The Study About Mechanical Properties Of High Volume Fly Ash Concrete Under The Action Of Freeze-Thaw Cycle

Due to the high volume fly ash concrete have good social,economic and environmental benefits, its widely used in practical engineering. According to the engineering durability requirements, it is necessary to study its anti-freeze durability. Combined with the need of an engineering in ningxia, the best proportion design was seeked out which possess a good anti-freeze property and the biggest economic benefit to the engineering.Meanwhile, the concrete anti-freeze performance evaluation method was seeked and dynamic elastic modulus damage prediction model was established using the hydrostatic pressure theory and damage theory. The main research method and the results are as follows:1.According to Dunstan model designed the mix proportion while the air content set in between 3.5% ~ 5.5%.The loss value was analyzed after the natural freeze-thaw cycle of 150 times, and finded magnifying fly ash admixture and water-binder ratio have an adverse effect to the concrete frost resistance.2. The average bubble spacing coefficient is important parameter which influences frost resistance though analyzing the influential factors of frost resistance. Its should be regard as a dynamic value in freeze-thaw cycle process, and its can be solved using theoretical and assumptions in whichever stage.3.When the average bubble spacing coefficient in concrete below 200μm, the high volume fly ash concrete have good anti-freeze capability after some analysis about the assumptions and theoretical calculation value was got. The proportion design whose water-binder ratio is 0.45 and fly ash admixture is 60% is the best proportion design that project needs.4. The limit average bubbles spacing coefficient first increased and then decreased with the growing of fly ash, after analyzing the influence of fly ash to the limit average bubbles spacing coefficient in the same water-binder ratio level. The fly ash volume at apogee in change curve with the increasing of water-binder ratio and decreases. So each water-binder ratio level, there exists an optimal fly ash admixture value at each water-binder ratio level. When water-binder ratio is 0.45, the optimal fly ash admixture with the best frost resistance is 60 %.5. The freeze-thaw damage prediction model was established based on Loland damage model. Assumed the dynamic change curve of the maximum static water pressure value,and combined with experimental validation, the calculation value of damage prediction model coincide with experimental result was found.6. Assuming the maximum static water pressure value is linearly varying in natural freeze-thaw cycle,and combining with graphics analysis,the maximum static water pressure growth acceleration value is increased with the fly ash admixture in the way of quadratic function,When the fly ash content at 40% ~ 60% ,the maximum static water pressure value is relatively grown slowly,and when the fly ash content more than 60%, speed obvious change. So think 0.45 in water-binder ratio level within, more than 60% of the fly ash content is not easy. So the fly ash content should not exceed 60% when the water-binder ratio set in 0.45.