Pore Solution Composition Of Calcium Sulfoaluminate Cement Based Material And Its Effects On Steel Corrosion

Calcium sulfoaluminate cement(CSA)is an important building material,which is widely used in Marine engineering.As a qualified cementitious material,it is not enough only to meet the requirements of work and mechanical properties.Reinforcement corrosion is an electrochemical process which is closely related to the pore solution composition of cement-based materials.However,there are few studies on the effect of CSA-based materials pore solution on steel corrosion.Therefore,the composition of the pore fluid of CSA-based material and its influence on the corrosion of steel bars were systematically studied in this article.In this study,a new method suitable for CSA was designed to analyze the composition of pore solution by using the ex situ leaching method together with calculation of modifying concentration.Based on thi,the pore solution constitution of CSA was studied,and then the method of preparing simulated pore solution was proposed.With SPS as the research medium,the influence mechanism of main characteristic ions in CSA pore solution on steel passivation was studied by cyclic voltammetry(CV),electrochemical impedance spectroscopy(EIS),corrosion potential and other test techniques.What's more,a numerical model of the influence law was established.Secondly,in the context of steel corrosion caused by chloride ion,techniques,such as mott-schottky curve(M-S)and cyclic polarization curve,were applied to study the coupling effects of chloride ion and the main ions on corrosion resistance and development.Then the influence mechanism and regularity are discussed to establish the prediction model of critical chloride content in the context of CSA SPS.Finally,this article explores the steel corrosion in CSA mortar with mixed-in NaCl,which revealed the corrosion behavior of steel reinforcement in CSA,and proved that the influence mechanism based on SPS is helpful to understand the corrosion behavior of steel reinforcement in CSA.The main research results are as follows(1)compared with the traditional ex situ leaching and pore water expression method,the new method is easy to operate and can accurately reflect the real situation of pore fluid.It is an effective method to study the composition of pore fluid of cement-based materials.Compared with OPC,the pore solution composition of CSA is mainly characterized by low concentration of OH-,but high concentration of SO42-and Al(OH)4-.According to this,the method of preparing CSA SPS was proposed.(2)The variation of OH-concentration changes the composition of steel passivation film.Too high or too low will deteriorate the passive film.SO42-does not affect the passive film composition,but has a destructive effect on passivation,and the negative effect decreases with the increase of OH-concentration.However,Al(OH)4-can inhibit the adverse effect of SO42-and improve the stability of passivation film without changing the concentration of OH-.The prediction model of SO42-critical concentration can be obtained from the interaction among the three ions,which can be used to determine whether steel bar can passivate at early stage of CSA hydration.(3)With the presence of Cl-,the corrosion resistance of reinforcement increases with the increase of OH-and Al(OH)4-concentration,while decreases with the increase of SO42-concentration.In addition,SO42-can also make the steel bar to form loose corrosion products,resulting in a rise in the corrosion rate.The critical chloride content can be calculated by the concentration of the three ions.Compared with OPC,the steel bars in CSA mortar are characterized by early corrosion,low critical chloride content and fast corrosion rate.Such corrosion behavior conforms to the properties of CSA pore solution and the influence mechanism of pore solution composition on steel corrosion.