自密实混凝土流变性及可泵性的流固耦合模拟研究

Self-compacting concrete (SCC) is widely applied to concrete pumping construction because of its better pumpability. In this project, numerical simulation as the main studied method will be employed to investigate mechanisms of action between the rheological property and pumpability of non spherical aggregates SCC under pumping technology together with process modeling and experimental validation. Firstly, the micro numerical model of SCC will be established, where it is simplified to two-phase as the mortar and aggregate. They are described as Bingham fluid and non-spherical particle, respectively. The coupling of computational fluid dynamics (CFD) and discrete particle method (DEM)will be employed to simulate the interactions between aggregate and mortar/aggregate, macroscopic rheological property and pumping behavior; Then, some rheological tests will be adopted to calibrate the micro-contact parameters of numerical model, such as the slump, L-box, ICAR rheometer tests. The calibrated numerical model and interface performance parameters getting from the pumping tests will be coupled to simulate the pumping process of SCC. And it is further verified by comparing the pressure loss; At last, according to analyzing the numerical results, the effect mechanism of the non-spherical aggregate characteristic affecting the rheological property of SCC and the relationship between the rheological property and pumpability will be explored. The model among aggregate characteristics - rheological properties - pumpability will be established. The obtained results have important significance for ensuring the better performance of SCC under pumping technology and the smooth operation of the pumping.

自密实混凝土(SCC)因其更好的可泵性被广泛用于混凝土泵送施工。本项目以数值模拟为主要研究手段，过程建模和实验验证相结合的方式对非球形骨料SCC泵送工艺下流变性与可泵性之间的作用机理进行研究。首先构建SCC的微观数值模型，将其简化由砂浆和骨料两相组成，且分别采用宾汉姆流体和非球形颗粒来描述，采用计算流体动力学（CFD）与离散颗粒法（DEM）耦合来模拟骨料与骨料、骨料与砂浆之间的相互作用、宏观流变特性以及泵送行为；而后采用坍落度、L箱和ICAR流变仪等试验来校正数值模型微观接触参数，将已校准的数值模型与泵送实验测量得到的界面性能参数相耦合模拟SCC泵送工艺过程，且通过比较压力损失进一步验证。最后通过模拟结果分析，探索非球形骨料特征对SCC流变性能的作用机制、流变性与可泵性间的作用机理，建立骨料特性-流变性能-可泵性模型。研究成果为保证泵送工艺下SCC更好性能和泵送施工的顺利进行具有重要意义。

泵送工艺是一种具有迅速、及时、且保证质量和降低劳动消耗等优点完成混凝土的运输和浇筑这项繁重的、关键性工作的施工手段。本课题以数值模拟为主要研究手段，理论推导和实验测试相结合对新拌混凝土的流变性、泵送工艺和流变性与可泵性之间的作用机理进行了研究。通过坍落度、L箱、U型箱和ICAR流变仪试验实验研究了新拌混凝土的流动、流变性能；分别采用单向流（CFD）、两相离散元（DEM+DEM）和流固耦合（DEM+CFD）三种不同的数值处理方法模拟了新拌混凝土在相应流变仪中的流动行为和流变性能，通过一系列试验确定了骨料物理及力学参数，L箱流动试验校正了流固耦合模型的正确性；对新拌混凝土泵送过程中在管道中的流动进行了理论、实验和数值模拟研究，理论推导出新拌混凝土在管道中流动的流量-压力基本方程，全尺度泵送试验验证数值模拟结果；采用DEM-CFD流固耦合模拟了新拌混凝土在水平管、向上垂直管、锥管、弯管和组合管中的流动行为，结合理论推导和数值模拟结果，探索了新拌混凝土泵送工艺过程中流变特征与可泵性之间的作用机理：新拌混凝土在管道中的流动表现为中间柱塞流，管壁附近剪切流，柱塞区新拌混凝土流速最大且相等，类似柱塞向前流动，其拌合物流变性能与新拌混凝土流变参数相近，剪切区流速从柱塞边界到管壁附近从最大逐渐减小到0，且在管壁形成一定厚度的润滑层，润滑层的流变性能近似砂浆或水泥浆，其屈服应力和塑性粘度远小于柱塞层拌合物的流变参数，润滑层的形成大大降低了新拌混凝土在管道流动中的摩擦阻力，进而降低泵送管道中所产生的压力损失；影响泵送压力损失的另一个主要因素为柱塞流速度，其值越大，泵送压力损失越大，柱塞区速度主要取决于泵送流速、管径、柱塞区混凝土的流变性能、润滑层的流变性能、柱塞流的直径等。此研究成果为保证泵送工艺下新拌混凝土更好性能、泵送回路设计和泵送施工的顺利进行具有重要意义。