| The modular construction of intelligent substation promoted by China's national power grid is becoming more and more popular,where the prefabricated cabin is the core product.Glass fibre reinforced concrete?GRC?is considered to be an ideal material for prefabricated wall panels in result of its light weight,high strength,good toughness,strong corrosion resistance,convenient preparation and processing,low cost and so on.It is reported in literatures that the durability of the material of prefabricated wall panels is the key factor affecting the service life of the structure.Based on the theory of porous media and composite materials,combining macroscopic and microscopic methods,using test methods of durability and accelerated aging and combined with advanced analytical testing techniques,it is systematically studied that the effects of different cementitious materials such as portland cement,calcium sulphoaluminate cement,mineral admixture,and fiber content on long-term mechanical properties,shrinkage properties,carbonation resistance,chloride ion permeability resistance and aging resistance.The experimental conclusions are summarized as follows:The long-term mechanical properties and shrinkage properties of glass fiber reinforced concrete with different binder materials and fiber content were studied.As the content of glass fiber going higher,the flexural strength of GRC increases obviously,but the compressive strength decreases slightly.The flexural strengths of GRC at 90 days,which are prepared with calcium sulfoaluminate cement,portland cement,portland cement with 30%fly ash and portland cement with 30%fly ash and 10%silica fume are higher than that of the reference group without glass fiber by 61.1%,66.3%,123.2%and 91.1%,respectively.The autogenous shrinkage values and long-term drying shrinkage values of GRC prepared with calcium sulphoaluminate cement are the lowest,however,it is the highest that of portland cement.The autogenous and dryin shrinkage values of GRC can be reduced by fly ash when it is added to portland cement.The drying shrinkage value of GRC which is prepared with portland cement and 2%glass fiber by volume fraction reachs 874.9??at 90 days,while that of GRC containing2%glass fiber by volume fraction which is prepared with calcium sulfoaluminate cement,portland cement with 30%fly ash and portland cement with 30%fly ash and 10%silica fume is 652.7??,730.6??,718.0??,respectively.The effect of glass fiber content on reducing the shrinkage values of GRC is limited.The drying shrinkage of GRC with 2%glass fiber by volume fraction was fitted with CEB-FIP1990 model,and it is in good agreement.The results show that CEB-FIP1990 model is suitable to GRC with portland cement,calcium sulphoaluminate cement and portland cement with mineral admixture.The ratio of autogenous shrinkage values to drying shrinkage values over time was fitted with the formula???,it is in good agreement except the GRC prepared with calcium sulfoaluminate cement.The results show that the model is suitable to GRC prepared with portland cement and portland cement with mineral admixture except calcium sulfoaluminate cement.The carbonation depth of paste of different binder materials carbonized by 20%CO2 for90 days was determined.The distribution of complete carbonization zone,partial carbonation zone and non-carbonation zone of portland cement paste,portland cement paste with 30%fly ash and 10%silicc fume,calcium sulfoaluminate cement paste and calcium sulfoaluminate cement paste with acrylate emulsion after carbonation were studied by XRD and FT-IR analysis and the mass fraction of major phases ware quantitatively studied too.The partial carbonation zone of portland cement paste is 0-6 mm,and the non-carbonantion zone is 6 mm above.The partial carbonation zone and non-carbonation zone of portland cement paste with 30%fly ash and 10%silica fume is 0-3 mm and 3 mm above,respectively.The distribution of complete carbonization zone,partial carbonation zone and non-carbonation zone of calcium sulfoaluminate cement paste and that of paste with acrylate emulsion is same,which is 0-9 mm,9-18 mm and 18 mm above,respectively.The carbonization products are mainly composed of calcite,and a small amount of aragonite is found in portland cement paste with 30%fly ash and10%silicc fume,calcium sulfoaluminate cement paste and calcium sulfoaluminate cement paste with acrylate emulsion after carbonation.According to the RCM method,the rapid chloride ions migration coefficient of the six groups of