Salt is a natural mineral that can sometimes end up in your concrete mixture. It can either be present in the sand and aggregate or it can end up in the concrete if you are building in a seaside environment. It appears as white streaks or powdery crystals on the surface of cured concrete.
The effects of salt can damage concrete if left untreated, especially large areas of walls and floor. The problem is worse near the sea where salt in the wave spray and in the air can affect concrete structures. Constant exposure to salt can cause problems for concrete structures.
How does salt damage concrete structures?
Concrete is an alkaline material. Any exposure to mildly acidic substances or those containing chlorides could break the bonds between the cement and aggregates. Salt is sodium chloride, so it can weaken concrete and make it brittle in a few ways:
- Salt can lower the pH of concrete. This makes the pores in the surface bigger which can allow more moisture, water and other chemicals seep into the concrete.
- Salt is hygroscopic which means that it attracts and absorbs water. It can retain water in concrete which leads to damage, rot and increased pressure inside the structure.
- Salt speeds up the carbonation process. Under ideal conditions, contractors want the carbonation process to be slow so that the concrete can cure properly.
- Salt introduces chlorides to the concrete. These chlorides seem up concrete corrosion and make the structure brittle.
How to treat salt damage in concrete
The first sign of salt in concrete will be white streaks or a white powder on the surface of the structure. To treat salt and prevent further damage, rinse the surface of the concrete with clean water. Scrub the salt away with a brush, leaving no white substance behind.
Next, apply a good sealer to the surface of the concrete to prevent salty moisture from entering the concrete. Sealers help to keep water and moisture out of the concrete pores. Ideally, you will want to use a sodium or lithium silicate densifier sealer as these chemically react with salt in the concrete to permanently protect the structure.
If you cannot get a proper concrete sealant, then apply a protective coating to the surface of the concrete. This could be a layer of plaster or a few coats of paint – ideally, both will help to form a protective coating that will prevent salty moisture from penetrating the surface of the concrete structure.
The best way to prevent salt damage, however, is to ensure that you use clean water when mixing the concrete and use sand from a freshwater river bed. Then, apply a sealer or protective coating as soon as the concrete has cured. Prevention is the best cure, so look after you concrete structures from the outset – especially in coastal environments.
LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges.
LafargeHolcim Tanzania has been supplying the country and neighbouring countries with our world-class Tembo cement brand for over 30 years. Our head office and fully-integrated plant are located in Mbeya, Southwest Tanzania.
At LafargeHolcim Tanzania, we believe customers come first. We listen to your specific requirements to supply and develop the best solutions for your needs. As the new leader in building materials, you can also rely on our cutting-edge research and development capabilities that have resulted in the finest materials for your construction projects, whether large or small.