Abstract
A partial replacement of Portland cement (PC) by ground granulated blast furnace slag (GGBFS) is an effective method to improve the durability of concrete due to its lower diffusivity and higher chemical resistance compared to PC. Further, the microstructure of GGBFS blended cementitious materials controls the physicochemical properties and performance of the materials in concrete. Therefore, understanding of cement hydration and cementing behavior of GGBFS is essential to establish microstructure property relationship for predicting performance. In this study, hydration, microstructure development, and chloride ingress into GGBFS-blended cement have been investigated. Solid-phase assemblage and pore solution chemistry of hydrating PC and cement blended with GGBFS were predicted using thermodynamic model and compared with experimental data. A mathematical model integrating PC hydration, GGBFS reaction, thermodynamic equilibrium between hydration products and pore solution, ionic adsorption on C-S-H, multi-component diffusion, and microstructural changes was developed to predict chloride ingress into GGBFS blended cementitious materials. The simulation results on chloride profiles for hydrated slag cement paste, which was prepared with 50% of replacement of PC with GGBFS, were compared with experimental results. The model quantitively predicts the states of chloride such as free, adsorbed on C-S-H, and chemically bound as Friedel’s salt.
Highlights
Cementitious materials have been using in various reinforced concrete structural components as well as in nuclear waste repositories [1]
The reaction of clinkers and slag contribute to continuous increase of hydration products and decrease of porosity
The agreement between simulation results and experimental data on hydrate assemblage indicates that the model can be used to predict mineralogical distribution and pore solution concentration in slag-blended cement
Summary
Cementitious materials have been using in various reinforced concrete structural components as well as in nuclear waste repositories [1]. Extensive use of supplementary cementitious materials, such as ground granulated blast furnace slag (GGBFS), fly ash, and silica fume, is anticipated to reduce CO2 footprint of Portland cement (PC) but to achieve better performance of concrete in numerous environments [2]. The slag incorporation into cement reduces the total porosity as well as significantly influences pore size distribution, increases fine pores. It has effect on chloride binding and diffusion. Several factors such as porosity, pore size distribution, tortuosity, mineralogical distribution, and the characteristics of calcium alumino silicate hydrate (C-A-S-H) influence on the ionic transport into slag-blended cementitious materials [4]. Geochemical code, PHREEQC [5], coupled with empirical expressions for dissolution of clinker minerals and reaction of slag is used to calculate hydration products and pore solution composition, and the determined properties are given to a reactive transport model together with microstructure properties to predict ionic transport into the materials
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