GRC were determined,and the diffusion coefficient of GRC prepared with portland cement and 2%glass fiber by volume fraction is the largest,which is 13.1×10-12m2·s-1 and higher than that of calcium sulphoaluminate cement,9.8×10-12m2·s-1.It is effective that add fly ash and silica fume to portland cement to reduce the diffusion coefficient,which is 4.1×10-12m2·s-1.And the diffusion coefficient of GRC prepared with porland cement with 30%fly ash,10%silica fume and acrylate emulsion and calcium sulfoaluminate cement with acrylate emulsion is 21.4%and 36.6%lower than that of the reference group,reaching 7.7×10-12m2·s-1 and 2.6×10-12m2·s-1,respectively.Based on the changes in mass loss and relative dynamic elastic modulus after the freeze-thaw cycle test,the freeze resistance of the six groups of GRC was evaluated.The frost resistance of GRC prepared with calcium sulfoaluminate cement and 2%glass fiber by volume fraction reachs 200 times,while that of GRC with acrylate emulsion reachs 150 times.The others of GRC show no obvious destruction after 250 freeze-thaw cycles,whoes mass loss are within 3%and the relative dynamic elastic modulus are still above 90%.The pore distribution and porosity of the four groups of GRC before and after 200 freeze-thaw cycles were analyzed by X-CT.The results show that the porosity of GRC prepared with calcium sulfoaluminate cement and 2%glass fiber by volume fraction is higher than that of GRC prepared with portland cement.The porosity increased further after the addition of acrylate emulsion,but it decreases after the freeze-thaw test along with the reduction in the number of pores of 0.001 mm3 to 1 mm3.The aging resistance of GRC prepared with four binder materials were studied systematically.The results show that the aging resistance of GRC prepared with portland cement is the lowest,whoes flexural strength under standard curing for 90 days had reduced to12.5 MPa,and then it went to 9.7 MPa when it aged for 150 days in hot water at 50°C.And it demonstrates that the glass fiber does not work no longer.Adding fly ash and silica fume,the aging resistance of GRC is improved.After ageing for 150 days of GRC prepared with 30%fly ash and silica fume with 2%glass fiber by volume fraction,the flexural strength is reduced from 13.5 MPa to 12.3 MPa,which is much higher than that of plain mortar without glass fiber at 7.3 MPa.The glass fiber still plays an important role.The GRC prepared with calcium sulfoaluminate cement and 2%glass fiber by volume fraction has highest aging resistance,whoes flexural strength decreases from 15.9 MPa to 13.1 MPa after aging in hot water at 50°C or 150 days.The addition of the acrylate emulsion can slow down the reduction of the flexural strength of GRC after aging to some extent.However,the flexural strength of GRC with emulsion after aging for 150 days is not higher than that of the reference group in the result of the reducing of the flexural strength of the matrix before aging.There is no significant downward trend in the compressive strength of GRC after aging,and the addition of emulsion also leads to a decrease in compressive strength.The surface morphology of the glass fiber in GRC after aging was observed by SEM.The results show that the surface of the glass fiber was corroded slightly of GRC prepared with portland cement and 2%glass fiber by volume under standard curing for 90 days.And the surface peeled off when it aged for 90 days.Aging for 150days,the surface layer had been completely corroded,and the fiber obviously went thin.There was no corrosion on the surface of fiber in the other groups after aging for 90 days and150 days.However,the flexural strength was still decreasing.GRC prepared with calcium sulfoaluminate cement has the optimal performance on shrinkage properties,resistance to chloride ion permeability and aging resistance,but carbonation resistance and frost resistance is a little lower The aging resistance of GRC prepared with 30%fly ash and 10%silica fume is comparable to that of calcium sulfoaluminate cement,and it also has obvious advantages in resisting chloride ion permeability,anti-carbonization and frost resistance,which is a better binder material for GRC.Although portland cement has higher performance on anti-carbonization and freeze-thaw resistance,its aging-resistance is significantly lower than that of calcium sulphoaluminate cement and composite cement with fly ash and silica fume.It is not suitable for GRC materials. |
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