A Study on the Properties of the Compressive Stress-Strain Curves of Lightweight Aggregate Concrete

Abstract

The remarkable differences are usually noticed between the stress-strain curves of lightweight aggregate concrete and the curves of river sand and gravel concrete in their gradient and the curvature of their curves.The shapes of stress-strain curves of various sorts of lightweight aggregate concrete were studied in detail by graphical analysis of curves showing their difference in stress-strain relations. And the characteristics of the finite difference curves obtained can be used commonly to classify the stress-strain curves for normal and lightweight aggregate concretes. The finite difference curves of stress-strain relations indicating cord modulus Δσ/Δδ on the ordinate and strain δ on the abscissa, were quite effective for distinguishing the characteristics of stress-strain curves, since they magnify the variation of the curvature of stress-strain curves.The graphical characteristics of finite difference curves may be summarized as follows.(1) The finite difference curves of stress-strain relations of concretes can be devided into three stages of comparatively linear parts, (1) early stage of slowly descending part, (2) steeply descending part and (3) last stage of slowly descending part.(2) Most finite difference curves consist of one or two stages. Typical patterns of finite difference curve are composed of (1)-(2) stages, (2) stage only or (2)-(3) stages of combination. These three typical patterns may also be corresponding to high strength type, medium strength type and low strength type of stress-strain relations, respectively.(3) The normal concrete and the lightweight aggregate concrete have similar combination patterns of three stages. The compressive strength of concrete corresponding to its above-mentioned patterns, however, varies with concrete composition (fine-coarse aggregate combinations).Since mechanical behaviors of concrete at a certain stress level are reflected in the characteristics of finite difference curve, the results of analysis of finite difference curves obtained in this report will offer a qualitative estimation of mechanical properties of concrete with various mix proportions and various aggregate properties.