Study On Retrofitting of Reinforced Concrete Beams Using Fibrous Concrete

Abstract

Reinforced concrete structures often require repairing and strengthening due to their degradation by various environmental factors, ageing or material damage under extreme loading conditions and also sometimes due to mistakes during construction period. Nowadays, many different techniques are being used to repair RC structures. One of the retrofitting techniques is the use of FRC. In this study, steel fiber reinforced concrete (SFRC) containing randomly distributed short discrete steel fibers which act as internal reinforcement so as to enhance the properties of the cementitious composite (concrete).  The principal reason for incorporating short discrete fibres into a cement matrix is to reduce cracking in the elastic range, increase the tensile strength and deformation capacity and increase the toughness of the resultant composite. These properties of SFRC primarily depend upon length and volume of Steel fibers used in the concrete mixture. In India, the steel fiber reinforced concrete (SFRC) has seen limited applications in several structures due to the lack of awareness, design guidelines and construction specifications. Therefore there is a need to develop information on the role of steel fibers in the concrete mixture.

An experimental study was undertaken in which crimped Steel fibres of two different aspect ratios 30 and 60 with volume fractions (Vf) of 0.5%, 1% and 1.5% were used. The experimental work reported in this study includes the mechanical properties of concrete at different volume fractions of steel fibers. These mechanical properties include compressive strength, split tensile strength and flexural strength and to study the effect of volume fraction and aspect ratio of steel fibers on these mechanical properties. However, main aim of the study was significance of reinforced concrete beams strengthened with fiber reinforced concrete layer and to study the load deflection behaviour of these beams. The results obtained during investigation indicates that strengthening of beams using FRC improved structural performance measured in terms of ultimate load carrying capacity, crack pattern deflection and mode of failure. An increase in 13.1% in load carrying capacity of strengthened beam was observed where as an increase in 5.35% in load carrying capacity of retrofitted beams was observed. Further it was also observed that application of FRC delayed appearance and propagation of cracks.