| With the continuous development of China’s marine power strategy,the demand of maritime infrastructure construction is gradually expanding.As a new type of cementitious material,alkali-activated cementitious material is expected to provide a new idea for the ecological design and performance improvement of marine structures.Corrosion of steel bars caused by chloride erosion in marine environment is one of the important challenges to the safety of marine structures in service,and the improvement of chloride erosion resistance of marine building materials is an important way to ensure the long-term safety of marine structures.However,the hydration characteristics and microstructure characteristics of alkali-activated cementitious materials are different from those of portland cement,and the chloride binding and transport characteristics are also different from those of portland cement.The analysis of its chemical composition and hydration products shows that its chloride binding capacity has room for further improvement.Therefore,in this paper,Ca(OH)2 and γ-Al2O3 is used as modification materials to study the feasibility of improving the resistance to chloride erosion by promoting the generation of chloride binding precursor in alkali slag cementitious material.Firstly,the phase composition characteristics of modified alkali-activated cementitious material system were studied by means of phase analysis and thermodynamic simulation.Then,the chloride binding capacity and mechanism is analyzed under various characteristic composition conditions.Finally,the chloride transport characteristics,microstructure characteristics and macroscopic properties of the modified cementite system is studied.The main conclusions are as follows:(1)The addition of Ca(OH)2 and γ-Al2O3 promoted the formation of more AFm mineral phases in the hydration products of alkali slag,which is chloride binding precursors.The supplementary Ca(OH)2 is not completely involved in the reaction process of alkali-activated slag,and there is surplus in the reaction products.After the chloride salt erosion,the surplus Ca(OH)2 is completely reacted and converted into F salt or other phases.The thermodynamic simulation results are in good agreement with the experimental results.(2)The supplementation of Ca(OH)2 and γ-Al2O3 promoted the formation of F salt in the slag system under the chloride salt environment,which promoted the improvement of the chemical biding capacity of chloride.The relative content ratio of Ca(OH)2/γ-Al2O3 in the initial material is an important factor affecting the chloride binding capacity of the material system,and the higher the ratio,the higher the chloride binding capacity in the alkali slag.In the experimental range,9% Ca(OH)2 and 3% γ-Al2O3 can increase the chloride binding capacity of alkali-activated slag by 32.18%..(3)The addition of Ca(OH)2 increases the chloride concentration on the surface of alkali slag specimen,but it improves the chloride binding capacity of the matrix,thus hindering the transport of chloride to the interior of the specimen,and reducing the chloride erosion depth and diffusion coefficient.The addition of γ-Al2O3 prevents the erosion of chloride by increasing the density of matrix,thus reducing the depth of chloride erosion,diffusion coefficient and chloride concentration in the specimen.When they are mixed together,the chloride concentration on the surface of the specimen increases,but the chloride erosion depth and chloride diffusion coefficient decrease significantly.(4)After chloride erosion,the harmful pores in the internal pores of each sample decreased,the total porosity decreased,and the surface morphology was more smooth and uniform.In terms of macroscopic properties,The addition of Ca(OH)2 and γ-Al2O3 shortens the setting time,fluidity and compressive strength of alkali-activated cementitious materials,among them,The addition of γ-Al2O3 delayed the setting time of alkali slag and refined its pore structure. |
