Shrinkage properties of plain and recycled steel–fibre-reinforced rapid hardening mortars for repairs

This article investigates the time dependent transport properties and shrinkage performance of rapid hardening plain and fibre reinforced mortars for repair applications. Two plain and two SFRC mixes with 45 kg/m3 of recycled clean steel fibres made with rapid hardening cements (CSA – calcium sulfoaluminate cement and RSC – calcium aluminate cement) are studied. It is found that mixes with CSA cement have much lower shrinkage values (around 220 and 365 microstrains) compared to mixes with RSC cement (around 2690 and 2530 microstrains), but most of the shrinkage in these mixes is autogenous. Nonetheless, fibres reduce the drying shrinkage of RSC cement mixes by approximately 12%. Model code 2010 and ACI equations can be used to estimate the shrinkage development with time for these mixes provided suitable parameters for each cement type are adopted. Inverse analysis using finite element method is successfully employed to determine the moisture diffusivity and the hygral contraction coefficient of each mix. A comparison is made between the values of shrinkage strain predicted by the numerical models over time, for different depths, and code equations. A simple analytical procedure is used to assess cracking and/or delamination risks due to restrained shrinkage for these materials in overlay applications.