Alternative Building Materials

This section presents a summary of various alternative building materials and technologies that have been developed to reduce energy consumption as well as cost [31-37].

a) Autoclaved aerated concrete (AAC)

Autoclaved aerated concrete is known more by its patented or trade name such as Siporex, Trustone and Environcrete in various parts of the world. It is a factory- produced light weight precast concrete which is available in a wide variety of shapes and sizes. A typical 200 mm thick AAC wall can be about half the weight of an ordinary hollow-core concrete block. Further, AAC blocks can be bonded by a thin layer of adhesive and thus do not need mortar. AAC blocks are made from a mixture of Portland cement, lime, silica sand or fly ash, water and aluminium powder or paste. When mixed, millions of tiny hydrogen bubbles expand the mix to approximately five times its original volume. AAC can be reinforced and can be easily cut using ordinary carpentry tools. It is a stable, non-polluting, fire resisting, thermally and acoustically insulating, and durable material. However, it needs to be plastered for protection from rain.

b) Fly ash

Fly ash is a by-product of coal in thermal power plants. It consists of organic and inorganic matter that is not fully burnt, and can be recycled for use in a variety of building materials. The properties of fly ash make it suitable for the manufacture of bricks, hollow and solid blocks, cellular concrete, partial replacement of cement, filler material in concrete, wood substitute, and also for use in the manufacture of emulsion paints, building distempers, etc. Using fly ash in building materials can result in a number of advantages. For example, fly ash bricks can replace burnt clay bricks, which require use of fertile agricultural soil. They are dimensionally stable having a smooth finish and fine edges, and are available in a number of sizes. They also have good resistance to weathering and need not be plastered. The bricks can be made in a number of colours using pigments. This material is being tried and tested at Central Building Research Institute, Roorkee. It has been used at IIT Delhi and The Energy Resources Institute, Gwalpahari and shown to have good results [31]. Fly ash is also used to make FaL-G (hydraulic cement). The name FaL-G stands for fly ash (Fa), Lime (L) and Gypsum (G) which are its ingredients. It can be used as an alternative to ordinary Portland cement as a binder, and to burnt clay bricks as a masonry block. It can also be used for road pavements, and in plain concrete in the form of Fal-G concrete.

c) Compressed earth blocks

The manual production of earth blocks by compressing them in small moulds has been practised for centuries. The process has now been mechanised and a variety of presses are used, including mprocessanual and hydraulic . The soil for compressed earth blocks consists of a mixture of pebbles (1.5 parts), sand (5 parts), silt (1.5 parts) and clay (2 parts). About 5 % cement is used to stabilise the earth blocks. Products range from accurately shaped solid, cellular and hollow bricks, to flooring and paving elements. Compressed earth blocks are sun dried and do not need to be burnt. They are also economical, strong, energy saving and simple to manufacture. Soil stabilised hollow and interlocking blocks can provide better thermal insulation than bricks. Mud blocks stabilised with Fal-G are much stronger, absorb less water, and are cheaper than cement stabilised blocks. Development Alternatives, New Delhi [32] and Auroville, Pondicherry have carried out extensive research on this material. A number of buildings at Auroville, Pondicherry have been built using compressed earth blocks.

d) Clay red mud burnt bricks

Clay red mud burnt bricks are produced from alumina red mud or bauxite, an industrial waste of aluminium producing plants, in combination with clay. The brick possesses all the physical properties of normal clay bricks. Incidentally, they also solve the problem of waste disposal and environmental pollution. In addition, they have good architectural value as facing bricks due to their pleasing colour.

e) Lato blocks

Lato blocks are bricks made from lateritic soil and cement or lime. The blocks are moulded under pressure to produce strong and good quality blocks which consume lesser energy than conventional bricks, and hence are cheaper. They are available in various colours ranging from cream to light crimson.

f) Precast hollow concrete blocks

Precast hollow concrete blocks are manufactured using lean cement-concrete mixes and extruded through block making machines of the egg laying or static types. They need lesser cement mortar and enable speedy construction as compared to brick masonry. The cavity in the blocks provide better thermal protection. Further, the blocks may not need external or internal plastering. These can be used as walling blocks or as roofing blocks along with inverted precast tee beams.

