Properties of Portland Blast Furnace Slag Cements Affecting Their Autogenous Shrinkage Behaviors

Abstract

In Japan, Portland blast furnace slag cements that contain 30–60% of blast furnace slag (BFS) are classified in the slag cement class B in JIS R 5211. Even if slag cements are classified in a category, different autogenous shrinkage behaviors are observed among them. In this study, class B slag cements are collected from eight different plants in Japan. Physical and chemical properties of slag cements are investigated to find the cause of different shrinkage behavior. Physical properties of slag cement are expressed in terms of surface area, mean particle size and particle size distribution. The experimental results showed that the collected slag cements can be differentiated into two different groups based on physical properties. However, different behaviors of autogenous shrinkage cannot be explained, because slag cements, which contain finer particles, have not displayed significant differences in the shrinkage of mortar specimen. Therefore, chemical properties of slag cement could be the main reasons behind the different shrinkage behavior among slag cements. To compare the chemical property of slag cements, the phases of mineral (C3S, C2S, etc.) and content of cement and slag mineral (%) in slag cements are analyzed by thermal gravimetric analysis (TGA) and X-ray diffraction (XRD) Rietveld analysis. The results showed that in each plant, different types of BFS are used for producing the slag blended cements, and different quantity levels of slag minerals are found in BFS used in each cement plant. In slag cements classified as Class B in JIS R 5211, different physical and chemical properties are observed. However, the chemical properties of BFS in slag cement mainly influences the shrinkage behavior of slag cement. If the user of BFS cement is concerned about the shrinkage behavior of the concrete, the chemical composition of BFS should be checked to ensure that the concrete has sufficient resistivity against shrinkage.