Rheology of low clinker concretes with tailored superplasticizer polymers - Control and modelling of viscosity and thixotropic structural build-up

为了解新拌胶凝材料性能的基本机理，需要系统研究新拌水泥浆体的微观结构与流变性能之间的关系。本研究的目的是研究高效减水剂/颗粒之间的相互作用对水泥基悬浮体的微观结构、粘度和触变结构的影响。由于水泥基悬浮体的多分散性、不透明性、高固相分数和水化反应，了解其内部结构并不容易。因此，对新拌水泥浆体的内在结构缺乏基本的了解，而这对混凝土的和易性至关重要。此外，初始新鲜状态微观结构影响硬化膏体的微观结构，从而影响强度和耐久性[1]。水泥悬浮体的微观结构是由颗粒间的相互作用决定的。简单地说，当吸引力超过排斥力时，粒子就会聚集。因此，了解高效减水剂对微观结构的影响，并获得可靠的估计水泥悬浮液中的颗粒间相互作用是了解流变性能的关键一步，在这项研究中，将使用特定的聚合高效减水剂与膦酸酯或聚羧酸酯官能团和主链长度，侧链长度和侧链密度的变化，制备浆料和砂浆。粘度和触变积聚将使用旋转流变仪测定。同时，显微结构的演变观察与原位激光背散射测量装置（动态光学反射测量与选择性多深度焦点）。然而，在本研究中，结构破坏的动力学依赖于剪切载荷没有解决。最后，超塑化剂技术对微观结构的影响，以及粘度和触变结构的建立将讨论胶体表面相互作用，水化动力学和微观结构模型的基础上。

To understand the fundamental mechanisms of properties of fresh cementitious materials, systematic research is required on the relationship between microstructure and the rheological properties of fresh cement paste. The aim of this research is to examine the effect of superplasticizer / particle interactions on the microstructure, viscosity and thixotropic structural build-up of cementitious suspensions.Understanding the internal structure of cementitious suspensions is not an easy task due to polydispersity, opaqueness, high solid fraction and hydration reactions. Thus, there is a lack of fundamental understanding of the intrinsic structure of fresh cement paste which is of great importance for the workability of concrete. Furthermore, the initial fresh state microstructure affects the microstructure of the hardened paste and consequently strength and durability [1]. The microstructure of a cementitious suspension is determined by the interparticle interactions. In simple terms, particles agglomerate when attractive interactions exceed repulsive interactions. Therefore, understanding the effect of superplasticizer on microstructure and obtaining a reliable estimate of the interparticle interactions in cementitious suspensions is a crucial step towards understanding the rheological properties.In this research, pastes and mortars will be prepared using specifically polymerized superplasticizers with either phosphonate or polycarboxylate functional groups and variations in backbone length, side chain length and side chain density. Viscosity and thixotropic build-up will be determined using rotational rheometry. Simultaneously, the evolution of microstructure is observed with an in situ laser backscattering measurement device (Dynamical Optical Reflectance Measurement with Selective Multi Depth Focus). Whereas, the kinetics of structural break-down in dependence of shear load is not addressed in this research. Finally, the effect of superplasticizer technology on microstructure as well as viscosity and thixotropic structural build-up will be discussed on the basis of colloidal surface interactions, hydration kinetics and a microstructural model.