Studies on Potential Usage of Fly Ash in Steel Fiber Reinforced Concrete for Rigid Pavements

Abstract

The ever-growing needs of transportation systems have always necessitated continuous research to make pavements functional, stable, safe, serviceable and durable. With demands exponentially increasing and available resources decreasing, search for materials, construction techniques and performance appraisal is more than ever. Any material when rejected as worthless after its utility period was over is termed as waste material. The tendency of throwing such material not only led to resource crunch and also their collection, conveyance, processing and disposal posed severe problems. Serious attempts began to seek no waste, low waste and waste utilization. Recovery, recycle and reuse of wastes, product, plant and process modifications are being tried. Highway construction industry also has embraced these methods where in waste is being utilized as ingredients in paving material. Industrial wastes like coal ash, blast furnace slag, bottom ash, rubber tires have significant potential to replace conventional materials for various applications in highway construction. Steel fiber reinforced concrete has been investigated and successfully employed in various applications in Civil Engineering projects. The present work is an experimental and analytical investigation to study the usage potential of steel fiber reinforced fly ash concrete(SFRC) with special emphasis to serviceability and durability. Issues like material characterization, cause effect relationship between fatigue failure and load stress level, and temperature gradients effects have been addressed. Concrete grades M40 and M30 have been considered for the investigation as these are widely used. The mixes have been designed as per relevant Codes of Practice. Cubes for compression tests, prisms for modulus of rupture and flexural fatigue tests have been cast, cured and tested. To study the effect of temperature profile on performance and to know the load deformation characteristics of the proposed material, 900 mm x 900mm x 150mm slabs have been used. The use of fly ash in plain concrete as cement replacement tends to reduce all the strengths at the age of 28 days. Along with steel fibers (Vf= 1%), fly ash concrete (with 40% cement replacement) overcomes this deficiency and the enhancement ofstrength of 10% was observed. The steel fiber fly ash concretes have shown better fatigue performance comparative to the reference concrete. A new fatigue equation for projection of design fatigue life has been proposed. The thermal absorption characteristics were found to be unchanged by addition of fly ash to the conventional concrete. Investigations on influence of nonlinear temperature profiles on performance have shown that the resulting temperature stress is 10-30% higher than that obtained using the conventional linear temperature gradient assumption and its incorporation in pavement design has been highlighted.