Mechanisms of Degradation in Rheological Properties Due to Pumping and Mixing

Abstract

Abstract Excessive mixing and/or pumping can result in a degradation of rheological properties specifically for self-compacting concrete (SCC) or grouts. Consequently, adverse effects on the concrete performance and structural defects are experienced. In order to identify the dominant factors that influence the rheological properties in the process chain, our study focused on rheological behavior of cement-based grouts after mixing and pumping by examining the results from field and laboratory trials that measured the effects of several pumping parameters on grout characteristics, by describing the effects of compressive stress, shear stress, and sedimentation on grout properties at a laboratory scale, and by analyzing the results using rheographs. The underlying physico-chemical mechanisms were studied using amount of plasticizer adsorbed and specific surface area development during initial hydration. Our observations revealed that mixing and shear stress during pumping, respectively, do exhibit the most pronounced influence on the rheological properties of grouts. Pressurization and sedimentation (while grouts settle) induce only little changes. The degradation of rheological properties is explained by an increase of the specific surface area available for adsorption of plasticizer. This increase seems to be due not only to dispersion of the particles but also to an accelerated creation of pre-hydrates.