Physio-chemical characterisation of ultra-fine-slag-based ultra-high-performance concrete

Abstract

Ultra-high-performance concrete (UHPC) meets the demand of modern infrastructure due to its exceptional strength and durability. The effects on concrete strength of the size and shape of fine aggregates, and binder content and type, were investigated. Particle packing concepts were adopted for fine aggregate optimisation, and the shape of the fine aggregate was assessed using an aggregate image measurement system. Further, the effects of binder content, binder type and curing age were investigated through compressive strength, thermo-gravimetric analysis (TGA) and quantitative X-ray diffraction. Mixtures with a 2.36 mm nominal maximum size of aggregates (n.m.s.a.) and angular aggregates exhibited higher compressive strength than those with a 1.18 mm n.m.s.a. No significant increase in the compressive strength was observed in mixtures with a binder content greater than the optimum 1000 kg/m3. The study also revealed that ultra-fine slag is a feasible alternative to silica fume. The TGA and X-ray results of concrete paste samples at different curing ages showed that the degree of hydration was relatively low (38.3%) with no further significant increase beyond 7 days. This work contributes to the fundamental understanding of the effect of raw materials on UHPC strength, which helps in rational selection of materials and mixture proportioning.