PERFORMANCE OF FIBER BASED CONCRETE IN SHEAR

Abstract

Shear failure in concrete is known to be brittle and catastrophic. A thorough knowledge of the different modes of shear failure and the mechanisms involved is necessary to prevent them. Also, shear strength of concrete is an important consideration in the design of RC members. Usually vertical steel known as stirrups are provided in beams to build-up shear resisting capacity. These stirrups are discrete elements and hence do not provide a continuous medium in the body of concrete. Therefore, the failure of concrete due to shear induced tension occurs in brittle manner. This mode of failure has to be suppressed through appropriate measures. Induction of ductility into the body of concrete, thus, becomes a primary requirement. Ductility can be induced by incorporating randomly distributed synthetic fibers, embedded into the body of concrete. The concrete so produced is referred to as Fiber Based Concrete (FBC). Ductility can also be induced in concrete by introducing steel bars in a continuous mode. It is, therefore, considered imperative to study the growth of shear resistance and ductility in concrete members through an appropriate combination of fibers and longitudinal steel. This has framed the primary aim of this thesis to study the performance of fiber based concrete in shear. The experimental investigation consists of casting 28 No. of beam specimens to study the shear behaviour and more than hundred specimens that includes cube, cylinder and prisms to study the mechanical properties as compressive strength, tensile strength. Seven different types of fiber volume fractions have been added to the concrete mix ranging from 0% to 0.6% with increment of 0.1%. The analytical study of experimental data has been done and the load deflection trend for various fiber volume fractions has been studied. The first diagonal cracking strength, ultimate shear strength, mid-span ultimate deflection, crack pattern and modes of failure were discussed concisely. The highest percentage increase in ultimate shear strength was found as 19% and the optimum dosage of synthetic fiber for shear strength was found to be 0.4%. At 0.4% fiber volume fraction, the split tensile strength shows an increase of 83% and flexural tensile strength shows an increase of 79%. Based on the regression analysis, relation between cube and cylinder strength was also proposed for synthetic fiber based concrete.