Zinccoated concrete reinforcement

The characteristics of zinc-coated steel bar reinforcements and the mechanical interaction between reinforcing steel and concrete are discussed quite extensively in the literature. There exists a controversy on the information obtained from the literature, which obviously depends on variations in the chemical composition of cement and aggregate. These variations have a distinct effect on the interaction between galvanised reinforcing steel and concrete. The results of the laboratory tests concerning the corrosion resistance of galvanised reinforcement vary discernably to a great extent, whereas the results of practical experiments carried out over a period of 10 to 30 years indicate that the corrosion resistance of the structures exposed to the actions of moisture and salt is extremely good. In the research project tests were performed using an ordinary Finnish Portland cement as binding agentand the Finnish hot-rolled ribbed reinforcing steel bar A400H in reinforcements. By means of these tests the durability of zinc-coated reinforcement during transport, storage and bending was tested as well as chemical reactions between zinc coating and fresh concrete, and their prevention by using chromatetreated galvanised steel bars. Bonding of the ribbed reinforcing bar to the concrete and the durability of the reinforcement in reinforced concrete beams in corroding salt water under repeated load were also studied. The tests for mechanical and chemical interaction between the reinforcement and the concrete were performed as comparison tests on untreated, hot-dip-galvanise and spray-galvanised reinforcing bars. The tests indicated that the spray-galvanised and hot-dip-galvanised bars withstood transportation and storage well in addition to bending of the main reinforcing bar carried out in conformity with the appropriate standard however, some cracking in zinc coatings occurred at the stirrup bends of small radii. The reactions between fresh concrete and zinc coating that envolve hydrogen will decrease bonding between concrete and reinforcing steel, but the reactions can be prevented by using the passivation treatment in which reinforcing steel bars, following zinc coating, are immersed in a 2 % K2Cr2O7 water solution for one minute and subsequently rinsed with water. The bond strength of the hot-dip-galvanised ribbed reinforcing bar treated in this way is approximately equal to that of the untreated bar and the bond strength of the spray-galvanised bar about 40 % lower than that of the untreated bar. The results of corrosion tests on steel bars embedded in concrete, which continued for 1.5 years, indicated that spray galvanising and hot-dip galvanising effectively protected the steel bars under moist conditions and in water, but corrosion also occurred in sea brackish water. Practical experience and test results have established that zinc coating affords good protection to steel reinforcement against corrosion in structures exposed to high humidity or water. These types of structure with regard to Finland are, for example, bridges, piers, balconies, exterior walls of buildings and most interiors of farm buildings. Thin prefabricated structures are also suitable for application. In applications exposed to salt actions, usually to the effects of chlorides, such as the edge beams of motorway bribes, concrete structures manufactured using chloride-containing aggregates, structures in marine environments and some structures of the chemical industry, zinc coating delays the onset of corrosion and retards it considerably, but does not prevent corrosion completely. The results of practical experiments carried out in these circumstances indicate that the durability is good for 10 to 30 years, whereas the laboratory test results vary considerably. The advantages of zinc-coated steel bar reinforcement as a whole, even under saline conditions, are probable, but this cannot be ascertained until more practical experience has been gained, for example, from sea structures in the Netherlands.