rehabilitation and retrofitting of structures in nptel
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I need rehabiliation and retrofitting of structures notes. Can u please upload or send me the notes to my id sunilkumarddg[at]gmail.com
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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 the concrete.
Ferrocement Technology is the solution
Under laboratory loads Ferrocement bends largely alongwith reinforcement without cracking.
Under further loads, several cracks do take place, width being very negligible to few microns.
Under very large loads only little wider cracks of low value less than 0.1mm take place. After this, structure will deform greatly but no collapse can take place. However on release of loads the cracks close. The deflection recovery has been found to be 97%. Sometimes it is said it has inbuilt property of prestress concrete to less extent In view of this significant feature of Ferrocement it is termed to have mechanism called ‘Crack arrest mechanism’
Corrosion of Reinforcement
The corrosion of reinforcement in Ferrocement is most insignificant. The water cement ratio is the least giving least extra water to react with wiremesh reinforcement. There may be corrosion of brown colouring with wiremesh reinforcements which is not strong enough to burst cement matrix. In view of evenly spread wiremesh reinforcement, the corrosion is the most negligible and can be said to be not at all causing any damage. We can say the minute corrosion is dormant in the case of Ferrocement. This is the feature of Ferrocement unless it is manufactured with inferior materials and inferior workmanship in slipshod manner. In view of this and cement matrix being of superior quality, spalling / splitting will not take place.
We have been practicing Ferrocement Technology since more than 25 years by now. In our Ferrocement products, we maintain water cement ratio to be 0.35 to 0.4. We invariably vibrate our Ferrocement products either on machinery set up under controlled conditions or in- situ. In all our products to make it dense, we use admixtures to produce maximum strength and add many positive aspects to the materials. We use non- metallic fibers in the top of finished matrix. In view of such method of manufacture, we do not find any deterioration of our product and no problem so far as water proof quality of Ferrocement is concerned. In our Ferrocement products, there is no carbonation phenomena. We claim our method of manufacture is most meticulous with high quality and superior materials and workmanship. We are confident that our structures are bound to perform in a far superior manner.

Historically Ferrocement has proved to be durable and without corrosion as below:-
- A small Ferrocement boat constructed in 1887 was in operational condition till 1968 after which it was shifted to lounge of the Vereniging Nederlands Cement industries’ office in Amsterdam.
- Several structures constructed by Mr. Pier Luigi Nervi during early 1940’s in number of cities in Italy have been reported to be in good condition.
- During 9th International Symposium, Prof. Khan A.M. in a joint paper alongwith Prof. Rafeeqi S.F.A. and
- During 9th International Symposium, Prof. Khan A.M. in a joint paper alongwith Prof. Rafeeqi S.F.A. and Prof. Lodi S.H. from Karachi, Pakistan presented a paper “Performance of Park Structure made by Ferrocement”. They carried out experiment to study condition of a water storage tanks from the point of view of durability and corrosion constructed by students of Engineering college in about 1993. He has concluded that the water tank structure made up of Ferrocement material has sustained the atmospheric condition satisfactorily. No significant corrosion effect of wiremesh was visible.
In our experience with Ferrocement Technology at international level having attended all the Nine International Symposiums we have not come across any structure that has collapsed or is damaged due to corrosion.

As a matter of fact, United Nations Industrial Development Organisation (UNIDO) have published a book in 1972 ‘Ferrocement boats’ and recommended the use of Ferrocement Technology at the earliest.

Food and Agricultural Organisation (FAO) of UNO (United Nations Organisation) organized international conference, Ferrocement fishing boats in the year 1972. It has recommended adopting Ferrocement Technology for fishing vessels in view of Ferrocement being a sound technology.

Similarly, Royal Institute of Naval Architecture (RINA, UK) and National academy of Sciences of USA have recommended in about 1972 use of Ferrocement technology as early and as fast as possible.
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