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close this bookJournal of the Network of African Countries on Local Building Materials and Technologies - Volume 1, Number 3 (HABITAT, 1991, 46 p.)
View the document(introduction...)
View the documentForeword
View the documentThe role of a Network in strengthening local technological capacity in the production of Building Materials
View the documentMalawi: Production process, application and acceptance of fibre concrete roofing products*
View the documentNigeria: Natural-fibre Shwishcrete technology for low-cost roofs*
View the documentNigeria: Appraisal of coir-fibre cement-mortar composite for low-cost roofing purposes*
View the documentMalawi: Improved concrete roof tiles and roof-tile machines*
View the documentEast African roof thatching techniques being tested in India*
View the documentCorrugated roofing sheets from coir-waste or wood-wool and Portland cement*
View the documentPublications review
View the documentEvents
View the documentBack Cover

Corrugated roofing sheets from coir-waste or wood-wool and Portland cement*

* Developed by the Central Building Research Institute (CBRI), Roorkee, India.

Recent investigations at the Central Building Research Institute, CBRI, Roorkee, India, on coir-waste/wood-wool have shown that these can be utilised in the production of corrugated roofing sheets.

The production of coconut in India is estimated at 6000 million nuts per annum. About 50 per cent of the husk is used for making coir mat, cushions etc. The remaining, a potential industrial raw material, is mostly used as fuel. Shearing waste "baby- fibre" and coconut pith also account for a large amount of agro-industrial waste. Unlike other cellulosic materials, coconut fibre is free from water soluble polyphenols, thus, resulting in a strong board in conjunction with ordinary Portland cement (IS:269-1976). It is this property of the fibre and pith which has made them attractive for use in making corrugated roofing sheets. The physical properties of "baby-fibre" used in the process are as follows:

Physical properties of coir baby-fibre

1. Bulk density, kg/m3

150-280

2. Fibre length, cm

5-26

3. Fibre thickness, mm

0.10 to 0.40

4. Resilience

Does not break when folded over 0.3 cm diameter rod

5. Water absorption in 24 hours at 20°C, percentage

100-200

6. Water solubles at 20°C, percentage

0.5 to 0.6

7. ph value of the water extract at 20°C

6.6

Wood-wool used largely as packing material, is obtained mostly from softwoods such as fir, chir, kail, and deodar which yield good-quality fibre of suitable length, thickness and width. Use of hardwood for producing wood-wool requires judicious selection as many of the species affect the setting and strength development of cement. A mechanized plant (see figure 1) of capacity 100 sheets per day has been designed and installed at CBRI for the manufacture of corrugated roofing sheets (2000 × 1000 × 12mm).

For making corrugated sheets, a weighed quantity of the fibre (coir-waste or wood-wool) is soaked in water for some time. A fixed quantity of Portland cement is then thoroughly mixed with the water-soaked fibre. The cement-coated mixed stuff is then uniformly spread on the drag (or bottom part) mould. The cope (or top part) mould is placed in position on the loaded drag mould. The assembled mould is pressed down hydraulically to help press the raw materials to the required pressure. Wedges are next inserted in the slotted pins of the drag mould to hold the cope mould in position so that the cast sheet is kept pressed to the required form during its setting period. The wedged mould assembly is then rolled out of the press and transported on a trolley to the curing yard. After three to four hours, the sheet is demoulded by removing the wedges and separating out the cope and drag moulds. The green sheet is next removed from mould and kept under a shed for natural curing in vertical stacks for a period of about eight days. During the curing period, the sheet becomes hardened and develops adequate strength. It is later given a cement wash on both sides and on drying, it is trimmed off to the required size. A water-proofing paint is then applied on the top side of the sheet and the painted sheet is ready for use.

Major plant and machinery requirements

The mechanized plant (see figure 1) developed for making sheets comprises the following equipment: (a) moulds; (b) hydraulic press (20 ton capacity); (c) roller tracks; (d) stripping device; (e) gantry cranes; and (f) power trimming device.


Figure 1. Corrugated roofing-sheet-making plant

Electric power requirements

Electric power is required for operating the hydraulic press of 10 HP; two trimming devices each of 3 HP; three gantry cranes, each of 2 HP and for other allied uses.

Properties of the corrugated sheets

Physical properties of the corrugated roofing sheets compared with asbestos cement sheets.


Physical property

Coir-fibre sheet

Asbestos-cement sheet

Pitch of corrugation, mm

150

146

Depth of corrugation, mm

55

48

Length of the sheet, m

1.5 to 2.0

1.5 to 3.0

Width, m

1.0

1.05

Thickness, mm

7

6

Weight kg/sq m

11.0 to 12.0

13.5

Water permeability through the coated side

NIL

-

Water absorption in 24 hours percent, at 25°C

-

25

Breaking load, kg/cm:




(a) at 1 m span

2.5 to 2.7

5.0


(b) at 50-60 cm span

5.0


Thermal insulation kCal cm/mh °C

0.09

0.24

Fire resistance

Very good

-

Special features of corrugated roofing sheets

1. Coir-fibre/wood-wool corrugated sheets require 30 per cent less cement compared with asbestos cement sheets.

2. The sheets are light and can be transported over hilly and rough roads without any breakage.

3. The sheets are strong and possess good bending strength. A person can safely walk over them.

4. The sheets possess good thermal insulation and are expected to provide greater comfort in tropics compared with asbestos- cement or galvanized iron sheets.

5. Their preparation needs neither heavy machinery nor high capital investment. The sheets are 50 per cent cheaper than asbestos-cement sheets.

6. They can be laid on roofs like asbestos-cement sheets.

7. The roofs made do not require any further finishing or waterproofing treatment.

8. They have good fire-resistance property.