Optimization of fly ash particle size distribution for cementitious systems with high compactness

Abstract

Compactness is of special importance for aggregates in concrete; however, the particle-size distribution (gradation) of powdery ingredients is commonly disregarded especially for pozzolanic materials such as fly ash. Without good gradation, powdery materials will result in higher void ratios, as in the case of aggregates, and the products obtained after hydration will still have some voids. Using a vacuum sieve, this study found the particle-size-distribution of fly ash in accordance with the Dinger-Funk particle-size distribution modulus, q, and explored the effects of various fly ash particle-size distributions on the compressive and flexural strengths of 7-, 28- and 90-day-old fly ash-blended cement mortars. After defining the optimal size distribution, the mechanical properties of cement mortars were assessed for several fly ash replacement levels. Results reveal that q of 0.4 yields the best mechanical property results. Further, the cement mortar with a 20% fly ash replacement level and a previously optimized particle-size distribution offered improved mechanical properties and high-compactness results over the control cement mortar after 90 days. Experimental results clearly indicate that only by properly adjusting the particle size distribution of fly ash used in the mixtures, better mechanical properties than the control mixtures without any fly ash addition can be achieved at a fly ash replacement ratio of 20%. The findings of current study are believed to greatly contribute to new lines of research on more effective replacement techniques for different pozzolanic materials without risking basic properties expected from cement-based materials. (C) 2018 Elsevier Ltd. All rights reserved.