Preparation Of PH-Sensitive Carrier Of Inhibitor And Study On Its Corrosion Protection In Simulated Concrete Pore Solution

Reinforced concrete has been widely applied in infrastructure constructions around the world due to its low cost and high mechanical strength.Steel corrosion is one of the key factors reducing the life span of the concrete.Therefore,efficient prevention and repair of the corrosion damage of the steel bar are necessary.In basic medium,the steel bars surface in concrete forms a stable passive film that protects steel bars from corrosion.Carbonation will reduce the pH in the concrete pore solution.When the steel bars are subjected to carbonization with destroyed passivation film,corrosion of steel bars will initiate.It is necessary to apply a pH-sensitive carrier for the loading of inhibitors.We have applied carrier for the loading of inhibitors to prevent the reaction between the inhibitors and the coating,and thereby extending the shielding properties of the coating.The inhibition behavior of Q235 steel treated with four kinds of corrosion inhibitors in simulated concrete pore(SCP)solution was analyzed using open potential(OCP),electrochemical impedance spectroscopy(EIS),weight loss measurement,and scanning electron microscope(SEM).The effective inhibitor was selected as the loading material.The effects of different concentrations and chemical additives on the morphology and structure of calcium carbonate(CaCO₃)microspheres were investigated.CaCO₃microsphere with uniform particle size,good dispersibility,and higher content of vaterite was used as a container.Studies on the adsorption of polyelectrolyte onto halloysite nanotubes(HNTs)were conducted.Four polyelectrolytes—poly(dimethyl diallyl ammonium chloride)(PDDA),poly(styrensulfonate)(PSS),chitosan(CS)and gelatin(GEL)were chosen.Smart carriers were loaded with corrosion inhibitors under vacuum.Thermal Gravimetric Analysis(TGA),UV–VIS spectrophotometer(UV-vis),attenuated total reflection-Fourier-transform infrared spectroscopy(AT R-FTIR),X-ray diffraction(XRD),SEM and transmission electron microscope(TEM)tests were performed to evaluate the storage capacity,pH sensitivity,structure and morphological features of carriers(CaCO₃and HNTs).Then,the corrosion resistance property of different fillers dispersed epoxy coatings on Q235 steel bars in SCP solution was examined by the EIS technique and contact angle test.The results of the paper are as follows:(1)The inhibition efficiency of these four corrosion inhibitors follows the order:sodium lignosulfonate(SLS)>sodium phytate(SP)>sodium citrate(SC)>sodium salicylate(SS).(2)Calcium carbonate micro-containers were prepared with 0.35 mol/L CaCl₂ and 0.35 mol/L Na₂CO₃ solution as well as used ethanol as adjusting reagent.Release behavior of SLS from the CaCO₃ under various pH of the aqueous solution showed higher release in the acidic medium.(3)The highest release concentration of PSS/PDDA/SLS/HNTs-containing epoxy coating was observed at the basic medium.And the SLS/HNTs composite fabricating by CS and GEL(GEL/CS/SLS/HNTs)shows weak pH sensitivity.(4)The epoxy coatings containing SLS/CaCO₃ or PSS/PDDA/SLS/HNTs composites exhibit better anti-corrosive performance.Based on the above experimental results and analysis,for the above two modified coatings,the former is suitable for the later stage of steel corrosion,while the latter is suitable for the early stage of steel corrosion.