Comparative Study On The Microstructure And The Volume Expansion Ratio Of Corrosion Product Under Different Corrosion Environments

Chloride induced reinforcement corrosion has been recognized as one of the major reason that cause performance deterioration of reinforced concrete structures. When the steel corrodes,a large of the corrosion product form at the steel-concrete interface,and then cause cracking of concrete cover. Finally, reinforced concrete structure is damaged by increasing corrosion product. Cover cracking due to corrosion expansion is the most important critical index for durability degradation of reinforced concrete,so related research has been closely watched. At present, many scholars at home and abroad have devoted themselves to carry out the related research work by means of the corrosive test?empirical formula?theoretical model?etc,and a series of research results have been achieved. But so far,the research involving comparison about microstructure of corrosion products in different corrosive conditions and volume expansion rate of corrosion product in certain conditions are seldom referred. Funded by Projects of the National Natural Science Foundation of China(51278304) and Shenzhen Science and Technology Plan Projects-Basic Research(JCYJ201206-13174456685), this paper will conduct experiments to observe and analyze microtopography of the rust layer in different corrosion conditions and analyze and calculate percentages of the components and volume expansion rate of corrosion product in certain conditions(such as oxygen?moisture?testing methods).The study contents are as follows:(1) The cylindrical specimens used for dry/wet cycling test and impressed current tests were obtained. When the maximum crack width reached 0.1mm on the surface of the specimen, the cracking time in experimental conditions were record. In addition, in the impressed current tests, the rust overflowed surface of sample and longitudinal cracks were found. But in the dry/wet cycling test, surface of sample was bright and clean.(2) By optical microscope, the corrosion pits on the surface of the steel were observed. Under the chloride erosion environment, localized corrosion occurred and corrosion pits formed on the surface of the steel. However, corrosion pits developed with the “persimmon” type in the impressed current tests and along the direction of current with strip in the dry/wet cycling test. By SEM, corrosion product were observed. Microtopography of the rust layer mainly included scaly with petals type,acicular,honeycomb,flocculent,globular clusters,layered, etc in the impressed current tests, and scaly with mesh type,granular,block,etc in the dry/wet cycling test.(3) X-ray diffraction spectrogram was analyzed and the following conclusion were drawn. Under the certain conditions( including Current density of 100 ?A/cm2?half immersion mode and so on),in the impressed current tests volume expansion rate of corrosion product is 2.39. In the dry/wet cycling test with high temperature and humidity, volume expansion rate is 2.55, and comparing with value in the impressed current tests,is closer to the value(2.69) in local natural state.These basic findings of the paper could significantly contribute to assess the service life of RC structures as well as to predict the required repair time of corroded structures in marine environments. Therefore, it is important and has a great academic significance.