Study On Performance Of Sea Sand Concrete Modified By New Admixture

With the gradual acceleration of urbanization in China,the amount of concrete is increasing and the demand for river sand is increasing.However,due to excessive exploitation,the river sand resources in China are short and the Marine resources are rich.In recent years,obtaining sea sand from the Marine environment has become the mainstream trend of the construction industry.Instead of river sand,sea sand can effectively alleviate the shortage of river sand,but the harmful substances contained in sea sand such as chloride ions and shells will induce the corrosion of steel bars and reduce the durability of concrete.In this paper,the new antiseptic and impervious admixtures YYO and YYOL are respectively added in the concrete mixing process to reduce the chloride ion content in the free state of concrete and improve the durability of concrete.This requires a large number of basic experiments to study its feasibility and effectiveness.In view of this,the mechanical properties,durability and chloride ion content of modified sea-sand concrete with new anti-corrosion and anti-seepage additives were studied and its microstructure was observed.The main research contents are as follows:(1)According to the national standards,the apparent density,fineness modulus,mud content and other indicators of sea sand were detected.The main differences between sea sand and river sand were reflected in the high density,smooth surface,small amount of shell residue and high content of chloride ions.(2)according to the procedure to calculate the sea sand concrete mixture ratio design of the trial batch mixing ratio,on the basis of trial mix proportioning keep unchanged water regulating water-cement ratio and sand rate calculation in the other two groups mixture ratio,through strength test choose water/cement ratio 0.40 from three groups of mixture ratio,sand ratio of proportion of 37%for the final,using the "absolute volume method" is calculated for each part of the dosage,According to the final mix ratio,ordinary concrete NAC,sea sand concrete SRNC,two groups of modified sea sand concrete SRNC1,SRNC2 were prepared.(3)Silver nitrate titration method was used to detect the chloride ion content of hardened concrete.The chloride ion content of SRNC1 and SRNC2 of the two groups of modified sea sand concrete with the addition of new anti-corrosion and impermeable agent was reduced to 35%and 46%of that of ordinary sea sand concrete.(4)The mechanical property test results show that the strength of sea sand concrete at different ages is similar to river sand concrete.The compressive strength and flexural strength of sea sand concrete within 7 days increase rapidly,the strength at 28 days is no different from that of ordinary concrete,and the strength at 90 days is slightly lower than that of ordinary concrete.The compressive strength of modified sea-sand concrete srNC17d is 75%of that of 28d,and the compressive strength of modified sea-sand concrete 90d is 43.4 MPa.The measured value of elastic modulus of sea-sand concrete is greater than that of ordinary concrete.The new admixture has little influence on short-term strength of sea-sand concrete.(5)The freeze-thaw resistance and carbonization resistance of sea-sand concrete are poor,and the chloride penetration resistance is good.After adding anti-corrosion and antiseepage agent,the improvement was remarkable.The frost resistance grade of sand concrete is D125,the carbonization depth reaches 26.28 mm,and the chloride ion migration coefficient is 7.83.The frost resistance grade of modified sand concrete SRNC1 is D200,the carbonization depth of 28d is 15.89 mm,and the chloride ion migration coefficient is 6.81.The frost resistance grade of SRNC2 of modified sea-sand concrete reaches D200,the carbonization depth of 28d is 16.31 mm,and the chloride ion migration coefficient is 7.26.(6)SEM scanning shows that sea sand concrete is denser than river sand concrete.Element scanning shows that chloride ions are evenly distributed in mortar of sea sand concrete.Chlorine content of ordinary sea sand concrete is 3%,and that of modified sea sand concrete is 1%.The content of chlorine elements near the interface transition zone of sea sand concrete is more concentrated,and the chloride ions are hindered by stones in the process of movement,and accumulate around stones,resulting in the formation of F salt and micro-cracks near the transition zone.