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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Title: Effect of Admixture Combination on Top-Bar Effect of Highly Flowable and Self-Consolidating Concrete Mixtures
Author(s): K.H. Khayat, E.K. Attiogbe, and H.T. See
Publication: Special Publication
Appears on pages(s): 33-44
Keywords: bond; reinforcing bars; self-consolidating concrete; top-bar effect; viscosity-modifying admixture
Abstract:This paper summarizes a testing program undertaken to evaluate the uniformity of bond strength between concrete and reinforcing bars positioned at various depths of experimental wall elements. In total, four self-consolidating concrete (SCC) mixtures and three conventional flowable mixtures were prepared with different combinations of viscosity-modifying admixtures and high-range water reducers. The concrete mixtures were used to cast experimental wall elements measuring 1.54 m in height, 1.1 m in length, and 0.2 m in width. Two of the walls were steam-cured, while the remaining four elements were air-cured. Each wall had 16 reinforcing bars, four per row positioned at four levels, that were subjected to pullout tests at 1 and 28 days of age.
The concrete mixtures were prepared with Type III cement, 20% Class F fly ash substitution, and a low w/cm of 0.37, which is typical of structural precast concrete construction. The targeted 1-day compressive strength was 40 MPa. Uniform distribution of in-situ compressive strength and adequate bond to the reinforcing bars were obtained with relatively small variations along the experimental wall elements. The 1- and 28-day top-bar effect ratios varied between 1 and 1.4 for the majority of the test results. These values were lower for the air-cured mixtures compared to the steam-cured mixtures. The top-bar effect is shown to be sensitive to the type of VMA used in the SCC.
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