Durability Of Marine Concrete With Nano-particles Under The Combined Action Of Cl~- Corrosion,Carbonation And Dry-wet Cycles

Marine concrete refers to concrete applied in Marine engineering construction.With the development and utilization of Marine environmental resources,people have higher and higher requirements on its durability.However,the Marine concrete structure has a bad service environment and is damaged by various Marine environmental factors and corrosive media.In particular,Marine concrete structures located in tidal areas are not only affected by the dry-wet cycle caused by tidal action,but also by the erosion of Cl^-in seawater and CO₂ in air,which greatly aggravate the deterioration of Marine concrete structures under the joint action of various factors.Therefore,it is very important to study the durability of Marine concrete under the combined action of Cl^-erosion,carbonation and dry and wet cycle.Because of its small particle size and high specific surface area,nanomaterials have derived many special effects（such as volume effect,surface effect,small size effect,etc.）,which have been widely used in many fields.The use of nanomaterials to improve the durability of concrete has become a research hotspot in recent years.In this paper,nano-SiO₂ and nano-Al₂O₃ were added into concrete respectively,to study the anti-Cl^-erosion and anti-carbonation properties of nano-marine concrete under the combined action of Cl^-erosion,carbonation and dry and wet cycle,and to further reveal the durability improvement mechanism through microscopic tests.The main research contents of this paper are as follows:（1）By comparing the slump and compressive strength of nano-concrete and ordinary concrete,the improvement rule of nano-SiO₂ and nano-Al₂O₃ on the slump and compressive strength of concrete is revealed.（2）Set up verification tests for the interaction between Cl^-erosion and carbonization,study the influence of Cl^-erosion on carbonation and the influence of carbonation on Cl^-erosion,and reveal the interaction mechanism between the two.The test results show that Cl^-erosion has a blocking effect on carbonation.Carbonation has a double-sided effect of hindering and promoting Cl^-erosion,On the one hand,in the carbonation zone,carbonation increases the density of the concrete and hinders the diffusion of Cl^-;on the other hand,carbonation reduces the Cl^-binding capacity of the concrete,leading to an increase in the free Cl^-content at the junction of the carbonation and non-carbonation zones,which promotes the diffusion of Cl^-.（3）The durability test of concrete under the combined action of Cl^-erosion,carbonation and dry-wet cycles was conducted to study the influence law of the dosage and type of nanomaterials on the Cl^-erosion and carbonation resistance of concrete under the combined action of three factors.The internal structural morphology and phase composition of concrete were analyzed by microscopic tests,and the mechanism of nanomaterials improving the durability of concrete was revealed.The experimental results show that the addition of nanomaterials can promote the hydration process of cement,refine the pore structure of concrete,and improve the Cl^-erosion resistance and carbonation resistance of concrete under the action of three factors.