REPAIRS, REHABILITATION AND RETRO-FITTING

After, we in India, started manufacture of concrete in years 1930’s, the negative aspect of concrete started  showing after sometime as below:-

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.

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.

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’

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.

- 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.

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.

For the present international Ferrocement society, Bangkok, founded in 1991 and Committee 549 of USA and  certain publications by RILEM, Paris, have been guiding by publishing documents for the design and construction  of Ferrocement structures.