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

Ultra-high-performance concrete meets the demand of modern infrastructure due to its exceptional strength and durability. The effect on concrete strength of size and shape of fine aggregates, and binder content and type, were investigated. Particle packing concepts were adopted for fine aggregate optimisation, and 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, thermos-gravimetric analysis and quantitative X-ray diffraction. Mixtures with 2.36 mm nominal maximum size of aggregate and angular aggregates exhibited higher compressive strength. No significant increase in the compressive strength beyond the optimum binder content of 1000 kg/m3 was observed. The study also revealed that ultra-fine slag as a feasible alternative to silica fume. The thermos-gravimetric 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 seven days. This work contributes to the fundamental understanding of the effect of raw materials on ultra-high-performance concrete strength, which helps in rational selection of materials and mixture proportioning.