Durability Analysis Of Reinforced Concrete Structures In Coastal Saline Soil And Anti-corrosion Measures

There is a huge content of chloride in coastal saline soil, which will cause a high extent of corrosion to reinforced concrete structures buried in that kind of saline soil. It is very meaningful to analyze the corrosion influence of coastal saline soil on reinforced concrete, establish the numerical model concerning chloride ingress into concrete and predict the service life of structures exposed to saline soil since they are essential parts in designing concrete cover. Taking saline soil in Lianyungang as the example of coastal saline soil, the factors affecting chloride transport process in the pore solution of concrete were studied in this paper. Additionally, evaluations about the efficiency of anti-corrosion measures to increase life expectancy were presented. The main researches and achievements were as followings:(1) Chemical experiments were conducted to analyze salt characteristic of coastal saline soil, including salt type and salt content profile. It was proposed that saline soil in Lianyungang belong to chlorine saline soil with a class between low and middle. High content of chloride distributed from the surface to the depth of 2m. The chloride concentration decreased with soil depth in a pattern of line or parabola.(2) A comprehensive model to simulate chloride ingress into concrete exposed to saline soil was given, which took three transport mechanisms into consideration, including diffusion, migration and capillary suction in concrete pore solution. The calculated results by this model agreed well with chloride profile obtained from concrete samples in situ. With finite element method, influences of binding, diffusion potential and capillary action on chloride transport were conducted. It was shown that binding will reduce the amount of chloride in pore solution. The diffusion potential generated by multi-ions transport, which was unique characteristic when exposed to saline soil rather than other saline environments, accelerated chloride ingress and caused a higher corrosion risk than sea water. And the initial unsaturated state of concrete pore structures led to chloride accumulation at the surface layer of concrete due to capillary action. Thus, capillary action affected chloride content distribution at the surface layer of concrete at early stage. Then the influences moved to the deep layer at late stage. It eventually increased chloride concentration at steel surface.(3) Based on seasonal variations of saline soil, effects on chloride distribution in concrete brought by changes of temperature and salt content were conducted. It was put forward that seasonal variations of temperature reduced free chloride concentration when compared with that of constant room temperature state. Salt content in saline soil varied in one year cyclically in the trigonometric type. It resulted in cyclical changes of chloride distribution at the surface layer of concrete with a width of 15mm. Step and peak appeared in this area in turns. However, salt seasonal variations had little effects on chloride content at deep layer of concrete.(4) Evaluations of anti-corrosion measures on increasing service life of reinforced concrete exposed to saline soil in Lianyungang, such as increasing thickness of concrete cover, surface treatment and adding supplementary cementitious materials were presented in this paper. Increasing the thickness of concrete cover could effectively boost durability of reinforced concrete. The service life was doubled once the thickness of concrete cover increased 10mm. Adding supplementary cementitious materials like slag could enhance binding capacity of concrete, and metakaolin> slag >fly ash. However, silica fume would significantly damage concrete binding capacity. Surface treatment would slow down the chloride transport process, and silane>epoxy coatings>acrylic coatings. It was suggested that the thickness of concrete cover buried in saline soil in Lianyungang be at least 50mm.