STRENGTH AND DEFORMATION BEHAVIOUR OF CONCRETE UNDER BENDING, EXPANSION AND COMPRESSIVE STRESS

FESTIGKEITS- UND VERFORMUNGSVERHALTEN VON BETON UNTER BIEGUNGS-, ZUG- UND DRUCKBEANSPRUCHUNG

ACCORDING TO PREVIOUS EXPERIENCE, CONCRETE BEHAVES LIKE A BRITTLE MATERIAL IN THE SHORT PERIOD STRESS TEST AND IN MORE RAPID STRESS PROCESSES, EVEN IN THE FRACTURE STATE. THE PERMANENT DEFORMATION ABOVE THE WORKING LOAD, EVIDENT FROM THE BENDING OF THE SIGMA-EPSILON LINE OF THE SHORT PERIOD STRESS TEST IS NOT DUE TO CREEP OF THE CONCRETE BUT TO THE FORMATION OF CRACKS IN IT. THE TYPE AND EXTENT OF DEFORMATION OCCURRING IN INDIVIDUAL CASES DEPEND PARTICULARLY ON THE TYPE, COMPOSITION, STRENGTH, STATE OF HYDRATION OF THE CONCRETE, AS WELL AS ON THE TYPE, EXTENT AND PERIOD OF STRESS. IN TESTS CARRIED OUT BY THE RESEARCH INSTITUTE OF THE CEMENT INDUSTRY THE TRANSVERSE STRAIN IN THE COMPRESSION TEST ON NORMAL SAND AND GRAVEL CEMENT UP TO THE CRITICAL STRESSING (CA. 70 TO 90% OF SIGMA (MAX)) WAS CLEARLY LESS (BUT IN THE FRACTURE STATE CLEARLY GREATER) THAN THE LONGITUDINAL COMPRESSION. THE STRAIN IN THE BENDING TEST WAS ABOUT TWICE AS MUCH AS IN THE TENSILE TEST BUT CLEARLY LESS THAN THE TRANSVERSE STRAIN IN THE COMPRESSION TEST. CONCRETES HAVING AGGREGATES WITH A SMALLER MAXIMUM PARTICLE SIZE AND A HIGHER CEMENT CONTENT IN GENERAL EXHIBIT SOMEWHAT GREATER STRAINS UP TO THE CRITICAL STRESSING BUT THEREAFTER THESE ARE SMALLER. THE DEFORMATION BEHAVIOUR OF LIGHT CLOSE TEXTURED CONCRETE WAS VERY SIMILAR TO THAT OF THE CEMENT PASTE.