|Journal of the Network of African Countries on Local Building Materials and Technologies - Volume 3, Number 2 (HABITAT, 1994, 42 p.)|
*** Submitted by the Central Building Research Institute (CBRI) Roorkee, India
A variety of agrowastes such as saw dust, sugarcane, coir fibres, rice husk, wheat stalk are available in many countries. These materials could be used easily to produce various types of building boards and panels. Unpulped straw such as rice and wheat straw can be converted into binderless boards and rigid building panels by applying heat and pressure techniques. Methods for the preparation of building boards and blocks from rice husk, corn stalk, corn cob etc. are already in existence in some countries. Glued hot mat boards have been prepared from reeds and other types of straw. They are being used for certain walling and shadow roofs. Coconut fibre and wood shavings have also been used in conjunction with Portland cement binder to produce mineral bonded panel products. Similarly, there are quite a number of research findings and investigations aiming at using agro-industrial wastes for producing a variety of building products by employing cold and hot pressing techniques or using a range of organic and inorganic hinders.
Feasibility studies for producing normal particle board and building components from coconut husk have been conducted by CBRI. However, the use of synthetic binder such as urea formaldehyde is completely ruled out because of their prohibitive cost and scarce supply. A normal particle board requires a 8 to 10 per cent by weight adhesive to obtain an acceptable strength and finish which amounts to nearly half of the cost of the finished board. Even the raw materials for making the adhesive are quite costly. However, work is in progress to find out what type of non-petroleum based binders could serve the purpose.
Soft wood and magnesium oxychloride are normally used for making wood-wool boards. Difficulties are however, encountered with the use of Portland cement. The hydration and strength development of cement is strongly inhibited by the extractivies in the agro-industrial wastes. The important inhibitors are sugar, tannin, quinone, phenol and other water soluble compounds. Mineralization with CAO, CACl2, Na2CO3 etc. appears to help considerably in reducing the inhibiting action of these reactors. Investigations carried out in the CBRI have identified several other types of wood suitable for making wood-wool boards with cement as binder. However, some agro wastes like coconut husk and its by product, groundnut husk, rice husk etc. have no inhibiting action on normal Portland cement and these have been used to produce such boards. A corrugated roofing sheet using some agricultural wastes and wood-wool and cement has also been developed.
Tiles of size 25 × 25 × 1 cm and 49 × 24 × 1 cm have been produced in strong mild steel moulds and pressed on compression testing machine at about 20 to 30 ton load. After 24 hours water absorption, the tiles were demoulded. The weight of a 49 × 24 × 1 cm and 25 × 25 × 1 cm tiles was 2.5 kg and 1.1 kg respectively. The flexural strength of the tiles ranged from 7.5 to 35 kg/cm2. Most of these tiles pass the standard requirement of Indian standard, IS: 2098 for flexural strength. Different combinations of cement (80 to 98 per cent) rice husk (1 to 11 per cent) fly ash (8 per cent) and coir fibres (1 to 3 percent) were tried. Tiles on vibrating table were also produced. To increase flexural strength wire mesh and bamboo mesh were also incorporated.
These tiles can be bonded with epoxy resin and fixed on to wooden frame to form a partition wall. Tiles in which Na2SiO3 is used are more cost effective but they are affected by water, and hence are not useful.
Light roofing sheet from cellulosic waste has also been developed by CBRI. The basic material is cellulosic waste like waste paper, paddy straw etc. with resin as binder and impregnated in molten asphalt. Cold moulded sheets are normally sun-dried before impregnation with asphalt and normally the final product is painted with fire retardant paint (see process flow diagramme).
Waste material from timber, wood scrapings and straws are converted in hot press to make ceiling tiles. Resin is used as a binder. This process has also been developed at CBRI (see process flow diagram).
PROCESS FLOW DIAGRAM FOR ASPHALTIC LIGHT ROOFING SHEET FROM WASTE PAPER
PROCESS FLOW DIAGRAM FOR MANUFACTURE OF CEILING TILES