DETERMINATION OF THE COMPRESSION - ELASTICITY MODULUS OF CONCRETE

BESTIMMUNG DES DRUCK-ELASTIZITAETSMODULS VON BETON

IN THE NEW EDITION OF DIN 1048 SHEET 3, CYLINDERS OF 15 CM DIAMETER AND 30 OR 60 CM HIGH, AND PRISMS 70 X 15 X 15 CM ARE SPECIFIED FOR THE E MODULUS DETERMINATION. FOR THE E MODULUS THE COMPRESSION IS DETERMINED USING MEASURING SECTIONS WHICH ARE APPLIED TO THE SURFACE OF THE CONCRETE IN THE COMPRESSION DIRECTION. THE DEFORMATION OF THE CYLINDER PRODUCED BY THE LONGITUDINAL COMPRESSION AND TRANSVERSE EXPANSION UNDER UNIAXIAL LOADING IS UNEQUAL THROUGHOUT ITS HEIGHT BECAUSE TRANSVERSE EXPANSION OF THE COMPRESSION SURFACE OF THE CYLINDER IS PREVENTED DUE TO FRICTION AT THE COMPRESSION PLATES OF THE TEST PRESS. THIS AFFECTS THE RESULT OF AN E MODULUS MEASUREMENT IF THE TEST LENGTH ALSO INCLUDES THE SAMPLE REGION ON WHICH THE END-FACE-FRICTION ACTS. IN THE TESTS THIS EFFECT ON THE E-MODULUS WAS FOLLOWED IN THE MEASUREMENT CARRIED OUT ON 30 AND ON 60 CM HIGH CONCRETE CYLINDERS MADE FROM 4 DIFFERENT MIXTURES. IT WAS POSSIBLE TO CONFIRM THAT WITH THE 30 AND 60 CM HIGH CYLINDERS SPECIFIED IN DIN 1048 SHEET 3, SUFFICIENTLY CONCORDANT E MODULI ARE TO BE EXPECTED SINCE UNDER OTHERWISE THE SAME CONDITIONS THE DIFFERENCES BETWEEN THE E-MODULI DETERMINED ON 30 CM HIGH AND THOSE ON 60 CM HIGH CYLINDERS USING TEST LENGTHS OF 15 CM AMOUNT TO ONLY ABOUT + 1%. THESE DIFFERENCES ARE CONSIDERABLY SMALLER THAN THOSE WHICH MUST BE RECKONED WITH IN GENERAL ON ACCOUNT OF THE NON-UNIFORM NATURE OF THE TEST SPECIMENS (HENCE THE SCATTER OF THE E-MODULUS IS + 4 TO + 6 % IN THESE TESTS).