Study On Chloride Diffusion In Coral Concrete Under Dry-wet Cycle

The south island reef is far away from the mainland,the transportation is inconvenient,and the resources such as sand and stone on the island are limited.South Island Reef is rich in coral reef（sand）resources,and using coral instead of sand and stone materials to configure concrete can effectively solve the above problems.In addition,the chloride salt corrosion of the concrete structure in the ocean tide area（dry-wet cycle area）is extremely serious.Carrying out the durability study of the chloride ion diffusion behavior of coral concrete in the dry and wet cycling area of the marine environment can provide a reference for coral concrete block masonry and reinforced coral concrete structure,which is of great significance to the construction of the ocean and the development of marine science and technology.The specific content includes:（1）Conducted a chloride ion diffusion behavior study on coral concrete in 3.5%Na Cl solution under dry-wet cycle conditions.The ion selective electrode method was used to measure the chloride ion concentration of coral concrete,and the distribution of chloride ion concentration along the depth of the test piece,the surface chloride ion concentration Cs and the apparent chlorid e ion diffusion coefficient Da were analyzed.The results show that the addition of mineral admixtures to coral concrete can improve the resistance to chloride ion corrosion.The best effect is to mix 15%fly ash+5%silica fume,and the effect of grinding fine slag is better than fly ash.（2）Conducted studies on the apparent morphology,physical and mechanical properties,and chloride ion diffusion behavior of coral concrete in 3.5%Na Cl+5%Na₂SO₄ mixed salt solution under dry-wet cycle conditions.It was found that the erosion of the concrete specimen in the mixed salt solution under the dry-wet cycle condition can be divided into chemical erosion and physical erosion,and the physical erosion damage plays a leading role.The mass loss rate of concrete specimens decreases first and then increases with the erosion time;the relative dynamic elastic modulus and the relative compressive strength increase first and then decrease with the erosion time;the thickness of the damaged layer keeps increasing with the erosion time.In addition,the sulfate ion in the mixed salt solution can improve the resistance of coral concrete to chloride ion attack.（3）Using microscopic test methods:X-ray diffraction analysis（XRD）,thermogravimetric and differential thermal analysis（TG-DTG）and scanning electron microscopy analysis（SEM-EDS）,to study phase composition,internal micro-morphology and corrosion degradation mechanism of coral concrete erosion products in 3.5%Na Cl solution,3.5%Na Cl+5%Na₂SO₄mixed salt solution under dry and wet cycling conditions.It was found that the erosion products of coral concrete in 3.5%Na Cl solution under dry-wet cycling conditions mainly include Friedel’s salt;the erosion products in the mixed salt solution of 3.5%Na Cl+5%Na₂SO₄ contain a large amount Expansive erosion products ettringite and gypsum.