CAUSES OF CRACKING IN YOUNG CONCRETE

URSACHEN FUER DAS ENTSTEHEN VON RISSEN IN JUNGEM BETON

THE CONCRETE IS EXPOSED TO DIFFERENT ENVIRONMENTAL CONDITIONS IN THE SOLIDIFICATION AND HARDENING PROCESSES WHICH BRING ABOUT TENSILE STRAINS. IF THESE STRAINS EXCEED THE STILL VERY LOW TENSILE STRENGTH OF THE FRESH CONCRETE, CRACKS ARE FORMED. TENSILE STRAINS IN FRESH CONCRETE MAY BE DUE TO VERY DIFFERENT CAUSES, PARTICULARLY TO CHANGES IN SHAPE AND SETTLEMENT OF THE CONCRETE FORM, RAPID TEMPERATURE CHANGE OF THE SOLIDIFIED CONCRETE, AS WELL AS QUICK DRYING OUT OF THE FRESHLY COMPACTED CONCRETE. BY MEANS OF TESTS THE QUESTION WAS PURSUED WHETHER EXCESSIVE DRYING OUT MAY BE THE ONLY REASON FOR CRACK FORMATION. IN SO DOING, THE EFFECTS OF WATER CONTENT, MILLED MATERIAL COMPOSITION, TEMPERATURE OF THE FRESH CONCRETE AND ENVIRONMENTAL CONDITIONS WERE STUDIED. CRACKS ARE PRODUCED BY PREMATURE DRYING OUT IF THE CONCRETE HAS A HIGH WATER CONTENT AND AT THE SAME TIME A HIGH WATER RETENTION CAPACITY, AND WHERE THERE IS A HIGH VAPOUR PRESSURE BETWEEN THE SURFACE OF THE CONCRETE AND THE SURROUNDING AIR.