Preparation And Properties Of Slag Based Quick Setting Geopolymer Composites

The complex geographical conditions and bad climatic conditions in northwest China make most concrete structures exposed to the natural environment of strong wind-blown sand,large temperature difference and multi-chemical medium corrosion for a long time,resulting in a series of diseases such as erosion wear,icing expansion,ion erosion and so on,which leads to cracking,spalling and dissolution expansion of concrete structures.Seriously affecting the safety and durability of concrete structures,so it is necessary to repair them.However,some concrete structures,such as high-speed railway bridge beams,piers and ballastless track slabs,have the characteristics of short construction window period and high working intensity in daily maintenance.Therefore,the research on rapid repair materials with high durability of concrete structures has important engineering significance and practical value.As a new type of green inorganic cementitious material,geological polymer slag has the advantages of fast curing speed,high early strength and chemical resistance,thus it is expected to be used as a rapid repair material for concrete structure by blending with other cementitious materials.In this thesis,the slag-based quick-setting geopolymer material was studied,the effects of different factors on its working and mechanical properties were explored,and then the optimal mix ratio was determined.Secondly,it was toughened by chitosan or glass fiber,and the effects of chitosan or glass fiber content on the working properties,mechanical properties and durability(wind-blown sand erosion resistance,sulfate erosion resistance and freeze-thaw resistance)of slag-based quick-setting geopolymers were discussed,and their microstructure was characterized by LF-NMR,FT-IR,XRD and SEM.Finally,the quick-setting mortar was prepared according to the optimal mix ratio of slag-based quick-setting geopolymer materials,and the feasibility of its application in practical engineering was verified.The research contents and conclusions of this paper are as follows:(1)Proportional design of slag-based fast-setting geopolymer materials: An orthogonal experimental design was used to investigate the effects of water-collision ratio,Na OH concentration,alkali exciter modulus and cement admixture on the working properties,mechanical properties and microstructure of the specimens.It was finally determined that the specimens could be prepared with a water-cement ratio of 0.45,a Na OH concentration of 7.14 mol/L,an alkali exciter modulus of 1.5 and a cement admixture of 40% to meet the experimental expectations.Under this ratio,the flow rate of the slurry was 171.5 mm;the initial setting time of the specimen was 4.8 min and the final setting time was 11.7 min;the6-h compressive strength of the specimen reached 25.94 MPa and the 6-h flexural strength reached 2.03 MPa.(2)Chitosan/slag based rapid setting geopolymer composites were prepared with chitosan as toughening modifier,and the effect of chitosan content on the properties and microstructure of rapid setting materials was analyzed.The experimental results show that with the increase of chitosan content,the overall working properties of the quick-setting materials shows an upward trend,while the mechanical properties first increase and then decrease,and the sulfate resistance and freeze-thaw cycle resistance of the samples are significantly improved.However,the sample still shows the erosion characteristics of brittle materials in the wind-sand erosion wear test.Considering comprehensively,when the content of chitosan is 0.6 wt%,the comprehensive performance of chitosan is better.(3)Glass fiber/slag based rapid setting geopolymer composites were prepared with glass fiber as toughening material,and the effect of glass fiber content on the properties and microstructure of rapid setting materials was analyzed.The experimental results show that with the increase of glass fiber content,the working properties and mechanical properties of quick-setting materials increase at first and then decrease;at the same time,the wind-blown sand erosion resistance,sulfate erosion resistance and freeze-thaw cycle resistance are obviously better than the blank group.Considering comprehensively,when the content of glass fiber is 1.5wt%,the comprehensive performance of glass fiber is better.(4)Synthesize the toughening effect of chitosan and glass fiber,selected the best content to prepare slag-based quick-setting geopolymer mortar and tested its mechanical properties.It mainly included the compressive strength,flexural strength and bonding strength with the old cement base at different ages.The experimental results show that the compressive strength and flexural strength of mortar increase with the extension of curing age,and after adding toughening materials,the bonding strength of the sample exceeds the minimum standard,which meets the requirements of relevant technical specifications.