Chloride erosion test and life prediction of HPC-NC gradient column under dry-wet cycles

In order to improve the durability of steel-reinforced concrete structures subjected to chloride erosion in marine tidal and splash zone, a new structure of high performance concrete(HPC) -normal concrete(NC) gradient column was proposed. A dry-wet cycle test method was designed to conduct the chloride erosion test. The transmission law of internal chloride ions under the influence of different test parameters was studied. A simplified calculation model of chloride ion distribution in concrete was established by theoretical derivation and fitting calculation, and the rationality of the model was verified. The life prediction of initial corrosion time of steel bars was performed for the designed gradient structure based on the simplified model. Research results show that the functional gradient structure can effectively adapt to the erosion characteristics of the upper part in the tidal and splash zone subjected to dry-wet cycles and the lower part subjected to long-term immersion. The combination of different admixtures inhibits the erosion of chloride ions, and the free chloride ion content in HPC is 17.7% lower than that in NC. The surface chloride ion content increases with time and tends to stabilize, which conforms to the exponential distribution. The chloride ion diffusion coefficient decreases with action time under long-term immersion or dry-wet cycles. Its reduction rate decreases with time, and finally tends to stabilize. Compared with the values from the test and related literatures, the relative error of chloride ion distribution curve obtained by the simplified calculation model is within 12%. The early warning times of initial corrosion of steel bars with and without admixture under the protective layer thickness of 60-80 mm are 41-85 and 26-47 years, respectively, proving that the addition of rust inhibitor and erosion inhibitor can significantly improve the service life of HPC-NC gradient column.