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| 13:11 12/15/2008 |
| When Water Is Detrimental To Construction And Health |
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Last decades there is high humidity in premises in the United Arab Emirates that is a subject of steadfast attention of public health authorities in the eastern countries. High humidity in premises is the reason of mustiness, reproduction of fungous mould. The mould itself is not dangerous, but millions spores which are in the air get into the respiratory ways and blood circulation system. Children especially react to them, and old people , persons with the weakened immunity, are inclined to allergic diseases. First of all, these are diseases of respiratory ways, including bronchopulmonary ones, diseases of skin and locomotor system. The high humidity is characteristic also for below grade premises: ground floors and especially cellars.
Aggressive water influence on brick and concrete constructions is an established fact for a long time as these materials have capillary-porous structure. Ground waters getting into constructions from below contain impurities of salts: chlorides, sulphates and hydrocarbonates. Crystallising and hydrating in pores salts repeatedly enlarge in volume that result in material destruction of supporting elements , plaster and paint exfoliation, and promote deformation of finishing covering, wall-paper curling, etc.
Ground waters migrating along capillaries of walls can wash away water-soluble salts out from materials destroying,for example, masonry mortar or brick weight containing chlorides and sulphates already in initial raw material. It leads to the further branching of a capillary-porous network and premature destruction of designs.
Considerable number of buildings in Arab Emirates suffer zero cycle problems where the lack of attention or a nonprofessional choice of materials and technologies lead to the emergence of the high humidity in premises and makes direct threat for health and for integrity of a construction alike.
The water penetrates from above, from outside an atmospheric precipitation. This influence besides the mechanical destructions connected with processes of freezing-defrosting has also chemical consequences. Strictly speaking, the rain water is a solution. The rain streams grasp from atmosphere a considerable quantity of gaseous industrial emissions such as carbon oxides, sulphur, nitrogen and phosphorus, ammonia, chlorine and chloride hydrogen. These gases partially dissolving in water transform the rain into the acid solution destroying concrete, marble, brick and other materials. Being new centres of aggression the quantity of pores , capillaries and microcracks increases, and the degree of the material destruction considerably increases. Besides, acid oxides of sulphur and nitrogen, and also chloride hydrogen being in the air are capable to cause displacement of such ecological parametre of atmosphere as carbon-dioxide balance. Thus, the free carbonic acid gas named in this case "aggressive" raises in the air . The carbonic acid gas is aggressive in the mineral building materials lime, marble and concrete transforming insoluble calcite CaCO3 into water-soluble hydrocarbonate of calcium Ca(HCO3)2: CaCO3+CO2+H2O=Ca(HCO3)2
As a result under the action of rain soluble salts are gradually washed away. The abovementioned information leads to the necessity to choose the effective protective measures providing durability and reliability of concrete and brick constructions.
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