Corrosion protection of rebar steel in marine atmosphere by nanocoating

Abstract

Rebar steel is an important building material which is basically used for construction works. This metal is reinforced with concrete for construction of bridges and houses. Such types of bridges and houses face corrosive problems in coastal areas because high concentration of Cl- ions marine atmosphere. There are several porosities on the surface bridges and houses. The chloride ions enter inside the building materials and develop electrochemical cell on the surface of rebar steel. Rebar steel undergoes process of corrosion reaction and creates several forms of corrosion like galvanic, pitting, stress and crevice. Chlorides ions develop internal and external corrosive effect for rebar steel and concrete hence disbanding occur between building materials. This corrosive ion decreases life of building materials, increase maintenance costs and sometimes major accident takes place. The hydroxides of magnesium and calcium are present in concrete. Chloride ion reacts with these hydroxides and decreases the pH value of concrete thus accelerate the rate of corrosion reaction. Nanocoating of Mg3(PO4)2 with DLC filler is applied to control corrosion of rebar steel in marine atmosphere. The uncoated and coated rebar steel with Mg3(PO4)2 were exposed to marine atmosphere in different seasons like summer, rainy and winter. The corrosion rate of metal was analyzed in these seasons. The results show that though corrosion rate is minimized it does not produce good results. Porosities are developed on the surface of rebar steel coated with Mg3(PO4)2 which is reactive with chlorine ion. DLC is used as filler to close the porosities of coated rebar steel and again the corrosion rate of rebar steel was analyzed in the above mentioned seasons. It is found that this filler has good inhibition effect in marine atmosphere. The corrosion of metal was determined by gravimetric and potentiostatic polarization methods. Coating work was completed with application of nozzle sprays and vapour deposition methods. Coating efficiency, surface coverage area and stability of coating material were calculated with Arrhenius, Langmuir isotherm, Temkin equation, free energy, enthalpy and entropy.