Study On Steel Corrosion Of UHPC Mixing With Simulated Seawater

In order to study the steel corrosion in UHPC, The paper use simulated seawater as mixing water of UHPC to research,On the one hand, the chloride bounding properties of UHPC matrix were studied. On the other hand, the corrosion of steel bar in UHPC is studied by using half cell potential method, macro current method and the actual observation,At the same time, through the compression test of concrete, the compressive strength of UHPC doped with chloride ion was studied, and the cracking resistance and relative resistance of UHPC were studied by electrochemical corrosion test of reinforced concrete.Specific conclusions are as follows:(1) It studied the binding property of chloride in ultra high performance concrete matrix which mixing with simulate seawater from test method, curing condition, chloride content, admixture composition. Th e result showed:High temperature decomposed the Friedel’s salt and final the free chloride content at 100 degree was higher than that at 50 in sample. Early high temperature humidity curing will reduce the final chloride binding. but with the increase of a ge, the chloride binding will increase gradually, and the more chloride is added, the greater the degree of chloride binding. For the composition of admixture, The addition of silica fume decreased the chloride binding in UHPC matrix by decreasing the calc ium silicon ratio of C-S-H gel and the p H value of the matrix, and dilution of three calcium. The higher alumina content in fly ash promotes the chloride binding in UHPC. For metakaolin, the chloride can accelerate the formation of Friedel’s salt which promotes the chloride binding in UHPC matrix.(2) After the hydration of concrete was completed, the half potential of the steel in UHPC with 0%, 1%,3% chloride ions are all between-100 m V to-200 m V, and the macro current is less than 10 u A, The half potent ial of the steel in ordinary concrete is between-300 m V and-500 m V, and the macro current is more than 10 u A.Referring to the United States ASTMC876-91 corrosion evaluation standards, Hartt W.H and Nam.I research and actual observation,Over 250 days of age, the steel in concrete was found:The steel in ordinary concrete has been corroded, but the steel in UHPC are not corroded,It shows that if there is not oxygen and water in UHPC, the possibility of corrosion in UHPC is very low. Further shows that using hal f cell potential method and macro cell method to detect the corrosion of steel in concrete has a certain feasibility.(3) The difference of compressive strength of ordinary concrete, high performance concrete and UHPC was studied from two aspects of curing condition and chloride content,The study found:The compressive strength of UHPC was 3 to 4 times of OPC, HPC. The compressive strength of UHPC 28-day in early high temperature hot water curing is same as the standard curing.When standard curing, The compressive strength of UHPC with 3% chlorine ion is higher than 0% chloride ions one.In early high temperature curing, the compressive strength of the UHPC doped with 3% chloride ion is lower than that of the UHPC without chloride ion.Because of the early strong effect of chloride ion, the ordinary concrete and high performance concrete with 3% chloride ions in the 7-day age were higher than that of 0% chloride ions, but the 28-day compressive strength was just the opposite.(4) Ordinary concrete and high performance concrete cracking is relatively uniform, destruction along the protective layer of the thinnest part of cracking,and the cracking develops rapidly, but cracking failure of UHPC is a tortuous curves, cracking is not uniform,And the damage is slow with the time passing.