Self-Curing, Shrinkage-Free Concrete

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Title: Self-Curing, Shrinkage-Free Concrete

Author(s): M. Collepardi, A. Borsoi, S. Collepardi, R. Troli and M. Valente

Publication: Special Publication

Volume: 234

Issue:

Appears on pages(s): 755-764

Keywords: expansive agent; shrinkage-compensating concrete; shrinkage-free concrete; shrinkage-reducing admixture; wet-curing

Date: 3/22/2006

Abstract:
The purpose of this research work was to make a drying shrinkage-free concrete (SFC) ,even in non-wet curing conditions. This concrete was produced by the combined use of: a) a water-reducing admixture, based on polycarboxylate (PA), in order to reduce both the mixing water and cement, and increase the amount of aggregate;b) a special polycarboxylate (PA/SRA) including, in its molecular structure, a shrinkage-reducing admixtures (SRA) based on polyethylene glycol capable of reducing the surface tension of liquid water filling the capillary pores; c) an expansive agent based on a special calcium oxide (CaO) manufactured in a kiln at relatively high temperatures (about 1000 °C). Traditional shrinkage-compensating concretes are theoretically based on the restrained expansion produced by portland-cement products containing either calcium sulfo-aluminate or free CaO as expansive agent. However, in practice this effect is cumbersome to achieve because these concretes must be wet-cured, for at least 3-7 days after the final set. On the other hand, with the concrete described in this paper, drying shrinkage is completely compensated even in the absence of wet curing. The concrete is demolded at 3 days and then exposed to air curing. Compressive strength and restrained expansion of laboratory specimens as well field cured concrete are given.