混凝土减缩剂的作用机理与作用条件

发布时间：2018-02-04 13:54

本文关键词： 干燥收缩减缩剂水泥石相对湿度孔结构　出处：《重庆大学》2015年硕士论文　论文类型：学位论文

【摘要】：本论文通过碟片法测试了水泥石在梯度湿度干燥条件下的干燥收缩与质量损失,分析了减缩剂的不同使用方法(内掺,外刷和浸泡)、掺量、品种等对水泥石干缩的影响。通过分析减缩剂对水溶液和Ca(OH)2溶液表面张力、水分蒸发速率、水泥石孔结构等的影响规律,揭示了减缩剂的湿度分段减缩机理。与此同时,对减缩剂在不同水灰比(0.3、0.4、0.5),相对湿度(100%RH~12%RH),龄期(7d、28d、56d)等条件下的减缩效果及其与高效减水剂的相容性进行评价,确定了减缩剂的有效作用条件。另外,还试验测定了减缩剂对水泥石的抗压强度的影响。研究结果表明,对于早龄期(7d)的水泥石,减缩剂内掺可以显著减小水泥石的干燥收缩,SBT-SRA对0.3水灰比水泥石的减缩率为47.15%,减缩剂外刷和浸泡的方法对水泥石的减缩效果不明显,最大的减缩率分别只有6.64%和8.27%;对于养护后期(56d)的水泥石来说,减缩剂的内掺和浸泡水泥石的方法均起到显著的减缩作用,最大的减缩率分别为45.53%和30.88%。减缩剂外刷的减缩效果较差,减缩率只有15.72%。减缩剂内掺会降低水泥石的抗压强度,且掺量越大,降低作用越明显。当SBT-SRA的掺量为0.2%时,0.4水灰比的水泥石28d抗压强度只有基准的84.5%;减缩剂以外刷或浸泡的方法使用时,对水泥石的强度有不同程度的提高,相同条件下水泥石28d抗压强度都比基准组略高。在减缩机理方面,减缩剂内掺大幅度降低孔溶液的表面张力是其减缩的最主要原因,同时减缩剂也通过降低孔溶液的蒸发速率(低湿度区)来达到减缩的目的;使用减缩剂细化了水泥石的孔结构,使有害孔的数量减少,从而减小水泥石的干燥收缩。减缩剂内掺时增大水泥石的总孔隙率,外刷和浸泡时则减小水泥石的总孔隙率,三种使用方法均对水泥石孔结构起到细化作用。不同湿度条件下,减缩剂的减缩机理不同:在高湿度区(85%RH,75%RH和55%RH),减缩剂主要以减小孔溶液表面张力,从而减小水分蒸发引起的收缩应力来达到减缩目的;在低湿度区(25%RH和12%RH),减缩剂则主要以减少水泥石中孔溶液蒸发速率的机制来减小由于毛细水蒸发引起的总的收缩应力,从而起到减小干缩的作用。当GRA-SRA与聚羧酸高效减水剂复掺时,在100%RH~85%RH湿度段,与基准组相比28d水泥石出现了一定程度的膨胀,在55%RH~12%RH湿度段,GRA-SRA与聚羧酸高效减水剂复掺起到了一定的减缩效果,但不如GRA-SRA单掺时的减缩效果好,可见聚羧酸高效减水剂对GRA-SRA的减缩具有一定的负面作用。通过对几乎涵盖全湿度范围的减缩剂的机理研究及其在不同作用条件下的减缩效果的评价,本论文对减缩剂产品的研发及其在实际工程中的推广应用都有较高的理论指导意义。
[Abstract]:In this paper, the drying shrinkage and mass loss of cement stone under the condition of gradient humidity drying were measured by disc method, and the different use methods of shrinkage reducer (mixing, brushing and soaking) were analyzed. By analyzing the influence of shrinkage reducer on surface tension, evaporation rate and pore structure of water solution and Ca(OH)2 solution. At the same time, at the same time, the shrinkage reducer with different water / cement ratio of 0.3U 0.4U 0.5, the relative humidity of 100RH ~ (12) RH ~ (12) RH ~ (2 +) is used for 7 days. The effect of reducing shrinkage and its compatibility with superplasticizer were evaluated under the condition of 28d ~ 56d, and the effective action conditions of the reducer were determined. The effect of shrinkage reducer on the compressive strength of cement stone is also tested. The results show that the shrinkage reducing agent can significantly reduce the drying shrinkage of cement stone when it is added into the cement stone at the early age of 7 days. The shrinkage rate of SBT-SRA is 47.15 for cement stone with water-cement ratio of 0.3.The shrinkage reduction effect of shrinkage reducer brush and soaking method is not obvious. The maximum reduction rates were only 6.64% and 8.27 respectively. For the cement stone in the late curing period (56 d), the shrinkage reducing agent and the method of soaking the cement stone play a significant role in reducing the shrinkage. The maximum shrinkage rate is 45.53% and 30.88 respectively. The shrinkage reduction effect of the external brush is poor, and the shrinkage reduction rate is only 15.72. The compressive strength of cement stone can be reduced by adding shrinkage reducing agent. When the content of SBT-SRA is 0.2, the compressive strength of cement stone with 0.4 water-cement ratio is only 84.5% of the benchmark. The strength of cement stone is improved in different degree when the method of brush or immersion outside of reducing agent is used. Under the same condition, the compressive strength of cement stone for 28 days is slightly higher than that of the reference group. The main reason of reducing shrinkage is to reduce the surface tension of pore solution by adding a large amount of shrinkage reducer. At the same time, the shrinkage reduction agent can achieve the purpose of reducing shrinkage by reducing the evaporation rate (low humidity region) of pore solution. The shrinkage reducer is used to refine the pore structure of cement stone, so that the number of harmful pores is reduced and the drying shrinkage of cement stone is reduced. The total porosity of cement stone is increased when the shrinkage reducer is added. The total porosity of cement stone is reduced by brushing and soaking, and the three methods are used to refine the pore structure of cement stone. Under different humidity conditions, the shrinkage reduction mechanism of reducing agent is different: 85 RH in high humidity region. 75 RH and 55 RH, the shrinkage reducing agent is mainly to reduce the surface tension of the pore solution, thereby reducing the shrinkage stress caused by water evaporation to achieve the purpose of reducing shrinkage. In the low humidity region, the shrinkage reducing agent mainly reduces the total shrinkage stress caused by capillary water evaporation by reducing the evaporation rate of pore solution in cement stone. When GRA-SRA is co-mixed with polycarboxylic acid superplasticizer, it is in the humidity section of RHn85RH. Compared with the reference group, the cement stone expanded to a certain extent at 28 days, and the addition of GRA-SRA and polycarboxylic acid superplasticizer in the humidity section of 55RH and RH played a certain effect of reducing shrinkage. But it is not as good as the reduction effect of GRA-SRA alone. It can be seen that polycarboxylic acid superplasticizer has a certain negative effect on GRA-SRA shrinkage. Through the research on the mechanism of shrinkage reducer covering almost the whole humidity range and the evaluation of shrinkage effect under different action conditions, we can see that polycarboxylic acid superplasticizer has some negative effect on the shrinkage reduction of GRA-SRA. . This paper is of great theoretical significance for the research and development of shrinkage reducer and its application in practical engineering.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU528.042

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