چكيده به لاتين
Cement-based materials can experience sulfate attack while being in sulfate-rich environments. This phenomenon has been seen and studied in concrete structures and specimens for a long time. However, there seems to be a vacancy for studying sulfate attack on soil-cement materials resulted from soil improvement methods like jet-grouting. These materials have different pore structures compared to usual concrete elements, due to differences in water to cement ratio, mixing methods, execution methods and compaction properties. These soil-cement materials would also experience dual sulfate attack (internal and external sulfate attack at the same time) for the ground water or soil may contain sulfate compounds. Using supplementary cementing materials is one of the suggested methods by previous studies to enhance the durability of concrete in sulfate-rich environments.
In this study, soil-cement specimens were made, using Firouzkooh 161 sand, S/C equal to 4, W/C equal to 1.2 with the water containing 2% of sodium sulfate by mass, and types 2 and type 5 portland cements. These samples were cured up to 90 days in 10% sodium sulfate solution under two types of exposures: total immersion and wetting-drying cycles. The effect of using natural pozzolan (10, 20 and 30 percent by mass) and slag (40, 50 and 60 percent by mass) as supplementary cementing materials was observed. results indicate that in 90 days, sulfate reactions do not have significant effects on specimens cured under total immersion exposure. In addition, it can be concluded that in sodium sulfate solution, the damage caused by physical attack occurs sooner than the damage resulted from chemical attack and the main destruction mechanism when the specimens experience wetting-drying cycles, is physical (salt) attack. Using supplementary cementing materials (natural pozzolan and slag) can improve the resistance of soil-cement materials under both chemical (depending on the type of material and chemical compounds) and physical attack (by declining the depth affected by wetting-drying cycles), despite the fact that it has negative effect on the usual concrete specimens’ resistance against physical attack recording to previous studies. The replacement ratios must be chosen carefully as some proportions can lead to an increased capillarity without significant decrease in the permeability and the depth affected by wetting-drying cycles (as can be seen for the specimens made by 30% natural pozzolan in this study).
