Early age cracking of self-compacting concrete

Paper i proceeding, 2006

This paper deals with early-age cracking (< 24 h) due to plastic shrinkage which was evaluated using a restraint ring test. A large number of different SCC constituents and mix compositions have been investigated; e.g. w/c-ratio from 0.38 to 0.67, silica fume, and different admixtures. For comparison, tests with standard concrete were made. The influence of different constituents and mixes on the plastic shrinkage crack tendency was observed, and the results indicated that a high crack tendency was generated when the concrete had a large autogenous shrinkage (silica addition, low w/c) and/or high water evaporation (high w/c). Retardation (retarder, high superplasticizer dosage) also increased the cracking. The minimum crack tendency was found to be at w/c 0.55. Moreover, the crack tendency could be reduced by shrinkage-reducing admixture (large positive effect on both autogenous shrinkage and evaporation) or by acceleration. A wax membrane was effective for concretes with high evaporation. Finally, the ring-test method and the experimental results were also verified by field studies.