Concrete structures which are subjected to freezing and thawing are likely to deteriorate earlier. Structures which are mostly affected under similar climatic conditions due to freezing and thawing are the exposed surfaces of the top 60 cm of walls, piers, parapets, cornices etc. the durability of such structures can be improved by adopting certain weather proofing measures. It has been observed that concrete surface if applied with curing compounds, linseed oil, epoxies etc, last longer.
In general protection measures against weathering are not adopted for new concrete surface unless they show some signs of deterioration, which is evident by the formation of fine cracks, close and parallel to edges and corners. It is better to treat such surfaces in earlier stages to avoid later uneconomical and difficult repairs. Concrete should be made waterproof to make it durable against freezing and thawing. The following methods of protection against weathering are known to have given good results.
- Application of oils & paints
- Application of varnishes
- Application of chemical solutions
1. Application of Oils & Paints
New concrete surfaces after completion of the curing should be allowed to dry for 1 or 2 weeks before waterproofing treatment is applied. Such new surfaces are brushed with a solution of 40 gm of phosphoric acid and 16 gm of zinc chloride to a liter of water. This is done to prevent the saponification of linseed oil. This treatment is not necessary for old concrete surfaces. Before adopting waterproofing measures the surface must be made clean and dry. After it apply two coats of linseed oil as mentioned below.
- A mixture of 50% raw linseed oil and 50% turpentine heated to a temperature of 800C is applied with ordinary brush as first coat
- Raw linseed oil heated to 800C is applied as a second coat with ordinary brush after 24 hours of application of the first coat.
After the second coat waterproofing coat becomes thoroughly dry, the entire treated surface is given two coats of standard white lead and oil paint. The application of the paint is necessary otherwise the previously applied oil treatment will deteriorate. In order that the colour of oil paint should match with the colour of concrete surface, lamp black or burnt sienna is added to the paint.
In case any open cracks formed in the surface area to be treated, these should be first repaired by filling the cracks and then the surface is brushed with oil.
2. Application of Varnishes
Sometimes varnishes are applied to concrete surfaces which are effective against attacks due to mineral and vegetable oils. There are various bituminous paints, pitches and mastics available these days. They save the surface against acid attacks.
3. Application of Chemical Solutions
Magnesium or Zinc Fluosilicate Solution
The treatment consists of applying two or more coats of the compound. For the first coat, a solution of 1 kg of the compound per 10 liters of water is used. For subsequent coats, about 2 kg of the compound per 10 liters of water are used. The solution is painted on the surface and each coat is allowed to dry before the next coat is applied. At the end, the surface is brushed and washed with water. This treatment hardens the surface and makes it impervious by chemical action. It protects concrete against the attack of all mineral and vegetable oils, salts and alkalies.
Sodium Silicate Solution
It is a viscous liquid and should be diluted with three times its volume of water. It should also be applied as above. It is better to scrub each coat with water after it has hardened before applying the next coat. The later coats are of a stronger solution. It also protects concrete against the same attacks as Fluosilicate.