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    Concrete carbonation

    Allcrete Industries

    A common problem with reinforced concrete structures is deterioration brought about by the corrosion of reinforcing steel and the subsequent spalling of concrete. This is most often caused by moisture penetrating to the depth of the steel, where it reacts in the presence of oxygen and chloride to cause the steel to corrode.

    This process is aggravated by carbonation, the result of the action of acidic environmental conditions bringing about a lowering of the alkalinity of the concrete from an initial pH of around 13.5 to around 8.5 over some years. At this stage the steel loses the passivating gamma-feric oxide layer which becomes unstable at this level of pore water alkalinity and corrosive reactions start to become evident.

    Aquron products from Allcrete Industries work to combat this process by sealing out moisture to a depth of 100mm or more; reducing oxygen permeability by a pore-blocking process; bringing up the alkalinity of the concrete as it impregnates it - Aquron 2000 has a pH of around 12; purging and binding chlorides in the colloidal silicate hydrogel formed in the pores and capillaries of the concrete (only chlorides in solution are available to participate in corrosion reactions and increasing the reactivity of the concrete, thus inhibiting electrochemical activity.

    No carbonation takes place in concrete when the pores are completely dry or when they are fully saturated. The effect of the Aquron treatment causes the pores and capillaries of concrete to be filled with an insoluble gel which remains active indefinitely, preventing moisture migration and putting a stop to carbonation.

    Because of the sub-surface molecular bonding of the process, the treatment does not change the appearance of concrete or affect the adhesion of subsequent coatings. Concrete treated within 24 hours of casting will be protected for life against carbonation problems and aged concrete, once treated, will become immune to further deterioration.

    Source: Building Products News.

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