再生微粉和矿物掺合料的级配对再生混凝土微观结构的影响机理

Recycling use technology of waste concrete can reduce the pollution of construction waste to the environment, and release the pressure of natural aggregate shortage in the concrete industry, so it has the very good social and environmental benefits. In the past the focus of the waste concrete research is mainly on the recycled coarse aggregate and recycled fine aggregate, but the research of the recycled powders (the diameter of the powders is under 0.16mm) which was extracted by the recycled aggregate crushing is relatively less. The recycled powder has a lot of hydrated cement paste and not completely hydrated cement, and it has higher activity. The recycled use of recycled powder meets the requirement of green concrete and the whole recycling use of waste concrete..In the former research we found that the particle size distribution of the cementitious material could improve the microstructure of concrete. So in this study we will use the theory of the dense packing powder to direct the mixing method and mixing ratio of recycled powder and mineral admixtures in the recycled concrete to make the particle size distribution of cementitious material tending to be more reasonable. We will explore the function of the particle size distribution of recycled powder and mineral admixtures to improve the microstructure of recycled concrete, and reveal the relationship between the particle size distribution of recycled powder and mineral admixtures, the microstructure of cement gel and the durability of recycled concrete.

废弃混凝土再生利用技术可以减少建筑垃圾对环境污染的同时缓解目前混凝土行业面临的天然骨料日益短缺的现实问题，具有非常好的社会和环境效益。以往对于废弃混凝土的研究更多地是在再生粗、细骨料方面，而对于再生骨料破碎、粉磨过程中产生的粒径﹤0.16mm的微细粉末的研究则相对较少。废弃混凝土在破碎过程中产生的这部分微细粉末含有大量硬化水泥石和未完全水化的水泥，具有较高活性，对其进行再生利用符合废弃混凝土全再生利用的要求。.申请者在以往研究中发现，水泥胶凝粉体材料的颗粒级配对提高混凝土微观结构密实度有明显影响，故本项目将利用粉体材料颗粒紧密堆积理论对再生微粉和矿物掺合料进行合理掺配后掺入再生混凝土中，使再生混凝土中水泥胶凝材料的级配趋于合理，探索再生微粉和矿物掺合料的级配对改善再生混凝土微观结构的作用机理，揭示出再生微粉和矿物掺合料级配——水泥凝胶体微观结构——再生混凝土耐久性能之间的关系。

废弃混凝土再生利用过程中会产生大量具有较高活性的微细粉末即再生微粉，对其进行再生利用符合废弃混凝土全再生利用的要求。本项目利用实验室废弃混凝土破碎制备得到再生微粉，对其粒径分布、活性系数等进行了研究，并采用物理激发、热处理激发、化学激发等不同激发方式激发其活性。根据粉体材料紧密堆积理论确定出再生微粉和粉煤灰、硅灰等矿物掺合料适合的掺配比例后进行砂浆及混凝土力学、耐久性、微观结构方面的实验，研究了水泥基胶凝粉体材料颗粒级配对水泥砂浆的力学性能及微观结构的影响规律，探索出再生微粉和矿物掺合料的级配与再生混凝土力学性能、微观结构及耐久性能之间的关系。结果表明，本项目中采用的废弃混凝土再生微粉活性较低，其28d活性系数为55%。当微粉掺量超过10%时，胶砂强度在各龄期均表现出明显的下降趋势。通过对比化学激发、热活化与机械力球磨物理激发等不同激发方式对再生微粉的活性激发效果发现，这三种激发方式对再生微粉的活性均有一定的提高作用，但将再生微粉球磨30min的物理激发效果最好，可以将再生微粉的活性提高到71%。物理激发可以改变再生微粉的颗粒级配，掺入砂浆中后可以发挥良好的级配效应，改善水泥凝胶体的微观结构。利用Andersen颗粒紧密堆积理论计算出了水泥的颗粒级配与紧密堆积的理想级配曲线之间的接近度D来评价二者的接近程度。当再生微粉取代水泥时，其颗粒级配变化会引起水泥浆体中粉体材料颗粒级配与最紧密堆积效果的接近度D值发生变化，将再生微粉与粉煤灰、硅灰进行复合掺配时，随着接近度D值逐渐增大，胶凝材料颗粒级配逐渐趋于紧密堆积状态。研究中选择经物理激发30min后的再生微粉与粉煤灰、硅灰等矿物掺合料以适合的比例进行掺配制备再生微粉混凝土试件，对其力学性能、抗碳化性能、抗冻性能及微观结构进行研究发现，这种复掺方式可以明显改善混凝土各方面性能及内部孔隙结构。本项目研究成果对于确立掺再生微粉和矿物掺合料的高性能再生混凝土配比设计方法有重要意义。