Durability Of Cementitious Composites In The Hygrothermal And Salt Coupling Environment

The coastal climate environment has the characteristics of is usually humid,hot,and salty,and offshore engineering in such a coupled environment for a long period may cause multiple damage to cementitious composites and structures.The hygrothermal and salt coupling environment causes multiple hazards to cementitious composites and structures.The Polyvinyl alcohol(PVA)fiber reinforced cementitious composites(PVA-FRCC)exhibit remarkable mechanical properties and durability,and many researchers at home and abroad have carried out extensive studies.The strengthening effect of nano-materials on cementitious composites has become a hot topic in recent years.It is vital to explore the durability of new type cementitious composites in the hygrothermal and salt coupling environment for their application in marine structural engineering.In this study,the effect of nano-SiO2 and PVA fiber on the durability of cementitious composites subjected to hygrothermal and salt coupling effect was investigated.For preparing the nano-SiO2 and PVA fiber reinforced cementitious composites,cement,fly ash,and silica sand was used as raw materials and nano-SiO2 and PVA fiber was used as modified materials.The effect of hygrothermal and salt coupling environment on the durability of cementitious composites was explored,and the reinforcement mechanism of nano-SiO2 and PVA fiber on the durability of cementitious composites was probed.The specific research contents and primary conclusions are as follows:(1)The impermeability pressures of cementitious composites in the hygrothermal and salt coupling environment was measured by the impermeability experiment.The influence of nano-SiO2 and PVA fiber on the impermeability pressures of cementitious composites in the hygrothermal and salt coupling environment was analyzed,and the corresponding influence laws were obtained.The influence mechanism of nano-SiO2 and PVA fiber on the impermeability of cementitious composites in the hygrothermal and salt coupling environment was revealed.The results indicated that the impermeability of cementitious composites decreased significantly in the hygrothermal and salt coupling environment.With the increase of the Nano-SiO2 or PVA fiber contents,the impermeability of cementitious composites increased first and then decreased in the hygrothermal and salt coupling environment,and the impermeability achieved the optimal when 1.2%PVA fiber and 1.5%nanoSiO2 were added.The pore structure of cementitious composites was tested by mercury injection test,and the influence mechanism of nano-SiO2 and PVA fiber on the impermeability of cementitious composites was revealed in the hygrothermal and salt coupling environment.(2)The charge passed through cementitious composites in the coupled environment was measured by rapid chloride ion penetration test(RCPT).The influence of nano-SiO2 and PVA fiber on the chloride penetration ability of cementitious composites in the coupled environment was analyzed,and the corresponding influence rules were obtained.The influence mechanism of nano-SiO2 and PVA fiber on the resistance to chloride ion permeability of cementitious composites in the hygrothermal and salt coupling environment was revealed.The results presented that the resistance to chloride permeability of cementitious composites decreased significantly in the hygrothermal and salt coupling environment.With the increase of the content of PVA fiber or nano-SiO2,the electrical flux of cementitious composites first increased and then decreased in the hygrothermal and salt coupling environment,and the optimal anti-chloride-permeability performances was achieved when the content of PVA fiber was 1.2%and the content of nano-SiO2 was 1.5%.(3)The effects of PVA fiber and nano-SiO2 on the compressive strength loss rate and mass loss rate of cementitious composites were studied by rapid freeze-thaw test.The influence of nano-SiO2 and PVA fiber on the frost resistance of cementitious composites in the hygrothermal and salt coupling environment was analyzed,and the corresponding influence rules were obtained.The influence mechanism of nano-SiO2 and PVA fiber on cementitious composites in the hygrothermal and salt coupling environment was revealed.The results presented that the frost resistance of cementitious composites was prominently reduced in the hygrothermal and salt coupling environment.With the increase of PVA fiber and nano-SiO2 contents,the compressive strength loss rate and mass loss rate first decreased and then increased,and the best frost resistance was achieved when 1.2%PVA fiber and 1.5%nano-SiO2 were added.The addition of PVA fiber and nano-SiO2 can improve the apparent morphology of samples after freeze-thaw damage.The microstructure of cementitious composites was tested by scanning electron microscope,and the influence mechanism of nano-SiO2 and PVA fiber on the frost resistance of cementitious composites was revealed.(4)The corrosion resistance coefficient of compressive strength of cementitious composites subjected to 30 dry-wet cycles in chlorine salt solution.were researched by chlorine erosion test.The influence of nano-SiO2 and PVA fiber on the chloride corrosion resistance of cementitious composites in the hygrothermal and salt coupling environment was analyzed,and the corresponding influence laws were obtained.The influence mechanism of nano-SiO2 and PVA fiber on the chloride corrosion resistance of cementitious composites in the hygrothermal and salt coupling environment was revealed.The results reveal that corrosion resistance coefficient of compressive strength of cementitious composites decreased observably in the hygrothermal and salt coupling environment.With the increase of the content of Nano-SiO2 or PVA fiber,the corrosion resistance coefficient of compressive strength first increased and then decreased.When the content of PVA fiber was 1.2%and the content of nano-SiO2 was 1.5%,the chloride corrosion resistance attained the optimal under dry-wet cycles.