REPAIRS, REHABILITATION AND RETRO-FITTING
Significance of Ferrocement repairs
After, we in India, started manufacture of concrete in years 1930’s, the negative aspect of concrete started showing after sometime as below:-
| - Deterioration due to poor workmanship, particularly high water content and corrosion of reinforcement and R.C.C. Technology being new.
| - Leakages in concrete due to rain water as well as in water retaining structures
| This menace become conspicuous after construction works which became old about 20 to 30 years. We started realizing the importance of water cement ratio that only since about 40 years before and we have become very much conscious and now most of our engineers try their best to have Water cement ratio to the extent of its requirement. Even then, we did not stop production of concrete with water content comparatively more. It had been accepted that concrete is heterogeneous material and theory of reinforced concrete design is on the basis of cracked section below neutral axis. With this acceptance, scores of water proof additives and other admixtures contributing to the increase in strength, durability, workability and waterproof quality of concrete have come into market. Now it is a foregone conclusion that you cannot have best quality of concrete unless admixtures are used in its manufacture. Also many instruments for diagnosis for defective concrete such as porosity, lamination of cement matrix with course aggregate, corrosion of reinforcement, location of corroded reinforcement, strength of concrete etc. have come in the market in a very big way. Systematic method of inspection observations with measurements of the defects in concrete in a qualitative and also in quantitative manner have been developed and schemes / system of management of diagnosis analysis to maintain / to restore water proof quality and repairs to its original strength have been developed.
| All the above methods / system of water proofing, repairs and rehabilitation of structure costs lakhs of crores of Rupees to the nation. In order to save such expenditure, in-convenience, loss of time and energy CAN WE NOT PRODUCE A CONCRETE FREE OF SUCH DEFECTS?
| The quality of concrete can be improved to a large extent now. We are able to produce concrete of strength M100 or even sometimes M 200 with least reason for corrosion of reinforcement. Now a days corrosion of reinforcement is prevented by epoxy coating and galvanizing of reinforcement. Because of theory of reinforced concrete with provision of design of cracked section, the defects are bound to develop in due course of time which may be delayed. Prestressed concrete is the solon to a large extent with pretension structures. However there is possible corrosion in post tension structures due to errors in proper grouting of cables. In any case structures now should be better than before.
| Concrete is heterogeneous material. It has features to loose bond with aggregate and steel reinforcement at early stages. It can be said it is not possible for concrete structure to last for hundred years.
| Now it is the time when we should think of concrete which should not crack at all and there should be no extra water more than required for reaction with cement. And concrete should not crack at all when put under design loads. That means we must view or think about the theory of reinforced concrete that is a structural member is designed as cracked section cracking accepted below neutral axis. Or crack formation can be thought to be delayed. In other words crack width and minimum depths to stop entry of corroding forces upto reinforcement. Also the crack width should be so minute and depth should be so shallow that water be trapped in stopping it to travel below upto the bottom of the depth or reach reinforcement surface. The effect of atmospheric pollution or carbonation can be minimized/eliminated by use of certain admixtures in...
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