再生混凝土流变性及其预测研究

Concrete rheology，the optimal method for describing the workability of fresh concrete，is affected by properties of each of its constituted material, as well as some potential interactions among them. Compared with natural aggregate, the presence of large amounts of residual old mortar, attached to the surface of recycled aggregate, may lead to a higher value in both its water absorption and absorption rate, making the corresponding fresh concrete vulnerable to problems like faster slump loss, inconsistent between liquidity and stability, difficulty in prediction of its rheology, etc. Moreover, the early cracking of recycled concrete may be also accelerated. Currently, this is a serious problem difficult to be solved in the study of recycled concrete...Based on previous research, this project utilizes a concrete rheometer and some visual microscopic test systems to study the complex characteristics of recycled aggregate to establish a time - dependent model in the moisture content of recycled aggregate; besides, the rheological properties of recycled concrete are comprehensively studied to reveal the influence of water absorption, as well as its time variability, on each rheological parameter of fresh concrete; then the fluid model and prediction model produced by using artificial neural networks, applicable to the rheology of recycled concrete, will be constructed, respectively, to ensure that it can be adjustable. Meanwhile, the relationships between the rheological properties of recycled concrete and its microstructure and early cracking are also established, and the optimal design of recycled concrete is realized finally...This study can make up an insufficient in the rheological properties of recycled concrete, and lay a strong theoretical foundation to achieve a better performance in the construction of the fresh recycled concrete.

混凝土的流变性是表征其工作性能的最理想方法，受各相组成材料特性及其相互作用等多因素的影响。相对于天然骨料，再生骨料表面附着的大量残余老砂浆导致其吸水率和吸水速率较高，使得新拌混凝土塌落度损失过快、流动性与稳定性难以统一以及流变性难以预测，并可能加速混凝土的早期开裂，是目前再生混凝土研究中的一个难点。.本项目在前期研究的基础上，利用流变仪和微观测试系统，通过再生骨料品质的复杂特性研究，建立再生骨料吸水时变模型，开展再生混凝土流变性研究，揭示再生骨料吸水率及其时变性对新拌混凝土流变性的影响规律，构建与之相适应的流体模型和人工神经网络预测模型，实现其流变性能可调控。同时，建立再生混凝土各流变特性参数与其早期力学性能、开裂以及微观结构之间的影响关系，实现再生混凝土配合比的优化设计。.本研究可弥补再生混凝土在流变性能方面研究的不足，为实现再生混凝土的良好施工性能奠定坚实的理论研究基础。

混凝土的流变性是表征其工作性能的最理想方法，受各相组成材料特性及其相互作用等多因素的影响。相对于天然骨料，再生骨料表面附着的大量残余老砂浆导致其吸水率和吸水速率较高，使得新拌混凝土塌落度损失过快、流动性与稳定性难以统一以及流变性难以预测，并可能加速混凝土的早期开裂，是目前再生混凝土研究中的一个难点。本项目首先针对不同来源再生骨料、再生粉体的性能差异开展了系统研究，着重分析了不同的废弃混凝土来源及破碎手段对于再生骨料/粉体各性能指标的影响，初步建立了再生粗骨料的吸水时变模型，提出了再生骨料品质量化方法；在此基础上利用ICAR混凝土流变仪和Brookfield砂浆流变仪，全方位揭示了再生粗（细）骨料含水率、取代率、级配、红砖含量，以及再生微粉的来源、需水量比、活性指数等品质特征参数相对于天然骨料和粉煤灰对新拌混凝土静态屈服应力和塑性黏度等流变性能的影响差异，揭示了再生混凝土的流变性能发展规律；此外，以混凝土流变理论为基础，研究了3D打印混凝土的泵送和挤出压力及流变发展规律，建立了3D打印混凝土可泵性及可挤出性与流变性的关系。