Study On Chloride Corrosion Durability Of Reinforced Concrete Marine Structures

In this paper, some experiments including concrete resistivity, electric flux, reinforced cracked rust damage and chloride ion penetration are studied. Combined with chloride ion diffusion theory, engineering fuzzy set theory and survival analysis theory, corrosion model of steel bars in reinforced concrete marine structures is established. Meanwhile, durability life prediction and statistical estimate are studied. Major research work includes:1) Concrete resistivity are tested by means of the RESI Resistivity Tester in two types of humidity environment. By changing properties of concrete material, 28-day concrete specimens including four amounts of cement, three kinds of water-binder ratios, four contents of fly ash, three contents of grounded furnace slag, as well as four contents of silica fume are grouped in detail. Test results show that concrete resistivity are more or less influenced by all properties of concrete material. Among them, effects from groups of water-binder ratios and mineral admixtures are more obviously. The smaller the water-binder ratios and the greater the admixtures amount, the greater the resistivity of concrete; effects on the resistivity from group of silica fume are most significantly in three kinds of mineral admixtures. The resistivity of concrete can significantly be improved by a small amount of silica fume, while the fly ash and grounded furnace slag require a higher proportion of dosage. Test references for the study on chloride ion diffusion velocity in concrete are provided by above tests measurements based on changing value of concrete resistivity.2) This electrochemical accelerated steel corrosion tests involve a total of 42 pairs for 7 groups of material factors including three kinds of water-binder ratios, three kinds of cover thickness, three kinds of bar diameter, as well as incorporation of 40% fly ash and 1% WACKER SILICONES powder. Reinforcement cracked rust damage pattern are studied from these groups of concrete specimens. Meanwhile, cracks development law of reinforced concrete cover after corrosion are analyzed. The results show that the early cracks time in reinforced concrete, the pace of development as well as the crack shapes are influenced by above material factors. Water-binder ratios the smaller cracks sooner; cover thickness the greater cracks development more slowly; bar diameter the smaller cracks sooner. According to different surface cracks width (ie, 0.2mm, 0.4mm, 0.7mm, 1.0mm and 1.5mm), a specimen from each group is broken and the rate of reinforcement corrosion can be determined by means of rust remover method. At last, fitting curve models between cracks width with the rate of reinforcement corrosion can be concluded. 3) Electric flux and chloride ion diffusion properties of concrete are tested based on different water-binder ratios as well as the incorporation of fly ash and silica fume. Effects by water-binder ratios and mineral admixture such as fly ash and silica fume for durability of reinforced concrete marine structures to resist chloride ion penetration are analyzed. Tests show that after admixture of appropriate fly ash and silica fume, electric flux of concrete specimens can significantly be reduced, and durability of resistance to chloride ion penetration can be well improved. Meanwhile, the fitting model of relationship between water-binder ratios with electric flux and chloride ion diffusion coefficient are established. At last, durability life about different material properties of concrete are predicted.4) Chloride ion diffusion process in concrete are described by improved Fick Second Law of diffusion, and starting corrosive time (T_i) of reinforcement in concrete can be predicted. According to the characteristics that corrosion rate on reinforced along its length direction and the direction perpendicular to the length is not synchronized because of chloride ion permeability leading to two-way erosion, steel pitting corrosion model—ellipsoid model is established on the basis of reinforcement corrosion changed by chloride ion. The example shows that the role of effect by attenuation value of chloride ion diffusion coefficient (m) in the model is fully considered, and this corrosion model is more suitable than other models in reinforced concrete structures under chloride ion penetration. It is the creation that determination the time (T_c+T_d) from steel started corrosion to occur in significant degradation to the function in marine concrete structures is instructive.5) Durability life of reinforced concrete marine structures are discussed by means of Product-Limit survival function estimation in survival analysis. Combined with the characteristics of durability failure for concrete structures, Fuzzy Comprehensive Evaluation method is practiced. Then durability assessment level and membership to durability life estimate for marine concrete structures is studied. As a result, a fuzzy eigenvalue formula about censored indicator function is established. More reasonable life expectancy statistics analysis results on durability of concrete structures can be obtained by this method.