ASR-Free Dry Shake Hardeners for Concrete Industrial Floors

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Title: ASR-Free Dry Shake Hardeners for Concrete Industrial Floors

Author(s): M. Collepardi, E.N. Croce, G. Fazio, J.J. Ogoumah Olagot and R. Troli

Publication: Special Publication

Volume: 234

Issue:

Appears on pages(s): 747-754

Keywords: alkali-silica reaction; cracking; dry shake hardener; fly ash; pop-out; slag

Date: 3/22/2006

Abstract:
In the dry shake hardeners (60% of quartz-based sand and 40% of portland cement), applied on the top of concrete industrial floors to improve their abrasion resistance, the alkali-content in terms of Na2O eq. can be as high as 6 g/L corresponding to 6 kg per cubic meter against 1.5-2.0 kg/m3 of Na2O considered to be the threshold value for the alkali-silica reaction. Due to this situation, coarse aggregates of the concrete substratum, in direct contact with the top layer of the cement-based hardener, are exposed to a higher risk of alkali-silica reaction at the transition zone due to the very high content of alkali in the hardener top layer. In order to prevent this type of ASR in concrete industrial floors, a special binder, containing 50% of ground slag or fly ash and 50% of portland cement, was used in combination with a quartz-based crushed sand on the top layer (40% weight of binder and 60% of quartz). Due to the presence of GGBFS or fly ash in the cement-based hardener, the ASR of the coarse aggregate of the sub-strate in direct contact with the top-layer was really prevented. However, this technique of manufacturing durable concrete industrial floors, was not accepted by the workers because they should wait too much more time for the hardening of the surface. A special mix was adopted with improved performance in terms of setting properties: a very fine ground slag, with a specific surface area of about 650 m2/kg, was combined with an accelerating admixture, and was succesfully adopted for both a durable concrete industrial floor and a trouble-free for the workers.