The average CS values of the SCC samples are presented in Fig. 7.
Similar to the increasing UPV over time for all mixtures, the CS
consistently increased over the 28-day curing period from 80 to 560 ksc.
The highest and lowest CS results were achieved with the control and
the 20% RHA + 20% urea mixtures, respectively. The incorporation of
RHA decreased the CS with increasing replacement level because the
coarse RHA decreasedthe packing density of the granular mixture. The
CS of urea-containing concrete decreased with increasing amounts of
urea at 7 and 28 days. This result can be explained by the retarding
effect of urea on the hydration of cement [6].