Effect of Class C Fly Ash on Compressive Strength of Concrete up to 28 Days.

This study investigates the influence of Class C fly ash as a partial replacement of cement on the mechanical properties of concrete. The primary focus is to evaluate the compressive strength development at various curing ages. Unlike Class F fly ash, Class C fly ash contains higher calcium content, which contributes to both cementitious and pozzolanic reactions, resulting in enhanced early-age strength. The experimental results indicate a noticeable improvement in compressive strength at 7 and 28 days compared to control specimens. The addition of Class C fly ash also led to a reduction in porosity and improved microstructural densification. Consequently, the modified concrete exhibited better durability in terms of reduced water absorption and permeability. These findings suggest that Class C fly ash can be effectively utilized to produce sustainable and high-performance concrete with improved early and long-term strength characteristics Keywords: Fly ash, Compressive strength ,Drying shrinkage, Permeable void ,Water sorptivity.