chapter  28
10 Pages

CARBONATION. THE EFFECT OF EXPOSURE AND CONCRETE QUALITY: FIELD SURVEY RESULTS FROM SOME 400 STRUCTURES

This paper summarises the results of field measurements of carbonation depths on a large number of structures. It is part of a larger project, a general study of carbonation with the long term aim of improving the durability of structures by more informed design. The project is funded by the Department of the Environment (DoE) through the Building Research Establishment. Laboratory studies of carbonation give measurements under controlled conditions. Exposure site conditions are more ‘natural’ but usually involve carefully prepared specimens of precise pedigree. Very old concretes are unusual in either laboratory or exposure site investigations. Field studies necessarily correspond to real structures but often the concrete mix is not well documented, the comparison of one structure with another is complicated by differences of micro and macro environment, and the results show large variability. In principle the variability could be overcome by taking large numbers of measurements but field work is expensive and this is rarely practical. Nevertheless an enormous amount of carbonation data on real structures already exists, stored in the archives of organisations concerned with testing real structures. By extraction and collation, the resulting block of data could be large enough for reliable conclusions to be drawn. Three Test Houses offered enthusiastic cooperation and, together with information from PSA and BCA archives and some tests made specifically for the project, data were collected for each of 437 structures or separate structural elements.