Autogenous and drying shrinkages of mortars and pore structure of pastes made with activated binder of calcium carbide residue and fly ash

Abstract

Present study evaluates the strength development and shrinkage characteristics of mortars made with a non-cement binder composed of calcium carbide residue and fly ash under several activation techniques. The activation techniques used for improving the strength development were adding NaOH to the binder (0.5, 1.0, and 1.5% by weight of binder), curing at a temperature of 60 °C, and combining both adding NaOH and curing at a temperature of 60 °C. The compressive strengths of mortars were examined at 3, 7, 28 and 90 days. The shrinkage characteristics of the mortars were evaluated in terms of the autogenous and drying shrinkages. The pore structure of the paste was also analyzed using mercury intrusion porosimetry. The results showed that all of the activation techniques could enhance the compressive strength of mortar and improve the pore structure of the paste made from the mixture of calcium carbide residue and fly ash. The technique to improve strength by combining addition of NaOH and curing at 60 °C was found to be the most effective method, and produced the mortar with a compressive strength as high as 51.1 MPa at 90 days. The shrinkage behaviors of the mortar made from the mixture of calcium carbide residue and fly ash were similar to the ordinary Portland cement mortar. The autogenous shrinkage was associated with the internal reaction process, while the drying shrinkage was depended on evaporation of water in pore structures during the drying process. Additionally, the use of NaOH as an activator significantly increased the magnitude of the autogenous and drying shrinkages of mortar. However, the drying shrinkage was greatly reduced with the activation by curing at 60 °C.