高寒地区大掺量粉煤灰混凝土的抗冻性能研究

发布时间：2018-10-08 17:34

【摘要】：粉煤灰作为掺合料加到混凝土中,可减少工业废渣,同时能起到降低混凝土拌合物水化热、减少早期开裂、提高混凝土后期强度等作用,但关于粉煤灰混凝土的抗冻性能优劣一直存在着许多不同的观点。高寒地区昼夜温差大,冬季长时间处于负温,大体积混凝土工程早期易开裂,而工程有时又必须在冬季施工。本文针对高寒地区大掺量粉煤灰混凝土的抗冻性能进行研究。首先,本文针对C30混凝土配合比设计参数进行四因素三水平L9(34)正交试验设计,通过分析混凝土拌合物的施工和易性和抗压强度的试验结果来优选配合比设计参数,获得高寒地区C30粉煤灰混凝土的较佳砂率为38%、减水剂掺量1.3%、单位用水量165 kg/m3、水胶比为0.41。然后再对不同水胶比、不同粉煤灰掺量、不同引气剂掺量的粉煤灰混凝土抗压强度进行分析,得出如下结论:粉煤灰掺量越大,早期强度降幅越大,而其28d~90d强度增幅越大;养护龄期大于28d,粉煤灰混凝土的含气量每增加1%,其抗压强度约降低4%~6%。其次,针对高寒地区混凝土长期经受冻融循环作用而不断发生破坏的问题,从分析冻融破坏机理入手,通过快速冻融试验,研究了粉煤灰掺量、引气剂掺量对抗冻性能的影响规律,然后通过亚微观的气泡特征参数分析不同粉煤灰掺量与不同引气剂掺量的粉煤灰混凝土的抗冻性能,得出如下结论:粉煤灰混凝土28d的抗冻等级明显低于未掺粉煤灰的基准混凝土,随着龄期的增长,粉煤灰混凝土的抗冻性能显著增强;粉煤灰掺量为35%的60d龄期混凝土的气泡间距系数最小,其耐久性系数最大,抗冻性能最佳;加入引气剂能有效改善粉煤灰混凝土的抗冻性能,当含气量在5.2%左右时,混凝土的气泡间距系数最小,抗冻性能最佳。最后,通过电通量试验研究不同粉煤灰掺量、不同引气剂掺量的粉煤灰混凝土的抗氯离子渗透性能,研究结果表明:延长混凝土的养护龄期,有利于提高其抗氯离子渗透性能;随着粉煤灰掺量的增加,其抗氯离子渗透性能先增加再降低,在掺量为45%左右时达到最佳;随着含气量增加,粉煤灰混凝土的抗氯离子渗透性能先增加再降低。在含气量为5.2%左右时,其抗氯离子渗透性能最佳。
[Abstract]:The addition of fly ash as admixture to concrete can reduce industrial waste slag, reduce hydration heat of concrete mixture, reduce early cracking, and improve the later strength of concrete, etc. However, there are many different views on the frost resistance of fly ash concrete. The temperature difference between day and night in the high cold area is large and the temperature is negative for a long time in winter. Mass concrete works are easy to crack in the early stage, and sometimes the construction must be carried out in winter. In this paper, the frost resistance of high-volume fly ash concrete in high cold area is studied. First of all, according to the design parameters of C30 concrete mix ratio, four factors and three levels L9 (34) orthogonal experimental design are carried out. By analyzing the construction of concrete mixture and the test results of ease and compressive strength, the design parameters of mix ratio are optimized. The best sand ratio of C30 fly ash concrete in high cold area is 38, the water reducing agent content is 1.3 and the water-binder ratio of 165 kg/m3, per unit water consumption is 0.41. Then the compressive strength of fly ash concrete with different water binder ratio, different fly ash content and different air entraining agent is analyzed. The conclusion is as follows: the greater the fly ash content, the greater the early strength decrease, and the greater the 28d~90d strength increase; When the curing age is more than 28 days, the compressive strength of fly ash concrete decreases by about 4% for every increase in the air content of fly ash concrete. Secondly, in view of the problem that the concrete in the alpine region is destroyed by freeze-thaw cycle for a long time, starting with the analysis of the mechanism of freeze-thaw failure, through the rapid freeze-thaw test, the content of fly ash is studied. The effect of air entraining agent content on freezing resistance is studied. Then the frost resistance of fly ash concrete with different content of fly ash and different air entraining agent is analyzed by sub-micro bubble characteristic parameters. The conclusions are as follows: the frost resistance of fly ash concrete for 28 days is obviously lower than that of standard concrete without fly ash, and the frost resistance of fly ash concrete increases with the increase of age. The air-entraining agent can effectively improve the frost resistance of fly ash concrete when the air content is about 5.2%, and the air-entraining agent can improve the frost resistance of fly ash concrete with 35% air entrainer, and the coefficient of bubble spacing is the smallest, the durability coefficient is the largest, and the frost resistance is the best when the air content is about 5.2%. The bubble spacing coefficient of concrete is the smallest and the frost resistance is the best. Finally, the chloride ion permeability of fly ash concrete with different content of fly ash and different air entraining agent is studied by electric flux test. The results show that prolonging the curing age of concrete is beneficial to the improvement of chloride ion permeability of concrete. With the increase of the content of fly ash, the penetration resistance of fly ash first increases and then decreases, and reaches the best when the content of fly ash is about 45%, and with the increase of air content, the permeability of fly ash concrete increases first and then decreases. When the gas content is about 5.2%, the resistance to chloride ion penetration is the best.
【学位授予单位】：重庆交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528

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