Hassan II Mosque - Restoration Works

Restoration Works

Structural deterioration in the concrete wall was observed ten years after the mosque's completion. This was explained as being due to exposure to the salt water of the Atlantic Ocean, in to which nearly half of the mosque’s foundation projects. Salt water migrating into the porous concrete caused the rusting of the rebar steel reinforcements resulting in expansion of the steel and causing cracking of concrete. Salt water had penetrated beyond the steel bar also into the structures.

Effective restoration works were instituted in April 2005. This involved use of moly-grade stainless steel combined with high-grade concrete to make the structure resistant to chloride attack, a process that evolved during 3 years of research. This is expected to enhance the building's life by 100 years. The works were carried out in four phases. In the first phase a leak-proof coffer dam was constructed to isolate and dry the work area. This was built 5 metres (16 ft) below the highest water level. In the second phase, the voids seen in the prayer hall were filled with concrete. In the third phase, the structural slabs and pillars on the exterior part of mosque exposed to the sea were demolished; 6,000 cubic metres (210,000 cu ft) of concrete was removed. In the fourth phase, new exterior protection works were built using high-strength concrete with 2205 (conforming to UNS S 32205 EN 1.442 standards) stainless steel rods as reinforcements for effective erosion control. Even though the many structural changes were made as per detailed design, still during execution of works, 100 external pillars, called “combs” because of their wave breaking characteristics, were exposed to salt water and wave action and had to be replaced with new pillars. These were made from high-strength concrete with 2205 stainless steel reinforcements. This necessitated an additional leak-proof dyke to be built behind the earlier one; total dyke quantity involved was 20,000 cubic metres (710,000 cu ft). All of these works involved use of 1300 tons of special steel (with 40 tons of Mo) of 8–20 millimetres (0.31–0.79 in) bars with yield strength of 850 N per mm2. The concrete quantity poured involved 100,000 cubic metres (3,500,000 cu ft) of non-reinforced bulk concrete and 10,000 cubic metres (350,000 cu ft) of high-strength concrete. The entire work was done at a cost of 50 million euros.