【作者】 董淑慧；

【导师】 张宝生； 葛勇；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2010， 博士

【摘要】 混凝土性能主要取决于其组成、结构以及在环境影响下结构的变化。在组成一定时,混凝土的结构及其变化,主要受外部环境因素和内部水泥水化程度的影响,而这些均与混凝土内部相对湿度的变化密切相关。混凝土内部相对湿度变化,主要受水分扩散和水泥水化的自干燥作用影响,与内部水源和外部养护条件息息相关。陶粒具有吸返水特性,对混凝土内部相对湿度变化和界面区结构具有重要影响,因此,把具有低、中、高吸水率和不同吸返水速率的三种典型陶粒所配制的混凝土作为主要研究对象,对不同养护制度下混凝土内部相对湿度随龄期发展变化规律,以及湿度梯度对水泥石水化进程的影响,进而对混凝土微观结构和收缩变形等宏观性能的影响规律及其机理,进行了较深入系统的研究,建立混凝土收缩值与相对湿度之间的关系,为揭示混凝土收缩、开裂的实质提供理论基础和试验依据。对混凝土内部相对湿度测试方法的研究结果表明,与当前主要采用的预埋测试法长期固定测量相比,采用温湿度探头进行适时测量得到的试验结果更为精确可信。对一维干燥条件下,不同原材料组成的混凝土内部相对湿度梯度分布进行了研究,结果表明:暴露于干燥环境之前的湿养护龄期越长,混凝土内部相对湿度下降速度越缓慢,在28d龄期时,完全湿养护的普通混凝土试件较湿养护14d、7d转入一维干燥条件下的试件,由干燥面表层向中心区的相对湿度高出0.6%~5.4%,内部相对湿度保持在85%以上的位置也由外到内发生改变,陶粒混凝土也有类似的规律。在同一龄期,采用预湿陶粒、陶砂配制的混凝土内部各部位的相对湿度值高于采用普通骨料配制的混凝土,且陶粒的含水率越大、陶砂取代率越高,则混凝土内部相对湿度越高,且降低越缓慢。采用中、高含水率陶粒配制的混凝土,相对湿度≥80%的龄期比普通骨料混凝土延长1倍以上;高含水率的QF陶粒混凝土,在360d龄期时,中心部位的相对湿度仍高于80%,表层相对湿度大于80%的龄期可达到60d~90d,而普通混凝土和YC陶粒混凝土仅有24d~48d;56d以前,矿物掺合料的掺量越高,混凝土内部各部位相对湿度降低速度越缓慢,高于未掺加掺合料的混凝土,而56d以后则相反,在360d龄期时,掺加15%粉煤灰和掺加20%矿粉混凝土内部相对湿度最高;在28d以前,0.45水灰比的混凝土内部各部位相对湿度均高于0.3水灰比混凝土,而28d以后,0.45水灰比的混凝土内部相对湿度随龄期降低幅度较快,逐渐接近、甚至低于0.3水灰比混凝土。对不同吸水率、不同预饱水程度的陶粒混凝土界面区水泥石微观结构的研究结果表明:陶粒对低水灰比混凝土界面区水泥石结构的影响程度远高于高水灰比混凝土;骨料含水率对界面区水泥石微观结构具有显著影响,普通骨料与低吸水率的YC陶粒混凝土中,界面区水泥石孔隙率和大孔含量均高于水泥石基体,而中、高吸水率陶粒混凝土则相反,界面区水泥石钙硅比高于基体,孔结构整体上呈细化趋势,且陶粒预湿含水率越大、吸返水能力越强、表面越粗糙,界面区水泥石结构越致密,QF陶粒混凝土界面区水泥石平均孔径尺寸较普通骨料混凝土降低20.6%,50nm以下的孔含量高达近80%。距界面0~10μm范围内,经1h预湿的陶粒BY和QF界面区水泥石显微硬度较基体水泥石分别高出43%和56%,较普通骨料界面水泥石分别提高79.6%和96.3%,随饱水程度的提高,显微硬度值降低,绝干陶粒BY界面区水泥石显微硬度值最高,距界面20μm以上到基体范围内则与之相反,界面增强层厚度约为40μm~60μm。同时,从界面至陶粒内部10μm范围内产生了一个明显的内增强层。在一维干燥条件下,随着距干燥表面距离的增加,即随混凝土内部相对湿度增大,水泥石的水化程度提高,界面区和基体水泥石的显微硬度均逐渐增加,距干燥表面5cm以内,显微硬度增加幅度较明显,距干燥表面距离超过10cm时,显微硬度增长趋于稳定。陶粒的预饱水程度与释水能力对混凝土内部相对湿度和收缩变形性能影响显著。随陶粒预湿含水率的提高,在干燥和自干燥条件下,混凝土内部相对湿度随龄期降低速度均减慢,早期自收缩和长期干燥收缩均减小,限制收缩应力达到最大值的时间延长,自收缩、干燥收缩与相应的相对湿度降低值之间具有非常显著的相关性;低吸水率的YC陶粒混凝土,180d龄期时的总收缩较普通骨料混凝土高约3%~8%,而高吸水率、高饱水程度的陶粒混凝土,总收缩较普通骨料混凝土减小2%~15%;BY100陶粒混凝土的自收缩、干燥收缩和总收缩均低于普通混凝土,自养护减缩效率可达47.7%;陶砂对混凝土自养护的作用效率更高。自养护材料的减缩效果可用自养护材料颗粒水分的有效作用距离、自养护材料颗粒的表面间距来表征。当陶砂掺量为50%时,其邻近颗粒表面间距为417μm,颗粒所含水分的有效作用距离达到临界距离256μm,混凝土自收缩可减少98.2%。自养护材料引入的水分存在着利用率,在计算为消除混凝土自收缩所需的自养护材料质量时,应考虑自养护材料所含水分的利用率,本研究所用陶砂的水分的利用率为63.7%。更多还原

【Abstract】 The properties of concrete depend upon composition of it and internal structure and changes of structure caused by environmental influence. When the composition of concrete is determined, internal structure and changes of it mainly affected by the outer environmental influence and internal hydration of cement, and the latter have close relations with changes of relative humidity inside concrete.Changes of relative humidity inside concrete mostly affected by internal water diffusion and self-desiccation caused by cement hydration, and are closely relative to internal water and outer curing conditions. Ceramsite has a characteristic of water absorbing and desorption, thus taking three types of ceramsite which has different water absorption and desorption rate as research object, systematic study was carried out on the change law of internal relative humidity with different ages and effect of humidity gradient on the progress of cement hydration and then on microstructure and macro-performance such as shrinkage deformation. And also