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

Abstract

Four high-workability (pumpable and self-compacting) concretemix designs are presented that incorporate steelmaking slagswith additions of both metallic and polymeric fibers. Electric arcfurnace slag (EAFS) as aggregate, and ladle furnace slag (LFS) andground granulated blast furnace slag (GGBFS) as supplementary cementitious material (SCM) are applied to optimize the sustainability ofthe mix design. The main variables in the microstructural analysis, theporosity and the pore structure of the hardened mixes, were assessedwith 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) observationsrevealed good quality concrete microstructures. Accelerated aging tests at a moderate temperature (72°C) produced a slight lengthening,which affected the dimensional stability of all the mixtures, which was also conditioned by their micro-porosity. The internal damageinduced by this test decreased the brittle fracture strength of the concrete mixes, although the use of GGBFS and LFS moderated thatdamage, due to the increased compliance of the cementitious matrix.