An Advanced Hybrid Admixture for High Performance Concrete

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Title: An Advanced Hybrid Admixture for High Performance Concrete

Author(s): M. Kinoshita and K. Saito

Publication: Special Publication

Volume: 235

Issue:

Appears on pages(s): 69-88

Keywords: admixture; autogenous shrinkage; high-strength concrete; hybrid; polycarboxylate; shrinkage reducing agent; surface tension; viscosity

Date: 3/22/2006

Abstract:
In recent years, the demand for super high strength concrete has been increasing for high-rise RC building, so that large amounts of high-range water-reducing agents have been used in Japan. However, there are some problems with conventional admixtures. On one hand, the viscosity of prepared fresh concrete is very high and it is not easy to cast by pumping on site. On the other hand, early age shrinkage cracking easily occurs due to autogenous shrinkage, because high strength concrete has low water-cement ratio (w/c) and high content of cement. Autogenous shrinkage is of importance for concrete with w/c lower than 0.4. Therefore, the authors have synthesized a new hybrid admixture, not only reducing the viscosity of fresh concrete, but also having the shrinkage reducing action on hardened concrete. The new admixture is one-liquid type of admixture prepared by blending a new high-range water-reducing agent with a shrinkage reducing agent. Several high strength concretes with 50-150 MPa were produced by using the new admixture at low w/c. In this paper we present data showing that the new admixture reduced the viscosity of fresh concrete and simultaneously reduced autogenous shrinkage compared with concrete containing conventional high-range water-reducing agent.