Title: Use of Viscosity-Modifying Admixture to Enhance Stability of Fluid Concrete

Author(s): Kamal Henri Khayat and Zubeir Guizani

Publication: Materials Journal

Volume: 94

Issue: 4

Appears on pages(s): 332-340

Keywords: bleeding; flowable concrete; homogeneity; segregation; settlement; stability; admixtures;

DOI: 10.14359/317

Date: 7/1/1997

Abstract:
The placement of concrete in congested areas requires the use of a highly fluid mixture that can spread readily into place with minimal consolidation. The incorporation of a high-range water reducer along with a viscosity-modifying admixture can enable the production of fluid concrete having sufficient cohesiveness to reduce bleeding, segregation, and settlement. Such stability can be secured even when the concrete is subjected to high shearing action resulting from pumping, casting, and consolidation. This paper presents the results of a study carried out to investigate the effects of viscosity-modifying admixture concentration, placement height, and mode of consolidation on enhancing the stability of mixtures made with various water-to- cementitious material ratios and consistency levels. In the first phase, bleeding and settlement are determined using 70-cm high columns cast with concrete containing various viscosity-modifying admixture dosages, water-to-cementitious material ratios (0.50 to 0.70), and slump values (140 to 220 mm). In the second phase, bleeding, settlement, and segregation are evaluated for concretes with 220-mm slump cast in 50-, 70-, and 110-cm high columns. The mixtures are made with a water-to-cementitious material ratio of 0.50 and various contents of viscosity-modifying admixture. The effect of excessive external vibration on stability is also evaluated. Regardless of the water-to-cementitious material ratio, slump, casting height, and mode of consolidation, the incorporation of a viscosity-modifying admixture is shown to significantly enhance the resistance to bleeding, settlement, and segregation. Concrete containing 0.07 percent viscosity-modifying admixture and no silica fume can secure greater stability than similar concrete made with 0.035 percent viscosity-modifying admixture and 8 percent silica fume. A simple and accurate method for measuring surface settlement is proposed. Such method can be useful in optimizing highly stable, yet flowable mixtures. The American Concrete Institute also publishes ACI Materials Journal. This section presents brief synopses of papers, committee documents, standardization, and Committee Actions appearing in the current issue. Xerographic copies of these items are available at $7.00 ($5.00 to ACI members). Payment must accompany order. Items related to standards are available free to ACI members for a limited time. See the specific synopsis. From the July-August 1997 issue