Substitution of Fly Ash, Slag, and Chemical Admixtures in Concrete Mix Designs

The Florida Department of Transportation (FDOT) requires contractors for FDOT’s projects to submit a proposed concrete mix design prior to the production of any concrete. The contractor must use mix designs approved by FDOT. Substitutions of ingredients other than coarse aggregate must be justified through trial mixtures, and authorized in writing by FDOT engineers. The study reported herein investigated whether substitutions of fly ash, slag, air-entraining admixtures, and Types A, D, and G admixtures could be performed and be allowed in FDOT approved concrete mix designs. Substitutions of the ingredients were performed on two typical FDOT hot weather mix designs in this study. The concrete properties considered were slump, air content, and compressive strength. Test data for substitution mix designs were compared with the data for the original mix design. Results show that the substitutions cause variability in concrete properties for both the fly ash and the slag mix designs. Statistically reliable conclusions cannot be made because of small sample sizes for test data sets. This study is preliminary in nature; more extensive research based on statistically significant sample sizes is needed to validate the findings from this study.