【作者】 沈毅；

【导师】 金贤玉；

【作者基本信息】 浙江大学 ， 结构工程， 2004， 硕士

【摘要】 一般来说，混凝土28天的某项性能指标作为混凝土该项性能的参考指标。因此，以前大部分的试验研究都是针对混凝土28天及其后的性能进行的，很少研究混凝土在28天前及较早龄期的性能。随着对混凝土研究的深入，混凝土的早龄期性能的研究开始受到重视。那么，早龄期混凝土是指何种状态下的混凝土呢?瑞典的水泥与混凝土研究协会的S．G．Bergstrom认为早龄期混凝土的“早龄期”概念并不是单纯指时间，用来指混凝土水化程度或者说混凝土的成熟度比较合适，也可以说混凝土某一项性能指标在达到使用者要求之前的时间可以称为“早龄期”。 但是，混凝土的成熟度是一个比较难把握的参数，而时间是一个比较直观，容易掌握的参数，所以本人在试验中将养护时间作为参考指标，研究不同混凝土在各个龄期下的性能变化以及各项性能指标之间的联系。 本人的试验研究内容包括以下四个方面： （1）普通混凝土（C40）和高强混凝土（C80，C90）的早龄期抗压强度，抗拉强度，应力—应变全曲线分析； （2）普通混凝土（C40）和高强混凝土（C80）的早龄期断裂参数(K_Ic^S，CTODc)测试； （3）普通混凝土（C40）和高强混凝土（C80）早龄期孔结构测试； （4）普通混凝土（C40）和高强混凝土（C80）早龄期受荷对后期性能的影响。 研究结果表明混凝土在早龄期各项性能的发展有一定的规律，彼此之间存在联系。通过试验研究得到： （1）普通混凝土和高强混凝土各性能指标发展规律不太相同，高强混凝土的“成熟”速度要比普通混凝土快； （2）混凝土宏观力学性能，包括强度，断裂参数，他们随龄期的发展曲线都很相似，就是在早龄期阶段增长较快，而后增长速度放慢；如果把混凝土内部孔隙的减少看作是混凝土随龄期增长，那么孔隙率同以上各项性能具有相似的发展规律；浙江大学硕士论文 （3）混凝土的应力一应变曲线是研究混凝土对外部荷载作用的反应的一种较理想的方法;混凝土的断裂参数值的变化和内部孔结构变化同混凝土强度发展之间存在必然的关系，都是混凝土水化进行的不同角度的体现;混凝土在一定条件下具有自愈合的能力。更多还原

【Abstract】 The investigations done in this paper is one of the projects aided by National Natural Science Foundation of China (NSFC 5017 8063).Generally, the 28-day compressive strength of concrete determined by a standard uniaxial compressive test is accepted universally as a general index of concrete strength. So the tests done before are to investigate the properties of 28-day concrete and its long-term characteristics, less about young concrete. Further investigation on concrete asks us to learn more about young concrete. Addressing the question of how early is early age, S.GBergstrom of the Swedish Cement and Concrete Research Institute said:Time is not a very good measure of "early". The time when the concrete has reached a certain maturity, is dependent on so many factors: cement type, reactivity of the cement, temperature, admixtures, etc. The time factor is not significant in the general case if you are not specifying the case very carefully. Then of course the degree of hydration gives a much better indication, which however is not always available if we deal with the practical side. You can also use another more practical definition perhaps, giving the time the property you are interested in has reached the level you need. All times earlier than that level are evidently early ages; which means that the definition depends on the way you will use concrete. The form stripper would say that he needs about 15MPa, whereas a slipformer does not need as much as that. These two have quite different concepts about early age. The answer is that there is no universal answer. When we try to define the area where we are going to work, we will, as a rule of thumb and for the normal concrete, in normal situations, say about 24hours, some say about 48hours, but that is just to indicate the order of magnitude...While, as S.GBergstrom said: "Then of course the degree of hydration gives a much better indication, which however is not always available if we deal with the practical side." In my testing process, I still use the time as indication to investigate the properties of concrete at various early ages in order to give an explicit definition to "early age".I did four experimentations in lab of HKUST civil engineering department.(1) Compressive strength, tensile strength, complete stress-strain curves analyzing of NCS and HSC at early age.(2) Fracture parameter investigation (Ks Ic , CTODc) of young concrete for NSCand HSC using TPFM.(3) Research on porosity, pore size and pore size distribution of young concrete.(4) Observation on the function of "self-healing" of concrete by preloading it. . Testing results show that each property of young concrete has its own developingrule and has certain relationship with each other. Some conclusions can be drawn from this experiment:(1) Either NSC or HSC has its own rule of development, simply speaking, HSC has a high mature rate.(2) Strength and fracture parameters, as well as other parameters of concrete have similar developing rule. Stress-strain curve analyzing is a content method to study the behavior of concrete against external load.(3) There are certain relationships between fracture parameters, pore structure and strength development of concrete. They are all the representations of hydration process of concrete. Concrete has capacity of self-healing in proper conditions.更多还原