Erosion Of Golden Mussels-based Fouling Organisms On Concrete In Water Transfer Project And The Related Protection Methods

In water transfer project,fouling organisms can easily attach on the surface of concrete structures with an extremely high density.Among them,Golden mussels become a major challenge in the water supply projects in south China,leading to erosion damages on concrete and seriously affecting the service life of concrete structures.Therefore,it is very urgent to investigate the biodeterioration mechanism and prevention methods for the erosion damage caused by golden mussels.This thesis is based on Dongguan-Shenzhen water supply project in Guangdong province.First,in order to clarify the reasons for erosion and related influence on concrete caused by golden mussels-based biofouling system,the metabolites of the biofouling system and degradation of concrete were analyzed.The coupled effect between biological metabolic acid erosion and current scour was then simulated and investigated,including the chemical composition,pore structure,erosion depths and surface quality of the unit loss.Finally,different types of coating were applied for field plate tests and laboratory tests,and the protection effect of coatings on the biological adhesion and protection of concrete were investigated.The investigations on the filtrated solution of biofouling system and core samples of concrete indicate that in the water transfer project,a large amount of golden mussels was attached on concrete surface,and accompanied by sediment,algae,bacteria,fungi and algae.The erosion damage of concrete was caused by the micro-ecological system consisted of golden mussels,sediment,algae,bacteria and fungi.The aggressive metabolites of the micro-ecological system were acetic acid and propionic acid.The organic acid can lead to the decomposition of hydration products(calcium hydroxide and hydrated calcium silicate).Besides,fouling organisms promoted the carbonation of concrete.Laboratory investigations on the erosion of cement paste caused by the coupled effect between biological metabolic acid and current scour shows that the erosion effect of bio-organic acids on cement paste was more pronounced than carbonation because of the high solubility of corrosion product(carboxylate).As a result,the porosity of cement paste increased with the erosion time.Further,there was a direct relationship between the erosion depth and square root of time.The erosion depth in cement paste exposed to flowing organic acids was 2.72 times higher than in static organic acids.The mass loss per unit area of cement paste exposed to flowing organic acids was 3.77 times higher than in static organic acids.The coupled effect of organic acids and scour significantly accelerated the deterioration process of cement paste compared with static organic acids erosion.The mass loss per unit area reflected the chemical effect of organic acid and physical effect of flow washout,thus is more suitable for the performance degradation assessment of cement-based materials.According to both the field and laboratory tests,an adhesion force of 4 N was needed forthe golden mussels to attach on concrete surface at early adhesion stage(0~6 month).When stable adhesion was formed(6~12 month),the adhesive force increased to 6~8 N;the attached amount of fouling organisms also increased to about 1200/m2.There was a negative correlation between the attached amount of biological adhesion and contact angle of coating,indicating that coatings with a low surface energy was more suitable for the prevention and treatment of golden mussels attachment.Among the four types of coatings,Kansai BIOX coatings was the best antifouling and protection coating;but because of its low hardness,it can only be applied in water transfer channels with low sediment concentration.China Nuclear 2000 B coating also presented a good protective effect: although its performance was inferior to Kansai coating,its microhardness was higher,thus can be widely applied in water transfer project.The effect of alkali activated coating was similar to China Nuclear 2000 B coating,but the cracking problems needed to be solved.The worst-performing was Xypex coating.The contact angle,micro hardness and acid resistance of the coating can be used as the evaluation indexes of the protective coatings.