Tailoring a new restrained shrinkage test for fiber reinforced concrete

The progress of concrete research during the last three decades has highlighted the possibility of enhancing the properties of cement-based materials, such as compressive strength or workability of the fresh mixes, as well as for other important properties like toughness, durability or volumetric stability. Among these, the resistance to shrinkage cracking is gaining an increasing attention, due to its strict relation to durability. In fact, shrinkage cracking occurs in all concrete structures when the free deformation of concrete is restrained. The higher the shrinkage deformation and the degree of restraint, the higher the risk of cracking, for the same concrete strength. Fiber Reinforced Concrete (FRC), now widely available into the market, allows for a better crack control due to the higher post-cracking strength; the latter is related to the links provided by fibers between the crack faces. However, shrinkage-cracking resistance should be determined with tailored methodologies measuring the crack development under restrained shrinkage conditions. The aim of this paper is a critical discussion on the current standard test procedures and, eventually, a proposal for a novel and enhanced testing set-up for measuring the shrinkage-cracking resistance of FRC. The effects of polymer fibers and Shrinkage Reducing Admixture (SRA) are discussed with reference to the time-to-cracking and the crack width development.