A stoichiometric approach to find optimum amount of fly ash needed in cement concrete

Abstract

This study aimed to find the optimum amount of fly ash that can be replaced with cement using a stoichiometric approach. For this purpose, the balanced chemical reactions between cement, water and fly ash were studied. This new proposed methodology uses information like chemical composition of cement, elemental composition and crystallinity in fly ash sample, and can easily find the optimum amount of fly ash that can replace cement. Considering the chemical composition analysis and percentage crystallinity in fly ash sample, the quantity of fly ash that can replace cement came out to be 30%. To assess the performance of control group and partially replaced cement (PRC) samples, specimens were casted and different tests like compressive strength, split-tensile strength, density and sorption were conducted. The experimental results showed that PRC samples gained almost 95% compressive strength as that of control group at 90 days. The resistance to water intrusion as measured with sorption test showed that PRC samples had almost 50% less depth as compared to control group. The improvement in mechanical and durability properties of PRC samples supports the outcome of studied chemical reactions. The fly ash consumed the cement hydration product i.e. calcium hydroxide for producing binder gel; which enhanced the strength, lowered permeability and made the concrete denser. The development of compressive strength and density with time shows good agreement with an R2 value of 0.96.