Effect of a novel shrinkage-reducing polycarboxylate superplasticiser on plastic shrinkage cracking of mortars

Abstract

Plastic shrinkage cracking propagating at early ages inevitably impairs the performance of concrete structures. To mitigate it, using a recently developed shrinkage-reducing polycarboxylate superplasticizer (SR-PCA) with outstanding shrinkage-reducing and water-reducing effectiveness can be a promising approach. This present work aims at investigating the effect of the SR-PCA on the plastic shrinkage cracking and clarifying the underlying mechanisms. For comparison, a traditional polyether type shrinkage reducing admixture (SRA) and a polycarboxylate superplasticizer (PCA) were also used. Based on the investigations on horizontal shrinkage, settlement, bleeding, evaporation mass loss, cement hydration, surface tension of pore fluid and capillary pressure, the underlying working mechanisms of SR-PCA were identified. The results indicate that the SR-PCA is able to reduce the crack area, maximum crack width and average crack width by up to 55%, 48% and 50%, respectively. Furthermore, prolonging the bleeding duration and initial time of capillary pressure build-up caused by retarding the cement hydration, lowering the evaporation mass loss, and a lower development rate of capillary stresses and capillary pressure peak value induced by decreasing the surface tension of pore fluid are responsible for preventing the plastic shrinkage cracking of mortars containing SR-PCA.