【作者】 章瑞；

【导师】 水中和；

【作者基本信息】 武汉理工大学 ， 材料学， 2010， 硕士

【摘要】 水泥基材料是一种非均质的多相复合材料,其中各种组成材料的热膨胀性能存在差异性。环境温度发生变化时,材料内各组分间会产生不均匀热膨胀,并产生界面热应力,导致界面出现微裂纹,严重时甚至引起结构失效。本文着重研究水泥基材料组分热膨胀性能的差异及其热相容性,观察水泥基材料在热循环作用下的热疲劳效应,并在深入研究了硬化水泥石热膨胀性能及其机理的基础上,调节材料各组分热膨胀的协调性。试验结果表明,在20～85℃的温度范围内,硬化水泥浆的线膨胀系数是粗集料的二倍多,两者的热膨胀性能存在明显的差异。微观上,多次热循环后,热裂纹出现于界面过渡区,并且沿集料边缘方向扩展,微裂纹宽度随热循环次数增加而增大。宏观上,水泥基材料的抗压强度随热循环次数的增加而逐渐下降。硬化水泥石的热膨胀率和热膨胀系数随水灰比的增大而减小。粉煤灰、矿粉、硅灰和偏高岭土等矿物掺和料的加入,均可不同程度的降低硬化水泥石的热膨胀率和热膨胀系数,其降低程度随矿物掺和料掺量的增加而增大。掺加碳纤维或聚丙烯纤维,对水泥石热膨胀的限制作用大致相当。聚合物乳液对硬化水泥石的热膨胀性能的限制作用,因其种类和性质的不同而改变。硬化水泥石的热膨胀系数随着水灰比的增大而不断降低,主要是由于水灰比的增大导致水泥石内孔隙增多,较多的孔隙为材料的膨胀提供了较大的缓冲空间。矿物掺和料的掺入可降低水泥浆体Ca(OH)2(CH)含量并改变其孔隙率,从而有效的限制硬化水泥石的热膨胀性能,其中CH含量对水泥石热膨胀性能的影响大于孔隙率的影响。纤维对硬化水泥石热膨胀性能的限制作用,主要是由于纤维具有较低的热膨胀系数,并且纤维与水泥浆体黏结成一体相互约束。聚合物的种类、掺量都会不同程度的降低水泥石的热膨胀率和热膨胀系数,这是由于聚合物在C-S-H凝胶和未水化水泥颗粒表面形成了一层密实的聚合物薄膜,并且增强材料韧性,从而降低水泥石自身的热膨胀系数。更多还原

【Abstract】 A cement-based composites may be regarded as a highly heterogeneous material system with multiple components that have different thermal expansion properties. The thermal expansion divergence of components are generated in the cement-based composites.When the temperature changes, the thermal induced deterioration into the cement-based materials will happen due to this effect, such as the thermal induced stress and micro-or macro-scale cracking, even the structure damage. In this paper, the thermal expansion divergence of components was measured, and both thermal expansion differences were explored. The microstructure of the cement-based composites was observed after some thermal cycles.With in depth research in the thermal expansion properties and mechanism of the hardened cement paste, thermal expansion incompatibility of components was adjusted.It comes to conclusion that, thermal expansion coefficient of hardened cement paste is over two times than that of aggregate, which proved that the thermal expansion divergence of components happens subjected to the temperature change. After thermal cycles, the thermal induced microcrack appeared and propagated along interfacial transition zone between hardened cement paste and aggregate, and the width of microcrack was enlarged with the increase of thermal cycles in microscopic scales. The compressive strength of cement-based materials decreases with the increase of thermal cycles in macroscopic view.The thermal dilation rates (TDR) and coefficient of thermal expansion (CTE) of hardened cement pastes (HCP) decreases with the increase of the water-cement ratio. Replacing Portland cement with mineral admixtures (fly ash, ground granulated blastfurnace slag, silica fume and metakaolin) were found to lower the TDR and CTE of HCP, the extent of this lowering effect increases with the increasing replacement proportions of mineral admixtures in the pastes.Carbon fiber and polypropylene fiber were also found to lower the TDR and CTE of HCP, the lowering effect were similar. The polymer latex could also limit thermal expansion properties of HCP, the restriction effect differ from the types and properties of the polymer latex.The CTE of HCP decreases with the increase of the water-cement ratio for the higher water-cement ratio lead to the more pore in HCP, which supply buffer space for the dilation of materials. The restriction of the mineral admixtures to the thermal expansion properties of HCP are mainly due to the change of the porosity and the amount of portlandite (CH) in the pastes, among which, CH content is more important than porosity as a factor affecting the CTE of the cement paste. It is revealed that the fibers could lower the TDR and CTE of HCP because of the lower CTE of fibers, furthermore the fibers and cement paste are binding together. The types and amount of the polymer latex could lower the TDR and CTE in different extent, this is because the polymer film is formed by polymer latex on the surface of the C-S-H gel and unhydrated cement particles, so the CTE of HCP is lowered and the toughness of HCP is reinforced.更多还原