SCALE EFFECT ON CONCRETE IN TENSION

Scale effects in the mechanical behaviour of concrete are important ph enomena and are the object of many studies internationally. The Labora toire Central des Ponts et Chaussees has been working for several year s on the scale effect on the distribution function of the tensile stre ngth of concrete. Very many direct tensile tests have been performed o n specimens of different volumes, made of concretes having different f ormulations. From these experimental investigations has been derived a general law that can be used to determine the distribution function ( mean and standard deviation) of the tensile strength of the concrete v ersus the volume of the tensile specimen, for concretes having compres sive strengths between 30 MPa and 130 MPa, from knowledge of just the compressive strength obtained on a standardized cylinder (in France) a nd the ratio of the volume of the tensile specimen to the volume of th e coarsest aggregate in the concrete. It should be emphasized that thi s law is valid only if, on the one hand, the mode of preservation of t he direct tensile specimens is identical to that of the compressive sp ecimens and, on the other, the aggregates used in the concretes are co mmon aggregates, which eliminates light aggregates and very hard aggre gates with a high Young's modulus.