Prediction of compressive strength development for blended cement mortar considering fly ash fineness and replacement ratio

Utilization of upgraded fine fly ash in cement-based materials has been proved to be an effective method to improve compressive strength at early ages. The addition of fine fly ash has introduced dilution effect, enhanced pozzolanic reaction effect, nucleation effect and physical filling effect into cement-fly ash system. In this study, an integrated reaction model is adopted to quantify the contributions from cement hydration and pozzolanic reaction to compressive strength. A modified model related to the physical filling effect is utilized to calculate the compressive strength increment considering the gradual dissolution of fly ash particles. Via combination of these two parts, a numerical procedure has been proposed to predict the compressive strength development of fine fly ash mortar considering fly ash fineness and replacement ratio. The reliability of the model is validated through good agreement with the experimental results from previous articles. In addition, parametric analyses are performed to further analyze the effects of fly ash fineness and replacement ratio on compressive strength. The results indicate that compressive strength increases linearly with the increase of fly ash fineness. While its slope is less affected by fly ash replacement ratio, it increases along with the extension of curing time. Moreover, the fineness of fly ash can improve the relationship between compressive strength and replacement ratio. For ultrafine fly ash mortar, the 28-day compressive strength of mortar shows an evident trend of first increase and then decrease with the increase of replacement ratio. Under the condition of ensuring the same compressive strength, upgraded finer fly ash can replace more cement, thus realizing energy saving and CO2 emission reduction.