Building materials Degradation state of the chella historic site

The chella Necropolis merinid is located upstream from the mouth on Wadi Bou Regreg left bank, 2 km northeast of downtown Rabat. The site climate is wet oceanic influence with average annual rainfall 400 to 500 mm / year and 16C average annual temperature. The construction material of this historical monument type stone size up the very large door with its original architecture and forming a coating, however close behind which the wall is made of coarse rubble, and likely mostly calcarenite, sand limestone, crystalline limestone and coquina. The stone, paving, and walls are being degraded. To surface rocks natural aging phenomenal we adds air pollution action suffered by the city in recent decades, particularly due to urban development and a concurrent increase in road Traffic which represents about 95% of the pollution source. This accelerates the coatings decomposation and the stone erosion. Opposite the site, at Chella door the concentration measured of certain gaseous pollutants (SO2, NO2 ...) exceeds the standard (190 ug / Nm 3). The rainwater analysis collected in this site shows a concentration of 14 mg / l average sulphate. The Chella historic site deterioration is linked to the aging of its concentrations, air pollution, and assault by salt spray and water, algae development, lichens and other vegetation types and the burrowing animals action, insects, birds and other creatures. All these phenomena are added to the natural process of the rock surface weathering and contribute to the monument deterioration. This study aims to inventory the various aspects of these monuments deterioration and the explanation of construction materials evolution. The alteration work is mainly related to the interaction of many external factors: exposure conditions the ambient atmosphere first composition, climate and weather conditions, position in the construction, architectural features. The most important parameters are those that control water flow to the surface blocks in the rock exposure to rain, rising damp, runoff etc .... Thus, exposure to heavy rains favors surface dissolution and gully erosion, while water runoff eroding the areas of external the rock and causes the salts migration(including gypsum). In sheltered areas, the atmospheric particles accumulate; the calcium salts crystallize on the surface, or may replace calsite. The black crusts formed gypsum and fly ash or white crusts (after calcite crystallization) can develop. In places subject to the calcium salts crystallization (oxalate and gypsum), the blocks are cracked or peeling. The investigation revealed that; various types of diseases affect all buildings in the Chella Necropolis, and a degradation form is never alone but with other types, which likely reflects the close relationship existing between the causes of these degradation. The evolution degree of the same disease varies between base, middle and the top and between the exterior and interior on the same wall. The filler adhesion, the colonization by vegetation, crusts the honeycomb and tasks moisture recur despite recent restorations. We must also note the presence different sizes cracks: micro-cracks KZS coatings and coating cracks metric crosses the wall