Preparation And Properties Of Geopolymer-based Straw Fiber Composites

Geopolymer,as a new environmentally friendly material widely used in the construction field,has the advantages of low energy consumption and low carbon emissions compared with traditional cements.It can be a good substitute for cement so that it is one of the hotspots in the field of materials at present.In order to overcome the brittle defects of geopolymers,the straw was used as the reinforcing and toughening material,the slag and metakaolin were used as gel materials,and the modified water glass was used as the alkali activator,the slag-based geopolymer fiberboard and slag-metakaolin-based geopolymer fiberboard were prepared by semi-dry process respectively.In this paper,orthogonal experiments and single factor analysis were used to explore the optimal preparation conditions of geopolymer fiberboard.The mechanical properties,water resistance,high temperature resistance and frost resistance of the geopolymer fiberboard were tested.At the same time,geopolymer fiberboard was analyzed by SEM to explore the strengthening mechanism.The results of the study were as follows:?1?By the test of hydration characteristics of metakaolin-based geopolymer with15 plant fibers,the effects of different plant fibers on the highest geopolymerization temperature(T_max),the time required to reach the highest geopolymerization temperature(t_max),the inhibition coefficient?I?and the fitness coefficient?C_A?were investigated.The results showed that all plant fibers inhibited the geopolymerization.However,the compatibility coefficient of all fibers was more than 93%,which indicated that the metakaolin-based geopolymer has good compatibility with all plant fibers.What is more,the wood fibers are more compatible than no-wood fibers as a whole.Compared to cement,the geopolymer has better compatibility with plant fibers without adding any additives.Therefore,these plant fibers have very good application prospects.Therefore,these plant fibers possess good application prospects for the production of geopolymer particleboard without adding any additives.?2?The optimal preparation parameters of the slag-based geopolymer fiberboard were obtained by orthogonal experiment and single factor analysis.The optimum combination of factor is A₃B₂C₂,and the optimal preparation parameters are that the water glass modulus was 1.9,the water-to-binder ratio was 0.4,and the fiber content was 12%.The optimum curing temperature is 40?and the optimum curing time is 7days,the bending strength of the fiberboard is up to 10.2 MPa,the internal bonding strength is 1.6 MPa,and the holding screw strength is 2098N.The 24h water immersion experiment showed that the water absorption was 4.2%,the thickness swelling rate was3.2%,and the bending strength loss rate is 10.1%,which can reach the superior product requirements specified by Cement Particleboard?GB/T 24312-2009?.?3?The optimal preparation parameters of the slag-metakaolin based geopolymer fiberboard were obtained by orthogonal experiment and single factor analysis.The optimal preparation parameters are that the water glass modulus was 1.9,the water-to-binder ratio was 0.4,the fiber content was 12%,and the metakaolin incorporation was15%.The optimum curing temperature is 40?and the optimum curing time is 7 days,the bending strength of the slag fiberboard is up to 10.0 MPa,the internal bonding strength is 1.18 MPa,and the holding screw strength is 2022N.The 24h water immersion experiment showed that the water absorption was 3.1%,the thickness swelling rate was 1.3%,and the bending strength loss rate is 8.8%,which can reach the superior product requirements specified by Cement Particleboard?GB/T 24312-2009?.?4?The results of TG analysis show that both geopolymer fiberboards have excellent high temperature resistance and their TG curves are very similar.When the temperature was between 200?and 660?,the bound water in the fiberboard began to depart and the plant fibers were carbonized.When the temperature reached about660?,the C-S-H gel in the matrix began to decompose.?5?The results of 50 freeze-thaw cycles test showed that both geopolymer fiberboards have good frost resistance,and the appearance of the fiberboards after the freeze-thaw remained intact.By analyzing the SEM image of the fracture surface of the fiberboards before and after freeze-thaw,it can be seen that the proper amount of plant fiber can contribute to the reinforcement and toughening of the fiberboards,and the adding of metakaolin made the matrix gel smooth and compact,which can help to improve the frost resistance of fiberboards.?6?The results of XRD and FTIR showed that the bond between the plant fiber and the matrix gel belongs to physical bond instead of chemical bond.