Title:
Air-Void Stability in Self-Consolidating Concrete
Author(s):
Kamal H. Khayat and Joseph Assaad
Publication:
Materials Journal
Volume:
99
Issue:
4
Appears on pages(s):
408-416
Keywords:
admixture; air void; consolidation
DOI:
10.14359/12224
Date:
7/1/2002
Abstract:
Ensuring an adequate and stable air-void system in flowable concrete is essential to guarantee proper resistance to freezing and thawing. Ten self-consolidating concrete (SCC) mixtures were prepared to evaluate the influence of mixture proportioning on the stability of the air-void system during agitation. Samples were taken at different time intervals over a period of 95 min after the initial water-cement contact to analyze the air-void system and determine its variation with agitation. Bingham rheological parameters (plastic viscosity and yield stress), slump flow, filling capacity, V-funnel flow time, and surface settlement were evaluated. The modified point-count method was employed to determine the characteristics of the corresponding air-void system. Test results show that the air-void characteristics of SCC can be similar to those found for normal-slump concrete. In general, greater air-void stability can be obtained when the SCC is proportioned with a higher content of cementitious materials and a lower water-cementitious materials ratio (w/cm). For mixtures with a relatively low content of cementitious materials and a high w/cm, the air-void stability increases when a viscosity-modifying admixture is incorporated. To prevent coalescence of small air bubbles during agitation, the plastic viscosity and yield stress values should not exceed 10 N.m.s and 2 N.m, respectively. Such limits are also shown to yield greater air-void stability after 95 min of occasional agitation.