| Saline soil is widely distributed in China,which contains a large number of corrosive ions,such as Cl-,SO42-,Mg2+,CO32-,etc.,making the ordinary concrete structures in saline soil areas unable to reach the normal service life specified in the design.Magnesium oxychloride cement concrete(MOCC)has good salt resistance without modification,and has good applicability in saline land areas.At present,both carbonation and erosive ions have a great impact on the durability of MOCC in saline soil areas.In recent years,scholars at home and abroad have studied the durability of MOCC under the action of single factor of carbonization and salt solution immersion,and achieved certain results.However,MOCC is not in a single factor environment during its service in saline land areas,and is often subject to the combined effect of multiple factors.Therefore,with the support of the National Natural Science Foundation of China(51868044),this paper studied the mechanical properties,mass changes,relative dynamic elastic modulus and PH value changes of MOCC under single carbonation,and analyzed the durability deterioration of magnesium oxychloride coating reinforced concrete(MOCCRC)under the action of single salt solution,carbonation and salt solution coupling.The main research contents of this paper are as follows:(1)According to the influence of carbonization on MOCC,two different kinds of admixtures(single doped nano CaCO3 and single doped quicklime)are designed ω1 value and internal compactness ω2 values are taken as durability evaluation parameters,and combined with microscopic analysis,the carbonization mechanism and rule of MOCC under carbonization are obtained.The results show that the main reason for carbonation is that the hydrated products absorb CO2 to produce carbonated products,which will reduce the surrounding alkaline environment.The addition of two kinds of admixtures improves the carbonation degree of MOCC,so the mechanical properties are also significantly enhanced.The MOC doped with nano calcium carbonate is within the range of 8%,and the larger the amount,the more obvious the increase effect.The effect of adding MOC of quicklime is the best when the dosage is≤2%.(2)The MOCCRC was subjected to solution immersion test,and passedω1 value ω2 values and corrosion current density are used as durability evaluation parameters to study the durability degradation process of MOCCRC.The research shows that the corrosion degree of reinforcement is related to the deterioration degree of concrete cover.The faster the deterioration of concrete cover is,the faster the corrosion of reinforcement is.The corrosion degree of reinforcement from large to small is:sulfate environment>chloride environment>coupling salt environment.The corrosion current density in all environments is less than 0.4 μA·cm-2,low corrosion.(3)Aiming at the durability study of MOCCRC specimens immersed in carbonation salt solution,carbonation and three different salt solution environments(chloride environment,sulfate environment,coupling salt environment)are designed based on ω1 value ω2 values and electrochemical parameters(polarization curve,corrosion current density,Nyquist diagram,Bode diagram)to analyze the durability of the test piece.The results show that under the premise of reducing alkaline environment,carbonization also indirectly accelerates the rising trend of corrosion current density.The corrosion degree of steel bars from large to small is:chloride environment>sulfate environment>coupling salt environment.Due to the higher concentration of chloride,it is easier to corrode the reinforcement.(4)Probabilistic analysis of MOCCRC specimens soaked in the collected solution and carbonation salt solution ω2 values are analyzed,and it is found that Weibull distribution can effectively describe ω2.The results show that according to the reliability function R(t),when the reliability function is 0,GH1-1,GH2-1 and GH3-1 immersed in single salt solution are 21831d,4251d and 15892d respectively,while GH1-2 and GH2-2 immersed in carbonation and solution are 735d and 508d respectively.It can be found that the degradation rate becomes faster under carbonation. |
