High Strength Concrete: an Investigation of the Flexural Behaviour of High Strength RC Beams

This paper describes an investigation to obtain fundamental information on the mechanical behaviour of high strength concrete (HSC) mixes and the flexural behaviour of high strength reinforced concrete (HSRC) beams. In the first part of the paper the design of HSC mixes using local aggregates is described. HSC mixes of strength from 80 to 120MPa at 28 days (lOOmm x lOOmm cubes) were produced at low w/c ratios, with the use of pozzolanic additives (silica fume) and superplasticiser The principal aim at the mix optimisation stage was focused on the role of w/c ratio, concrete ingredients, and their relative contents in producing HSC. Furthermore, compressive strength, splitting tensile strength, elastic modulus, Poisson's ratio, and stress-strain behaviour; were obtained for moist cured cubes and for cylinders. Based on the experimental data, and other reported data, an expression was developed for predicting the strength of HSC mixes based on their ingredients. A new relationship between the compressive strength and splitting tensile strength is also proposed. The second part of this paper is concerned with the flexural behaviour of HSRC beams. Three concrete mixes were selected from the first stage and employed in this part of the investigation. Flexural tests were carried out on singly reinforced beams. The variables were concrete strengths, and tensile steel ratios (1.03% - 4.04%). Test results are presented in terms of load-deflection behaviour; ductility indices, and cracking propagation. An empirical design method has been established in the context of HSC beams subjected to pure flexure. Moreover; the BS 8110 design recommendation is critically examined at ultimate strength capacity for HSRC beams having concrete strengths far beyond the present Code limits.

Professor S. Sarkar, O. Adwan and J.G.L. Munday