| Geopolymer is a new kind of green building material due to its unique three-dimensional network structure,has excellent mechanical property,chemical stability,high temperature resistance properties and so on.Furthermore,it has a lot of advantages,including rich source of raw materials,simple preparation process,environmental protection,no pollutants and so on,has been extra attention in the filed of building and toxic wastes.However,it has short research and application due to rich source of raw materials and lack of relevant norms and standards.Thus,the promotion and application of geopolymer are limited.In this paper,fly ash-metakaolin composite based geopolymer were prepared by fly ash and metakaolin as the basic powder and sodium water glass as activator,the heat flow,microstructure,pore structure,characteristic band,the phase composition and ion leaching rate were analyzed by ICC,SEM,MIP,FT-IR,XRD and AAS testing techniques respectively.The influence of molar ratio of H2O/Na2O,SiO2/Al2O3 and Na2O/Al2O3 on the structure and mechanical property,thermal stability,efflorescence,shrinkage and carbonation performance of FMG were systematically studied.Obtaining the mixture ratio with excellent durability of FMG.The main results are as follows:?1?By studying the influence of oxide composition on the structure and mechanical property of FMG,the results show that:the maximum hydration heat of FMG samples is gradually increasing when the molar ratio of H2O/Na2O decreased from 14 to 10,the molar ratio of SiO2/Al2O3 increased from 3.9 to 4.3 and the molar ratio of Na2O/Al2O3 decreased from 0.90 to 0.70.Low H2O/Na2O ratio is conducive to the preparation of geological polymers with lower porosity,more abundant gel pores and higher compressive strength.Increasing the molar ratio of SiO2/Al2O3 can promote the formation of gel phase and improve the compressive strength,although the pore structure change is not obvi ous.?2?By studying the influence of oxide composition on the thermal stability of FMG,the results show that:the sample can keep the 28d compressive strength when the thermal treatment temperature below 600?.The sodium nepheline will be formed when thermal treatment temperature is between 600?-800?,which causes sharply decreased on shrinkage and residual compressive strength.Some specimens will rupture at 1000?.The compressive strength of specimens HN-10 and NA-0.70is 30.91MPa and 42.49MPa respectively when the thermal treatment temperature is800?,is higher than OPC·42.5 of the ratio of water/ash?14.0MPa?.?3?By studying the influence of oxide composition on the shrinkage performance of FMG,it is found that:the autogenous shrinkage and dry shrinkage of all FMG specimens is obvious in the first 7 days,then decrease in the range from7-day to 42-day.The shrinkage rate tends to be stable after 42-day.The shrinkage is mainly related to the total porosity.The total porosity and the proportion of gel pores of FMG specimens will decrease and increase respectively in the process of autogenous shrinkage and drying shrinkage.?4?By analyzing the influence of oxide composition on FMG efflorescence performance,it is found that:the pH value of leaching is gradually increasing when FMG after a certain period of efflorescence.Na+and OH-in the leaching will react with CO2 in air to form the white efflorescence products?Na2CO3·H2O?on the surface of specimens.The higher porosity will promote the dissolution of Na+,Al3+,Si4+and OH-of specimens.The soluble silicon and aluminum in the leaching will polymerize again at 28-day of efflorescence to form gel phase and reduce the concentration of Al3+and Si4+.?5?By analyzing the influence of oxide composition on the carbonization performance of FMG,it is found that:the compressive strength of FMG decreases obviously after carbonization.A large amount of carbonate and bicarbonate will form and fill the pores with the carbonation time increased,which will make up for the loss of compressive strength.The surfaces of HN-14,SA-3.9,SA-4.0,SA-4.1and NA-0.9 were covered with a large amount of carbonate and bicarbonate at60-day carbonation.Furthermore,the degree of carbonation was the most serious.?6?The workability?fluidity and setting time of slurry?,mechanical properties and durability of FMG is comprehensively considered,it is found that:the optimal ratio range of fly ash-metakaolin composite base geopolymer is H2O/Na2O between11-12,SiO2/Al2O3 between 4.2-4.3,and Na2O/Al2O3 between 0.70-0.80.Using the optimal ratio to prepare FMG,compressive strength is higher than 80MPa before28d,residual strength remains 30MPa after 800?thermal treatment,the autogenous shrinkage and drying shrinkage of 90d is below 1800?10-6 and2000?10-6 respectively.At the same time,the amount of Al3+and Si4+is below1.50?10-4%and 2.50?10-4%respectively during efflorescence.And efflorescence products?Na2CO3·H2O?are found on the surface of specimens.The compressive strength was above 40MPa,and there was no obvious car bonation on the surface of the sample after 60d carbonation. |
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