Fracture mechanics as the basis for structural design of fibre and textile reinforced concrete

Fibre and textile reinforced concretes are composites with cementitious matrices and reinforcement in the form of discrete fibres or yarns. Since the matrices are brittle and defect sensitive, which may also be the case for some reinforcements such as glass and basalt, the behaviour is evidently governed by fracture mechanics. The review presented here discusses relevant developments, specifically at Indian Institute of Technology (IIT) Madras, related to these two materials with the objective of characterising them in a rational manner, so as to improve the performance and structural design. The main highlight of the work has been the development of testing methods and models to represent the post-crack response of the composite, such that this could be the input in the engineering of better materials and for structural design. Key research contributions arising from the work have been reviewed, including the use of interface finite elements to represent the cracking; development of a toughness test method that led to the IS: 17161, slab and pavement design methods, the inverse analysis procedure for determining the tensile constitutive relationship, fatigue and creep responses of fiber reinforced concrete; and the uniaxial tensile test method, including appropriate specimen fabrication and end conditions, the transition in the stress-strain response from softening to trilinear to bilinear, efficiency factors, size effects in the tensile response, durability criteria for design, and degradation mechanisms of textile reinforced concrete. For both types of composites, pilot projects, mostly novel in the Indian context, have been undertaken based on the research outcomes, with many of these currently being in service on the IIT Madras campus.