Test Studies On Frost-Resistance And Self-Healing Properties Of High Volume Fly Ash Concrete

Fly ash concrete has been a large number of applications in engineerings.It could be helpful, not only for the utilization of fly ash and reducing environmental pollution, but also improving quality of the concrete, reducing concrete hydration heat and overall cost. Fly ash concrete can achieve well social, economic and environmental benefits. For the increasing durability demanding of concrete, it is necessary to study the durability of the high volume fly ash concrete (HVFC).In order to fit the requirements of one Ningxia engineering, a series of researches on fly ash concrete frost-resistance has been made to find the appropriate content of fly ash in the HVFC. The comparative studies of the different fly ash concrete has been carried. The main research methods and results are as follows:(1) According to Dunstan model, water-binder ratio and fly ash content almostly emerge negative linear correlation in the same strength grade. By adjusting the water-cement ratio, the maximum content of fly ash can be 72% in C25 concrete. Concrete strength and water-binder ratio showed a linear relationship at different ages and different fly ash content. Water-binder ratio and concrete strength at different ages show a quadratic relationship.(2) With appropriate air-entraining agent, C25 concrete with different fly ash content at 28d age,basicly meet the ati-freeze requirements.However,at the 60d age the frost resistance has been comprehensive improved. The fly ash content is a decisive factor to the concrete frost-resistance in the high volume fly ash concrete. With the same water-binder ratio and 50% fly ash content, the mass loss show exponential relationship to the fly ash content,and the dynamic elastic modulus and fly ash content have show a quadratic relationship.(3) CAI Hao model has been employed to establish a theoretical model of concrete frost damage, based on concrete impermeability and ultimate tensile tests.(4) According to test results, we got different freeze-thaw damage model of fly ash concrete. By introduction of freeze-thaw angle and frost-criteria factorωproposed by Professor Wang Lijiu, freeze-thaw test curves have been transformed to normalized curves. Conclusions have been achived that the same concrete under different judgment criteria have different frost-criteria factorω.(5) Fly ash concrete have good self-healing abilities after freeze-thaw cycles, but the splitting tensile strength recovery was worse than axial compressive strength. When the fly ash content below 50%,the concrete have better self-healing abilities at 28d age than at 60d age.If the fly ash exceed 65% at the concrete,the self-healing abilities will be worse. The micro-explanation of fly ash concrete self-healing abilities,has been given by SEM micro-morphology analysis of concrete.