Investigation on engineered cementitious composites with hybrid fibers

Abstract

Concrete is a relatively brittle material when it is subjected to normal stresses and impact loads, whereas the tensile strength of concrete is approximately one tenth of its compressive strength. So, the reinforcement in concrete is used in order to withstand tensile stress and to recompense for the lack of ductility and strength. The addition of fiber reinforcement considerably increases the strength of concrete, but inorder to produce concrete with homogenous tensile properties, the development of micro cracks must be controlled. Introduction of fibers in concrete has been brought in as a solution to develop concrete with improved flexural and tensile strength. The purpose of adding fiber is for extensive post cracking behaviour and to considerably enhances the energy absorption capacity and ductility of the composite. Engineered Cementitious Concrete (ECC) is a new generation High Performance Fiber Reinforced Cementitious Composite (HPFRCC) similar to fiber reinforced concrete. ECC has remarkable ductility with medium fiber content, it also ECC has the mixture of sand, cement, water, fiber, and chemical additives without any coarse aggregate in so as to maintain the unique properties of the ECC. It exhibits more tensile strain value ranging from 3% to 7% for the volume fraction of fiber around 2% or less. It also exhibits strain capacities 500 600 times higher than normal concrete. The experimental research carried out in this thesis is based on the use of different types of fiber in a single ECC mix. This attempt was made to obtain better tensile strength, strain hardening and flexural toughness for application of ECC in various structural and non structural applications. Themain objective of this thesis is to develop the Hybrid Engineered Cementitious Composites (HECC) with low modulus and high modulus fibers. In this research work, four different fibers were used such as Poly Vinyl Alcohol (PVA), Polypropylene (PP), Glass and Steel. These fibers were used in monolithic hydrid form in the ECC for the volume