High volume fly ash (HVFA) concrete mixtures are being considered more frequently due to their cost and sustainability advantages. While the long term performance of these HVFA concretes typically meets or exceeds that of conventional concretes, their early age performance is often characterized by excessive retardation, delayed setting times, and low strengths. Extending an HVFA mixture to a ternary blend that incorporates a fine limestone powder may provide a viable solution to these deficiencies, particularly the retardation and setting issues. In this paper, a nano-limestone powder and two other limestone fillers of increasing median particle size (4.4 μm and 16.4 μm) are investigated for their propensity to accelerate early age reactions and reduce setting times in a Class C fly ash/cement blend. The fineness of the fly ash has measurable effects on its efficacy in accelerating hydration and decreasing setting times. Companion specimens prepared with a fine silica powder suggest that the fine limestone may act favorably through both a physical and a chemical mechanism. Isothermal calorimetry and Vicat needle penetration measurements on pastes are accompanied by strength measurements on mortars, to verify that the limestone powder substitutions are not negatively impacting strength development. A linear relationship with a reasonable correlation is found to exist between 1 d and 7 d compressive strengths of mortars and their accompanying cumulative heat release values as determined using isothermal calorimetry.
Citation: Cement and Concrete Composites
Pub Type: Journals
Blended cement, high volume fly ash, isothermal calorimetry, limestone, particle size, setting, strength