【作者】 徐路军；

【导师】 杜应吉；

【作者基本信息】 西北农林科技大学 ， 结构工程， 2010， 硕士

【摘要】 粉煤灰混凝土已经在工程中得到了大量应用,它不仅可以实现对粉煤灰的有效利用,减少对环境的污染,还可以改善混凝土质量,降低水化热及混凝土的综合成本等,从而取得良好的社会效益、经济效益和环境效益。工程中对混凝土的耐久性提出了越来越高的要求,因此对大掺量粉煤灰混凝土(HVFC)深入进行耐久性试验研究是非常有必要的。结合宁夏某工程,本文对粉煤灰混凝土的抗冻性能做了系统研究,以寻找满足工程要求的大掺量粉煤灰混凝土中粉煤灰的最佳掺量,同时对不同龄期及不同粉煤灰掺量时混凝土的抗冻性能进行了对比研究,主要研究成果如下:(1)根据Dunstan模型设计等强度混凝土时,水胶比与粉煤灰掺量大体呈线性负相关关系。通过调整水胶比,可以得到粉煤灰最大掺量72%的C25混凝土。不同龄期及不同粉煤灰掺量的混凝土强度与水胶比均呈线性关系。水胶比相同时,不同龄期的混凝土强度与粉煤灰掺量呈二次曲线关系。(2)在掺加适量引气剂后,不同粉煤灰掺量的C25混凝土28d龄期时虽然基本满足抗冻要求但差异性较大,而在60d龄期时其抗冻性能均得到明显改善。在大掺量粉煤灰混凝土中,当含气量水平相同时,粉煤灰掺量对抗冻性能有着决定性的影响。在相同水胶比条件下,粉煤灰掺量在50%以上时,质量损失与粉煤灰掺量呈指数关系,动弹性模量变化与粉煤灰掺量呈现二次曲线关系。(3)在混凝土抗渗、极限拉伸等试验的基础上,利用蔡昊模型对混凝土的冻融损伤进行预测,建立了混凝土冻融损伤的理论模型。(4)根据混凝土的抗冻试验结果,拟合出混凝土的冻融次数与质量损失和动弹模变化的关系,最后得到不同粉煤灰掺量时混凝土的冻融破坏模型。利用王立久教授提出的冻融角及抗冻因子等概念,将试验得到的混凝土冻融曲线进行归一化分析,得到同一混凝土不同判别标准下具有不同抗冻因子ω等结论。(5)粉煤灰混凝土具有良好的冻融后自愈合性能,但是劈拉强度的恢复相对较差。粉煤灰掺量在50%以下时,混凝土28d龄期时受冻比60d龄期时受冻后的自愈合性能更好。而粉煤灰掺量超过65%时,由于28d龄期时未达到混凝土的受冻的临界强度,自愈合性能反而较差。最后,通过扫描电镜对混凝土进行微观形貌分析,给出了粉煤灰混凝土的自愈合现象的微观解释。更多还原

【Abstract】 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.更多还原