Title:
Variation of Formwork Pressure with Thixotropy of
Self-Consolidating Concrete
Author(s):
Joseph Assaad, Kamal H. Khayat, and Habib Mesbah
Publication:
Materials Journal
Volume:
100
Issue:
1
Appears on pages(s):
29-37
Keywords:
concrete; formwork; friction; lateral pressure; thixotropy.
DOI:
10.14359/12460
Date:
1/1/2003
Abstract:
An experimental investigation was carried out to determine the influence of thixotropy on the development of formwork lateral pressure. Five self-consolidating concrete (SCC) mixtures prepared with different combinations of cementitious materials and set-modifying admixtures were evaluated. An experimental column measuring 2100 mm in height and 200 mm in diameter was used to determine lateral pressure distribution using five pressure sensors mounted at 50, 250, 450, 850, and 1250 mm from the base. This paper offers a comprehensive review of key factors affecting formwork pressure developed by fresh concrete and presents the results pertaining to the influence of thixotropy on variations in lateral pressure of SCC. The results show that the lateral pressure exerted by the plastic SCC is directly related to thixotropy. With the increase in thixotropy, the initial lateral pressure registered following casting decreases, and the rate of drop in lateral pressure is accelerated. This is attributed to the reversible effect of the thixotropy which enables the material to regain its shear strength, internal friction, and cohesion when left at rest without any shearing action. Immediately after casting, any decrease in lateral pressure was attributed to the increased internal friction resulting from the use of ternary cement and greater concentration of coarse aggregate. The use of a set-retarding agent resulted in a delay in cement hydration that led to a slower rate of drop in lateral pressure. Conversely, the incorporation of a set-accelerating agent resulted in an increase in the rate of pressure drop.