High early strength-high performance concrete produced with combination of ultra-fine slag and ultra-fine silica: Influence on fresh, mechanical, shrinkage and durability properties with microstructural investigation

Abstract

This study relates to High early strength- High Performance concrete (HPC) produced with incorporation of Ultra-fine Slag (UFS) and Ultra-fine Silica (UFSi). Compressive Strength development was studied from an early period of 14–15 h of casting up to 180 days. The variations in workability and its retention levels after 60 min of mix preparation were recorded. Elastic modulus, compressive strain behaviour, flexural parameters, early age shrinkage and few durability properties were measured for resulting optimal concrete mixes. Modifications induced at microstructural level were assessed by Scanning Electron Microscopy (SEM) and Nanoindentation tests. Incorporation of UFS and UFSi resulted in reduction of fresh properties beyond certain addition percentages. Usage of UFS as part replacement to GGBS in HPC mixes showed considerable improvement with regards to mechanical and durability aspects. Incorporation of UFSi was evaluated to prominently improve early age strength of concrete in combination with UFS at optimal quantities, while moderately improving other mechanical properties. Early age shrinkage induced stress levels and the brittleness of concrete were observed to increase with use of selected admixtures under multiple blend system. Improvement in the microstructure was observed with denser hydrated matrix offering enhanced homogeneity and better bonding with aggregates. Increase in strength governing hydration phases was evidenced for optimal addition of UFS and UFSi. Durability behaviour was significantly enhanced for combination of UFS and UFSi owing to microstructural improvement through pore refinement.