Showing posts with label Concrete. Show all posts
Showing posts with label Concrete. Show all posts

Monday, December 13, 2010

Methods of reducing corrosion for structural Reinforcement


Better grade of concrete with lower w/c ratio and well compacted.

A polymeric coating is applied to the concrete member to keep out aggressive agents. A polymeric coating is applied to the reinforcing bars to protect them from moisture and aggressive agents.


Fly Ash -  Using a Fly Ash concrete with very low permeability, which will delay the arrival of carbonation and chlorides at the level of the steel reinforcement. Fly Ash is a finely divided silica rich powder that, in itself, gives no benefit when added to a concrete mixture, unless it can react with the calcium hydroxide formed in the first few days of hydration. Together they form a calcium silica hydrate (CSH) compound that over time effectively reduces concrete diffusivity to oxygen, carbon dioxide, water and chloride ions. 

Modified quality of steel reinforcement which are less susceptible to corrosion such as special grade of stainless steel, CRS (Corrosion Resistant Steel),TMT steel etc.

Pre-applied impermeable coating (Epoxy, CECRI & CBRI coating)
Stainless steel or cladded stainless steel is used in lieu of conventional black bars
Admixtures (Nitrites and Nitrates) for concreting, which are to be added in the green concrete.

Electrochemical injection of the organic base corrosion inhibitors, ethanolamine and guanidine, into carbonated concrete.

Other inorganic inhibitors, which are known to be migratory in nature. The migration process is diffusion through water and diffusion through vapour phase.

Structural design aspects of corrosion control involve factors such as configurational (geometrical) considerations that minimize or, if possible, eliminate exposure to corrosives



Saturday, November 6, 2010

Strength of Concrete

Strength of concrete depends upon amount of cement content, quality and grading of aggregates, water of concrete ratio, compaction and curing Strength of concrete increase very fast in the initial stage.

In the 7 days the strength gained is as much as 60 to 65 present of 25 days strength it is customary to assume the 28 days strength as the full strength of concrete however concrete gains strength beyond 28 days also.



The strength/grade of concrete is specified and measured in newtons/sq. mm., meganewtons/sq. meter or even megapascals, in fact the numerical figure will be the same in each case. 
E.g. a strength of 20 newtons/sq.mm. is the same as 20 meganewtons/sq.metre

Compressive strength of concrete
The characterize strength of concrete is defined. As compressive strength of 150mm size cubes after 28 days. Concrete mixtures can be designed to provide a wide range of mechanical and durability properties to meet the design requirements of a structure. The compressive strength of  concrete is the most common performance measure used by the engineer in designing building and other structures.
The compressive strength is measured by cylindrical concrete specimens in a compression-testing machine. The compressive strength is calculated from  




Tensile Strength
The tensile strength of concrete is usually considered about one-tenth of the compressive strength; that is, concrete which has a compressive value of 2,000 pounds per square inch should have a tensile strength of about 200 pounds per square inch. Although there is no fixed relation between the two values, the general law of increase in strength due to increasing the percentage of cement and the density, seems to hold in both cases.