Paper of Efflorescence in Bricks and Efflorescence and Leaching in Concrete by Sir. Kaushal Kishore
Materials Engineer, Roorkee
Efflorescence is the usual terms for deposit of soluble salts, formed in or near the surface of a porous material, as a result of evaporation of water in which they have been dissolved.
EFFLORESCENCE IN BRICKS:
Usually sulphate of magnesium, calcium, sulphate and carbonate (and sometimes chloride and nitrates) of sodium and potassium are found in efflorescence. These salts may be traced to the brick itself, sand used in construction, the foundation soil, ground water, water used in the construction and loose earth left over in contact with brick work. Bricks with magnesium sulphate content higher than 0.05 percent should not be used in construction. Soluble salt content in sand (chloride and sulphate together) should not exceed 0.1 percent.
Water, if it finds access to brick work, moves along its pores by capillary action and carries with it dissolved salts. As the solution evaporates from the exposed surface of the brick work, the salts are left as deposit on the surface or on layers just below it. Disintegration or flaking of the brick surface is caused by the mechanical force exerted by salts as these crystallize just below the exposed surface. Magnesium sulphate, in particular, disintegrates bricks and pushes out plaster.
1. Well fired bricks should be used in construction.
2. Sand should be tested for its salt content.
3. Proper D.P.C. should be provided in the building.
4. Efflorescence on brick work traceable to salts in the materials can be removed by dry brushing and washing repeatedly. Such efflorescence may re-appear in dry season but usually are less in intensity. Finally these disappear as the salt content of the bricks is gradually leached out.
TESTING BRICKS FOR EFFLORESCENCE
Distilled water to be filled in a dish of suitable size. The dish should be made of glass, porcelain or glazed stone ware. Place the end of the bricks in the dish, the depth of immersion in water being 25 mm. Place the whole arrangements in a warm (for example, 20 to 30oC) well ventilated room until all the water in the dish is absorbed by the specimen and the surface water evaporate. Cover the dish with suitable cover, so that excessive evaporation from the dish may not occur. When the water has been absorbed and bricks appear to be dry, place a similar quantity of water in the dish and allow it to evaporate as before. Examine the bricks for efflorescence after the second evaporation and report the results as:
(a) NIL – When there is not perceptible deposit of efflorescence.
(b) SLIGHT- Not more than 10% area of the brick covered with a thin deposit of salt.
(c) MODERATE- Covering upto 50% area of the brick.
(d) HEAVY- Covering 50% or more but unaccompanied by powdering or flacking of the brick surface.
(e) SERIOUS- When, there is a heavy deposit of salts accompanied by powdering and/or flacking of the exposed surfaces.
EFFLORESCENCE AND LEACHING IN CONCRETE:
When water percolates through poorly compacted concrete or through cracks or along badly made joints, the lime compounds with in the concrete leached out which leads to the formation of salt deposits on the surface of concrete, known as efflorescence. This caused primarily by calcium hydroxide Ca(OH)2 one of the hydration products and slightly soluble in water, migrating to concrete surface through the capillary system. After evaporation, the solid Ca (OH)2 reacts with the atmospheric carbon dioxide CO2 to form calcium carbonate CaCO3, a white deposit on the concrete surface.
Early efflorescence can be removed with a brush and water. Heavy deposits may require acid treatment of the surface of the concrete. The acid used is HCl diluted from the concentrated form in a ration of 1:20 or 1:10. The action of the acid stops when it has been used up by the reaction with lime, but the concrete should be washed in order to remove the salts which have been formed.
Efflorescence and leaching in concrete is harmful. In addition to blemish and ugly appearance, the process of carbonation of concrete is accelerated. In reinforced concrete, the chances of corrosion of steel are increased due to carbonation and higher permeability of concrete. It is therefore necessary the concrete making materials should be of good quality, mineral and chemical admixtures preferably be used, properly proportioned (preferable design mixes) as per required durability and grade of concrete. All the materials should be properly mixed, placed, compacted, finished and cured.
1. I.S. : 3495 (Part-III)- 1976 – Method of tests of burnt clay building brick) Part-III, determination of efflorescence (Second Revision)
2. A.M. Neville, Properties of Concrete, Fourth Edition.
We are thankful to Sir Kaushal Kishore for publishing his paper on Efflorescence. This paper will help civil engineers understand what is Efflorescence and how can they get rid of it