【作者】 杨林虎；

【导师】 朱涵；

【作者基本信息】 天津大学 ， 建筑材料， 2010， 博士

【摘要】 橡胶集料混凝土是一种“年轻”的新型建筑材料,仅有不到三十年的研究历史,它的诞生是对水泥混凝土科学发展的推进。橡胶集料混凝土表现出了一系列与普通混凝土显著不同的工程性能,基于目前人们对橡胶集料混凝土的认识:（1）抗开裂性能显著增强;（2）抗渗、抗氯离子侵蚀性能大幅提高;（3）基体变形能力增强,能够吸收更多应变能。这些独特的宏观性能是与它的微观结构密切相关,并影响到其结构性能。因此,从微观角度进一步“解析”橡胶集料混凝土和探讨橡胶集料混凝土对结构性能的影响具有十分重要的意义。本课题取材于国家自然科学基金项目“橡胶集料混凝土的机理研究”和“弹性混凝土工程与力学性能及应用研究”。主要研究了橡胶集料对混凝土中物相结构的影响,橡胶集料混凝土的孔结构,基于应力集中理论的裂缝发展延缓机制,此外,还建立了橡胶集料混凝土梁受弯承载力的计算方法以及延性的评价方法。本文所采用的主要研究方法有: （1）试验研究,主要包括SEM试验,X射线衍射试验（XRD）,压汞试验（MIP）,以及基本力学性能试验;（2）数值计算,采用有限元软件ANSYS进行计算分析;（3）理论分析。本文主要研究成果如下:（1）XRD试验结果表明,尽管水泥的化学成分复杂,并且水化反应时会释放大量的热,但掺入橡胶集料后,在其水化产物中并没有发现新的物相结构;掺加橡胶集料的水泥净浆的水化产物中氢氧化钙（CH）晶体的衍射峰强度显著降低。据此笔者推断,掺加橡胶集料后,水泥基材料后期强度的提高幅度将增大。并且这一推论初步得到其他研究人员试验数据的支持。笔者认为:这是因为橡胶集料的憎水性在橡胶集料表面外围一定厚度范围内形成了低水灰比环境,该环境使CH、Aft等晶体的发育程度受阻。因此在水泥水化反应的初期阶段在橡胶集料表面由各种晶体“搭建”起来的“框架结构”的体积减小,这可能是导致掺加橡胶集料的水泥基材料后期强度持续大幅提高的原因之一。（2）采用压汞试验对橡胶集料混凝土的孔结构和分形特征进行了量化研究。试验结果表明,橡胶集料混凝土的最可几孔径、平均孔径、中值孔径以及孔隙率均增大;但孔径分布更趋于均匀。橡胶集料混凝土的孔隙分形维数D值随着橡胶集料掺量的增加而减小,它表明橡胶集料的引入使得橡胶集料混凝土的孔结构分布更趋于规则。（3）橡胶集料对混凝土中裂缝发展的阻碍机制非常复杂,难于具体量化分析。本文建立了含椭圆形孔洞的矩形板有限元分析模型,研究了基于应力集中理论的橡胶集料阻碍裂缝发展的机理,诠释了橡胶集料混凝土在宏观力学上表现出的高延性特点。计算中采用了应力集中系数（SCF）作为研究方法。计算结果表明:随着椭圆形状系数的增加,SCF显著增大;软性填充材料能够显著降低椭圆孔洞处的应力集中,使得孔洞沿x方向和y方向的影响范围都明显减小,因为软性填充物所分担的拉应力随椭圆形状系数的增加而逐渐增大。这些结论成功诠释了低温下橡胶集料混凝土仍能表现出延性破坏的原因。（4）提出了橡胶集料混凝土新的应力应变关系曲线;基于这一关系曲线,建立了橡胶混凝土梁的受弯承载力的计算方法。该计算方法中,考虑了橡胶集料混凝土峰值压应变和极限压应变对承载力的影响。橡胶集料混凝土的极限压应变比普通混凝土的显著增大,梁的中和轴明显下移,使得橡胶集料混凝土梁的受压区高度显著增大。计算结果表明,在相同混凝土强度等级下,橡胶集料混凝土梁的受弯承载力比普通混凝土梁提高0¹0%（橡胶集料掺量在0¹2%之间,即λ₁≤1.5;λ₂≤2.0时）。在影响橡胶集料混凝土梁受弯承载力的各种因素中,橡胶集料混凝土的应变系数λ₂对承载力的影响十分显著,而λ₁对承载力的影响较小。通过一算例,计算了相同截面的橡胶集料混凝土简支梁和普通混凝土简支梁的受弯承载力。该算例表明,前者的受弯承载力比后者提高了7.6%。（5）以新建的橡胶集料混凝土应力应变关系曲线为基础,通过梁构件的截面曲率延性系数（CDF）建立了橡胶集料混凝土梁延性的评价方法。在钢筋混凝土梁构件的弯拉设计中,不仅要满足承载力要求,还要满足一定的延性要求。橡胶集料混凝土的诞生开辟了从材料自身角度出发来增加构件延性的新途径。所建立的延性评价方法表明,除了配筋率、钢筋屈服强度外,混凝土的峰值压应变、极限压应变也是影响截面延性的主要因素。最后,本文与其他文献中的延性评价方法进行了比较,证明了本文评价方法的准确性和可行性。此外,运用该方法计算的橡胶集料混凝土梁的延性是普通混凝土的1.64².59倍。更多还原

