# On the Feasibility of Using Industrial Urea to Mitigate Thermal and Shrinkage Cracking in Concrete
## 5 Conclusions  
This study investigated industrial urea as an additive to concrete for limiting crack formation. As a result, concrete mixed with urea showed relatively excellent performance in terms of carbonation durability and shrinkage reduction, and a sharp decrease in temperature at an early age. In particular, the possibility of controlling both the dry shrinkage strain and the high hydration heat simultaneously was demonstrated. The experimental comparisons with existing mixtures provided the following results:  
1. The increase in the urea mixing ratio strongly influenced the workability of concrete. A separate measure is required to prevent segregation when the mixing ratio of urea exceeds 15% of the binder weight. Although this study considered reducing water content and inserting additional viscosity agents, as the workability and compressive strength development of concrete, a urea mixing ratio of \(\sim\)10% was believed appropriate;
2. The abrupt temperature variations occurring immediately after mixing concrete with urea strongly affected diverse factors such as the setting time, strength development at the initial aging stage, and the hydration heat curve. Compared to conventional mixing ratios, it was found that the initial setting time was delayed by up to 12 h compared to the standard mixing ratio. Moreover, the results of the hydration heat development revealed that the time required to reach the peak temperature was  
Figure 8: Hydration heat history of the concrete mixture.  
delayed by up to 28 h. Since excessive condensation delay may result in unexpected consequences in the construction process, it should be considered in determining the mixing ratio of urea;
3. Mixing with urea can considerably decrease the strength of concrete at an early age due to a low-temperature condition. The strength characteristics of long-term aged concrete showed that the strength of 5% and 10% urea mixing ratios recovered to that of conventional low-heat mixing ratio using supplementary cementitious materials. However, that of the 15% mixing ratio was only 70% of the conventional ratio;
4. Concrete mixed with urea showed excellent resistance to carbonation compared to existing low-heat mixtures with SCM. It was due to the pH of urea in the microstructure. Even after most of the hydration of the cement is completed, urea in the microstructure of cement composites can maintain the alkalinity of them;
5. A higher mixing ratio of urea greatly mitigated the drying shrinkage, a disadvantage of low-heat concrete, more. It decreased the shrinkage reduction rate up to 48.7% compared to the control specimen. It was found that the decrease of dry shrinkage strain was proportional to the increased ratio of urea. This could be caused by the expansion of the microstructure due to CaCO\({}_{3}\) production.  
This research was funded by a grant (19 AUDP-B147695-05) from the Architecture and Urban Development Research Program funded by the Ministry of Land, Infrastructure, and Transport of the Korean Government.  
Not applicable.  
This research was supported by a grant (19 AUDP-B147695-05) from the Architecture and Urban Development Research Program funded by the Ministry of Land, Infrastructure, and Transport of the Korean Government.  
The author declares no conflict of interest.