A new insight on alkaline hydrolysis of calcium aluminate cement concrete: Part I. Fundamentals
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A new insight on alkaline hydrolysis of calcium aluminate cement concrete: Part I. Fundamentals S. Go˜ni, C. Andrade, J. L. Sagrera, Ma . S. Hern´andez, and C. Alonso Institute of Construction Science Eduardo Torroja (CSIC), c/Serrano Galvache s/n, 28033 Madrid, Spain (Received 25 July 1994; accepted 26 March 1996)
In this work a hypothesis to explain the alkaline hydrolysis degradation process of calcium aluminate cement concrete (CACC) is presented. The hypothesis is based on x-ray diffraction (XRD) data of some samples taken from real Spanish CACC structures. The identification from XRD data of a hydrated alkaline aluminate could serve as a guide to differentiate both processes of normal carbonation and alkaline hydrolysis.
I. INTRODUCTION
The calcium aluminate cement (CAC) was patented at the beginning of this century by Lafarge Fondu International.1 This cement has the advantage of a much more rapid hardening than ordinary Portland cement (OPC), and has, in general, a higher resistance to chemical attack. It was used until some failures were detected.2–5 During the 70s, it was prohibited in most countries for structural uses. In Spain CAC was widely used between 1950 and 1975, mainly for floor beams in apartments and buildings. Now its use is forbidden in prestressed structures, and it is restricted for reinforced ones. It is not the aim of the present paper to review all the failures detected in Spain, but to summarize the most important chemical features identified as those responsible for the failures, and to comment, in particular, on the case known as “Alkaline Hydrolysis” (AH), which in the authors’ opinion has been misinterpreted in literature.6–8 A. Recent failures of CACC in Spain
Isolated cases of failure of calcium aluminate cement concrete (CACC) structures were detected in Spain over many years,9,10 until an accident happened in 1990 with one fatality and some injuries. Because of the serious consequences of realizing that there are more than 400,000 floors in flats made with CACC in Catalu˜na alone, and therefore facing the risk of a sudden collapse, several measures were taken by the local authorities. One was to promote a large survey of all the apartments built between 1950 and 1975 and to start repairing them.11 Particularly, in the structure that collapsed in Barcelona in November 1990,12 the complete loss of cementitious characteristics of the moist zones of the collapsed beams could be identified. These zones, which were of a dark color, could be broken up with the fingers. However, in adjacent dry zones, the color was much lighter and the concrete still preserved reasonable strength since it could be broken only with a hammer. The phenomenon was 1748
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J. Mater. Res., Vol. 11, No. 7, Jul 1996
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initially related to the “Alkaline Hydrolysis”, because the aggregate used in the beams was like granite, which may leach alkaline ions. However, it was not explained why moisture played such an i
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