The sea wall's new, 500m extension comprises pre-cast non-reinforced concrete elements, which the authorities in Doha wanted to protect with a specialist coating in order to prevent deterioration from the damaging effects of salt-laden winds, the harsh climatic conditions, constant attack from salt spray, impact damage, tidal action and currents.

Following consideration of a number of protective coatings and intensive testing carried out by the MMAA's Materials and Laboratory Division, Cementitious Coating 851 was chosen on the basis of its ability to meet the specification and its 10-year track record of use in marine environments. Extensive testing was required, as the inherent dampness and high humidity experienced in the Doha environment placed considerable restraints on the types of protective coatings that could be used. Inferior materials could literally fail within months of application due to the highly demanding conditions.

The Cementitious Coating 851, which is supplied in two pre-packaged components for easy mixing on-site, forms a hard, highly alkaline coating which waterproofs and damp-proofs the concrete, protecting it from the effects of aggressive acid gases, moisture and chlorides. It is particularly suited for use in marine environments, as it can be applied to damp substrates, can cure under water and due to its cement base, tolerates much lower levels of surface preparation than conventional coating systems. It also confers outstanding resistance to wash-out when immersed in water and achieves a compressive strength of 10.5N/mm 2within one day, rising to 32.0N/mm 2after 28 days. Being cement based, it chemically reacts with the substrate to form an integral part and has a design life equivalent to that of the concrete to which it is applied.

Cementitious Coating 851 is normally applied in two coats at 1mm, of which a 2mm coating is equivalent to 1m of good quality concrete in terms of resistance to water permeability. In addition, Taywood Engineering has assessed the chloride ion diffusion of 851 for the past 10 years and to date no steady state flux of chloride ions has been detected. It is resistant to water penetration at 10 bar pressure.

The product can be applied by brush, trowel or spray, but it was spray applied in this instance, to enable rapid application of the product in very hot, humid conditions. Cementitious Coating 851 can be applied at temperatures as high as 350C, or as low as 50C. Due to its solvent-free composition, it exhibits minimal hazard during application and is non-toxic when cured.

Apollo Enterprises, acting as sub-contractor to the main contractor, Doha-based M/s Amcon, was able to apply two coats of the product in the same day, due to its ability to dry within 2-3 hours. Cementitious Coating 851 is normally available in concrete grey and white, but a special grey colour was specifically created for this project to ensure the extended section of the sea wall matched the appearance of the existing 10km.

As this existing pre-cast section was never protected with a specialist coating when originally constructed, the concrete has spalled significantly and the steel reinforcement has corroded. As a result of this deterioration, the MMAA opted to protect the new sea wall section from the outset, to avoid costly remedial measures in the future. The next stage of the project will involve carrying out concrete repairs to the existing 10km sea wall and coating it with a protective system.