Efflorescence in concrete simply means the appearance of white powder on the surface of the concrete. Efflorescence is the formation of salt deposits, usually white, on or near the surface of concrete after it has dissipated and causes a change in appearance.

Light colored concrete shows deposits much less than dark colored concrete.

pay attention: Over time, the pupil becomes less extensive and should eventually stop occurring, unless there is an external source of salt.

Efflorescence in Concrete - What, Why and How
Efflorescence in Concrete – What, Why and How

Efflorescence is usually caused by a combination of the following factors:

  • One or more components of concrete may contain salts.
  • A higher water-cement ratio resulting in a more porous concrete that allows movement of water and salt solutions
  • Inadequate curing which may leave un-hydrated products near the surface of the concrete
  • exposure to rain or other water sources (moisture allows salts to be carried to the surface where they accumulate as water evaporates)
  • The slow rate of water evaporation gives the salts time to penetrate the surface (which is why weathering is more of a problem during the winter months; in the summer, the higher temperatures can cause evaporation and hence the formation of concrete. Salt may be deposited inside. On the surface)
  • The variability of concrete (such as from compaction or curing) can result in local problems where water can penetrate through the concrete more easily.

Measures to prevent/control the occurrence of flowering include:

  • Use ingredients with as little soluble salt as possible.
  • Use a waterproofing mix to reduce the permeability of the concrete/mortar. Note that since some of these products themselves can cause bloating (such as water-soluble soap) always check with the manufacturer.
  • Again use denser concrete to reduce permeability. However, this may increase the shrinkage.
  • Use Cement : Lime : Sand No mortar stronger than required for application to reduce possible soluble salt levels.
  • Lime hydrated lime should be free of calcium sulfate.
  • Avoid premature drying.
  • Apply curing compounds or sealers on the same day to reduce the risk of wetting.
  • Protect hardened concrete from exposure to moisture from rising groundwater by maintaining surface sealers and site drainage and placing plastic membranes under the slab.
  • For masonry, make sure flashing, damp-proof courses and coping are properly detailed, cover the top course at the end of each day’s work, forming a ‘V’ or concave shape to compact mortar on exposed surfaces. Cover tool joints with additives, provide wide eaves and avoid getting wet from sources such as sprinklers.

Before removing the pupil, the things that may have caused the problem must first be corrected so as to limit or reduce the risk of it reoccurring.

Method-1 (brushing)

Soluble salt deposits can be removed with a stiff-bristled broom. Note that all brushed-off material must be completely removed by vacuum cleaning or other means. If the result is not satisfactory, scrub with clean water and then wash the surface lightly. Note that adding water may cause further coagulation. Frequent dry brushing is probably the best treatment for deposits that form.

Insoluble salt deposits (hard, white, scaly or crusted) cannot be removed by rinsing with water, although the use of a high-pressure water jet is effective.

Method-2 (using dilute acid solution)

Application of a dilute acid solution is also effective in most cases, and in some cases, it may be the only method (as described below).

Extreme care is required when handling acid. When diluting hydrochloric acid, always mix the acid with water, never the other way around. Ensure good ventilation and avoid contact between acid and reinforcement. Use only diluted acid to clean the concrete surface.

recommended ratios are 1 part hydrochloric acid to 20 parts water, Always saturate the surface with water before applying the dilute acid solution. When applying the solution, make sure the surface is moist but without any free water present. The applied solution must be allowed to react on the solid surface 10 to 15 minutes, Then the surface should be thoroughly washed and scrubbed with plenty of clean water. Repeat at least twice or until all traces of the acid solution are removed. The process can be repeated if necessary to achieve the desired surface finish.

pay attention: Washing with acid can cause color variations and change the texture of the surface. more dilute acid solution for colored finish (2% or 1 part acid to 50 parts water) may be needed. A small test area should be done first to assess the results.

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.