NEW ADMIXTURES INCREASES ENGINEERING OPTIONS
October 28, 2004

Recent developments in admixture technology have opened up remarkable new possibilities for the use of concrete in situations, including the repair and upgrading of older structures, that were previously the preserve of specialist products, or where more radical solutions were needed, reports the UK Cement Admixtures Association (CAA).

Among the new options now available to engineers are Corrosion Inhibiting Admixtures.

The need to strengthen and repair structures often results as a consequence of corrosion of the existing steel, caused by the ingress of chlorides. This is especially true on bridges and marine structures, where corrosion inhibiting admixtures are being increasingly used for susceptible new structures.

They are also, however, playing an increasingly important role in the repair of existing structures, where old concrete has been removed and new concrete used to replace it. In these situations, the remaining in-situ concrete is saturated with corrosion inhibiting admixture before fresh concrete, which also contains the admixture, is placed. The technique optimises the protection to the embedded steel.

Corrosion inhibiting admixtures do not prevent chloride from reaching the embedded steel; that is the job of the concrete, which should be of high quality with a low water cement ratio and preferably contain pfa or ggbs, both of which improve the chloride diffusion coefficient. Rather, the inhibitor is designed to increase the passivation state of the steel to give a higher corrosion threshold. This means that more chloride needs to penetrate to the steel before corrosion is likely to begin.

The development of this admixture has significantly increased the options available to engineers, not only in terms of design of new structures, but also in repairing and upgrading existing structures with concrete in order to meet current needs.

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