Impact of admixtures on the plastic shrinkage cracking of self-compacting concrete

Cracks accelerate the ingress of harmful fluids, impairing the durability of reinforced concrete structures. Plastic shrinkage cracking poses a problem in particular for concrete components such as slabs, in which a high percentage of the surface area is exposed to drying. In this study, the impact of different admixtures on the occurrence and on the extent of plastic shrinkage cracking of SCC was investigated. Plastic shrinkage cracking was measured according to ASTM C1579-06 in a climate chamber at a temperature of 30 °C and relative humidity of 60%. Starting directly after casting, the settlement, the capillary pressure and the mass loss were recorded. At the end of the test, the crack-width distribution was analyzed. A shrinkage reducing admixture and a paraffin-based curing compound were effective in preventing cracking. Based on the observed evaporation, settlement, capillary pressure and cracking behavior, the mechanisms for crack prevention were identified.