Research On Critical Strength Of Frozen Injury And Microstructure Of Cacium-Enriched Fly Ash Concrete

Most of northern regions have a long winter. Concreting in such regions is usually under minus-temperature, so it is essential to study the performance of concrete under minus-temperature. Originally from green concrete and concreting in minus-temperature, the critical strength of frozen injury of minus-temperature calcium-enriched fly ash concrete and the rule of strength development are studied in this paper. Through the test of resistance of freezing-thawing cycles and chloride diffusivity, the influence of curing system and calcium-enriched fly ash on the performance of concrete are studied; and through the modern methods (XRD , SEM, and so on), the hydration products, pore structures and microstructure are studied.This paper presents the results as follows, the compressive strength of minus-temperature calcium-enriched fly ash concrete decreases with the increase of calcium-enriched fly ash when the W/B ratios are the same. Natural change of temperature is better than constant negative temperature in promoting the hydration of cement for minus-temperature calcium-enriched fly ash concrete because of the difference of energy. Comparing with the standard curing, curing under minus-temperature for 7 days does harm to concrete, which performance of resisting freezing-thawing cycles and chloride diffusivity decreased after the 28d standard curing. Comparing with the reference concrete, the resistance of freezing-thawing cycles and chloride diffusivity in calcium-enriched fly ash concrete increase, because the pore structures and interface structure are optimized, so the durability of calcium-enriched fly ash concrete is perfect.As far as I am concerned, minus-temperature concrete has a kind of critical structure, which has a corresponding critical strength, but the contrary conclusion is not true. Calcium-enriched fly ash debases the numerical value of critical strength of frozen injury and improves the microstructure because of its form effect, activity, tiny aggregate effect and self-hardening property. So it is feasible to make it an important component of minus-temperature concrete.