relationship between relative humidity and shrinkage value of concrete which bring some theoretic basis and experimental foundation for unraveling the nature of shrinkage and cracking was set up.Investigation between different measurement methods for internal relative humidity of concrete shows that experimental results obtained by measuring whenever necessary using thermo hygrometer is more reliable than those obtained by currently used method which is pre-embedded method.Internal relative humidity gradient of concrete with different composition and under condition of one-way drying was studied and result shows that the longer moist curing lasts, the slower the internal relative humidity decreases. Comparing concrete under moist curing conditions for 28days with those under moist curing conditions for 14days, 7days, and the former has a bigger internal relative humidity that the latter at the same position in concrete and the difference comes up to 0.6%~5.4%. And also similar law can be applied to ceramsite concrete. In the same age the internal relative humidity of concrete with pre-wetting ceramsite is higher than that of normal concrete. The bigger the moisture content and replacement rate is the bigger the internal relative humidity of concrete is and the slower it decreases.Time during which the relative humidity is greater or equal to 80% for concrete with ceramsite containing high or medium amount of water is more than one times the length of that for normal concrete. At the age of 360 days relative humidity of centre part is still greater than 80% for QF ceramsite concrete and time during which the relative humidity is greater or equal to 80% can reach 60~90days, but time for normal concrete or YC ceramsite concrete is only 24~28days. Before the age of 56 days, the higher the amount of mineral admixture is, the slower the internal relative humidity decreases. But conditions are completely different after the age of 56 days. At the age of 360 days relative humidity is most high for concrete with 15% or 20% slag. Before the age of 28 days, internal relative humidity of concrete with a W/C of 0.45 is higher than that of concrete with a W/C of 0.3. However, after the age of 28 days internal relative humidity of concrete with a W/C of 0.45 decreases rapidly and is close or even lower than that of concrete with a W/C of 0.3.Microstructure of harden cement past in interfacial transition zone of ceramsite concrete was investigated, and results show that ceramsite has a more significant effect on microstructure of harden cement past in interfacial transition zone of concrete with low W/C than that of concrete with high W/C. Moisture content of aggregate has an apparent effect on the microstructure of harden cement past in interfacial transition zone. Amount of porosity and percent of large pore in ITZ of concrete with normal aggregate or with YC ceramsite containing low amount of moisture content are both higher than that of cement paste, but things becomes the opposite as to concrete with ceramsite containing high or medium amount of moisture. The ratio of CaO to SiO2 in the ITZ of the concrete is higher than that of cement paste and pore structure presents a trend