عملکرد پلیمرهای اتیلن وینیل استات و وینیل استات بر مشخصات مکانیکی، جمع شدگی و دوام مخلوط‌های پایه سیمان آلومینات کلسیم

Nowadays, the utilization of polymer modified cement base materials in waterproofing coatings and mortars is spreading. However, the influence of polymers on some types of special cements has not been investigates appropriately. In the current study due to the characteristics of calcium aluminate cement such as fast hardening and accelerating, the effects of some types of polymer materials on the properties of polymeric modified mixtures have been investigated. To this purpose the incorporation levels were 5, 15 and 25 percent by weight of cement. The water to cement ratio in all the mixtures was also 0.38. In order to keep the water content of the mixtures in a constant level, the water content of superplasticizer and the latexes (vinyl acetate and ethylene vinyl acetate) was considered as a part of the mix water. It should be mentioned that the polymers were replaced with sand. In this experimental study, a combination of dry and wet curing conditions was utilized. For this aim, after demolding of the specimens, they were cured in water for 6days, and after this period the specimens were cured in dry conditions at temperature of 25 degree of Celsius. The mechanical properties which studied in this research were compressive strength, flexural strength and flexural toughness. The shrinkage of the specimens has also been measured. It should be noted that in this study, the rapid chloride migration test was used to evaluate the durability properties of the cement base mixtures against diffusion of chloride ions. The results indicate that use of the polymers could improve the mechanical characteristics such as flexural strength and durability in regards of chloride ion diffusion as well as length change due to shrinkage. The polymer materials in calcium aluminate cement based mixtures have deceleration effect on cement hydration which results in lower compressive strengths compared to the plain mixture, which this effect is more evident at higher replacement levels. Despite the considerable reduction in compressive strength results at early ages especially for the mixtures with high contents of polymers, the differences at later ages were significantly lower. For instance, at 5% incorporation level, similar results with the plain mixture were obtained. In contrast to the compressive strength test results, high levels of polymer materials increased the flexural as well as flexural toughness in comparison with the plain mortar. It is noteworthy that incorporation of ethylene vinyl acetate in the mixtures could provide improved characteristics compared to the mixes with vinyl acetate at replacement levels of 5% and 25%. However, at 15% replacement level, similar results were obtained for the aforementioned polymers. The rapid chloride migration coefficient in the plain mix increased with age. However, using the polymers compensated for this effect and lower permeability values were obtained at later ages. It should be mentioned that the Rapid Chloride Migration Test coefficients were so low that the mixtures could be considered as relatively impermeable mortars. The shrinkage was also influenced by content of the polymer materials and those with higher contents have reduced length change.