Superior Sodium Sulfate Resistance of a Chemically Activated Phosphorus Slag–Based Composite Cement

Abstract

This study is devoted to durability performance of a chemically-activated phosphorus slag-based composite cement (CAPSCC) against sodium sulfate attack. For this purpose, enough mortar specimens were prepared from phosphorus slag (80% by weight), Type II portland cement (14% by weight), and a compound chemical activator (6% by weight) at water-to-cement ratio of 0.37 and exposed to 5% sodium sulfate solution after being cured. Mortar specimens of both Types II and V portland cements (PC2 and PC5) were also prepared and used as control for comparison purposes. Based on experimental test results, after 12 months of exposure to 5% sodium sulfate solution, PC2, PC5, and CAPSCC exhibited 12.7, 7.5, and 2.1% loss in compressive strength, respectively. Measurements of expansion and weight changes were also done. Advanced studies by X-ray diffractometry and scanning electron microscopy were performed to characterize the products of the degradation process. All obtained results together confirmed the superior performance of CAPSCC against sodium sulfate solution that can be attributed to its very low potential for the formation of sulfate attack products, especially ettringite.