The volumetric stability, chloride binding capacity and stability of the Portland cement-GBFS pastes: An approach from the viewpoint of hydration products

An optimization of Portland cement (PC)-supplementary cementitious materials (SCMs) system focusing on the characteristics of hydration products is significantly important to decrease the thermal and chemical shrinkages and increase the chloride binding capacity, consequently to decline the diffusion rate of chloride into cement-based materials. In the present study, ultrafine granulated blast furnace slag (GBFS) was added into ultrafine Portland cement (PC) pastes to obtain homogenous hydration products, and then the hydration heat, chemical shrinkage, chloride binding capacity and stability of the PC-GBFS pastes were investigated. The results show that with the increase of the GBFS addition, the ultimate hydration heat of the PC-GBFS pastes increased initially and then decreased sharply, and the chemical shrinkage increased slightly with the increase of the GBFS addition. The cement pastes with 40-60% GBFS had acceptable hydration heat and chemical shrinkage, more important, its total bound chloride and non-water-soluble bound chloride increased by 24% and 177%, respectively, compared to those of Portland cement paste. Additionally, about 50% of chemically bound chloride in the form of Friedel's salt was water-soluble chloride due to ion-exchange, and 5-20% of physically bound chloride in C-S-H was non-water-soluble chloride after desorption. (C) 2019 Elsevier Ltd. All rights reserved.