REPAIR OF CONCRETE STRUCTURES USING FIBER REINFORCED CONCRETE

Abstract

Fiber reinforced concrete is a concrete mix which utilizes fibrous material as reinforcement. These randomly oriented, uniformly distributed fibers exhibit a variety of properties when mixed with concrete. Steel fibers, however, show that they aid in controlling drying and plastic shrinkage, also reducing permeability thus reducing bleeding of water. FRC does not increase the flexure strength of concrete to such a remarkable extent, it does however increase overall structural strength , reduce steel reinforcement requirement, improve post cracking ductility, reduce crack widths and exhibits crack control which increases durability. They also increase resistance against abrasion and impact loading, due to low permeability also resists freeze and thaw. After carefully testing the materials required for the concrete we moved to a comparison between FRC, PCC and RCC. This was a preliminary step required to set a base to decide whether the use of FRC in repair works would be feasible or not. The results showed that FRC showed a slightly higher compressive strength that PCC. This increment was not appreciable enough to be mentioned in great detail and it may have been due to slight changes in the mix and testing conditions due to human error and weather changes. FRC did, however show a higher deflection when it came to flexure testing, in comparison to PPC. This proved that FRC does in fact increase post cracking ductility. These results were a step in the right direction clearing a path for us in using them in repair works of concrete structures. The results of the comparison tests are described in detail in the chapters to follow. Result obtained from flexure tests on the repaired reinforced concrete beams painted a clear picture of the capabilities of FRC. RCC beams repaired with showed a decreased loading capacity as compared to the beam repaired with PCC. However, FRC greatly enhanced ductility of the concrete member as compared to the PCC repaired member. The decreased loading capacity of the FRC repaired member was probably due to inadequate bonding with the beam and/or due to changes in the mix conditions. The results, conclusion and recommendations are discussed in the later parts of the document. Tests on columns gave a clearer picture of the use of FRC in the repair or axially loaded compression members. FRC repaired columns greatly increased the compressive strength of the column as compared to the members repaired with PCC. PCC repaired columns showed medium crack widths, FRC showed a great reduction in crack widths and the cracks appeared with a significant delay as compared to the PPC repaired sample. There was also no spalling of the surface concrete in the FRC repaired sample. These results along with all others are also explained along with conclusions and recommendations in the chapters to follow. This document provides a guideline on how Fiber Reinforced Concrete may be used in repair works, although further research is required in this field to understand the effects of these fibers in more detail. This document will provide preliminary steps in how to use FRC in repair works and what the outcome will be in comparison with the outcome of the repairing concrete members with Plane cement concrete.