Design of reactive powder concrete mortar mixes through high strength and durability

This research investigates the characteristics of reactive powder concrete (RPC) through comprehensive analysis. The primary methodology involved evaluating both fresh (uncured) and hardened RPC specimens. The initial phase incorporated silica fume (SF) as a cement replacement at concentrations of 5, 10, 15, 20, and 25%, fly ash (FA) substitution at levels of 5, 10, 20, 25, and 30% of the cement content, plus binary combinations where SF constituted 10% cement replacement while FA proportions ranged from 10 to 30%. Material behavior was assessed through slump flow testing procedures. Hardened concrete evaluation encompassed dry density measurements, compressive strength analysis conducted at 7, 28, 56, and 90-day intervals, along with tensile splitting strength and flexural strength determination at 28 days. Results demonstrate that FA substitution alone provides superior workability compared to SF+FA combinations and pure SF, whereas SF replacement individually exhibits enhanced compressive, tensile splitting, and flexural strength performance relative to standalone FA and binary SF+FA mixtures. The subsequent investigation phase examined the influence of nano-silica (NS) on fresh and hardened RPC characteristics. NS replaced cement at 1, 2, 3, 4, and 5% levels, combined with 10% SF and 20% FA. Findings revealed that increased NS content diminishes workability due to elevated water demand for hydration and mixing processes as particle fineness increases. Regarding hardened properties, the optimal composition comprises 10% SF, 20% FA, and 3% NS, attributed to NS’s effective interaction with calcium hydroxide generated during cement hydration, which facilitates additional C-S-H formation through enhanced pozzolanic reactions. This mechanism results in improved mixture performance and strength development.