Impact of the Hybrid-Aluminum Additive on the Hydration Kinetics of Portland Cement in Fiber-Reinforced Cement Composites

A hybrid-aluminum additive (HAA) synthesized from industrial wastes including aluminum dross and flue gas desulfurized (FGD) gypsum was used as an additive for fiber-reinforced cement composites (FRCC). The impact of this additive on hydration kinetics was observed by the temperature change over time for the various HAA mixtures with ordinary Portland cement (OPC), sand, cellulose fibers, polyvinyl alcohol (PVA) fibers, and water, based on the method described in ASTM C186-98. The results showed that the hydration kinetics of OPC in the FRCC was improved by using HAA. In addition, when the amount of HAA was at 3% of the OPC weight, the hydration reaction rate was improved by 41%. The HAA additive acted as an accelerating agent by shortening the setting time and enhancing the temperature of the hydration reaction. This suggests that the cement paste can set faster, reducing the cycle time in FRCC processing. Even though further addition of the HAA increased the reaction rate, the setting time of OPC was too short to form a green sheet for the actual production of FRCC on an industrial scale. In addition, the heat released during the test, representing by the temperature change of the sample, was too high which could have a negative impact on the finished FRCC products.