大掺量粉煤灰混凝土抗冻临界强度的研究

发布时间：2018-05-17 12:26

本文选题：粉煤灰 + 负温混凝土　；参考：《重庆交通大学》2017年硕士论文

【摘要】：随着工程行业的快速发展,大量水泥混凝土用于建筑结构工程。水泥生产给环境造成了巨大破坏,大掺量粉煤灰混凝土能在有效减少水泥用量的同时将火电厂产生的废渣—粉煤灰作为混凝土掺合料加以利用,降低对环境的污染,也节省工程造价,具有广阔的应用空间。近年来,由于工期等客观条件限制,越来越多的大体积混凝土构筑物需要在冬季施工,早期受冻对混凝土性能影响显著。因此,亟待对大掺量粉煤灰混凝土在负温下的性能进行研究,本文针对高寒地区用大掺量粉煤灰混凝土的力学性能与耐久性能进行了一系列研究,具有一定的价值。首先,本文针对大掺量粉煤灰混凝土力学性能,经过初步探究,采用3种水胶比、5种粉煤灰掺量的15种不同配方的混凝土进行试验,测试其不同龄期的抗压强度、劈裂抗拉强度、抗折强度,并对其力学性能进行分析。结果表明:影响大掺量粉煤灰混凝土强度的主要因素是水胶比,同时粉煤灰掺量对抗压强度的影响比其他力学性能更敏感;随着粉煤灰掺量的增大,新拌混凝土早期力学性能显著降低,但后期增长快速,粉煤灰掺量小于35%时,其90d力学性能不低于普通混凝土。其次,本文通过采用抗压强度保证率的方式确定负温混凝土抗冻临界强度。采用水胶比0.4,粉煤灰掺量25%、35%、45%、55%的四种混凝土,标准养护混凝土分别测试其18h~48h、60d的抗压强度;负温混凝土早期成型后经受不同的受冻制度,再转标养,以测试其60d抗压强度能否达到标准养护混凝土对应龄期抗压强度的95%为依据,并对预养护龄期与最终抗压强度进行线性拟合,从而求出负温混凝土各自的抗冻临界强度,进而分析粉煤灰掺量与受冻制度对混凝土抗冻临界强度的影响。结果表明:粉煤灰掺量增大,抗冻临界强度值减小,达到抗冻临界强度所必要的时间随之增加;在冻害对其损害程度方面:恒负温一次气冻多次水冻水融一次水冻。最后,本文研究混凝土达到其抗冻临界强度后经受不同的受冻制度后对其耐久性的影响。采用快速冻融法和抗渗透性试验,测试负温组混凝土的冻融循环次数与电通量能否达到标准养护组的95%。试验结果表明:以抗压强度保证率确定的抗冻临界强度并不能使其抗冻性能达到未受冻混凝土的95%,对耐久性要求高的结构物,应适当延长其受冻前的预养护时间,冬季施工大体积构筑物所用混凝土推荐粉煤灰掺量为35%。同时,本文还用气泡间距系数分析仪对大掺量粉煤灰混凝土气泡结构进行微观分析,发现其气泡数量随粉煤灰掺量的增加而增大,建议大掺量粉煤灰混凝土采用气泡参数评价时其龄期应在60d后。
[Abstract]:With the rapid development of engineering industry, a large number of cement concrete used in structural engineering. Cement production has caused great damage to the environment. Large amount of fly ash concrete can effectively reduce the amount of cement and use the waste slag-fly ash produced by thermal power plant as concrete admixture to reduce the pollution to the environment. Also saves the project cost, has the broad application space. In recent years, due to the limitation of time limit and other objective conditions, more and more mass concrete structures need to be constructed in winter. Therefore, it is urgent to study the performance of high-volume fly ash concrete under negative temperature. This paper has a series of research on mechanical properties and durability of high-volume fly ash concrete in high and cold regions, which has certain value. Firstly, according to the mechanical properties of fly ash concrete with large amount of fly ash, the concrete with 15 different formulations of 3 kinds of water-binder ratio and 5 kinds of fly ash are tested, and the compressive strength of concrete of different ages is tested. The splitting tensile strength and flexural strength are analyzed. The results show that the main factor affecting the strength of concrete with large amount of fly ash is water binder ratio, and the influence of fly ash content on compressive strength is more sensitive than that of other mechanical properties, and with the increase of fly ash content, The mechanical properties of fresh concrete decreased significantly in the early stage, but increased rapidly in the later stage. When the content of fly ash was less than 35%, the mechanical property of fresh concrete was not lower than that of ordinary concrete for 90 days. Secondly, the freezing critical strength of negative temperature concrete is determined by means of compressive strength guarantee rate. Four kinds of concrete with water / binder ratio of 0.4 and fly ash of 25% are used. The standard curing concrete is tested respectively for its compressive strength of 18 hours or 48 hours or 60 days, and the negative temperature concrete is subjected to different freezing systems after early forming, and then transferred to standard. On the basis of testing whether the compressive strength of 60 days can reach 95% of the corresponding age compressive strength of the standard curing concrete, and the linear fitting between the pre-curing age and the final compressive strength, the freezing critical strength of the negative temperature concrete is obtained. Furthermore, the influence of fly ash content and freezing system on the critical strength of concrete is analyzed. The results show that with the increase of fly ash content, the critical strength of freezing resistance decreases, and the necessary time to reach the critical strength of frost resistance increases, and the degree of damage caused by freezing injury is as follows: constant negative temperature, air freezing, water freezing and water thawing. Finally, the influence of different freezing systems on the durability of concrete is studied. Rapid freeze-thaw method and permeability test were used to test whether the freeze-thaw cycle times and electric flux of negative temperature group concrete could reach 95% of the standard curing group. The test results show that the critical strength determined by the compressive strength guarantee rate can not make the freezing resistance of unfrozen concrete up to 95% of that of unfrozen concrete. The pre-curing time before freezing should be appropriately prolonged for structures with high durability requirements. The recommended amount of fly ash for the construction of large-volume structures in winter is 35. At the same time, the bubble structure of concrete with large amount of fly ash is analyzed by using the bubble spacing coefficient analyzer. It is found that the number of bubbles increases with the increase of the amount of fly ash. It is suggested that the age of large fly ash concrete should be 60 days after the bubble parameter evaluation.
【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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