Effect of fly ash on the mechanical properties of mortar

Abstract

Class F fly ash is used to replace the OPC on the mass basis of the total cementitious material (CM) at the replacement portion of 0%, 10%, 20% and 40% while the water and CM ratio is constant at 0.4. The flexural and compressive strengths of all mixes are determined up to 90 days. The results show that within the range of investigation, the fly ash improves the consistence of fresh mortar but reduces both flexural and compressive strengths of mortar at early age depending on the replacement portions. At 90 days, the 10%FA flexural strength gained is equal to the control sample strength while the flexural strengths of 20%FA and 40%FA continue to develop to the strength of the control sample. At 28 days, the compressive strength of 10%FA is higher than that of the control samples and the compressive strength of 20%FA, 40%FA is nearly the same as the control samples at 90 days. Both flexural and compressive strengths of 40%FA will be gained with long term curing in water, and should be investigated in further research. The relationship between compressive strength and flexural strength regardless of fly ash content is almost fit with some previous researches.