BEHAVIOUR OF GALVANIZED REINFORCEMENT IN CONCRETE

UNTERSUCHUNGEN UEBER DAS VERHALTEN VERZINKTER BEWEHRUNG IN BETON

THE STUDY WAS INTENDED TO ANSWER THE FOLLOWING QUESTIONS: (1) WHAT CHANGES DOES THE ZINC LAYER ON CONCRETE-REINFORCING STEEL UNDERGO IN ALKALINE CONCRETE? (2) IS AN IMPROVEMENT IN CORROSION PROTECTION OBTAINED IN CARBONATED CONCRETE DUE TO THE GALVANIZING OF THE REINFORCEMENT? (3) WHAT CHANGES IN TECHNOLOGICAL CHARACTERISTICS OF CONCRETE REINFORCING STEEL OCCUR DUE TO THE GALVANIZATION PROCESS? REGARDING QUESTION 1, THE HOT-GALVANIZED REINFORCING STEEL WAS EMBEDDED IN CEMENT (MORTAR) AND THE ZINC WHICH WAS REMOVED WAS DETERMINED IN RELATION TO THE TIME AND THE STORAGE CONDITIONS (40,60,80 AND 100% RH.). TWO PORTLAND CEMENTS AND TWO BLAST FURNACE CEMENTS WITH HIGH AND LOW CHROMATE CONTENTS WERE USED. IT WAS SHOWN THAT THE REMOVAL OF ZINC VIRTUALLY STOPS AFTER A WEEK AND IS THUS LESS THAN 10 MICRON. THE HIGHEST VALUE FOR ZINC REMOVAL AFTER 2 YEARS WAS ABOUT 12 MICRONS. COATINGS OF PURE ZINC AS WELL AS THOSE PRODUCED BY HOT-GALVANIZING BEHAVED SOMEWHAT SIMILARLY. GALVANIZED STEELS SHOWED A MORE PRONOUNCED ZINC REMOVAL. REGARDING 2: COMPARISON TESTS WITH UNGALVANIZED AND GALVANIZED CONCRETE REINFORCING STEEL IN CARBONATED CONCRETE SHOWED THAT GALVANIZING CAN RELIABLY PREVENT THE OCCURRENCE OF RUST EVEN UNDER UNSUITABLE CONDITIONS. 3 TYPES OF REINFORCING STEEL WERE EXAMINED, IE SMOOTH BARS ST II A, CONCRETE RIB STEEL ST III A WITH HIGH ELONGATION AT BREAK AND CONCRETE RIB STEEL ST III A WITH LOW ELONGATION AT BREAK. REGARDING 3: NO CHANGE IN STRENGTH ELONGATION AT BREAK, OR BENDING BEHAVIOUR WERE FOUND DUE TO GALVANIZING WHILE AS A RULE A SLIGHT INCREASE IN THE YIELD STRENGTH OCCURRED AFTER GALVANIZING. WITH MARKED DEFORMATIONS OF THE STEEL, CRACKS AND SOMETIMES ALSO PEELING OF THE ZINC LAYER OCCURRED. THE EFFECT OF THIS DAMAGE ON THE CORROSION BEHAVIOUR MUST BE ELUCIDATED BY FURTHER TESTS.