Improved prediction model for compressive strength of self-compacting concrete incorporating fly ash and tuff powder at different curing ages

Tuff powder (TP), an abundant mineral additive in Xizang, China, offers a cost-effective and performance-enhancing alternative to fly ash (FA). To quantify their cementitious characteristics, eight groups of mortars with varying FA and TP contents at different curing ages were tested for compressive strength to derive cementitious coefficients. Additionally, nineteen groups of SCCs with different water-to-binder ratios, superplasticizer contents, TP and FA contents, sand ratios, and gravel contents were examined to develop an improved compressive strength prediction model. The model’s accuracy was further verified using five groups of SCCs prepared with additional modifiers and aggregates of different types, contents, and gradations. Results indicate that the cementitious coefficients of TP and FA align with their intrinsic cementitious properties. The improved model shows strong agreement with experimental results for compressive strengths at 3 and 7 d, and demonstrates superior accuracy for 28-day predictions compared to the original model, effectively capturing the synergistic effects of FA and TP. Furthermore, a mix design method integrating the improved model with paste rheology theory is proposed to predict both compressive strength and workability of SCC.