Effect of granular urea on the properties of self-consolidating concrete incorporating untreated rice husk ash: Flowability, compressive strength and temperature rise

This article presents the effect of granular urea on the flowability, compressive strength and temperature rise of self-consolidating concrete (SCC) that includes untreated rice husk ash (RHA) with granular urea (urea) in its composition. The slump flow test was used to assess the horizontal free flow of the concrete in the absence of obstructions. Powder materials were used in the amounts of 450, 550, and 650 kg/m3. Ordinary Portland cement (OPC) was replaced with RHA at a percentage replacement of 20%wt. The granular urea-powder materials (OPC + RHA + urea) ratios were augmented by 0, 5, 10, and 20%wt of the powder materials. Moreover, the water-powder materials ratio (w/p) was 30%. The unit weight, setting time, slump flow and loss, J-ring flow, V-funnel, temperature rise, and compressive strength of the samples were measured for up to 120 days. The results show that when urea is mixed with SCC, the temperature rises less, which has the effect of producing high flowability without segregation when the appropriate percentage of urea is also used. However, this composition also produces SCC with a longer setting time and lower compressive strength than those of conventional SCC. A longer setting time can be beneficial when it is necessary to delay this process in practice. It should be noted, too, that the effect of urea on the compressive strength depends on the concrete age-that is, for a concrete age of 91 days, the effect is very similar to that achieved when only water (as opposed to both water and urea) is included in the mixture. These findings suggest that adding granular urea and RHA to SCC can reduce the concrete temperature and improve the flowability, especially in mass concrete construction or in hot tropical areas.