Investigation On The Seawater Corrosision Resistance Of Geopolymer Concrete

Traditional Portland cement concrete structures in marine environment presented poor durability due to degradation of hydration products,steel bar corrosion,and etc.,resulting in much shorter service life.Compared to Portland cement,the reaction products of geopolymer showed superior stability,dense structure,and low corrosion resistance.Therefore,geopolymer concrete is expected to be used in marine structures.In this paper,the influence of Cl^-,Mg²⁺and SO₄^2-on the properties of geopolymer paste was studied.Meanwhile,the corrosion resistance of geopolymer paste to Cl^-,Mg²⁺and SO₄^2-was also discussed,and the seawater corrosion resistance of geopolymer concrete was evaluated by chloride penetration and sulfate resistance test.The corrosion of steel bar in geopolymer system was revealed.The main research contents and results are as follows:The effects of Cl^-,Mg²⁺and SO₄^2-on the properties of geopolymer slurries were studied,and the influence of the introduction of ions into the seawater on the reaction products of geopolymer was discussed.The results showed that:the inner addition of Cl^-,Mg²⁺and SO₄^2-had no significant effect on the rheological and mechanical properties of geopolymer.The ability of geopolymer to solidify Cl^-and SO₄^2-was lower than that of portland cement,but its ability to solidify Mg²⁺was higher than that of cement,up to 90%.Geopolymer have better resistance to Cl^-,Mg²⁺and SO₄^2-than portland cement,and the resistance of geopolymer hardened paste to Cl^-,Mg²⁺and SO₄^2-erosion was not affected by the inner addition of seawater.In the case of inner-doped ions,geopolymer do not generate new products,and gypsum products are generated only under the MgSO4 attack,indicating that geopolymer reaction products have good stability under seawater environment.The resistance to chloride ion penetration and sulfate resistance of geopolymer concrete and cement concrete were comparatively studied.The results show:the unsteady chloride ion transfer coefficient(D_RCM)of geopolymer concrete is 2.89×10^-12 m²/s,which was significantly smaller than that of cement concrete(10.53×10^-12 m²/s).Under the action of sulfate attack and dry-wet cycle,the sulfate resistance of geopolymer concrete was better than that of cement concrete.In addition,the incorporation of sea sand has little effect on the sulfate resistance of geopolymer concrete.The destruction of the geopolymer concrete is mainly the dissolution of the slurry,no obvious cracks are generated on the surface of the concrete,and the cement concrete appears expansion failure at 75 days.The electrochemical corrosion of steel bars in geopolymer mortar under seawater erosion environment was studied.Compared with the Portland cement paste,the open circuit potential of the steel bar in the geopolymer varies with the increase of the infusion age,and it is difficult to determine whether the bar is desensitized from the change of the corrosion potential over time.After 90 days of soaking,the charge transfer resistance R_wt of the geopolymer bar decreased by 17%,while the R_wt of the Portland cement decreased by95%,and the mortar resistance of the geopolymer at all ages was greater than that of the Portland cement mortar,indicating a good protection effect on steel bar;The mixed seawater will reduce the mortar resistance of the geopolymer and the charge transfer resistance of the steel bars,and increase the corrosion current density.The i_corr after 90 days of soaking is 4.2 times and 14.8 times the blank,and the mortar resistance is only 79%and70%of the blank.that is,the higher the concentration of added seawater,the more obvious the effect is and the more easily the steel is corroded.This study can provide theoretical basis and technical support for the application of inorganic polymer concrete in marine concrete,and has significant economic and social benefits.