Title:
Connection between the rheology of concrete and rheology of cement paste
Author(s):
C. F. Ferraris and J. M. Gaidis
Publication:
Materials Journal
Volume:
89
Issue:
4
Appears on pages(s):
388-393
Keywords:
aggregates; cement pastes; concretes; plasticizers; rheological properties; workability; Materials Research
DOI:
10.14359/2575
Date:
7/1/1992
Abstract:
Although the workability of concrete is one of the concerns in any application of the material, many research investigations are directed toward examination of only the paste fraction. This paper presents a step toward connecting concrete rheology and cement paste rheology by introducing a new parameter, the "gap," which is related to the spacing between aggregates present in concrete. This is in addition to the more customary parameters, such as yield stress, shear rate, and viscosity. Data obtained on cement pastes using a parallel plate rheometer are presented and discussed. The main conclusions are: 1. Maintaining constant rotation speed of the rheometer plates (which represent aggregate in concrete) requires more force as the plates are brought closer together. At small separations, a yield strength can be developed in cement paste, in contrast to Newtonian fluids. 2. Addition of dispersing agents (e.g., superplasticizers) has an unusually large effect at small separations. 3. The measurement of paste rheology as a function of the gap between parallel plates (simulating aggregate) is a more refined approach to predicting concrete flow because it combines observations on the properties of paste with attention to the volume fraction of paste. Neither the properties of paste nor its volume fraction alone give a reliable indication of concrete flow.