Enhancing microstructure and durability of concrete from ground granulated blast furnace slag and metakaolin as cement replacement materials

Recycling of industrial wastes and by-products can help reduce the cost of waste treatment prior to disposal and eventually preserve natural resources and energy. In this work, the pore structure and interfacial transition zone (ITZ) of concrete incorporating ground granulated blast furnace slag (GGBS) and metakaolin (MK) were analyzed. Some techniques including mercury intrusion porosimetry (MIP), microhardness tester and scanning electronic microscopy (SEM) were employed to characterize the effects of GGBS and MK on the pore structure, microhardness and morphology of ITZ at 28 days. The compressive strength and durability including carbonation resistance, chloride penetration resistance and freeze-thaw resistance were experimental evaluated in relation to their pore characters and ITZ. Meanwhile, the influence of silicon, as the major component of GGBS and MK, on thermodynamic stability of hydrate phases was further investigated. The experimental results show that GGBS and MK have positive impact on pore refinement and ITZ enhancement of concrete. The development of the compressive strength and durability is closely related to the evolution of the pore structure and ITZ. Thermodynamic stability analysis indicates that silicon, as the major component of GGBS and MK, influences the stability of hydrate phases according to changes in Gibbs free energy of reaction