5.2 S ERVICEABILITY L IMIT S TATES
5.3.3 Additional Comments .1. Spalling
5.3.3.4 Whole Building Behaviour
The one fire test on the concrete frame at the large test facility at Cardington reported by Bailey (2002) showed up some interesting features. The structure was tested at an age of around three and a half years. The first was that the columns cast from high strength concrete did not spall in spite of a moisture content of per cent, although the dosage of polypropylene fibres of 2,7 kg/m3 was higher than the recommended value of 2 kg/m3 in EN 1992-1-2. There was some splitting on the arises of the column although this was likely to have been caused late in the test.
The slab, however, underwent substantial spalling, the reasons for this were the use of a flint-type aggregate, the moisture content of per cent, a concrete cube strength of 61 MPa at 28 days (cylinder strength of approximately 50 MPa) compared with the design mix strength class C37.
However before extrapolating the results from Cardington to other structures, a number of points need to be noted (Chana and Price, 2003). The first is that the original emphasis on the project was to investigate optimization of the construction process. The second was that the high moisture contents were due to the structure being in a relatively cool unventilated enclosure where drying would have been at the very least slow. The third is that the structure was of flat slab construction with steel cross bracing. This means that the lateral movements noted during the test would almost certainly have been less had the structure had in situ concrete lift shafts or stair wells, but the increased restraint may have exacerbated the spalling of the slab. The movements noted were enough to have buckled the steel flats in the bracing.
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