【作者】 孔丽娟；

【导师】 张宝生； 葛勇；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2008， 博士

【摘要】 混合骨料混凝土是指以轻骨料代替部分普通粗、细骨料,体积密度主要介于1950kg/m3~2200kg/m3之间、强度介于40MPa~80MPa之间的中高强度混凝土。它既能改善轻骨料混凝土的缺点,即提高弹性模量,减小徐变,又能发挥轻骨料混凝土的优势,减轻自重,因此,在现代结构工程,特别是大承载、大跨度、高预应力混凝土工程中将具有很好的经济、技术意义。本文通过系统研究陶粒的掺入对混凝土拌合物性能、早期开裂性能、力学性能、耐久性能以及内部显微结构的影响规律,揭示了混合骨料混凝土组成、结构与性能之间的相互关系,为合理配制混合骨料混凝土提供了理论依据。本文进行的主要工作及取得的研究成果有:采用SEM、XRD、EDXA、显微硬度及孔结构分析等微观结构测试手段,研究了陶粒的掺入对混凝土内部显微结构的影响。研究表明:与普通骨料相比,轻骨料与水泥石的硬度及弹性模量均更为接近,故在普通混凝土中掺入部分轻骨料可使混凝土内部结构更趋于均匀,骨料与砂浆间的弹性更为协调。同时陶粒的吸返水能力不同,其对附近水泥水化程度和水泥石结构的影响也不同,且影响程度随水灰比和龄期的改变而有所差异。吸水率越大的陶粒其细化附近水泥石孔结构的能力越强,特别是100nm~1000nm的大孔含量显著减少;在吸水率2.6%的页岩陶粒附近的显微硬度试验结果中仍可看到类似普通骨料的界面薄弱区。当水灰比高时,未预湿陶粒对附近水泥石的致密作用显著;当水灰比较低时,饱和预湿陶粒的自养护作用同样使得骨料附近水泥石结构致密,且随龄期增长愈加明显。并在此基础上提出了“界面影响因子”的概念及计算公式,从而在一定程度上为研究多因素改变的骨料对界面结构的影响提供了一个定量综合的相对比较方法。通过研究陶粒对混合骨料混凝土拌合物性能及早期开裂性能的影响规律可以发现,陶粒在混凝土内部的吸水作用虽然会使拌合物的流动性有所降低,但对浆体粘度的增大有利于提高混凝土匀质性,当同时复掺粉煤灰、引气剂和减水剂时,可配制出坍落度为210mm,而分层度仅为3.3%的施工性能良好的混合骨料混凝土;陶粒在混凝土内部的返水作用则可改善混凝土早期抗开裂性能,且陶粒掺量越多、预湿程度越高,“界面影响因子”越大,改善效果越显著。重点研究了与结构工程联系比较紧密的混凝土力学性能和耐久性能。研究表明:在满足工程要求的强度与弹性模量范围内适当地掺入部分轻骨料可以提高混凝土的比强度。本研究条件下,当水灰比为0.32时,陶粒掺量以不超过50%为宜;当水灰比为0.49时,陶粒掺量以不超过25%为宜。并在不同掺量陶粒对混凝土应力-应变关系影响的研究基础上,提出了混合骨料混凝土本构方程。此外颗粒强度较高的陶粒对提高混凝土抗压强度及弹性模量均有利,而吸水率较高的陶粒不但可以改善轻骨料与水泥石的界面粘结性能,从而提高混凝土的劈拉强度,且对混凝土后期的强度增长有积极作用。预湿程度高的陶粒配制的混凝土早期强度较低,但对提高混凝土后期强度增长率有利。陶粒的掺入对混凝土抗冻性及高水灰比混凝土的抗渗性有利,且陶粒掺量越多,“界面影响因子”越大,对耐久性能的改善越明显,此外陶粒对低水灰比混凝土抗冻性的改善作用还随龄期的增长而愈加显著。但陶粒的掺入会使得低水灰比混凝土的抗渗性有所降低,特别是早期抗渗性降低明显,故此条件下陶粒掺量不宜高于50%。配制水灰比较高的混合骨料混凝土选用低吸水率陶粒可获得较好的抗渗及抗冻性能;当配制低水灰比混凝土时则宜选择吸水率适中的陶粒。并且在满足混凝土施工性能的前提下,选择未预湿的干陶粒对提高混凝土抗渗及抗冻性能均有利。在综合分析骨料组成、结构与混凝土各种性能之间关系的基础上,提出了混合骨料混凝土的骨料选配原则,并对其进行了试验验证,发现骨料的优选可大大改善混凝土的内部结构与性能。更多还原

