 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. industrial urea; cement; hydration heat reduction; shrinkage strain +
Footnote †: journal: Applied Sciences  
**Citation:** [PERSON]Y. On the Feasibility of Using Industrial Urea to Mitigate Thermal and Shrinkage Cracking in Concrete. _Appl. Sci._**2021**, _11_, 2483. [[https://doi.org/10.3390/appl11062483](https://doi.org/10.3390/appl11062483)]([https://doi.org/10.3390/appl11062483](https://doi.org/10.3390/appl11062483))  
**Citation:** [PERSON] On the Feasibility of Using Industrial Urea to Mitigate Thermal and Shrinkage Cracking in Concrete. _Appl. Sci._**2021**, _11_, 2483. [[https://doi.org/10.3390/appl1](https://doi.org/10.3390/appl1)]([https://doi.org/10.3390/appl1](https://doi.org/10.3390/appl1))  
and heals cracks within the cement microstructure [10; 11]. Recent studies [12; 13] suggested that precipitating CaCO\({}_{3}\) within the cement microstructure by mixing bacteria made of urease, which catalyzes the hydrolysis of urea with concrete, was helpful for enhancing the strength and durability of cement and self-healing cracks [14; 15; 16]. In general, these bacteria are made through the hydrolysis of urea and are fixed to other substances such as ceramsite or graphite nanoplatelets and hydrogels for mixing with concrete [17; 18; 19]. In recent years, urea-based bacteria have been increasingly used for healing cracks in concrete because CaCO\({}_{3}\), a reaction product, is completely compatible with the cement matrix; therefore, this approach is efficient and sustainable [20; 21]. Many studies have investigated different types of bacteria and urea hydrolysis techniques [9; 22]. However, almost no studies have investigated the direct mixing of industrial urea with concrete for limiting crack formation and shrinkage. As mentioned above, the reaction properties of cement composites mixed with urea strongly influence the process of generating cracks in concrete. The primary reaction of urea with water decreases the initial temperature of concrete and reduces thermal cracks in concrete. Moreover, the secondary reaction, expanding the internal cement matrix and producing CaCO\({}_{3}\) production, reduces shrinkage cracking before and after cement hardening. Thermal and shrinkage cracks cause the greatest damage and occur most frequently among concrete cracks caused by material factors [1; 23]. In reality, if industrial urea used as a concrete additive can positively control the two abovementioned causal factors of cracks, it will produce eco-friendly concrete composites and reduce costs by automatically repairing cracks in concrete. This is because industrial urea is produced mainly using CO\({}_{2}\) and NH\({}_{3}\), both of which criteria material [24; 25].