The Effect Of Modified Recycled Powder On The Impermeability And Corrosion Resistance Of Reinforced Concrete Structures

The utilization of construction waste is a key step to promote the sustainable development of the construction industry,which has significant ecological and economic benefits.In this paper,we conducted an experimental study on the modification methods and application of recycled powder(RP)from construction waste recycling.Functionalizing the recycled powder by chemical modification,hydrophobic modified RP and corrosion-resistant RP were prepared to enhance the impermeability and corrosion resistance of reinforced concrete structures.The main contents are shown as follows:(1)A superhydrophobic surface design concept of"rough structure and low surface energy material"was adopted to prepare hydrophobic RP.Through a two-step hydrolysis-condensation reaction,the hydrophobically RP(HDTMS/SiO₂/HNTs@RP)were prepared on the RP surface.The structural characterization of the hydrophobic RP showed that the amorphous SiO₂ film was wrapped around the surface of HNTs and RP,and the alkanes chains of HDTMS were distributed in the outermost layer,constituting an encapsulated core-shell structure.Then,a stable superhydrophobic coating was prepared by applying hydrophobic RP and water glass as hydrophobic slurry on the concrete surface.The wettability of the hydrophobic coating can be controlled by adjusting the mass ratio of HDTMS/SiO₂/HNTs@RP to water glass solution,which has a maximum contact angle of156°and a rolling angle of 6°,when the mass ratio is 1:2.The mechanical wear test show that the contact angle is still above 150°after 30 times of friction,which indicate that the hardness and relatively larger scale RP particles can enhance the friction resistance of the hydrophobic coating.After corrosion test,the corrosion current of the coated specimens was2.95×10^-8 A/cm²,which is 3 orders of magnitude lower than ordinary specimens,and the R_coatwas 1253.5?·cm²,which is 20 times higher than ordinary specimens.The R_ct was 1.7×10⁶?·cm²,and protection efficiency reached 99.3%.The results showed that the hydrophobic coating could effectively enhance the impermeability of the concrete and reduce the corrosion of the steel.(2)Mg-Al hydrotalcite(Mg-Al-LDH)intercalated with NO₂^-was prepared in situ on the surface of the RP(NO₂^--LDH@RP).The component characterization indicated that the modified RP could adsorb aggressive ions such as Cl^-,CO₃^2-and release NO₂^-.The morphology characterization showed that NO₂^--LDH was uniformly loaded on the surface of the RP,forming an encapsulated core-shell structure.The results of chloride ion isothermal adsorption equilibrium curves indicated that the C-NO₂^--LDH@RP made by co-precipitation method had better chloride ion adsorption capacity,and its equilibrium adsorption amount reached 124.8 mg/g.The repair behavior of C-NO₂^--LDH@RP was investigated by pitting breakdown curves and EIS.And the corrosion potential and pitting breakdown potential increased gradually with time,and the passivation current decreased gradually.After 24 h,E_corr=-182.1 m V,E_b=+286.4 m V,i_corr=1.1×10^-6 A/cm²,which is 2 orders of magnitude lower than pitting steel.The R_ct=753.22 k?·cm²,protection efficiency reached 96.27%,indicating that C-NO₂^--LDH@RP can significantly promote the passivation of the steel and reduce the chance of pitting corrosion on the metal substrate.The WBE test shows that the doped C-NO₂^--LDH@RP densed the pore structure,while avoiding the unnecessary leakage loss of corrosion inhibitor NO₂^-and reducing the risk of depassivation of the steel bars at the defective site.(3)The effects of hydrophobic RP coating and NO₂^--LDH@RP on mortar's water absorption,chloride ion permeability and pore structure were investigated.The hydrophobic RP coating showed excellent hydrophobicity in the static test,however,the coating failed under long-term immersion conditions.As a comparison,the NO₂^--LDH@RP was more significant in improving the mortar's impermeability,with a 15.3%decrease in the fast chloride ion migration coefficient,and the mortar pore volume was 0.1355 m L/g,which decreases by 10.9%.This indicates that NO₂^--LDH@RP can not only adsorb corrosion ions and release corrosion inhibitors,but also effectively dense the pore structure of mortar,which has a significant effect on the improvement of the impermeability and corrosion resistance of mortar.