Autogenous Shrinkage and Basic Creep in Self-Consolidating Steel–Fiber Reinforced Concrete: From 1.5 Year Experimental Data to Predictive Models

The volume stability of self-consolidating steel-fiber reinforced concrete (SFRC) plays a pivotal role in ensuring the durability and serviceability of modern infrastructure, particularly in complex structural applications such as high-rise buildings, long-span bridges, and underground tunnels where vibration-free placement and dimensional stability are critical. While self-consolidating SFRC combines the flowability of self-consolidating concrete (SCC) with the crack resistance of steel fibers, its long-term autogenous shrinkage and creep behaviors under sustained loads remain insufficiently quantified, posing risks to structural integrity. To address this gap, this study systematically designed three self-consolidating SFRC mixtures with steel-fiber contents of 0.6%, 1.0%, and 1.4%, alongside plain SCC reference groups, using a proposed mix design method. The autogenous shrinkage and basic creep properties were experimentally tracked for 550 days. The results indicate that the incorporation of steel fibers effectively reduces both autogenous shrinkage and basic creep deformation, with the 0.6% fiber content showing the most significant confinement effect. However, self-consolidating SFRC with fiber contents of 1.0% and 1.4% exhibits greater autogenous shrinkage and basic creep deformation. This is attributed to the increased sand ratio and paste content in these mixtures, which are necessary to maintain their self-compacting performance as the fiber content rises. Improved prediction models with suitable values of parameters were developed to accurately forecast the autogenous shrinkage and basic specific creep of both self-consolidating SFRC and SCC. Additionally, the characteristic of significantly higher autogenous shrinkage growth rate observed in self-consolidating SFRC and SCC within the first 90 days needs to be given sufficient attention in practical engineering applications. This work advances the implementation of self-consolidating SFRC in engineering scenarios demanding both constructability and long-term dimensional stability.