Fracture Behaviour of Steel, Synthetic and Hybrid Fibre Reinforced Concrete using AE and DIC Techniques

Bhosale, Aniket and Prakash, Suriya S (2019) Fracture Behaviour of Steel, Synthetic and Hybrid Fibre Reinforced Concrete using AE and DIC Techniques. Masters thesis, Indian institute of technology Hyderabad.

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Abstract

Concrete matrix is weak in tension. Moreover, the tensile failure of concrete without any reinforcement is very brittle, which is uncontrolled and sudden fracture. Addition of fibres to concrete matrix helps in improving the ductility and fracture energy of the concrete in tension. Among various types of fibres hooked end steel fibres and synthetic polyolefin fibres were considered in this study to understand the effect of these fibres in tensile response of concrete matrix. The improvement in fracture response of fibre reinforced concrete (FRC) with the inclusion of various types and combinations of fibres is widely studied. Synergistic effect of different fibres on the improvement of fracture behaviour of concrete is a widely accepted phenomenon. However, the fracture mechanisms behind their improvement need to be clearly understood for the optimum use of these fibres in structural elements. In this work, fracture behaviour of synthetic fibre-reinforced concrete (SynFRC), hybrid fibre reinforced concrete (HFRC) and steel fibre reinforced concrete (SFRC) is investigated using digital image correlation (DIC) and acoustic emission (AE) techniques. These results from fracture response are then used to develop tensile constitutive relationships by understanding the fracture mechanism with the help of inverse analysis. This work focuses on improvement in structural performance of FRC through a comprehensive study of the change in the fracture process zone (FPZ) due to addition of different types of fibres and their combinations. Three distinct fibre dosages of 0.50%, 0.75%, and 1.00%, of macro-synthetic polyolefin fibres, hooked end steel fibres and their hybrid combination are regarded as research parameters. Test results show that it is possible to retain sufficient workability in the fresh state and obtain good fracture resistance through a hybrid combination of hooked end steel fibres and macro-synthetic polyolefin fibres. Test outcomes indicate that HFRC offers higher post-cracking resistance when compared to SynFRC. SFRC showcases superior performance in the fracture test than that of HFRC and SynFRC. Full-field strain measurements from DIC are used to measure the crack openings at different stages during the fracture tests. Results of DIC analysis show good agreement with experimental measurements. Continuous monitoring of strain contours depicts more effective engagement of fibres along the depth of the beam with higher dosages for HFRC when compared to that of SynFRC. Also, HFRC had longer cracks than SFRC at a particular stage in fracture test. AE parameters were investigated to acknowledge the efficiency of the fibres in improving the fracture behaviour and toughness of SynFRC, SFRC, and HFRC. AE parameters such as hits, events, AE energy, and 3D-crack source locations are pre-sented to illustrate the role of different fibre dosages on the Mode-I fracture response. The source locations of AE events were found out and classified into tensile or shear cracks and then were utilised to identify the fracture process zone (FPZ). AE energy and fracture energy were found to have good correlation wherein the energy increased with fibre dosage. SFRC demonstrated highest energy dissipation capacity followed by HFRC and SynFRC.

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