A granular type of urea was used (Fig. 3). The urea was a solid
nitrogen fertilizer product with a nitrogen content of 45.95%. Its
properties are shown in Table 2. The admixture was high-range waterreducing standard type F, complying with ASTM C494 [12]. The pH of
the water that was discharged into the mixer from the municipal water
supply ranged from pH 6 to 8. The fine aggregate was river sand with a nominal maximum size of 4.75 mm. The coarse aggregate was crushed
limestone rock with a nominal maximum size of 10.0 mm. Both
aggregates conformed to the requirements of ASTM C33 [13].