Microstructure and Dimensional Stability of Slag-Based High-Workability Concrete with Steelmaking Slag Aggregate and Fibers

Four high-workability (pumpable and self-compacting) concrete mix designs are presented that incorporate steelmaking slags with additions of both metallic and polymeric fibers. Electric arc furnace slag (EAFS) as aggregate, and ladle furnace slag (LFS) and ground granulated blast furnace slag (GGBFS) as supplementary cementitious material (SCM) are applied to optimize the sustainability of the mix design. The main variables in the microstructural analysis, the porosity and the pore structure of the hardened mixes, were assessed with mercury intrusion porosimetry (MIP), X-ray computed tomography (XCT) and water capillary penetration analysis. Moreover, shrinkage was observed to decrease when adding metallic fibers and LFS. In general, scanning electron microscopy (SEM) observations revealed good quality concrete microstructures. Accelerated aging tests at a moderate temperature (72 degrees C) produced a slight lengthening, which affected the dimensional stability of all the mixtures, which was also conditioned by their micro-porosity. The internal damage induced by this test decreased the brittle fracture strength of the concrete mixes, although the use of GGBFS and LFS moderated that damage, due to the increased compliance of the cementitious matrix.