Shrinkage-free fiber-reinforced mortars

Shrinkage compensating mortars are in general cementitious materials containing expansive agents that produce a compressive stress due to the restraint exerted by a metallic reinforcement. This compressive stress reduces or disappears at later ages. To be successful, the mortar must be wet-cured because the expansion can occur only in the presence of water. The present work is devoted to studying the behaviour of expansive mortars fibre reinforced with fibres, containing CaO as expansive agent and a special superplasticizer based on a polyacrylate with a special chemical group acting as shrinkage reducing admixture (SRA). The aim was to verify if it is possible to maintain expansion or at least to avoid shrinkage at later ages even in the absence of wet curing. The expansion effectiveness on the bending behaviour of fibre reinforced conglomerates was also investigated. The presence of fibres different in shape and/or material did not modify nor restraint expansion and shrinkage trend. Not even the flexural strength was modified by the simultaneous presence of fibres and expansive agent, despite the fact that this combined addition should have produced a prestressed state localized around the fibres. In addition it seems that the shrinkage free superplasticizer does not negatively influence the compressive strength of cement mortars.