【作者】 李贺东；

【导师】 徐世烺；

【作者基本信息】 大连理工大学 ， 结构工程， 2009， 博士

【摘要】 超高韧性水泥基复合材料(Ultra High Toughness Cementitious Composites,简称UHTCC)是一种新型的高性能纤维水泥基复合材料,它利用不超过2.5%体积率的短纤维增强,使用常规的搅拌工艺便可加工成型,硬化后的复合材料具有显著的应变硬化特性,极限拉应变能力在3%以上,并可以有效地将极限裂缝宽度限制在100μm以内,有的甚至可以限制在50μm以内,在某种意义上可称为“无缝混凝土”。UHTCC的开发与应用必将有助于解决我国混凝土结构因混凝土韧性差、易开裂、开裂后裂缝宽度难以控制等缺点所引起的一系列工程难题。本文结合自然科学基金项目(50438010)和南水北调项目(JGZXJJ2006-13)开展了一系列的研究,主要内容总结如下:1.配制了23组应变硬化水泥基复合材料,利用改进的直接拉伸试验方法测试其直接拉伸性能,并依此判定属于UHTCC的配比。2.依据直接拉伸试验过程和试验结果,合理描述UHTCC应变硬化以及试件开裂的全过程。3.依据UHTCC直接拉伸应力应变试验曲线,对UHTCC材料在极限抗拉强度之前的应力应变关系进行了合理简化,并给出了相应的抗拉本构方程。4.利用双边对称开口薄板直接拉伸试验证明了UHTCC材料极限抗拉强度具有对缺口的不敏感性。5.利用四点弯曲试验研究了UHTCC的抗弯力学性能及在弯曲荷载条件下UHTCC材料的裂缝无害化分散能力。6.根据UHTCC抗弯力学性能特点,在参考已有纤维混凝土弯曲韧性评价方法的基础上,考虑材料显著的变形硬化特征,提出了适用于评价UHTCC的弯曲韧性评价方法。7.关于使用四点弯曲试验反分析确定UHTCC的极限抗拉应变,结合材料受弯及受拉特性,在分析JCI及UM反分析方法的基础上,提出了更为合理且简单易行的反分析法。8.使用UHTCC制作小尺寸的平板式永久性模板和U型永久性模板,用这些模板浇注混凝土复合梁试件,而后进行的四点弯曲试验证明了UHTCC材料是制作参与性永久性混凝土模板的理想选择之一,它不仅可以明显提高结构的极限承载力改善结构延性,更能有效地将混凝土中的有害裂缝分散为多条细密的无害扁平裂缝,尤其是U型UHTCC永久性模板,能够有效地将裂缝宽度在整个梁深都控制在非常细的范围内。更多还原

【Abstract】 Ultra High Toughness Cementitious Composite (UHTCC) is a new kind of high performance cementitious composite, which is reinforced with less than 2.5% short fibers by composite volume fraction and can be mixed with normal procedures, while the hardened composite possesses significant strain hardening properties with the ultimate tensile strain above 3% and ultimate crack width below 100μm. Some UHTCCs even can well control the ultimate crack width under 50μm, which is harmless to safety, durability and bearing capacity of structures, thus the corresponding composites can be called ’Crack Free Concrete’. It can be expected that the research and application of UHTCC will be great helpful to solve the widely existing problems caused by the lack of toughness, small deformability and easily cracking of concrete in engineering. Accordingly, a series of experiments and analyses regarding the basic mechanical properties and elementary applications of UHTCC are conducted:1. Uniaxial tensile test is the only test method to verify a cementitious composite is strain hardening or not. Appropriate specimen preparation and testing method for uniaxial tension are proposed for strain hardening cementitious composites. Uniaxial tensile tests are conducted to confirm which of the 23 composites, designed by the author, satisfy the basic properties requirement of UHTCC.2. The tensile strain hardening process and the whole cracking process of UHTCC are reasonably described according to the experimental results and the phenomena observed in uniaxial tensile tests, besides, UHTCC’s ability of dispersing wide harmful crack into harmless ones is also evaluated accordingly.3. Reasonable simplifications of tensile stress versus strain relationship before ultimate tensile strength are conducted according to experimental curves, and the corresponding constitutive equations are also given accordingly.4. Property of notch insensitivity of UHTCC is verified with uniaxial tension tests on the double-notched plate specimens.5. Third-point bending tests are conducted to study the flexural properties of UHTCC, and great attention is paid to observe the ability of dispersing harm crack into harmlessly ones of UHTCC under flexural loading.6. Appropriate flexural toughness evaluating method is porposed for UHTCC. 7. Regarding how to measure the ultimate tensile strain of strain hardening material with third-point bending test, new reverse method named NRA method is proposed after analyzing the existing methods of JCI method and UM method.8. Flat-shape and U-shape small scale permanent formworks made of UHTCC are cast with different surface corrugation, and concrete is cast above to make UHTCC permanent formwork/concrete composite beams. Third-point bending tests on composite beams confirm that UHTCC is an ideal material for production of participating permanent formwork, UHTCC permanent formwork can promote structural toughness and structural bearing capacity, especially, it can effectively disperse the wide harmful crack into multiple fine harmless flat cracks. It’s observed that the use of U-shape permanent formwork can effectively control the crack width under a very fine level along the whole depth of the beams, which may be greatly beneficial for improving structural durability.更多还原