Özet:

Even though a reduction in pollution and CO2 emission can be achieved by the utilization of fly ash in cement-based materials, using a high volume of fly ash results in a reduction at the early age strength development and also setting time delays. In order to assess hydration mechanism and microstructural characteristics of high-volume fly ash blended cement mortars, nano-sized calcite was introduced into the mortars to evaluate the combined effect of fly ash (FA) and nano-sized calcite (NC). For this purpose, twelve mixtures in which fly ash to Portland cement ratios and NC (used as minor addition up to 5%) percentages were varied as 0.0, 0.25, 0.54, 1.0 and 0.0%, 2.5%, 5%, respectively, were designed. Consistency, setting times, compressive strength, ultrasonic pulsive velocity and SEM analysis were conducted at varied curing ages (which depends on the testing method) in terms of fresh and hardened properties and micro-structural characteristics. Experimental test results confirmed that fresh and hardened properties of standard mortars were significantly improved with the combination of both FA and NC especially at early ages. Even though decrease in early age compressive strength values was obtained as FA amount was increased, (comparing to control mixture which was 43.2 MPa at 90 days) higher compressive strength result (45.9 MPa) was obtained at 90-day curing age of mixture including 50% of FA content being utilized by NC of 2.5%.

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