# On the Feasibility of Using Industrial Urea to Mitigate Thermal and Shrinkage Cracking in Concrete
## 4 Results and Discussion  
### Slump and Setting Time  
Due to its strong aqueous substrate, urea increases the amount when it is mixed with concrete, and it thereby impacts the physical properties of fresh concrete. Table 4 shows the experimental results of unhardened concrete for each designed mixture.  
The urea mixture shows a proportional increase in slump according to the increase in the phase of the mixture amount. Relative to the standard OPC mixture, the slump of the U5 and U10 mixtures increased by 20 mm and \(\sim\)35 mm, respectively. Because this phenomenon may cause segregation due to an excessive increase in liquidity during mass production, additional care must be taken when using it. The slump decreased to 220 mm in the mixture with up to 15% of urea (U15V) because a viscosity agent was added to this mixture and the unit water content decreased. This slump was the same as that of the U10  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Mixture ID**} & \multirow{2}{*}{**Slump (mm)**} & \multirow{2}{*}{**Air Content (\%)**} & \multicolumn{2}{c}{**Setting Time (h)**} & \multirow{2}{*}{**Wet Density (kg/m\({}^{3}\))**} \\ \cline{5-6}  & & & **Initial** & & **Final** \\ \hline OPC & 165 & 5.4 & 8.5 & 10.8 & 2246 \\ U5 & 185 & 4.9 & 10.5 & 14.2 & 2230 \\ U10 & 220 & 4.5 & 13.2 & 17.0 & 2209 \\ U15V & 145 & 3.6 & 20.9 & 25.7 & 2204 \\ U15W & 220 & 5.7 & 16.5 & 22.7 & 2231 \\ SCM & 120 & 3.5 & 8.8 & 10.7 & 2217 \\ LHC & 140 & 3.4 & 8.4 & 12.0 & 2228 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Test results of fresh concrete.  
mixture, because the total volume of urea aqueous solution in the U10 and U15W mixtures was similar: U10, 165 (w) + 28 (u) = 193 L; U15W, 147 (w) + 42 (u) = 189 L.  
Figure 2 shows the results of setting tests conducted according to ASTM C191 [32] in which the penetration resistance of concrete was measured 30-60 min after placing. The main focus of the assessment of the initial and final setting points of cement is the retardation performance of elements. Because the elements show a sharp decrease in temperature owing to the reaction with water, cement composites with a low temperature at early placing require a greatly increased setting time. The experimental results indicate that in contrast to the slope of the curve, which is similar in almost all mixtures until the final setting time is reached after the initial setting, the starting point of the curve, that is, the initial setting point, differs greatly for different mixtures. For the U15V mixture with considerable urea and the U15W mixture, the initial setting point was retarded by up to more than 12 h and 8 h, respectively, relative to that of OPC. This phenomenon is attributed to the fact that the top surface is left in a wet state for a long time owing to the increased amount of initial bleeding as the amount in an unhardened state increases; furthermore, the concrete placing temperature decreases sharply immediately after mixing [33]. The SCM and LHC mixtures showed similar tendencies to the standard OPC mixture, indicating that the initial reaction of low-heat cementitious materials does not have a significant effect on the setting properties.