The modifying effects of styrene butadiene rubber and styrene acrylic polymers on the properties of cementitious mixtures with calcium aluminate cement

In this research, the mechanical characteristics and durability of mixtures containing calcium aluminate cement (CAC) and polymer materials have been evaluated. The investigated polymers were two types of commercial polymers including Styrene butadiene rubber (SBR) and Styrene acrylic. The levels which the polymers have been used were 5, 15 and 25% by weight of cement and the water-cement ratio was kept constant at 0.38. In order to investigate and compare the influences of polymer materials on the durability characteristics and mechanical properties, the tests to determine the compressive strength, flexural strength, tensile strength, coefficient of rapid chloride migration (RCM), water sorptivity and water absorption were carried out. The specimens were cured under wet conditions at early ages (7 days) and air cured at later ages (After 7 days until the time of testing). According to the results, the plain calcium aluminate cement mix had high early strengths and appropriate durability characteristics. However, increasing the chloride permeability was observed due to the conversion of the early hydrate products to the stable ones. Despite the lower compressive strenths, modification of the mixtures with polymers led to improvements in the mechanical characteristics such as flexural and tensile strengths, It is also worth noting that the reduced compressive strength of the modified polymer mixes compared to the plain mix was decreased with age, approaching the values abserved for the plain mix. Significant influences on reducing the sorptivity rates, rapid chloride migration coefficient and water absorption were also observed for the polymer modified mixes. However, the mixes with Styrene acrylic did not have enhanced performance in the wet curing conditions. It appears that the Styrene butadiene rubber mixes could provide more suitable results compared to the Styrene acrylic ones. Comparing the results at different ages revealed that dry curing period had a significant effect on the strength growth process, mechanical and durability properties of the polymer modified mortars.