Strength and microstructural analysis of concrete incorporating ash from sunflower seed shells combustion

The aim of the study involves determining the added value of shells of sunflower seeds ash (SSA) as a mineral admixture in concrete and the effects/mechanisms through which it affects the concrete microstructure. The chemical effect of this type of ash was estimated by examining its chemical composition, pozzolanic activity index, and SEM investigation while its physical effect was observed at the level of concrete with ash incorporated. Four concrete mixtures with different shares of cement replacement by ash were prepared (0, 5, 7.5, and 10%). The water to binder ratio was 0.5, and binder content 400 kg/m3 in all mixtures. The properties of fresh and hardened concrete with ash incorporated were compared with the corresponding properties of the reference concrete. The results indicate that SSA achieved all the known possible effects of mineral admixtures; filler effect, heterogonous nucleation effect, dilution effect, and a certain degree of chemical effect. However, replacing more than 5% of cement mass with SSA will adversely affect mechanical properties of concrete.