“IMPROVEMENT IN WORKABILITY AND STRENGTH OF CONCRETE EMBEDDED WITH STEEL FIBER, POLYPROPYLENE FIBER & CLASS-F FLY ASH”

Abstract

In construction industry concrete is major material used nowadays. Concrete has better resistance in compression while steel has more resistance in tension. Conventional concrete has limited ductility, low impact and abrasion resistance and little resistance to cracking. To improve the pre cracking and post cracking behavior of short discontinuous and discrete fibers are added to the plain concrete to make it fibrous concrete. The concrete containing cement, water, aggregates and discontinuous discrete fibers is called Fiber Reinforced Concrete (FRC). The ductility of FRC depends on the ability of the fibers to form bridging cracks at higher levels of strain due to higher loads applied. The fibers interlock and stay around aggregate particles and considerably reduce workability, while the mix becomes more cohesive and less to segregation. The fibers are dispersed and distributed randomly in the concrete during mixing and thus improve concrete properties in all directions. The brittle character of concrete that limits its application, can be overcome by the inclusion of fibers (like steel, glass, carbon, polypropylene, and natural) and can be practiced among others that minimizes the weaknesses of concrete, such as low growth resistance, high shrinkage cracking, low durability, etc. To enhance the characteristics of concrete; hybrid fibers are incorporated besides fly-ash . In this effort a variety of fiber additives can be combined with concrete to design for specific applications and optimize chemical and strength properties. The combination of fibers, often called hybridization, is introduced by using different fiber proportions of steel and polypropylene. The fly-ash contributing 5 - 10 percentage were used in concrete mixes by volume of cement and poly-propylene fiber, steel (crimped) fibers and hybrid fiber( poly-propylene and steel (crimped) fibers) of various proportions i.e. ranging from 0 – 4% as additives for each of the concrete mixes of M30 grade as per IS code method of mix design. Super plasticizer was also used in all mixes to make concrete better in workability. Besides cubes and beams of M30 grade concrete were cast 5 and 10 % fly ash and different percentages of steel fiber and polypropylene fiber and hybrid fibers respectively, by volume of cement and identifies fiber combinations that demonstrate maximum compressive and flexural strength of concrete. Finally we obtained that by addition of fiber and mineral admixture the concrete increase their properties as compare to normal concrete mass. Keywords: Fibrous concrete, polypropylene fiber, steel fiber, hybrid fabric, strength –properties, fly-ash.