热处理下橡胶混凝土结构及性能演变规律研究

Reutilization of billions of scraped tyres is concerned seriously around the world. Utilizing scraped tyres as an alternative to conventional aggregates in concrete is a kind of resource saving, environment friendly way for its disposal. Rubber concrete shows many excellent performances, but the low compressive and flexural strength due to poor development of the interfacial transition zone(ITZ) between rubber and cement paste limit its application. The ITZ is one of the crucial factors in controlling the development of strength characteristics, which can be a particular issue in the case of recycled rubber aggregates. It has been suggested that enhancement of bonding in ITZ could be achieved by modifying the surface properties of recycled aggregate. But the inertial surface of waste rubber prevented many modifying approaches to achieve good result. In my former research, it was found that not only the compressive and flexural strength of rubber mortar significantly improved after heat treated in vacuum furnace, but also the pyrolysis products of rubber could firmly adhered to the smooth surface of glass flask, which provides a totally new method(heat treatment) to improve the ITZ between rubber and cement paste. In this project, the changes of structures and properties of rubber concrete before/after heat treatment will be investigated; the evolution of crystal phases, pore structures and properties of cement stone will be studied. The mechanical property evolution of rubber at different temperatures will be tested. The pyrolysis mechanism of rubber will be analyzed. The bonding mechanism between cement stone and the pyrolysis products of rubber will be revealed. The size and structure improvement of ITZ will be illustrated. The properties of rubber concrete before/after heat treatment will be tested; the relationship between heat treatment system and the size, rubber crumb content of rubber concrete specimen will be analyzed with the compressive strength criteria to achieve the heat treatment system design method. This project will opened up a new way for improving the organic particles and silicate matrix interfacial binding. And will provide basic interface theory for effective concrete reinforcing with elastic materials. This study is of great significance not only in theory, but also in technology.

废旧轮胎的处理问题越来越受到国内外关注，以废旧轮胎颗粒为骨料的橡胶混凝土具有诸多优点，但橡胶颗粒的表面惰性导致其与水泥基体的界面结合薄弱，强烈降低橡胶混凝土抗压抗折强度，已有改性方法效果不够理想。申请者在前期研究中发现橡胶砂浆经真空热处理后，抗压抗折强度都有很大提高，橡胶颗粒热解产物可以与硅酸盐玻璃表面发生牢固粘接，这为改善橡胶水泥基体结合提供了新的思路。本项目拟在已有工作基础上，进行热处理作用下橡胶混凝土结构与性能演变的基础研究工作。研究水泥石在热处理作用下结构及性能演变规律，探明橡胶颗粒在热处理作用下基本力学性能演变及热解机理，阐明橡胶热解产物与水泥基体界面浸润粘接机理，揭示橡胶颗粒水泥基体界面过渡区结构演变及橡胶混凝土宏观性能变化规律，形成热处理制度设计方法。此项目将为改善有机颗粒与水泥基体界面结合开辟新的途径，为弹性颗粒有效增韧混凝土提供基础界面理论，理论上和技术上都有极强意义。

将废旧橡胶颗粒作为骨料用于水泥混凝土材料是一种资源节约、环境友好的废旧橡胶利用途径，不但能够大量利用废旧橡胶，而且为解决混凝土固有的脆性问题提供了新的方法。国内外学者发现橡胶颗粒可以改善混凝土的多种机械、物理性能和耐久性能。本项目利用橡胶材料热作用下变形软化特点来改善橡胶水泥基体界面结合。研究了水泥基体在低温热处理下结构和性能变化：结果表明，水泥石在250℃以下热处理过程中，其主要矿物成分都没有发生明显变化，只有在较高温度（200℃、250℃）时水泥石中的少量成分钙矾石会发生分解。因此在250℃以下热作用过程中水泥石的结构没有发生明显变化，其力学性能没有明显变化；研究了橡胶颗粒在低温热处理下的结构与性能变化：结果表明，橡胶颗粒在250℃以下热处理过程中，内部助剂小分子大量扩散出橡胶颗粒，表面发生降解，具有良好粘接性能，其降解过程分为低温和高温两个阶段，符合不同动力学方程；研究了热处理对废旧橡胶混凝土力学性能和界面结构的影响：结果表明，经真空250℃热处理后，橡胶-水泥石界面过渡区孔隙被橡胶颗粒及其热解产物充填，降解橡胶颗粒与水泥基体发生粘结，界面变得模糊，界面过渡区厚度与未经热处理界面相比显著改善。经250℃热处理后，橡胶混凝土外观没有明显变化，而抗压强度有明显提高，而且100目橡胶混凝土抗压强度提高率大于5目橡胶混凝土。橡胶混凝土孔隙率降低。研究了热处理对废旧橡胶砂浆抗硫酸盐侵蚀性能：结果表明，橡胶砂浆试样经硫酸盐侵蚀后抗折强度与空白试样相比有所提高，抗压强度降低速率减缓，橡胶砂浆经真空250℃作用后，橡胶-水泥石界面因橡胶颗粒的降解粘接而得到了改善，提高了橡胶砂浆的抗折抗压强度，橡胶颗粒中的小分子助剂会挥发扩散在橡胶砂浆中的毛细孔中，使毛细孔成为憎水性孔，进一步减缓了Mg2+离子和SO42-离子在砂浆孔隙中的扩散，提高了橡胶砂浆的抗硫酸盐侵蚀能力。同时本项目对橡胶-水泥基体界面结构与形成机理进行了初步研究：橡胶-水泥石界面处存在四个厚度区域。第一个区域为橡胶颗粒表面小凹坑区域；第二个区域孔隙率高，水泥水化程度较低；第三个区域Ca/Si较低，而且相对稳定；第四个区域是橡胶-水泥石界面过渡区的厚度。这个区域Ca/Si随距离橡胶表面的距离增加而不断增加，CH含量随距离橡胶表面的距离增加而不断增加。此项目研究成果为弹性颗粒有效增韧混凝土提供全新的界面改善理论。