利用坍落扩展试验表征水泥基材料流变参数研究进展

Recent Advances in the Use of Slump-flow Test in Characterizing Rheological Parameters of Cement-based Materials

混凝土、砂浆和水泥浆等水泥基材料的流变性能是影响其浇筑、灌注和注浆等成型工艺难易程度的重要因素。合理评价水泥基材料的屈服应力、黏度等流变参数可以指导材料在工程中的合理应用。水泥基材料流变参数常用的表征方式有两种:一是利用流变仪测定剪切应力和剪切速率,表征浆体的流变参数;二是利用坍落扩展试验进行评价。后者与工程中材料的实际流动状态更为吻合,因此近年来被研究者所重视。水泥基材料坍落过程中变形区与未变形区分界处的剪切应力即为其屈服应力,但是对大流动性浆体,由于不存在未变形区,该方法不适用。对于大流动性浆体,可通过最终扩展度表征浆体的屈服应力。而浆体黏度的表征需要采用动态测试,即测定坍落度或扩展度随时间的变化规律才能予以表征。高速摄像方法能够对初期快速流动过程进行精细测定,具有一定的优越性。剪切应力和剪切速率的表征常用的是水平剪切模型,也可采用侧面滑移模型,但两者均不够完善。此外,截锥筒的形状和尺寸、提筒速度、表面张力、材料的颗粒组成等因素会对流变参数的表征产生影响。本文从屈服应力的表征、黏度的表征、剪切应力与剪切速率的表征、影响因素等方面,对利用坍落和坍落扩展试验表征水泥基材料流变参数的研究进展进行了总结,分析了不同方法的异同和优缺点,并提出了未来的研究方向,以期对利用坍落扩展测试表征水泥基材料流变参数的发展提供参考。

The rheological properties of cement-based materials such as concrete,mortar and cement paste are important factors that affect the technologies of casting,pouring and grouting,etc. A reasonable evaluation of rheological parameters such as yield stress and viscosity of cementbased materials can help a lot in guiding the material for its reasonable application in engineering.Two methods are commonly applied to evaluate the rheological parameters of cement-based materials. One is measuring shear stress and shear rate by rheometer to characterize the rheological parameters of the paste. The other is that evaluating the rheological parameters of cementbased materials by slump spreading test. In resulting of the latter method is more consistent with the actual flow state of materials in engineering,in which there has been growing interest in recent years.The yield stress is the shear stress at the boundary between the deformed zone and the undeformed zone during the slump of cement-based materials. However,this method is not applicable for large-fluidity pastes because there is no undeformed region. The yield stress of large-fluidity pastes can be evaluated by the final spreading value. The characterization of paste viscosity requires dynamic test,which means measuring the law of slump or spreading with time. The method of high-speed photography is advantageous because measuring the initial rapid flow process precisely is possible to be performed by it. A horizontal shear model is commonly performed to characterize shear stress and shear rate. As an alternative,the lateral slip model is able to characterize shear stress and shear rate as well. Nevertheless,both are not perfect. In addition,the shape and size of the truncated cone,the velocity of the lift cylinder,surface tension of pastes and particle composition of the material affect the characterization of the rheological parameters.This paper summarizes the research progress of cement-based materials rheological parameters is characterized by the slump and the slump spreading test,in which the characterization of yield stress,viscosity,shear stress and shear rate are considered and the influencing factors as well. Furthermore,similarities,differences,merits and demerits of various methods are discussed. In order to provide references for the development of the rheological parameters of cement-based materials by the slump spreading test,the possible research field in future is proposed.