GAS AND WATER PERMEABILITY OF REINFORCED CONCRETE STRUCTURAL ELEMENTS; BONDING STRENGTH AND PERMISSIBLE BENDING AND SHEAR ROTATIONS

GAS- UND WASSERDICHTIGKEIT VON STAHLBETONBAUTEILEN; VERBUND FESTIGKEIT UND ZULAESSIGE BIEGE- UND SCHRUBROTATIONEN

EXPERIMENTS WERE CARRIED OUT ON REINFORCED CONCRETE STRIP SLABS HAVING THE DIMENSIONS LENGTH/WIDTH/THICKNESS = 32/64/32 CM AND SUBJECTED TO BENDING STRESS IN ORDER TO DETERMINE THE LIMIT VALUES FOR THE BENDING ROTATION OF THE CROSS-SECTION AT WHICH WATER AND GAS PERMEABILITY IS STILL JUST GUARANTEED. TWELVE SLABS HAVING A REINFORCEMENT CONTENT OF BETWEEN 0.24 PERCENT AND 0.64 PERCENG WERE EXAMINED, THE REINFORCEMENT BEING STRUCTURAL STEEL 1, BOTH SMOOTH AND WITH OBLIQUELY RIBBED PROFILING, AND STRUCTURAL STEEL 3B; THE DESIGN CONCRETE QUALITY WAS BN 200 AND BN 250. GAS AND WATER PERMEABILITY WERE DETERMINED ON A SPECIAL TEST RIG ON TEST SAMPLES 1 M IN LENGTH, WHICH HAD BEEN SAWN FROM STATICALLY PRELOADED REINFORCED CONCRETE SLABS. TESTING OF THE GAS PERMEABILITY WAS CARRIED OUT WITH AIR; THE DECREASE IN PRESSURE, STARTING FROM 500 MMWS EXCESS PRESSURE, WAS DETERMINED IN RELATION TO TIME. WATER PERMEABILITY WAS TESTED AT 5 MWS OVER A PERIOD OF 24 HOURS, WHILE THE SATURATION OF THE BENDING COMPRESSION SIDE TURNED AWAY FROM THE WATER WAS OBSERVED. THE STUDIES SHOWED THAT THE SLABS WERE GAS AND WATERPROOF AS LONG AS THE STATIC PRELOADING DOES NOT LEAD TO AN IMPAIRMENT OF THE BENDING COMPRESSION ZONE. IF THE COMPRESSION ZONE IS IMPAIRED ONLY BY A SINGLE HAIRLINE CRACK, SOMETHING WHICH MUST BE FEARED GIVEN A RESIDUAL THICKNESS OF 2 - 3 CM - CORRESPONDING TO A CROSS-SECTIONAL ROTATION OF ABOUT 0.03 RAD, THE IMPERVIOUSNESS IS PRACTICALLY COMPLETELY LOST. IN CONTRAST TO THIS, WHERE THE BENDING COMPRESSION ZONE WAS UNIMPAIRED, NO STATIONARY PERMEABILITY WAS OBSERVED UNDER THE TEST CONDITIONS CITED, DESPITE GAPING CRACKS IN THE TENSION ZONE. THE PERMISSIBLE CONSTRICTION OF THE BENDING COMPRESSION ZONE AND THE DEGREE OF PLASTIFICATION OF THE STEEL (Y (E)/SIGMA (S) EQUAL TO OR SMALLER THAN 10) IS SO GREAT THAT GAS AND WATER PERMEABILITY OF REINFORCED CONCRETE STRUCTURAL ELEMENTS MADE OF WATERPROOF CONCRETE IN ACCORDANCE WITH GERMAN STANDARD DIN 1048 AND SUBJECTED TO BENDING STRESS CAN BE REGARDED AS CERTAIN AS LONG AS THE STATIC BEARING CAPACITY IS GUARANTEED. THE TEST SAMPLES, WHICH WERE GRADED AS GAS AND WATERPROOF, SHOWED NEITHER A DEPENDENCE OF THE WATER ABSORPTION OR AIR PRESSURE DECREASE ON THE BENDING ROTATION OR THE THICKNESS OF THE UNDAMAGED COMPRESSION ZONE, NOR A DETERMINATIVE RELATION BETWEEN WATER PERMEABILITY AND GAS PERMEABILITY.