Efficiency of steel fibers in geopolymer and Portland cement concrete: Comparative evaluation of fiber bonding and crack bridging stress

Abstract

The bond of steel fibers with Geopolymer Concrete (GPC) and Portland Cement Concrete (PCC) is evaluated. The pullout response of the steel fiber is related to the cohesive fracture response of steel fiber-reinforced GPC and PCC. The crack propagation in fracture tests of GPC and PCC with hooked-end steel fibers at dosages of 25 kg/m³ and 45 kg/m³ is evaluated using digital image correlation (DIC). With the addition of fibers, there is a more significant improvement in the fracture test performance of GPC compared to PCC. The steel fibers demonstrate a higher resistance to pullout from the GPC than the PCC. The dense geopolymer gel around the steel fiber enhances stress transfer, mobilizing significantly higher initial resistance during the fiber pullout. The stronger bond between the GPC matrix and the steel fibers increases the resistance to debonding during the initial stages of fiber pullout. The higher peak pullout load at low slip levels indicates more effective fiber engagement in generating crack-bridging stresses. This enhancement in fiber efficiency to pullout from the GPC matrix results in improved resistance to crack propagation and a significant increase in cohesive stress at small crack openings. The fibers provide better post-cracking load resistance in GPC than PCC, even at a fiber dosage as low as 25 kg/m³.