影响新拌水泥基浆体剪切变稠行为关键因素的研究

Cement-based materials, such as self-compacting concrete, self-levelling mortar and cement grout, are widely used in concrete structures, base reinforcement and prestressed elements. To ensure the quality of structures, the yield stress of materials are often very small, and their viscosity increases with shear rate, namely shear thickening. How to control the shear thickening behavior of cement-based materials is a question, which often arises in practice. This is seldomly studied in literature. This proposal aims at the shear thickening behavior of fresh cement-based paste. Based on rheology science, physical chemistry of surface, cementitious material science, the key factors affecting shear thickening behavior of cement-based paste are classified into the interactions between paritcles and the physical characteristics of particles. The average liquid film thickness(LFT) wrapped particles and the roundness of particles are used to represent the physical characteristics of particles; the zeta potential of particles of concentrated paste measured by electroacoustic method, combined with the adsorption of superplasticizer, are used to evaluate the influence of interactions between particles on the shear thickening behavior; rheometer is used to measure the rheological curves of cement-based paste with different compositions, flow index, yield stress, viscosity can be obtained. Based on the studies, the influencing laws of the interactions between paritcles and the physical characteristics of particles on shear thickening behavior of cement-based paste can be drawn.This can improve and enrich the design theory and method of self-compacting concrete and self- levelling mortar, and the development of new chemical admixtures.

自密实混凝土、自流平砂浆和灌浆料等水泥基材料被广泛应用于混凝土结构、基础加固和预应力构件等领域，为保证工程质量，要求这类水泥基浆体的屈服应力很小，粘度随剪切速率增加而增加，表现为剪切变稠。如何控制水泥基材料的剪切变稠行为以适应工程施工要求是工程施工中常遇到的问题，国内外对此研究报道较少。本申请拟以流变学、表面物理化学和胶凝材料学为基础，针对新拌水泥浆体的剪切变稠行为，将其关键影响因素分为颗粒间的相互作用及其物理特征。采用平均液膜厚度和颗粒圆度表征颗粒的物理特征；采用电声衰减法测浓浆的zeta电位，结合颗粒对减水剂的吸附量来表征颗粒间相互作用；采用流变仪测量不同组成水泥基浆体的流变曲线，得出流变指数、屈服应力、粘度等流变参数。在此基础上，得出各关键因素对水泥基浆体剪切变稠行为的影响规律，为丰富和完善自密实混凝土和自流平砂浆等水泥基材料的配合比设计理论与方法、开发新型外加剂提供理论指导。

本项目研究了影响水泥基材料剪切变稠的关键因素，包括水胶比、粉体材料、减水剂、增稠剂、乳化沥青、砂等，采用流变仪测试了浆体的流变性能，用H-B模型拟合测试的流变曲线，并用n值表征浆体的粘度随剪切速率的变化特性；采用电声衰减法测浓浆的zeta电位，采用光学显微镜观察了粉体材料的分散效果。研究结果表明，固液比及粉体的分散效果是影响浆体剪切增稠的主要因素，浆体越分散、固液比越高，剪切增稠性越明显，粉体材料的分散效果主要取决于颗粒间的相互作用，即静电和空间位阻作用，n值随分散效果的增加而增加；减水剂与增稠剂可能产生相互作用而影响浆体的流变性能；沥青乳液由于其球状外形及表面电荷，改善了浆体的分散性，不管固液比及乳液掺量，水泥沥青浆体均未表现出剪切变稠性，沥青乳液使浆体更趋向于宾汉姆流体。平均浆膜厚度与砂浆流变性能具有较好相关性，浆膜厚度的增加降低了砂浆的粘度、屈服应力及n值。