Study On The Properties Of Fiber-reinforced Geopolymer Mortar Under Sulfate Corrosion And Drying-Wetting Cycle Coupling

Under the alternating coupling of sulfate erosion-dry and wet,the concrete deteriorates such as expansion cracking,spalling and even pulverization,and the bearing capacity of the structure decreases rapidly and the reliability decreases.As a new type of inorganic cementitious material composed of silicon-oxygen tetrahedron and aluminum-oxygen tetrahedron polymerization,geopolymer has the advantages of high strength,corrosion resistance and green environmental protection,and has a wide range of application prospects in many fields.However,the performance and deterioration mechanism of geopolymer materials in sulfate environment are not fully studied,and their damage deterioration is more complex in sulfate erosion-dry and wet alternating environment.In order to improve the stability and service life of geopolymer concrete in sulfate erosion-wet and dry environments.The fiber-reinforced fly ash-metakaolin based geopolymer mortar was prepared from the main raw materials of fly ash,metakaolin,carbon fibers(CF)and polypropylene fiber(PP).Sulfate corrosion and drying-wetting alternation were applied at the same time.The appearance,microstructure,mass loss rate and mechanical properties of geopolymer mortar after sulfate corrosion and drying-wetting alternation coupling were studied by means of SEM combined with EDS spectroscopy,XRD and mechanical test.The main findings are as follows:In the process of sulfate erosion-dry and wet alternation,fiber-reinforced metakaolin-fly ash base geopolymer mortar has good apparent and quality stability,the geopolymerization reaction enhanced the strength of the specimen and optimized the internal structure of the specimen,so that the strength of the specimen first increased and then stabilized.The incorporation of fibers can improve the resistance of the specimen to sulfate attack,through microscopic analysis technology,it was found that the sodium sulfate solution evaporated on the surface of the specimen and formed white crystals,and no harmful crystals were produced inside the specimen.There is a material exchange between the geopolymer mortar specimen and the sodium sulfate solution,and the alkaline substances inside the specimen gradually seep out into the solution during the dry and wet alternating process,causing the p H value of the sodium sulfate solution to increase.The incorporation of appropriate amount of fiber can improve the mechanical properties of geopolymer mortar after sulfate erosion-alternating coupling of dry and wet,among which the addition of 0.60% carbon fiber has the most obvious effect on the compressive strength,axial compressive strength and static compressive elastic modulus of the specimen,and the addition of0.30% carbon fiber + 0.30% polypropylene fiber has the most obvious effect on the flexural strength of the specimen.Through SEM-EDS analysis,it was found that the fibers were staggered and distributed inside the specimen,and the incorporation of fibers inhibited the insufficiently reacted alkali initiator dissolved in the sodium sulfate solution to a certain extent,which provided favorable conditions for the geopolymer to continue to react to produce C-S-H gels in the later stage,and ensured the overall stability of the specimen.Based on the test results,it is concluded that the metakaolin-fly ash base geopolymer mortar has good physical properties and chemical stability under the coupling of sulfate erosion-dry and wet alternating.The incorporation of different types of fibers has a certain effect on the sulfate erosion resistance of the geopolymer,and the fiber content also has a certain effect on the sulfate erosion resistance of the geopolymer.In the future,it is necessary to comprehensively consider the fiber type and fiber content,and configure a high strength and strong sulfate erosion resistance to metakaolin-fly ash base geopolymer mortar.