Effects of water to binder ratio on the chloride binding behaviour of artificial seawater cement paste blended with metakaolin and silica fume

Abstract

• Effects of water to binder (w/b) ratios (0.2 and 0.4) and SCMs (silica fume and metakaolin) on chloride binding behaviour of seawater cement paste (SCP) are investigated. • Influence of water to binder (w/b) ratios (0.2 and 0.4) and SCMs (silica fume and metakaolin) on the porosity and pore size distribution of SCP is revealed by the 1 H Nuclear magnetic resonance (NMR) measurement. • The risk of steel corrosion in SCP with different w/b ratios is evaluated by the [Cl − ]/[OH − ] ratio. • The relationship between chloride binding ratio, porosity and [Cl − ]/[OH − ] ratio has been explored. This work investigates the effects of water-to-binder (w/b) ratio and supplementary cementitious materials (SCMs) including silica fume (SF) and metakaolin (MK) on chloride binding of seawater cement paste (SCP) by using a water extraction method. The chloride binding capacity, contents of chloride bound in Friedel’s salt and chloride adsorbed by C S H gel are quantified. The resistance to steel corrosion is evaluated by [Cl − ]/[OH − ] ratio. The results show that the chloride binding ratio (content of bound to free chloride) gradually increases with the w/b ratio decreasing from 0.4 to 0.2. In addition, the chloride ions adsorbed by C S H gel in SCP with w/b ratio 0.2 contributes more largely to chloride binding capacity than SCP with w/b ratio 0.4. Moreover, the incorporation of MK improves the chloride binding capacity of SCP while the utilization of SF doesn’t make much difference. In addition, the [Cl − ]/[OH − ] ratio in SCP keeps at a very low level during the whole experimental process, and decreases with the reduction of w/b ratio, the increase of content of MK and curing ages. The correlation of chloride binding ratio with [Cl − ]/[OH − ] ratio can be described by an exponential decay model while a linear relationship is observed between chloride binding ratio and the volume of macropores larger than 200 nm in diameter.