基于流变特性的混凝土组成设计方法

发布时间：2019-03-07 19:03

【摘要】：新拌混凝土的工作性能关系着混凝土的浇筑、施工、密实等过程,对混凝土的力学性能和耐久性能有重要的影响。传统混凝土工作性的评价方法主要通过坍落度、稠度、扩展度、扩展时间等单一参数进行表征,偏重于经验性和主观性,且缺乏科学精度;另外,在满足经济性和混凝土质量时原材料组成的优化设计也缺乏相应的理论指导。本文在不同富余浆体厚度、骨料堆积状态和三元胶凝组成时采用屈服应力、塑性粘度等流变参数评价了混凝土的工作性能,根据混凝土组成与流变参数之间的关系对各配比参数进行了优化,并提出了基于流变特性的混凝土组成设计方法。保持水灰比和砂率不变,建立了富余浆体厚度与坍落度、流变参数之间的关系。结果发现,改变富余浆体厚度主要是通过影响屈服应力来影响混凝土的工作性能。流变参数与富余浆体厚度之间存在着良好的y=axb函数关系。随着富余浆体厚度的增加,新拌混凝土的屈服应力和塑性粘度明显降低,坍落度明显升高;当富余浆体厚度相对较高时,屈服应力和塑性粘度趋于稳定。在固定水灰比和骨料参数下,通过建立不同富余浆体厚度时工作性能与流变参数间的关系,能够确定混凝土中适宜的胶凝材料用量。保持水灰比和水泥用量不变,测试了不同砂率时混凝土的流变参数,结果发现随着砂率的升高,屈服应力和塑性粘度先逐渐降低后升高,坍落度逐渐增大而后基本保持不变。根据砂率与流变参数的关系,能够确定出最佳砂率。将粗骨料分为5-10 mm、10-15 mm和15-20 mm三个粒径段,根据单纯型重心设计法设计不同粗骨料组成的混凝土。综合考虑混合粗骨料的堆积密度、比表面积和新拌混凝土的坍落度、屈服应力、塑性粘度,能够确定粗骨料的最佳比例组成。在固定水胶比、胶凝材料总量和砂率时,取水泥质量分数为0.4~1.0、粉煤灰和矿粉质量分数均为0~0.6,根据单纯型重心设计法建立了三元胶凝组成与混凝土流变参数、力学强度的函数关系,并对三元胶凝材料体系进行了优化。基于本研究所用原材料,在满足力学强度条件下,当新拌混凝土具有适宜的流动性能和流变性能时,粉煤灰最佳掺量为15~20%,矿粉最佳掺量为15~25%。根据上述研究成果,提出了基于流变特性的混凝土组成设计方法,能够合理的控制混凝土中的砂石比例,综合考虑多种性能因素确定适宜的胶凝材料用量和胶凝体系组成。不仅能够控制新拌混凝土的流动性、稳定性、匀质性等性能,还能够降低胶凝材料总量和水泥用量,能够有效地提高混凝土的质量。
[Abstract]:The working performance of fresh concrete is related to the pouring, construction and compacting process of concrete, and has an important influence on the mechanical properties and durability of concrete. The traditional evaluation methods of concrete workability are mainly characterized by single parameters such as slump, consistency, expansion time and so on, which emphasize on experience and subjectivity, and lack of scientific precision. In addition, the optimization design of raw material composition is also lack of corresponding theoretical guidance when the economy and quality of concrete are satisfied. In this paper, the rheological parameters such as yield stress, plastic viscosity and so on are used to evaluate the performance of concrete in different thickness of residual slurry, aggregate accumulation state and three-dimensional cementitious composition. According to the relationship between concrete composition and rheological parameters, the composition parameters of concrete are optimized, and the design method of concrete composition based on rheological properties is put forward. The relationship between the thickness of residual slurry, slump and rheological parameters is established by keeping the ratio of water to cement and sand ratio unchanged. It is found that the effect of yield stress on the performance of concrete is mainly due to the change of residual slurry thickness. There is a good y=axb function relationship between rheological parameters and residual slurry thickness. With the increase of residual paste thickness, the yield stress and plastic viscosity of fresh concrete decrease obviously, and the slump increases obviously, and when the thickness of surplus paste is relatively high, the yield stress and plastic viscosity tend to be stable. Under the condition of fixed water-cement ratio and aggregate parameters, the relationship between working performance and rheological parameters of different residual slurry thickness can be established, and the appropriate amount of cementitious material in concrete can be determined. The rheological parameters of concrete with different sand rates were tested with the same ratio of water to cement and cement content. The results showed that with the increase of sand ratio, the yield stress and plastic viscosity decreased at first and then increased, and the slump increased gradually and then remained unchanged. According to the relationship between sand rate and rheological parameters, the optimum sand rate can be determined. The coarse aggregate is divided into three segments: 5-10 mm,10-15 mm and 15-20 mm. The concrete with different coarse aggregate composition is designed according to the simple design method of gravity center. Considering the bulk density, specific surface area and slump of fresh concrete, yield stress and plastic viscosity, the optimum proportion of coarse aggregate can be determined by considering the bulk density of mixed coarse aggregate, specific surface area, slump of fresh concrete, yield stress and plastic viscosity. When the ratio of water to cement is fixed, the total amount of cementitious material and sand ratio are fixed, the mass fraction of cement is 0.4 脳 1.0, the mass fraction of fly ash and mineral powder is 0. 6%. According to the simple gravity center design method, the three-dimensional cementitious composition and the rheological parameters of concrete are established. The function relation of mechanical strength and the optimization of ternary cementitious material system were carried out. Based on the raw materials used in the study, under the condition of satisfying mechanical strength, when fresh concrete has suitable flow and rheological properties, the optimum content of fly ash and mineral powder is 15? 20% and 15? 25% respectively. Based on the above research results, the design method of concrete composition based on rheological properties is put forward, which can reasonably control the proportion of sand and stone in concrete, and determine the appropriate amount of cementitious material and the composition of cementitious system comprehensively considering various performance factors. It can not only control the fluidity, stability, homogeneity and other properties of fresh concrete, but also reduce the total amount of cementitious material and cement content, and can effectively improve the quality of concrete.
【学位授予单位】：中国建筑材料科学研究总院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528

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