Efflorescence in concrete simply means the appearance of white coloured powder material on the concrete surface. Efflorescence is the formation of salt deposits, usually white on a near the surface of the concrete after it has been finished and causing a change in appearance.
Light-coloured concrete shows the deposit much less than darker coloured concrete.
The alkaline salt present in the brick absorbs moisture from the air which on drying leaves powder deposited on the brick It is also caused if pyrite was present in clay used for brick making and water used for pugging contains gypsum.
Effects of Efflorescence :
Effects of Efflorescence in the damp wall leading to various damages like unhygienic condition, decay, dry of wood, the disintegration of masonry damage to furniture and internal de-colouration…..etc.
- One or many constituents of concrete may contain salt
- High water-cement ratio resulting in a more porous concrete that allows movement of outer and salt solution.
- In-adequate curing which may leave un-hydrated products near the surface of the concrete.
- Exposure to rain or other sources of water.
- The slow rate of evaporation of water allowing time for the salt to permeate to the surface.
- Variability of concrete can result in localized problems where water can permeate more easily through the concrete.
1.Use ingredients containing as tittle soluble salt as possible
2. Use waterproofing admixtures to reduce the permeability of concrete
3. Use denser concrete to reduce permeability
4. Avoid premature drying
5. Use cement, lime and mortars no stronger than required for the application to minimize possible soluble salt level . lime should be hydrated & lime-free from calcium sulphate.
6. For masonry ensure flashing, damp proof course are detailed correctly, cover the top course at the end of each day work.
Eradication of efflorescence
For the eradication of efflorescence problem the source of ingress of moisture should be determined first, the cause of ingress may be due to defective DPC or absence of DPC or other causes
- The first action is to stop the source of ingress of moisture.
- The second step should be to remove plaster from both inside and outside and leave it to dry.
- Then removing the defective bad brick or filling voids with mortar then by cement slurry or cement concrete.
- Check the mortar joint carefully and removing loose mortar where necessary.
- Wash the white patches surface with the acidic water and then wash it again with clean water.
- Plaster both inside and outer surface with cement mortar adding waterproofing admixture.
- If causes are due to the absence of DPC course or due to failure of DPC; new course of DPC should have to be introduced or replace the defective DPC by the new one.
It can also be done by following;
Brushing soluble salts deposited can be removed with a stiff bristle broom. Note that all brushed of materials should be totally removed by a vacuum cleaner or other means. If the result is not satisfying, scrub with clean water then lightly rinse the surface. Note that adding water may result in further deposits, repeated dry brushing as the deposit appears is probably the best treatment. Insoluble salt deposits cannot be removed by water washing although the use of high-pressure water jet is effective.
b. Using a dilute acid solution
The application of a dil. acid solution is also very effective in most cases and in some cases may be the only way. extreme care is required while handling acids. when diluting HCL acid, always add the acid to the water never the reverse.
Ensure good ventilation and also avoid the contact between the acid and the reinforcement. The concrete surface should be cleaned with only diluted acid.
The recommended proportions are 1 part HCL and 20 parts of water. The surface should be saturated always before the application of dilute acid. when applying the acid solution ensure that the surface is surface moist but without any free water is present. Then the applied solution should be allowed to react on the concrete surface for 10-15 minutes. The surface should be thoroughly rinsed and scrubbed with lots of clean water. Repeat rinsing at least twice or until an all traces of the acid solution have been removed. The process may be repeated if required to bring necessary surface finishing.
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