Microbially carbonated steel slag in sulfoaluminate-modified concrete: Time-dependent deformation and flexural creep responses

Abstract

To promote the high-value utilization of steel industry solid waste while maintaining the long-term performance of concrete structures, steel slag was carbonated through microbially induced mineralization to produce carbonated steel slag (CSS). CSS was then blended with fly ash (FA) to partially replace a Portland cement (PC)–calcium sulfoaluminate cement (CSA)–anhydrite binder. The effects of this FA–CSS blend on the shrinkage and creep of sulfoaluminate-modified Portland cement concrete (SMPC) and the time-dependent deflection of its flexural members were systematically examined. Shrinkage and creep tests were conducted at FA–CSS replacement levels of 0%, 20%, and 40%, together with sustained loading tests on beams at different loading levels and monotonic loading tests after unloading. Within the 121-day test period, FA–CSS replacement reduced the drying shrinkage and creep of SMPC. At a replacement level of 40%, the shrinkage strain of SMPC40 was approximately 20.0% lower than that of SMPC0. In the beam tests, the measured mid-span creep deflection of SL-40–0.3 was approximately 24.9% lower than that of SL-0–0.3. At a replacement level of 20%, a slight departure from proportionality was observed at a stress level of approximately 0.4 f cu . After 121 d of sustained loading, the tested SMPC20 beams exhibited more pronounced stiffness degradation and crack propagation at higher loading levels, whereas no reduction in ultimate load capacity was observed relative to the control beam without prior sustained loading. Among the ACI 209, B3, GL2000, and fib MC2010 models, fib MC2010 showed the closest agreement with the measured SMPC creep coefficients. An empirical modification of fib MC2010 incorporating correction factors for loading time and FA–CSS replacement level was then calibrated using the measured creep data. When combined with the ACI 318 deflection method, the resulting formulation showed good agreement with the measured time-dependent mid-span deflections of the test beams. The calibrated formulation provides a useful basis for time-dependent deformation analysis of the investigated SMPC system.