| With the increase of CO2emissions leading to global warming,the Chinese government has proposed to reach the carbon peak by 2030 and achieve carbon neutrality by 2060,which reflects the spirit of great power.However,as the main cementitious material of concrete,cement produces about 7%of the global CO2emissions every year.Therefore,it is of great significance to seek or develop an environmentally friendly material with both cement characteristics and green energy saving.As a new type of green building material,geopolymer concrete emits far less CO2than ordinary Portland cement in the production process.In addition,geopolymer concrete also has the advantages of durability,acid and salt corrosion resistance,wide source of raw materials and low cost.It has great application potential in marine engineering.However,the unique spatial structure of geopolymer concrete makes its brittleness more obvious,which limits its large-scale application.In view of such problems,the mechanical properties of geopolymer concrete can be improved by adding fibers.The research topic of this paper combines geopolymer with recycled aggregate and sea sand.The raw materials used are mostly renewable resources（recycled coarse aggregate）and industrial by-products（such as fly ash and slag）,which have the advantages of non-toxic side effects,no damage to the environment and sustainable development.Therefore,it is of great significance to study the preparation and mechanical properties of steel fiber geopolymer sea sand recycled concrete.The main work and achievements of this paper are as follows:（1）Based on the alkali-activated solution of sodium silicate and sodium hydroxide,geopolymer concrete with different ratios of fly ash to slag and fiber content was prepared,and its macroscopic mechanical properties were studied.The results show that when the concentration of sodium hydroxide is 10 mol,the mass ratio of sodium hydroxide solution to sodium silicate is 1:2,and the ratio of fly ash to slag is 4:6,the mechanical properties of geopolymer concrete specimens are the best.（2）Cubic compression test,axial compression test,static compression elastic modulus test and splitting tensile test were carried out on 156 fiber reinforced geopolymer concrete specimens.The effects of different fiber steel fiber types,fiber content and slag substitution rate on the mechanical properties of geopolymer concrete were revealed.The test data were normalized,and the test results of each group were comprehensively compared.The overall enhancement effect of steel fibers with different shapes on geopolymer concrete is:milling fiber<end hook fiber<wave fiber.（3）Direct shear test and composite shear test were carried out on 154 steel fiber geopolymer sea sand recycled aggregate concrete specimens.The effects of different steel fiber types,fiber content and axial compression ratio on the shear mechanical properties of geopolymer sea sand recycled aggregate concrete were revealed.The evaluation of steel fiber geopolymer sea sand recycled aggregate concrete based on equivalent shear toughness was given.（4）The relationship between cube compressive strength,shear strength,cylinder compressive strength and splitting tensile strength was fitted by Origin.Based on the test results,the compressive constitutive model of fiber geopolymer sea sand recycled aggregate concrete cylinder and the cube shear damage model are proposed.After comparison,the model is in good agreement with the experimental results of the stress-strain curve of geopolymer concrete.（5）Through a series of studies,the physical and mechanical properties of fiber geopolymer sea sand recycled concrete,the conversion formula of each strength index and the optimal dosage are obtained.The research results can provide reference for the research on the mechanical properties of fiber geopolymer sea sand recycled concrete and the practical application of engineering. |