of thinning. Moreover the bigger is pre-wetting rate of ceramsite and the stronger is water absorption and release and the rougher is the surface of ceramsite, the denser is the microstructure of ITZ. Mean pore size of ITZ in QF ceramsite concrete decreases up to 20.6% compared to that of normal aggregate concrete and the amount of pore which is smaller than 50nm accounts for about 80%. Microhardness of interfacial transition zone(0~10μm) of concrete with BY or QF ceramsite pre-wetting for 1hrs is about 43% and 56% higher than that of cement paste respectively and also 79.6% and 96.3% higher than that of concrete with normal aggregate. Microhardness of interfacial transition zone decreases with the increase of the degree of saturation with water. Microhardness of interfacial transition zone of concrete with BY ceramsite is highest. Under on-way drying condition, with the distance from the drying surface increases and internal relative humidity becomes big, the degree of hydration of cement paste and Microhardness of interfacial transition zone and cement paste is enhanced. Meanwhile this trend becomes more apparent when the distance from the surface is not more than 5cm and when the distance is more than 10cm the increase become steady.The degree of pre-wetting and the ability of water release of ceramsite have a significant effect on internal relative humidity and shrinkage deformation. With the moisture content of ceramsite increasing, internal relative humidity of concrete decreases slower under drying or self-desiccation conditions and autogenous shrinkage at early ages and long term drying shrinkage both decrease and the period during which restrained shrinkage stress reach its maximum value becomes long. There is apparent relativity between autogenous shrinkage at early ages or long term drying shrinkage and the decrease of internal relative humidity. At the age of 180 days the total shrinkage of normal aggregate concrete is about 3%~8% less than that of concrete made of YC ceramsite with low moisture content and 2%~15% more than that of concrete made of ceramsite with high moisture content. Autogenous shrinkage and drying shrinkage and total shrinkage of concrete made of BY100 ceramsite are all less than that of normal concrete, and shrinkage-reducing rate of internal curing comes up to 47.7%. Ceramsite sand has more efficient influence on the internal curing.The efficiency of shrinkage reduction of internal curing material can be characterized by two parameters, effective action distance of water in internal curing particles and distance between internal curing particles surface. When Ceramsite sand content is 50%, the distance between two particles surface is 417μm, and effective action distance of water in particles is 256μm, which reaches to the critical spacing, as a result, autogenous shrinkage of the concrete can be reduced 98.2%. The water introduced by internal curing material cannot be used completely, therefore, the water use ratio should be considered in the process of calculation the amount of internal curing material needed to compensate the autogenous shrinkage of the concrete, and the use ratio of Ceramsite sand is 63.7% in this research.更多还原