Influence of nano-SiO2 interfacial bonding agents on the water permeability and microstructure between new and old concrete
The effects of nano-SiO2 on the splitting bond strength and impermeability between new and old concrete were experimentally investigated.The application forms of nano-SiO2 include spraying diluted solu-tion and mortar as interfacial bonding agents and reinforcing phase.Monolithically cast substrate and four interface roughness groups were concluded for comparison.Furthermore,microstructure characteristics of the specimens with different bonding agents were inspected by means of scanning electronic microscopic(SEM).Finally,the influences and reinforcing mechanisms of nano-SiO2 were verified from the bond strength,permeability coefficient,and microstructures,respectively.The experimental results showed that both forms of the nano-SiO2 agents can improve the interfacial performances to a certain extent.And there is optimal concentration for each form,3.75％for mortar and 2.5％for spray treatment.Wherein,incor-porating into mortar-base is more effective than the spray treatment.The increase in surface roughness ben-efits reducing the seepage height and permeability coefficient of bonded specimens.The permeability coeffi-cient is more sensitive to the interfacial defects between overlays than the bond strength tests.Microstruc-ture observations verified that the presence of nano-SiO2 benefits the amount of hydrate products and leading to a more compact C-S-H phase,which inhibits the formation of connected porous networks.
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