The chloride ion attacks the passive layer although in this case (unlike carbonation) there is no overall drop in pH. Chlorides act as catalysts to corrosion. They are not consumed in the process but help to break down the passive layer of oxide on the steel and allow the corrosion process to proceed quickly as shown in…
Carbonation is the result of the interaction of carbon dioxide gas in the atmosphere with the alkaline hydroxides in the concrete. Like many other gases carbon dioxide dissolves in water to form an acid. Unlike most other acids the carbonic acid does not attack the cement paste, but just neutralizes the alkalinity in the pore…
Abstract Steel gets oxidise (corrosion) in the present of oxygen and water. Even present of oxygen in the concrete pore will not cause a corrosion at high alkaline environment. Concrete contains microscopic pores which contain high concentrations of soluble calcium, sodium and potassium oxides, this creates alkaline condition of pH 12–13. The alkaline condition leads…
The corrosion of steel reinforcement inside a concrete structure is undesirable in the following ways: (i) The presence of rust impairs the bond strength of deformed reinforcement because corrosion occurs at the raised ribs and fills the gap between ribs, thus evening out the original deformed shape. In essence, the bond between concrete and deformed…
Varnish is the solution of resins or resinous substances like amber, copal, shellac, gum resin etc. in solvents like oil, turpentile, alcohol etc. Depending upon the solvents used varnishes are classified as, oil varnishes, turpentilevarnishes, spirit varnishes and water varnishes. The desirable characteristics of an ideal varnish are 1. It should give glossy surface. 2. Should be…
Distempers are the cheaper variety of paints in which chalk is used as base and water is used as a carrier.The emulsifying agent which is commonly used is glue or casein. Distempers are available in powder form or in the form of paste. They are to be mixed with hot water before use.The surface to be distempered should be…
1. It should be possible to apply easily and freely. 2. It should dry in reasonable time. 3. It should form hard and durable surface. 4. It should not be harmful to the health of workers. 5. It should not be easily affected by atmosphere. 6. It should possess attractive and pleasing appearance. 7. It…
Paints are applied on the surfaces of timber, metals and plastered surfaces as a protective layer and at the same time to get pleasant appearance. Paints are applied in liquid form and after sometime the volatile constituent evaporates and hardened coating acts as a protective layer. Constituents of Paint The essential constituents of paints are:…
Cement is used widely for the construction of various structures. Some of them are listed below: (i) Cement slurry is used for filling cracks in concrete structures. (ii) Cement mortar is used for masonry work, plastering and pointing. (iii) Cement concrete is used for the construction of various structures like buildings, bridges.water tanks, tunnels, docks, harbours etc….
(a) Soundness Test: It is conducted by sieve analysis. 100 gms of cement is taken and sieved through IS sieve No. 9 for fifteen minutes. Residue on the sieve is weighed. This should not exceed 10 per cent by weight of sample taken. (b) Setting Time: Initial setting time and final setting time are the two important…