Corrosion-induced Cover Crack Monitoring And Prediction In Reinforced Concrete Based On BOTDA

Reinforced concrete structures were applied to the construction project since the early of19th century. It has been used for more than100years. The cracking of the protective layer caused huge losses. Due to the defects of the normal sensors and traditional monitoring tools, there still haven’t a suitable technology to monitor the whole process of steel corrosion in rein-forced concrete structures. BOTDA(Brillouin Optical Time Domain Analysis), a new type of sensor technology, has been developed in the last ten years. Due to the distributed propertiy and long period of life, it has been widely used in large-scale structures. However, it hasn’t been used in steel bar corrosion monitoring. In this article, we designed a special optical fiber sensorfirstly, then put them into a reinforced concrete specimen to monitor the whole process of the corrosion cracking. At last, we compared several different theoretical prediction model, and selected the most reasonable model as our base. The parameters in the base model are calculated using our monitoring data to improve the accuracy. The primary points of this article are as follows:(1)The characteristics of the fibre material, eoptical fiber sensor and its current application situation are induced. According to the actual corrosion mechanism of reinforced concrete structures, a new special optical fiber sensor was developed using to monitor cracking, corrosion and expansion strain in reinforced concrete structures.(2)A new instrument was developed which uses internal pressure to simulate steel’s corrosion and expansion. The developed optical fiber sensors are put inside and out surface of test concrete specimen. The gages are stickedon the outside surface too to compare the results. By using the new instrument to add water pressure to simulate the corrosion and expansion, we can measure the strain from the gage and distributed optical fiber sensor at all stages.Mean-while, we calibrate the crack and optical fiber strain relations after the crack appears in the test concrete specimen.(3)A accelerated corrosion test is applied to test the properties of our new designed optical fiber sensors which is placed in the concrete specimens. By comparing the different strain data of the reinforcement fiber sensor along the length of reinforcement, the serious rusting part can be determined. At the same time, the strain data are collected of all stages including the expansion and cracking.At last the specimens of different stages were cutted in the section where the sensors were buried. The rust layer’s thicknesses in different stages were observed by microscope and compared with the strain monitoring in the same stage.(4) Several different theoretical prediction models were selected and compared, the most reasonable model was choosed as our base. The parameters in the base model are calculated using our monitoring data to improve the accuracy. As the paramters are revised based on the data from the same structure and updated along the time, the prediction accuracy is improved significantly.