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

为了了解鲜水泥浆体性能的基本机理，需要对鲜水泥浆体的微观结构与流变性能之间的关系进行系统的研究。本研究的目的是研究高效减水剂/颗粒相互作用对胶凝悬浮液的微观结构、粘度和触变结构的影响。由于胶凝悬浮液的多分散性、不透明性、高固含量和水化反应，了解胶凝悬浮液的内部结构并非易事。因此，人们对新水泥浆体的内在结构缺乏基本的认识，而新水泥浆体的内在结构对混凝土的和易性至关重要。此外，初始新鲜状态的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]。胶凝悬浮液的微观结构是由颗粒间的相互作用决定的。简单来说，当吸引相互作用超过排斥相互作用时，粒子聚集。因此，了解高效减水剂对微观结构的影响，并获得胶凝悬浮液中颗粒间相互作用的可靠估计，是了解流变特性的关键一步。在本研究中，将使用具有膦酸盐或聚羧酸盐官能团以及主链长度、侧链长度和侧链密度变化的特异性聚合的高效减水剂来制备浆料和砂浆。粘度和触变性积聚将用旋转流变法测定。同时，利用原位激光后向散射测量装置（动态光学反射测量与选择性多深度聚焦）观察了微观结构的演变。然而，结构破坏的动力学依赖于剪切荷载没有解决在本研究中。最后，在胶体表面相互作用、水化动力学和微观结构模型的基础上，讨论了高效减水剂技术对微观结构、粘度和触变结构的影响。

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.