Thixotropic Behavior of Fresh Cement Paste with Highly Purified Magnesium Alumino-Silicate Clay: Measurements and Interpretation

Author(s): Kejin Wang, Gilson R. Lomboy
Paper category: Conference
Book Title: 8th International RILEM Symposium on Self-Compacting Concrete - SCC 2016
Editor: Kamal H. Khayat
ISBN: 978-2-35158-156-8
e-ISBN: 978-2-35158-157-5
Publisher: RILEM Publications SARL
Publication year: 2016
Pages: 253-262
Total Pages: 10
Language: English

Abstract: Highly purified magnesium alumino-silicate clays are composed of uniform, rod-shaped particles with a diameter of ~3nm and length of 1.5-2.0m. Attributed to their nanoscale size, rod shape, and unique surface charges, these clay particles tend to form an interlinked structure at rest and align along the shearing plane under shearing. This study is aimed at investigating the effects of such a nanoclay addition on thixotropic behaviour, especially the particle re-flocculation or structural rebuilding, of cement pastes. In the study, freshly mixed cementitious paste samples with different nanoclay content (0-3%) were subjected to a hysteresis loop flow test at 0, 15, 30, 45, 60, and 75 minutes after mixing. A statistical analysis was performed to determine the rates of changes in thixotropy with time. The results indicate that adding a small amount of nanoclay (0.5~1% by mass of cement) significantly facilitates the particle re-flocculation, or structural rebuilding, and effectively enhances the thixotropy of cement pastes. A method of calculating power densities due to flocculation and hydration in plain and clay-modified cementitious pastes is also proposed. The power densities can be divided into three portions, which reflect reversible bonds, initial unbroken bond, and increment in unbroken bond in a tested paste. The analysis of power densities of cementitious pastes studied suggests that increasing clay addition produces strong unbroken bonds immediately after mixing and promotes further breakable bonds with time. In plain cement pastes, the increase in unbroken bonds with time can be identified and differentiated from reversible bonds. Reversible bonds are likely dominated by flocculation, while unbroken bond may be contributions of both flocculation and hydration.

Online publication: 2016
Publication Type: full_text
Public price (Euros): 0.00