Approximate Composition of clay bricks:SiO2(55%)+Al2O3(30%)+Fe2O3(8%)+ Mg O (5%)+Ca O (1%)+ mHCO3- + 2mCO3−2+organic matter(1%) .

[I]Problems such as rising damp, moisture penetration and efflorescence on external walls, stains, fungi or algae growth, concrete corrosion, and loss of thermal insulation are due to water penetration. [II]Excess lime gets hydrated, swells and may decrease the mechanical strength of the bricks.[III]The earth surface where the brick structure is constructed and water (rain or otherwise) generally contain two most common chemicals: the SO4-2 and Cl- (generally of Na+) . For example, the crystallization of sodium sulphate from water solution in different shape is influenced by the change of temperature and quantity of water. Between –1.42ºC and 32.4ºC, it crystallizes decahydrate as monoclinic prisms; at more than 32.4ºC, it crystallizes in an anhydrous phase. Further, the anhydrous sulphate may also crystallize into unstable phase (Na2SO4•7H2O) if temperature below 24.4ºC and then again be transformed into Na2SO4•10H2O in humid environment. Na2SO4•10H2O does not dehydrate (reverse process) when the relative humidity is near 100%. It gets dehydrated if the vapor pressure of the hydrated salt is higher than atmosphere pressure whereby sodium sulphate can again absorb moisture in liquid or gaseous state and becomes Na2SO4•10H2O. These temperature and humidity conditions variations may cause fatigue phenomenon in the bricks and may, bring failure of the structure. [IV] There is still another way where by sodium sulfate will cause damage. It is named SULFATE ATTACK as follows: When the bricks containing in between the cement layer remain constantly in touch with water, the sulfates react with the tricalcium aluminate (C3A) in the cement to form tricalcium sulfoaluminate hydrate.

3[CaSO4 • 2H2O] + 3[CaO • Al2O3] + 26H2O → 3CaO • Al2O3 • 3CaSO4 • 32H2O.

Gypsum + Tricalcium aluminate + Water → Tricalcium sulfoaluminate hydrate.

This expands enormously and causes cracking which may lead to decomposition.

[V] Lastly the presence of Cl- ions can also damage the strength of the bricks and the effect is named as CHLORIDE ATTACK as follows: Na Cl may be carried out from rising damp, wind, sea spray or flooding especially during the cold climates and can affect the brick in two ways.(a) A 2% by weight of Na Cl in a brick increase the thermal expansion by the hygroscopic shrinkage (b) NaCl O formed penetrates in the solution and crystallizes when the brick structure dries out; generates pressures that lead to the powdering of the material and thus lower the mechanical strength of the brick.

Thanks a lot. Very comprehensive and interesting. I really appreciate your concern. It was very useful.

Can you suggest any percentage decrements if the brick is complete immersed in waste water (e.g. a brick is immersed in pond water for 1 year).