| Engineered Cementitious Composites（ECC）are suitable for use as engineering structural repair materials due to their advantages of crack resistance and toughening,and they have been widely used in the fields of highway bridge panel connection,bridge deck pavement,concrete dam foundation crack and seismic performance improvement of existing masonry structures.As the scope of engineering applications continues to expand,the risk of ECC being exposed to high temperature environment during service is increasing day by day.The degradation of mechanical properties and durability of ECC after high temperature action has also begun to attract extensive attention from scholars at home and abroad.Since the low melting point polyvinyl alcohol（PVA）fibers are difficult to overcome the ductility failure after high temperature,if basalt fibers（BF）with high strength and high melting point can be used to replace PVA fibers,it is expected to make up for the disadvantage of ECC with PVA fibers alone in terms of high temperature performance.Since there is still little information available regarding the mechanical characteristics and impermeability of basalt fiber reinforced cementitious composites（BF-ECC）under high temperature action,this paper mainly focuses on the effect of different temperature actions on the mechanical properties and impermeability of polyvinyl alcohol fiber reinforced cementitious composites（PVA-ECC）and basalt fiber reinforced cementitious composites（BF-ECC）.The main work accomplished in this study is as follows:（1）The mechanical properties and RCM test results of ECC showed that the ratio of PVA fiber with 2%volume fraction,12mm length,0.26 water-cement ratio and 45%fly ash admixture performed well in improving the compressive strength and permeability of ECC,compared with control cement mortar,the compressive strength was improved by 38.3%,and the DRCMwas reduced by 36.4%.The uniaxial tensile performance test based on the determined ratio showed that the tensile strain of PVA-ECC reached up to 3.4%,and the ductility was better than that of BF-ECC.（2）The flaking behavior,mass loss,compressive properties,bending properties and splitting and tensile properties of the identified pairs of ECCs after high temperature were investigated.The test results showed that PVA-ECC did not exhibit bursting and severe cracking behavior in the temperature range of 23℃-400℃,however,bursting and spalling behavior was observed for BF-ECC at 400℃.The mass loss rate,compressive strength,bending strength and splitting strength of PVA-ECC and BF-ECC showed an overall decreasing trend with the increase of temperature.ECC showed a significantly lower mass loss rate than PVA-ECC at the same temperature,and the deterioration of strength with temperature was relatively gentle compared with PVA-ECC.（3）The results of impermeability tests showed that the chloride ion diffusion coefficient and electric flux of PVA-ECC,BF-ECC（except 100℃）and cement mortar all gradually increased with the increase of temperature.the deterioration trend of BF-ECC was relatively gentle,and the DRCMof BF-ECC improved by 305.4%under air cooling after the action of high temperature at 400℃,while the DRCMof cement mortar The DRCMof cement mortar exhibited a larger degree of deterioration,with a DRCMenhancement of 872.5%at 400℃.All specimens exhibited larger DRCMand electric flux values under quenched water cooling compared to air cooling.It can be seen that BF-ECC exhibits better resistance to permeation after high temperature compared to PVA-ECC and mortar,and quenched water cooling increases the degradation of permeation properties of the specimens.（4）Based on SEM and mercury-pressure experiments,the microscopic pore structure and chloride diffusion coefficient of ECC following high-temperature action were examined.Results from electron microscopy demonstrated that the BF with the matrix was superior to that of PVA fibers,making the interior more dense.After the action of high temperature at 400℃,the melting of PVA fibers with low melting point left many dents and holes in the PVA-ECC cross-section,while the BF-ECC cross-section did not change significantly.The results of the mercury-pressure test also showed that the pores of BF-ECC at room temperature（23℃）were more dense than those of PVA-ECC,and the percentage of gel pores was relatively large,however,the percentage of gel pores of BF-ECC decreased by 78.3%after exposure to 400℃,and the percentage of transition pores and macropores was increased.the increase in total pore size of PVA-ECC was significantly larger than that of BF-ECC.meanwhile,based on Based on Fick’s second law and combined with the temperature deterioration coefficient given in this paper,the diffusion model of chloride ions after high temperature was further given and the service life of ECC and cement mortar after high temperature was predicted.The model prediction results show that the service life of BF-ECC is higher than that of PVA-ECC and cement mortar at the same temperature. |