【Abstract】 Combined aggregate concrete is one kind of moderate or high strength concrete, which is prepared by replacing part of normal weight aggregate with lightweight aggregate, and its density is between 1950kg/m3 to 2200kg/m3, its strength is between 40MPa to 80MPa. It can increase the elastic modulus and decrease the creep of lightweight aggregate concrete, as well as lighten the dead load of structure, so the application of combined aggregate concrete in modern construction, especially the heavy load-bearing, long span and high prestressed structure can bring good economic and technical meaning. In this paper, based on the study of the effect of ceramsite on the workability, mechanical property, early shrinkage cracking, durability and microstructure of concrete, the relationship among the composition, structure and performance of combined aggregate concrete is discovered, and the theoretical basis can be provided for preparing combined aggregate concrete.The main research work and compliments of this paper is:The influence of ceramsite on the microstructure of concrete was investigated using SEM, XRD, EDXA, microhardness measurement and pore structure analysis. The results show that, the addition of ceramsite into concrete can reduce the difference of microhardness and elastic modulus between aggregate and mortar, the internal structure of concrete seem to be more homogeneously. The ceramsite with different water absorption and releasing capacity has different influence on the hydration degree and structure of the adjacent cement paste, and the influence degree varies with the change of water-to-cement ratio and curing age. The ceramsite with high water absorption has strong effect on the refinement of the adjacent cement paste, especially the volume content of macropores within the range of 100nm~1000nm reduces sharply; however a weak interfacial zone can be observed surrounding ceramsite YH with a 1-hour water absorption of 2.6%, which is similar to that around normal weight aggregate. For concrete with a higher water-to-cement ratio, the dry ceramsite has strong effect on the densification of the adjacent cement paste. For concrete with a lower water-to-cement ratio, the ceramsite with high pre- wetting degree can also improve the structure of the cement paste around aggregate, and the improve effect becomes apparently with increasing the curing age. The concept and calculation formula of“interface influence factor”is put forward based on the interfacial structure research, and hence a quantitative and comprehensive comparison method for study the influence of aggregate on the interfacial structure can be provided.Through the study of the effect of ceramsite on the workability and early shrinkage cracking of combined aggregate concrete, it is found that, although the water absorption character of ceramsite can reduce the fluidity of fresh concrete, the increase of paste viscosity is advantageous to improve the concrete homogeneity. By mixing fly ash, air entraining admixture and water reducing admixture into concrete simultaneously, the combined aggregate concrete with a slump of 210mm and a segregation degree of 3.3% is prepared. The water releasing effect of ceramsite can improve the concrete early anti-shrinkage cracking, and the more content and higher pre-wetting degree of ceramsite, the higher the“interface influence factor”and the more obvious the improvement.The mechanical property and durability of concrete which is closely related to the requirement of structure engineering are investigated systematically. The results show that, in the engineering required range of the concrete strength and elastic modulus, mixing proper content of ceramsite into concrete can increase the specific strength of concrete. Under this study condition, for concrete with a water-to-cement ratio of 0.32, the ceramsite content is better no more than 50%, whereas the ceramsite content is better no more than 25% for concrete with a water-to-cement ratio of 0.49. The constitutive equations of combined aggregate concrete were put forward based on the study of the stress-strain relationship of concrete prepared with different ceramsite content. The ceramsite with higher particle strength has positive effect both on the concrete compressive strength and elastic modulus; the ceramsite with higher water absorption not only can increase the concrete splitting strength, but also has positive effect on the increase of concrete strength in long term; the ceramsite with high pre-wetting degree is negative to the early strength of concrete, but is advantageous to the later growth rate of concrete strength.The addition of ceramsite into concrete is advantageous to the concrete frost-resistance and the impermeability of concrete with a higher water-to-cement ratio, and the more the ceramsite content, the higher the“interface influence factor”and the more obvious the improvement. Furthermore, the improve effect of ceramsite on the frost-resistance of concrete with a lower water-to-cement ratio becomes more significant in the long term. However, the impermeability of concrete with a lower water-to-cement ratio has some decrease due to the addition of ceramsite, especially in early age, so under this condition the ceramsite content is better no more than 50%. In order to obtain good impermeability and frost-resistance performance of concrete, the ceramsite with low water absorption should be chosen for preparing combined aggregate concrete with a higher water-to-cement ratio, whereas the ceramsite with moderate water absorption should be chosen for that with a lower water-to-cement ratio. And in the premise of meeting concrete workability, the dry ceramsite can be chosen to improve the concrete impermeability and frost-resistance.The relationship among aggregate composition, concrete microstructure and performance is analyzed comprehensively, and the aggregate required for preparing combined aggregate concrete is put forward, furthermore, the proof test is carried out, and the selective preference of aggregate on the improvement of the structure and performance of combined aggregate concrete is testified.更多还原