http://www.deccanherald.com/deccanheral ... 051226.asp
Building helipads no more a herculean task
B G Prakash draws attention to an indigenous defence spin-off technology that could help build helipads and repair roads in no time.
Imagine a scenario: enemy aircraft penetrates air defence systems, fly over airfield and drop bombs on the runway. Craters are formed on the runway making it non-operational. Pilots cannot take off to defend or attack the enemy. Worthy war machines remain idle. The same runway needs to be attended to, repaired and rehabilitated at breakneck speed — usually overnight — to put it back into use.
War inventory, today, has indigenous supportive technology for such, expected contingencies. Helipads too can be built overnight. Commercially available Rapid Acting cement is used only for construction and cannot be used for runway repair. This indigenous technology is for civil use as well.
It started with a need in the armed forces felt to repair runway that gets damaged due to enemy bombing which leaves craters. Indian Air Force bought a mixer cum dispenser from a French company at an enormous cost. Since then, an alternative was looked at. In 1990 the DRDO sanctioned the concept of a Rapid Repair of Runway. Seven scientists and engineers set about making ‘Runway Rehabilitation using Quick Setting Cement’ a reality. Research and Development Establishment (Engineers) have since announced Rapigrout Cement — produced indigenously.
On an average, a crater in the runway is of 12 metre diameter and is two metre deep at the deepest point. Rapigrout is of a special variety that does not need conventional reinforcement with steel mesh or rods of steel or tor-steel. The shelf life of the French Mix is one year. Which means, if left unused, the ingredients go waste. But Rapigrout is claimed to have two years shelf life.
Rapigrout does not need the typical curing period. In fact, Rajendra Kumar Gupta, the scientist at Composite Research Center at R&D E(Engrs) claims that it is a non-curing cement. It gains in strength without conventional curing. It contains a ultra rapid hardening hydraulic binder. The cement is effective in the temperature range between minus 20 degree Celsius to 50 degree Celsius with additives. Additive C is used in cold weather and additive H is used in hot weather.
The scientists recommend use of hot water at just 28 degree C mixed with Additive L, a lime-based compound. The chemical reaction due to lime mixing with water produces heat and Rapigrout uses this indigenous heat to set rapidly.
It is well known that normal cement used in construction takes 7 days to reach normal level of curing provided it is constantly kept wet. A total of 28 days are needed for the cement concrete to set fully. Further, as authenticated by Border Roads Organization, at Himalayan heights, curing takes much longer due to sustained low temperatures.
On the other hand, Rapigrout takes just 10 minutes for initial setting and in 25 minutes, it sets finally.
Laboratory tests after 100 minutes reported results with the test blocks able to withstand 100 kilo gram per square centi metre load.
A crater of 12 m diameter and having 2 m depth at the deepest point needs about 12,000 cubic metre of slurry. Water content needed varies - in cold weather it is less than 28 per cent of the total weight of Rapigrout used; in hot weather 32 per cent water content is sufficient. Pre-packed aggregate of 47 milli metre size — a little less than two inch size — is mixed with this very finely powdered cement. Fineness of the cement particles
is better than in normal
cement. The finer it is the faster it strengthens.
Rapigrout has a shelf life of two years and can be stored at a temperature range of minus 20 degree C and plus 50 degree C in
airtight containers. Cost of Rapigrout is estimated to be five or six times the Rapid Acting cement.
R&D E does not want to give away full details and commercialisation is still some time away. A leading cement manufacturing company has signed a Memorandum of
Understanding with DRDO to facilitate research, trial and manufacture.
Building a Helipad or helicopter landing ground, using Rapigrout is yet to be tried - or, if it has been tried - is not admitted to.
The minimum area needed to land and take off with Helicopter is a circle of 15 m diameters.
Just 24 hours!
Preparing the slurry with appropriate additive will take some time, to be spread evenly on the
prepared site. The mix sets in less than two hours and is ready for operation. The whole helipad can be built in 24 hours.
Such needs arise not only in Siachen but where landslides destroy arterial mountain roads and helipads. The recent
earthquake in Kashmir destroyed mountain ways and made relief operations
impossible at several
If emergency helipads could have been constructed better relief measures could reach the needy too. Helipads can be built in 24 hours.
Mining industries in Bellary are going in a big way to buy helicopters out of compelling needs and some of them are already into building helipads without any proper monitoring apart from them being improperly specified private helipads. Before it is too late, guidelines can draw attention to flight safety.