Experimental investigation for the determination of stress-strain relationship for sintered flyash lightweight aggregate concrete

Abstract

Lightweight concrete offers better performance as structural concrete owing to its reduced dead load, better durability, and thermal insulating properties. However, it displays a reduction in certain mechanical properties related to its modulus of elasticity and ductility. The present experimental work investigates the stress-strain behaviour of concrete produced with sintered flyash lightweight as coarse aggregate (SFA). The specimens for determining stress-strain curves were tested under a closed-loop strain-controlled compression machine with 3000 kN capacity. To record the stress-strain behavior, extensometers were fixed in the central portion of the cylindrical specimen along its height to obtain a complete stress-strain curve. The loading rate was determined through experimental trials to obtain the full stress-strain curve at a loading rate of 0.4 μm/s. The stress-strain study has been conducted on a strength range between 15 and 45 MPa for analyzing the stress-strain behaviour of SFA-based concrete. The complete stress-strain behaviour during the ascending portion mainly consists of concave as well as convex shapes, while the descending branch shows a non-uniform shape and is relatively short. Based on the analysis of stress-strain curves tested under uniaxial compression, a constitutive relationship has been developed for the determination of strain at peak stress and ultimate strain for SFA concrete, and compared with existing empirical equations in the literature and codal provisions. From the study of complete stress-strain behaviour, ascending and descending branch constitutive equations of lightweight concrete have been developed and compared with experimental data, which mirrors the stress-strain behaviour under uniaxial compression. The results indicate that the ultimate strain to peak strain (εu/εo) decreases with the increase in compressive strength for concrete with SFA. The decrease in the εu/εo with an increase in compressive strength indicates that with an increase in compressive strength, concrete becomes brittle and the difference between εo and εu decreases. The ratio of residual stress to peak stress (σri/ σo) varies between 0.25 and 0.15, and no specific clear-cut trend has been observed with an increase in the compressive strength of concrete