【作者】 丁士卫；

【导师】 钱春香；

【作者基本信息】 东南大学 ， 材料学， 2006， 硕士

【摘要】 随着混凝土技术的发展,大体积混凝土和超长结构混凝土时有出现。在大体积混凝土中,由于水化热和各种环境辐射热量引起混凝土内部温度升高,在降温过程中引起的热变形如果受到结构限制,会引起开裂等缺陷,影响结构性能。在大型桥梁、隧道等超长混凝土结构中,一些冬夏温差变化较大的地区,由于温度变化引起的结构热胀冷缩,有时会造成结构破坏。本文研究了水泥石线性热膨胀系数的测试方法,并针对本试验方法制定了相关的试验制度。通过该方法,系统研究了水泥石线性热膨胀系数的影响因素,包括温度、水灰比、龄期、湿含量、掺合料、配合比等。研究表明:水泥石的线性热膨胀系数随着温度升高而增大,满足线性关系;随着龄期的增长而增大,满足对数关系;随着水泥石水灰比的增大而减小,满足对数关系。矿物掺合料可以使水泥石的线性热膨胀系数减小,同时含有一定水分的水泥石的线性热膨胀系数比干燥的要大。水泥石由固相物质和孔隙组成,固相物质包括各种水化产物、未水化的水泥和其它掺和料颗粒,而孔隙中包含水和空气。所以水泥石是固—液—气三相多孔体。影响水泥石热变形性能的因素包括:水泥石固相物质的成分及含量、水泥石的孔隙率及孔结构、水的含量和温度等。其中固相物质的成分及含量主要由原材料配比和水化程度决定;而水化程度和孔结构又由原材料配比和龄期决定;水的含量由孔结构和环境湿度决定。水泥石热膨胀系数随孔隙率增大而减小,一般认为水泥石中的空气不影响水泥石的热膨胀系数大小。研究结果表明:各种因素对水泥石线性热膨胀系数的影响大小为:孔隙率>龄期>温度>湿含量。水泥石内部不同尺寸的孔隙中,大毛细孔对热膨胀系数的影响最大,且影响均比较显著,气孔有一定影响,而小毛细孔和凝胶孔则对水泥石线性热膨胀系数没什么影响。更多还原

【Abstract】 With the developing of concrete technology, bulk concrete and super-long structural concrete are always adopted in civil engineering. Internal stress occurs resulting from the different temperature distribution, which caused by hydration heat and the varying environmental temperature. Crack is inevitable when the internal stress exceeds the ultimate tensile strength of the materials, which affects the performance of concrete structure.In this paper, the test method of the linear thermal expansion coefficient (as LTEC) of hardened cement paste is studied. Influence factors of thermal deformation are investigated, including temperature, water cement ratio, age, moisture content, admixture and mix ratio. It was found that the LTEC increases with aging, temperature rising and water-cement ratio decreasing. The admixture can make the LTEC of cement paste smaller than pure cement paste. The moisture content in cement paste enlarges the LTEC.Cement paste is assumed to consist of the solid-a mixture of hydration products, anhydrated cement and admixtures-and the pores which are partially saturated by water and dry air. The factors affecting the thermal deformation of cement paste are as follows: the constituent in cement paste and its content determined by mix ratio and degree of hydration, the pore structure effected by mix ratio and age, the water content determined by pore structure and environmental humidity , the temperature. We can conclude that the LTEC decrease with porosity rising.It comes to the conclusion that these factors, according to the importance, may be ranked as porosity, age, temperature, moisture content. Big capillary has evident effect for the LTEC of cement paste, and air pore has some effect, too. But the pores which has smaller size is inessential.更多还原