| Fireproof coatings for concrete structure are effective barriers applying in protecting firebanks of storage tank,or tunnels of roads and railways.Traditional fireproof coatings exhibit limited fire resistance,toxicity and high costs,while inorganic fireproof coatings exhibit flaws of low adhensive strength,heavy weight and easy to crack at high temperature,which also limits its wide application.Therefore,it is significant to explore an environment friendly fireproof material.In this study,geopolymer fireproof coatings are prepared from metakaolin and silica fume under activation of water glass.The superior Si/Al is confirmed on the basis of surface drying time,dry bulk density,compressive strength and adhesive strength.In addition,effect of expanded perlite,ratio between coarse and fine fly ash cenosphere（C-FAC and F-FAC）on geopolymer coating are evaluated via physical properties,durability and fire resistance tests.Finally,light-weight geopolymer fireproof coating reinfored by basalt and wollastonite fibers exhibits excellent adhesive strength,durability and fire protection performance.The results show that when Si/Al=2.5,the introduced silicon source is beneficial to the formation of N-A-S-H gel,and the mechanical properties of geopolymer fireproof coating reach the highest value.The bonding mechanism between geopolymer fireproof coating and cement matrix is mainly physical combination.After 15 times freeze-thaw cycles,network cracks appeared on the surface of the samples prepared with F-FAC,which was related to the high shrinkage of geopolymer.C-FAC could be used as rigid framework to alleviate the shrinkage of coating,which prevents the crack propagation and changed the direction of crack extention.After fire resistance test,the reverse temperatures of geopolymer fireproof coating were lower than 250 °C.XRD and SEM results show that part of amorphous gel transformed into nepheline at high temperature.Expanded perlite could improve porosity and reduce dry bulk density of geopolymer coating due to its highly porous structure.However,when the mass of expanded perlite increase excessively,mechanical strength of samples would dramatically decline.Thus,the mass proportion of expanded perlite in the system should not be more than 9%.Mass ratio of CFAC and F-FAC mainly affects the content of coarse aggregate and fine aggregate and pore distribution in geopolymer.When mass ratio of C-FAC and F-FAC =4:6 and expanded perlite content is 9wt%,the specimens remained considerable compressive and bonding strengths,which are 5.876 MPa and 0.402 MPa,respectively.At the same time,there is no cracks after freeze-thaw cycles and corrision tests,indicating the most reasonable aggregate accumulation and uniform pore distribution inside light-weight geopolymer fireproof coating.In order to further enhance performance of light-weight geopolymer fireproof coating,basalt and wollastonite fibers are taken part in sample preparation.The results show that basalt fiber and wollastonite fibers are helpful for keeping the integrity of the sample.When the contents of basalt fiber and wollastonite fiber are 0.5% and 1%,respectively,the residual strength after freeze-thaw cycle and corrosion test reach the highest level,and the bonding strength between the coating and cement matrix maintains well,without any cracks,swelling and slag drop.During fire resistance test,the reverse-side temperatures of specimens with fiber addition ascending faster compared to the control group（without fiber）at the initial stage,but surprisedly,the final temperatures are reduced by around 20 °C.This phenonmenon could be clarified that basalt and wollastonite fibers caused slight variation in porosity,which was closely related to thermal conduvtivity.Noatably,wollastonite could intersperse in the geopolymer matrix,pore wall and pores,acting as a reinforcement skeleton to consolidate the overall structure of the geopolymer due to its rigid and short fiber characteristics,which also helped maintaining lower final temperatures. |
