Combined use of superabsorbent polymers and nanosilica for reduction of restrained shrinkage and strength compensation in cementitious mortars

In cementitious mixtures with a low water-to-cement ratio, autogenous shrinkage and cracking due to restrained shrinkage pose a severe problem. To reduce the risk of autogenous shrinkage cracking, internal curing by means of superabsorbent polymers (SAP) was applied. The drawback is that macropores are created upon the release of water by the polymers. The latter reduces the mechanical properties of the material. To counteract this strength reduction, nanosilica is introduced to the internal curing mixture. The effect of additives on the restrained shrinkage of mortar was evaluated by means of the restrained shrinkage ring test accompanied by acoustic emission (AE). AE enabled the monitoring of the hydration process, indicating when the absorbed water was released by the SAPs, while it also pointed out the moment of fracture of the ring. Results showed that combining SAPs and nanosilica, a mixture was created that decreased shrinkage while maintaining the mechanical properties of the reference material.