From: D. K. Mishra To: Lalu Mansinha Cc: Sent: Sunday, January 09, 2000 5:09 PM
Subject: Re: Cyclone Shelter designs

Lalubabu,

Thanks for taking the time out and looking at the housing concept. I will try to answer your questions which by the way are really good ones and pertinenet as well.

1. Yes, FRC stands for Fiber Reinforced Concrete (its more like a micro-concrete or mortar rather than concrete in the usual sense)

2. The cement is ordinary, the fibers are also pretty ordinary steel fibers. Having worked for ACC in Bombay for a couple of years I know both these are readily available in India. In fact we will probably use a locally made cheaper variety of fibers in the long term. The costliest component of the product is the fiber and the wire reinforcement, both of which are available in India at cheaper costs than here.

3. Yes, uniform thickness is a must and can be achieved using our production methods. The sheets will have to be made in a factory set-up in Bhubaneswar and shipped to the villages where they can be rolled using portable rolling equipment. Although the uniformity of thickness is important, small deviation will not cause significant problems unless used to make water tanks, in which case micro-cracking must be closely controlled.

4. The durability with respect to corrosion due to saline environment of these sheets are well proven as water tanks made out of these for farms in New Zealand are in service for at least 20 years with out any sign of corrosion. I am personally carrying out laboratory tests on these sheets currently with excellent performance in this regard.

5. Regarding the stability and strength of the cylindrical structures made out of these sheets, we have good experience with water tanks. The tanks being 2.4 m high and 3.6 m in diameter are very stable structures and have been proven to be earthquake resistant even when substantially full with water and subject to motion of the water inside (remember a full tank carries 22 tonnes of water whereas it weighs only 1.5 tonnes itself). I believe the structure could be subjected to overturning rather than collapse in case of strong winds. The base ring has to be anchored into the ground to resist this and the structure can be designed for specific wind speeds. It may be unrealistic to design for 280 km/hr winds (which is probably once in a hundred year event!). Given the aerodynamic shape of a circular house, the wind pressures will be significantly less in any case. I intend to do a detailed analysis of this issue using structural analysis procedures once this goes any further.

The collapse of the wall itself is unlikely as it is braced by a reinforced concrete base ring, a mid-height joiner ring and the dome roof, each of which provide additional stability and strength.

6. This is a very technical question indeed and I am really surprised at your knowledge in this area. As you have rightly said the tensile stresses on the outside surface of the sheet causes micro-cracks which are controlled in terms of their thickness and spacing by use of stranded continuos wires placed eccentrically in the sheet. In fact the rolling makes these wires go into pre-tension helping further in crack-control. The cracks are so fine that they self-heal with time avoiding any chance of corrosion. Most of the water tanks made in this way are in use in coastal areas of NZ and Australia with very good record. In case of water tanks however, for additional impermeability we do in fact use a polymer sealant during rolling as the micro-cracks form in order to seal them and also a coat of paint is applied on top.

7. Once the sheet technology is transferred to Orissa I can see a multiple of applications. Besides water tanks and walls of houses there could be roofing sheet applications, application as form work, application in building small culverts and bridges and all sorts of membrane structures.

The basis problem with this technology here is that in spite of the best effort of the company to totally mechanise the manufacturing process, there are still too much labour involved to make products. This is why I strongly believe that the technology is very suitable for developing countries such as India with cheap labour. For example our water tank has a material cost component which is 30% of the total cost of the product where as labour component is perhaps as high as 60%. This will be atleast reversed in India and the whole thing will be very much cheaper and cost-effective.

I hope I have answered your questions. Please do let me know if I can help with any other issues.

Dhanada

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From: Lalu Mansinha
To: Cc: Sent: Sunday, January 09, 2000 9:27 AM
Subject: RE: Cyclone Shelter designs

Dear Dhanada:

I followed up your suggestion and looked up the cyclone shelter design based on the FRC (I presume this means Fiber Reinforced Concrete) sheets made by your firm in Australia. As I understand it, using fibers and a special cement, the FRC sheets are thin (1 cm thick), strong and flexible. Several questions: Are the fibres and the cement available in India? Are they cost effective? Is uniform thickness a must? If made by hand in village the thickness of the sheets can vary, but will the strength and flexibility be affected? What is the resistance of FRC to salt and (in modern times) to acid rain?

The pipe that is formed by rolling the fRC sheet into a very large cylinder makes the puter walls of the house. While the forming into a cylinder gives the wall some rigidity, will be sufficient to withstand 280 km/h winds, or flood waters. I think the flexibility of FTC sheets may make it flex in such strong winds so as to collapse the structure.

The rolling of thr FRC Sheet into a cylinder must setup tensile stress on the outside and compressive stress on the inside. Typically, concrete would form microcracks under tensile stress, which will initiate corrosion. Is the outside sprayed with a sealant?

Finally, has your company thought of using the FRC sheets as roofing?

The flexibility means they could replace the thatch in thatched roofs,

Provided the typical thatch roof frame in villagehouses take the load.

Thanks

Lalu

From: Sunil Bhagwani
To: D. K. Mishra
Cc: Lalu Mansinha
Sent: Monday, January 10, 2000 12:55 PM
Subject: Re: Cyclone Shelter designs

Suggest however that each house have at least two areas inside (maybe partitioned off using FRC) as kitchen and toilet. If these FRC partitions are connected to the exterior walls they would probably improve the rigidity of the whole.

Regards Sunil Bhagwani.

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From: Sunil Bhagwani
To: D. K. Mishra
Cc: Lalu Mansinha
Sent: Monday, January 10, 2000 1:17 PM>
Subject: Re: Cheap sealant alternative for Cyclone Shelter designs

Take paraffin wax (1 Kg), kerosene (4 liters). Heat both separately till the wax melts. Mix the melted wax into the hot kerosene. Apply as hot as possible to the FRC with a paintbrush. The microcracks constitute"porosity" which effectively absorb the highly fluid hot mix. The kerosene evaporates (on a hot day within 6 hours). Three things happen. One: the mix reacts chemically with the residual "alkaline elements" of the concrete (not too sure of my terminology but u should be able to confirm this Dhanada). This creates an interior inert compound that is totally water-proof and which reduces any chemical reactivity of the concrete. Two: the wax that remains inside the pores (micro-cracks) effectively seals them and is flexible enough for the sealant to last for at least 5 years (tried out in Gopalpur).The wax remaining on the outside offers some water-repelling action to the structure (though it normally does not last for more than six months in coastal areas).

Costs: 1Kg paraffin wax = RS. 48/-, 4 l kerosene = 48/- (Retail prices considered). Resultant mix can easily cover about 250 square feet. i.e. Rs. 0.38/sft. Add labour @ Rs. 0.2/sft, Misc 10% RS. 0.06. Total = 0.64/sft.

This probably would be much cheaper than the sealants that u are thinking of. U could try out the system and submit it to artificial aging processes if your lab is equipped for it. I have used this system on at least 10 buildings over the last 10 years. They are all still ok except one which was originally in a real bad state of corrosion when we started.

Sunil