Physical and permeability properties of cementitious mortars having fly ash with optimized particle size distribution

Abstract

Gradation of powder materials is often avoided in pozzolanic materials, such as fly ash and slag. Without good gradation, powder materials result in high void ratios similar to the case of aggregates and the products obtained after hydration would still have voids. It is therefore necessary to optimize the particle size distributions (PSDs) of pozzolanic materials for improved compactness. This study calculated the PSDs of fly ash using a vacuum sieve in accordance with the Dinger-Funk PSD modulus. The optimal PSD was defined, and the compressive strength of fly ash-blended cement mortars at 7, 28 and 90 days was explored. Properties including water absorption capacity, dry density, rapid chloride permeability and consistency of mortars having optimized fly ash compositions were analysed by varying the replacement levels. Results reveal that the water absorption capacity of the optimized fly ash-blended cement mortar was lower than that of the blended cement mortar having non-optimized fly ash. Moreover, at 90 days, the chloride permeability of the cement mortar blended with optimized fly-ash improved up to 39.1% when compared to that of blended cement mortar having non-optimized fly ash. The results showed that it is possible to use 20% optimized fly ash instead of 10% non-optimized fly ash by simply changing the PSD of fly ash used. Findings of this study clearly show that even slight modifications in the PSDs of pozzolanic materials can make marked contributions to the certain properties of mortars.