USE OF COMPUTATIONAL RHEOLOGY TO ANALYZE THE EFFECT OF STABILIZER IN CEMENT PASTE

摘要

Stabilizers (ST), also known as viscosity modifying admixture (VMA), are commonly used to improve the stability of the fresh concrete. Stabilizers are very variable in both chemistry and structure. By the use of STs in self-compacting concrete (SCC), the amount of cement and other powder materials can often be significantly reduced, while maintaining sufficient flowability and stability that is required for SCC. A new tool, named the PFI-theory, is applied to analyze the effects of different STs in cement pastes. This theory assumes that thixotropic behavior (reversible process) and a so-called structural breakdown (non-reversible), contributes to the overall rheological behavior of the cement based material. More precisely, the time-dependent behavior of the cement paste is attributed to coagulation, dispersion and re-coagulation of cement particles in combination with breaking of certain chemical formed linkages (i.e. hydrate bounding) between the cement particles. Due to its complexities, the model equations have to be solved by numerical means. Cement pastes containing different dosages of a ST based on high molecular weight polymer were evaluated in a coaxial cylinders viscometer. The objective is to analyze and compare the rheological properties of cement pastes using different dosages and types of STs. Measurements were conducted at several time intervals in the dormant period to distinguish better between thixotropy behavior, structural breakdown and workability loss by yield stress.