An investigation into age-dependent strength, elastic modulus and deflection of low calcium fly ash concrete for sustainable construction

Abstract

In the present experimental and analytical investigation, the age-dependent effect on the compressive strength, elastic modulus, and long-term behaviour of concrete having class F fly ash have been studied. The fly ash concrete mixes were prepared by replacing the cement with fly ash in the range of 25% to 60% with equivalent weight. A total of eight different mixes of plain and fly ash concrete were prepared. The strength in compression and static elastic modulus was measured experimentally at different ages varying from 7 to 180 days on cylindrical specimens for all the mixes of concrete. The reinforced concrete (RC) beams containing fly ash of overall size of 100 × 150 × 1800 mm (B × D × L) were also cast to observe the creep and shrinkage deflection under the sustained loading of 50% stress level. The microstructure study using scanning electron microscopy along with dispersive X-Ray spectroscopy on all plain and fly ash concrete mixes have also been conducted. The concrete having 40% fly ash content shows satisfactory performance at later ages (i.e. beyond 28 days) in terms of strength, modulus of elasticity, and deflection. It has been observed that the gain in strength from 28 to 180 days is more in fly ash concrete than the plain concrete. The gain in creep and shrinkage deflection from 28 to 180 days is reduced in fly ash concrete beams. Thus, the effective use of fly ash in the concrete enhances the mechanical properties due to its pozzolanic behavior. The assessment of existing models on the prediction of compressive strength and static modulus of elasticity has been done. New models for the prediction of age-dependent compressive strength and elastic modulus of concrete containing the varying percentage of fly ash have been proposed. The present experimental and analytical study can be useful for practicing engineers and designers in the design of concrete structures containing low calcium fly ash for sustainable construction.