Study on the origins and laws of the concrete corrosion in a highway tunnel lining in Guangdong
Chemical corrosion arising from long-term exposure to aggressive water environment is one of the common diseases of highway tunnels.It will cause the failure of concrete durability,hence threating the safety of the highway tunnel structure,and large amounts of money is needed for maintenance.However,existing studies generally lack engineering projects in reality as research background which makes the experimental and simulation parameter settings disconnected from the actual engineering.As a result,it is hard to accurately and comprehensively reflect the corrosion mechanism of highway tunnels under an actual complex erosive water en-vironment.In this paper,we aim at study the origins,laws and controlling factors of concrete corrosion in high-way tunnels.In order to achieve this goal,we selected a highway tunnel in Guangdong as the research object,utilized in-situ and laboratory chemical index testing of water,XRF testing to determine chemical erosion sources of the highway tunnel and conducted groundwater seepage experiments to reproduce the chemical erosion pro-cess of concrete.The results are as follows:① Calcium leaching from cement hydrate of concrete while tunnel lining concrete contacts with the groundwater with low Ca2+and high HCO3-concentration,hence forming a strongly alkaline CaCO3 solution and supersaturated precipitation.In addition,the partial pressure drop of CO2 promotes the further supersaturated precipitation of CaCO3 during the rapid ejection of groundwater through cracks and entering the highway tunnel.② At the early stage of the calcium dissolution,due to the Ca2+concen-tration difference between the liquid phase in cement and groundwater,the Ca(OH)2 moves relatively fast into groundwater.As the calcium dissolution progresses,the solid-phase Ca(OH)2 of cement continues to be con-sumed and hence the Ca2+concentration in drainage water spikes to a high level.It results in the Ca2+concentra-tion gap becoming narrow and the calcium dissolution rate gradually dwindling.Finally,under hydrodynamic conditions,the calcium dissolution keeps a dynamic equilibrium and the chemical characteristics of drainage water remain relatively stable.③ Groundwater with low Ca2+and high HCO3-concentration is conducived to calcium dissolution of concrete and supersaturated precipitation of CaCO3.In addition,too high or low ground-water seepage velocity is not beneficial to the above reactions.
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