【Abstract】 Crumb Rubber Concrete （CRC） is one type of“young”building materials, with less than thirty years of history. CRC exhibits many different mechanical behaviors from those of conventional concrete. Current studies reveal that （1） CRC improves its anti-cracking behavior; （2） CRC increases in the resistance to water and chloride penetration; and （3） CRC exhibits large deformability and energy-absorbing capability. These macro properties of CRC have a close relationship with its microstructure and would affect the structural properties. In this regards, it is important to“read”CRC in the view of microscopic scale and explore its influence on structural properties.The main methods applied in this paper are: （1） experimental research, including scanning electron microscope （SEM）, X-ray diffraction （XRD）, and mercury intrusion porosimetry （MIP） as well as some mechanical experiments; （2） numerical analysis; and （3） theoretical analysis.The conclusions are made as follows:（1） XRD results show that although the chemical constituents of cement is complicated, no new phase is found in the hydration products of the cement paste incorporating crumb rubber; The peak intensity of calcium hydroxide （CH） from the hydration products of the cement paste incorporating crumb rubber is reduced significantly compared to that from the control blends. This suggested that cement-based materials incorporating crumb rubber would have a larger growth in strength in late time, and this suggestion is preliminarily supported with a set of experimental data by other searchers.（2） Pore structure and fractal characteristic of CRC is analyzed quantitatively using MIP. The results show that the Mode Pore Diameter, the Mean Pore Diameter, the Median Pore Diameter and the porosity of CRC are increased compared to those of conventional concrete, and the pore distribution scope of CRC becomes wide. The fractal dimension D of the pores in CRC decreases with the increase of the crumb rubber content, which indicates that the pore distribution tends to becomes regular when rubber is added. （3） A finite element model for a rectangular plane containing an elliptic hole in the center is established based on stress concentration theory. This model illustrates the mechanism of rubber’s delaying the multiplication of the crack in CRC and explains why CRC exhibits high ductility. Stress concentration factor （SCF） is introduced to measure the stress concentration degree. It is found from the results that SCF increases significantly as the shape factor of the elliptic hole increases. Soft filler decreases the SCF and reduces the affected area of the hole along x and y directions. This research is helpful in explaining why CRC can exhibit ductile failure mode even in low temperature.（4） A modified stress-strain relationship for CRC is proposed. Based on this, theoretical formula for the flexural capacity of CRC beam, which take into account the peak compressive strain and the ultimate compressive strain of CRC, is established. The neutral axis moves downward remarkably because of the large ultimate compressive strain of CRC, which results in the compressive zone of CRC beam increases significantly. The calculation results show that with the same grade of concrete strength the flexural capacity of CRC beam is increased by 0¹0% （when rubber content is 0¹2%, namely,λ₁≤1.5;λ₂≤2.0）. An example shows that the flexural capacity of the CRC beam is increased by 7.6%.（5） Based on the modified stress-strain relationship of CRC, ductility evaluation method is proposed by means of curvature ductility factor （CDF）. The method indicates that the peak compressive strain and the ultimate compressive strain of concrete affect the ductility of concrete beam significantly as well as reinforcement ratio and yield strength of steel. In the end, a comparison shows that the calculated ductility of a reinforced CRC beam is about as 1.64².59 times as that of a conventional concrete beam.更多还原