Study On Chloride Transport Behavior Of Semi-immersed Coral Aggregate Concrete

In infrastructure construction of islands,many problems,such as lack of building materials,difficult transportation and high cost,which restrict the development and construction of islands to a large extent.Using the existing coral reef as aggregate to prepare coral aggregate concrete can alleviate the shortage of raw materials in the construction of the island and reef project to a certain extent.Moreover,part of the concrete structure of marine infrastructure is semi-immersed in seawater,that is,one part of which is exposed to the marine hot and humid climate environment,and the other part is immersed in seawater all the year round.Therefore,it is of great significance to study the chloride transport behavior of coral aggregate concrete in semi-immersed seawater and establish chloride transport model to ensure the durability of infrastructure near water.Based on the extreme hot and humid climate of the South China Sea islands and reefs,in view of the deterioration of the durability of concrete components semi-immersed in the sea water,considering the influence of multiple ions,the chloride transport law of coral aggregate concrete under"wick effect"was studied under the condition of single Cl^-erosion,Cl^-,SO₄^2-erosion,and Mg²⁺,Cl^-,SO₄^2-erosion,and the corresponding chloride transport model was established.（1）The changes of morphology,mass loss rate,chloride content,p H value of pore fluid,and phase composition of the coral aggregate concrete under the condition of single Cl^-erosion were studied,and the chloride transport model of coral aggregate concrete eroded by single Cl^-was established.The results shows that the chloride are paraboloid distributed in coral aggregate concrete,and the content is proportional to the erosion age.With the increasing chloride erosion age,the p H value in the pore solution decreased gradually,and the content of Friedel’s salt increased gradually.Moreover,the improvement ability of different admixtures to chloride resistance of coral aggregate concrete listed in descending order is silica fume,fly ash,and slag.（2）The variations of morphology,mass loss rate,chloride content,p H value of pore fluid,and phase composition of the coral aggregate concrete under the condition of Cl^-,SO₄^2-erosion were investigated.The chloride transport model of coral aggregate concrete under the erosion of Cl^-,SO₄^2-was established by considering the influence of SO₄^2-on chloride transport.Results indicates that a large number of white crystals are formed on the surface of the specimen due to the combined action of SO₄^2-and Cl^-.The mass of specimens increased slightly in the early stage of erosion,and then increase significantly.The effect of SO₄^2-on chloride transport was first inhibited and then promoted.Moreover,due to the existence of SO₄^2-,the p H value of pore fluid in concrete decreases obviously in the early stage,and slowly in the later.Besides the Friedel’s salt,two typical erosion products,such as Gypsum,and Ettringite were observed.The improvement ability of the admixture to chloride resistance of coral aggregate concrete listed in descending order is silica fume,slag,and fly ash.（3）In addition,the changes of morphology,mass loss rate,chloride content,p H value of pore fluid,and phase composition of the coral aggregate concrete under the condition of Mg²⁺,Cl^-,and SO₄^2-erosion were also studied.The chloride transport model of coral aggregate concrete under the erosion of Mg²⁺,Cl^-,and SO₄^2-was finally established by considering the influence of the main anions(Mg²⁺)and cations(SO₄^2-)in seawater on chloride transport.Results shows that only a few white crystals were formed on the surface of the specimen due to the joint action of Mg²⁺,Cl^-,and SO₄^2-.The presence of Mg²⁺,reduces the mass growth rate of the specimen,and inhibits the chloride transport in the coral aggregate concrete.Moreover,four kinds of erosion products,such as Mg（OH）₂,Friedel’s salt,Gypsum,and Ettringite were observed.The improvement ability of the admixture to chloride resistance of coral aggregate concrete listed in descending order is silica fume,fly ash,and slag.