Crack Propagation Analysis of Synthetic vs. Steel vs. Hybrid Fibre-Reinforced Concrete Beams Using Digital Image Correlation Technique

Improvement in fracture behaviour of fibre-reinforced concrete (FRC) due to the inclusion of various types and combinations of fibres is widely reported. The fracture behaviour of FRC needs to be fully understood for the optimum use of these fibres in structural elements. Fracture behaviours of synthetic fibre-reinforced concrete (SynFRC), hybrid fibre-reinforced concrete (HFRC) and steel fibre-reinforced concrete (SFRC) are investigated in this study using digital image correlation (DIC) technique. This work focuses on improvement in the structural performance of FRC through a comprehensive study of the change in the crack length, crack opening and fracture process zone (FPZ) due to different fibres addition and their combinations. Three distinct fibre dosages of 0.50%, 0.75%, and 1.00%, of macro-polyolefin fibres, hooked end steel fibres and their hybrid combination are regarded as research parameters. Test outcomes indicate that HFRC offers higher post-cracking resistance when compared to SynFRC. SFRC showcases superior fracture performance than that of HFRC and SynFRC. Full-field strain measurements from DIC are used to measure the crack openings at different load levels during the fracture tests. Results of DIC analysis show good agreement with experimental measurements. Continuous monitoring of strain contours using DIC reveals the effective engagement of fibres along the depth at higher dosages for HFRC when compared to that of SynFRC. Also, HFRC had longer cracks than SFRC at a particular load

Multi-linear tensile stress-crack width relationships for hybrid fibre reinforced concrete using inverse analysis and digital image correlation

This study aimed to analytically develop tensile stress-crack width constitutive relationships for hybrid fibre reinforced concrete (HFRC). An inverse analysis was performed based on the fictitious crack hinge model to derive the stress-crack width relationship through careful calibrations of model parameters with the digital image correlation (DIC) measurements. The studied parameters included fibre types, volume fraction (Vf) and their combinations. Multilinear stress-crack width relationships for steel, polyolefin and hybrid fibre reinforced concrete with three different fibre volume fractions of 0.50%, 0.75% and 1.00% were derived. The hinge parameters assumed in the inverse analysis were validated with the help of full-field strain measurements using the DIC technique. The relationship between the crack tip opening displacement (CTOD) and the crack mouth opening displacement (CMOD) was verified with the help of the developed equations through the inverse analysis. Afterwards, the simplified equations for predicting the stress-crack width relationships for various types of hybrid FRC were proposed. © 2020 Elsevier Lt

Effectiveness of Hybrid Fibers on the Fracture and Shear Behavior of Prestressed Concrete Beams

This study investigates the effectiveness of hybrid fibers (steel and macro‐synthetic) on the shear behavior of prestressed concrete beams. The hybrid fiber combination was selected to avoid workability issues at high volume dosages and ensure effective crack arresting over the crack opening range. Fracture studies included testing notched concrete prisms to identify the role of hybrid fibers in the crack bridging mechanism. Seven hybrid fiber reinforced prestressed concrete (HFRPC) beams were tested at a low shear span (a) to depth (d) ratio of 2.4. The effects of hybrid fibers on load–deflection behavior and strain in the strand are reported. Similarly, the crack opening, crack slip and crack angle variation regarding applied shear were investigated using the digital image correlation (DIC) technique. Test results of HFRPC beams showed considerable improvements in peak load and the post‐peak response with a higher hybrid fiber dosage. The crack opening and crack slip measurement across the major shear crack revealed continuous dilatant behavior. The kinematic response of critical shear crack reflects the sustained dilation response up to the ultimate load, which depends on the critical shear crack angle of the tested beams. As the fiber dosage increases, the shear crack slip and width are reduced, indicating the roles of hybrid fibers in improving ductility and the change in failure mode from brittle shear tension to relatively ductile shear tension. © 2022 by the authors. Licensee MDPI, Basel, Switzerland