Oskar Esping

Early age cracking of self-compacting concrete

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.

Investigation of early age deformation in self-compacting concrete

In the presented work, early age (< 24 h) autogenous deformation was measured and crack tendency due to plastic shrinkage was evaluated; see Esping and Löfgren [1]. For the autogenous deformation, a specially developed digital dilatometer was used which generated accurate measurements of the linear displacements of the concrete, which was cast in a vapour-proof flexible tube mould. The plastic shrinkage cracking tendency was evaluated by exposing concrete specimens to early drying conditions while these were restrained by an inner steel ring. 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 also made. The influence of different constituents and mixes on the autogenous deformation and plastic shrinkage crack tendency was observed. The results indicated that a high crack tendency arose when there was: large autogenous shrinkage (silica addition, low w/c, high fineness); high water evaporation (high w/c, low fineness); retardation (retarder or high superplasticizer dosage); low content of coarse aggregate. Minimum crack tendency was found at w/c 0.55.