Some properties of higher strength light-weight concrete under short-term tensile stress

Abstract

This paper describes two methods of checking the tensile strength of concrete, viz. by uniaxial tension and by axisymmetric compression through nitrogen-gas pressure applied to the bare concrete surface. Two lightweight aggregate concretes and a limestone aggregate concrete were tested over a range of cement contents and strengths. It is suggested that the nitrogen gas test could be used as a site test; excellent correlation was found between the two methods. The Bache/Nepper-Christensen model was successfully used to calculate the lightweight aggregate tensile strength in concrete. Typical tensile stress/strain relations are shown for the concretes and their mortar phase, together with ultrasonic pulse transit time and Poisson's ratio; it is thought that stable and unstable fracture propagation begin at about 65–70% and 95%, respectively, of the ultimate tensile stress. The tensile strain capacity of the light-weight concretes is significantly better than that of the limestone concrete, which, itself, has very good aggregate/matrix bond. The tensile strains and strain capacity of the concrete tested in the nitrogen gas test are less than half the values expected under uniaxial tension.