Mix proportions and mechanical properties of concrete containing very high-volume of Class F fly ash

Two types of Class F fly ash with 4.6% and 7.8% loss on ignition were used for an experimental investigation dealing with concrete incorporating very high volumes of Class F fly ash (HVFA). A rational mix design method was developed for concrete with 20-80% fly ash replacement for cement. Tests were performed for fresh and hardened concrete properties. Test results indicated that the setting times and the air content of fly-ash concrete increased as the fly ash replacement level increased. The compressive and flexural strength of the HVFA concrete mixtures demonstrated continuous and significant improvement at late ages of 91 and 365 days. Relation was formulated for flexural and compressive strength for all grades of HVFA concrete. The concrete mixture containing low-LOI fly ash exhibited superior mechanical properties than those of the corresponding mixture containing high-LOI fly ash. These results confirm the feasibility that up to 80% of Class F fly ash can be suitably used as cement replacement in concrete by using a rational mixture proportions.