Physical and chemical coupling effect of metakaolin induced chloride trapping capacity variation for Ultra High Performance Fibre Reinforced Concrete (UHPFRC)

This study investigates the physical and chemical coupling effect of metakaolin induced chloride trapping ability variation for Ultra High Performance Fibre Reinforced Concrete (UHPFRC). According to the previous studies, the skeleton of the UHPFRC is designed by the modified Andreasen & Andersen model and three ratios of silica fume (SF)/metakaolin (MK) are applied. Then, the diffusion of rapid chloride migration (D-RCM) of the designed UHPFRC is tested and the intrinsic mechanism of chloride permeability is analyzed. The obtained results show that the D-RCM of designed UHPFRC with 60% SF + 40% MK is the lowest in the designed UHPFRCs. Moreover, the process of chloride penetration can be divided into two period: chloride diffusion and chloride absorption. Additionally, on the one hand, an increased viscosity (due to the addition of MK) can increase the macro-pores of UHPFRC matrix, which consequently cause that the chloride could penetrate into the concrete easily; On the other hand, the added MK can improve the concrete microstructure and trap the chloride to form Friedel's salt, which is beneficial for improving the UHPFRC chloride permeability. Hence, to find an optimized content (balance point between positive and negative effects) of the MK is quite important to produce advanced UHPFRC. (C) 2019 Elsevier Ltd. All rights reserved.