g) Bamboo/timber mat based walls

These walls are made up of bamboo mat placed between horizontal and vertical timber/bamboo frames. The plastering is done using mud or cement mortar on either side. These are easy to construct, cost less and are popular in hilly areas as they can be self-assembled. However, these are not load bearing and need a supporting structure. This upgraded traditional technology is a relevant option for walling from the perspective of earthquakes to minimise damage in the event of a collapse

h) Rat trap bond

The rat trap bond is an alternative brick bonding system for English and Flemish bond. It is economical, strong and aesthetically appealing. It can save about 25% of the total number of bricks and about 40% of the mortar cost for a wall. The rat trap bond is simple to build and has better insulation properties.

i) Composite ferrocement system

The system is simple to construct and is made of ferrocement (rich mortar reinforced with chicken mesh and welded wire mesh). These reduce the wall thickness and allow a larger carpet area. Precast ferrocement units in trough shape are integrated with RCC columns. Ferrocement units serve as a permanent skin unit, and as a diagonal strut between columns. Inside cladding can be done with mud blocks or any locally available material. These are ideally suited for seismic areas.

j) Coconut fibre and wooden chips roofing sheets

Coconut fibre and wooden chips or fibre are soaked in water for two hours and after which the water drained off. These are then mixed with cement, laid over a corrugated mould and kept under pressure for 8 to 10 hours. After demoulding, the sheets are cured and dried before use.

k) Cement bonded fibre roofing sheets

These are made from coir waste, coconut pith, wood wool or sisal fibre in combination with cement as binder, for production of corrugated or plain roofing sheets. These sheets use lesser cement than AC sheets and are 50% cheaper than AC/CGI sheets. Besides, they are light weight, fire resistant, water proof and can be used for sloping roof options.

l) Micro concrete roofing tiles

Micro concrete roofing tiles are made of graded cement mortar layer and formed over sloping mould. They are used in pitched roofing systems and are less expensive than ACC/CGI sheets. These tiles are appropriate where fired clay tiles are not available, and timber supporting skeletal system is costlier. The rafter and purlin system cost less

when micro concrete roofing tiles are used. Further cost reduction can be made by using ferrocement rafters and purlins.

m) Stone patti roofing:

Stone patti roofing is a flat roofing system with sand stone slabs (patties) resting over steel or slender RCC section beams. The slabs are overlaid with terracing for insulation. This type of roofing is appropriate where (sand) stone slabs are available, and is more economical than RCC slabs. In places like the states of Rajasthan, Madhya Pradesh and Andhra Pradesh where large granite stone patties are available, the beams are not needed as the pattis can rest on walls.

n) Precast brick arch panel system

In this technique, precast brick arches of size 50cm x 50cm are cast on a platform. The arches are placed side by side over the partially precast joist. The haunches between the arches are filled with cement concrete to have a level surface on the top. Such roofs/floors are 30 percent more economical when compared with conventional RCC. o) Filler slabs

Filler slabs are normal RCC slabs in which bottom half (tension) concrete portions are replaced by filler materials such as bricks, tiles, cellular concrete blocks, etc. Filler materials are so placed as not to compromise structural strength; they replace unwanted and non-functional tension concrete, thus resulting in economy. These are safe, sound and provide aesthetically pleasing pattern for ceilings. An additional advantage of filler slabs is that they do not need plastering.

p) Particle boards

Particle boards are made from wood waste, cotton stalk and bagasse, and bonded by resin. They can be used as inserts, and with veneering, they can be used as an alternative to timber in panelling, false ceiling flooring, partitioning and furniture.

Table 3.14 gives the possible savings that could be achieved by using alternative building materials [37].

Table 3.14 Estimated cost savings on using innovative building materials [37]

S. No. Cost-Effective Technologies In place of Conventional options % of Saving

I. FOUNDATIONS

1. Pile foundation (under reamed) Traditional stone/bricks 15

2. Brick Arch foundations . Footings 25

II. WALLING (SUPER STRUCTURE)

1. 230 mm Thick wall in lower floors 330 mm brick walls 5 2. 180 mm Thick wall in bricks 230 mm brick walls 13 3. 115 mm thick recessed walls 230 mm brick walls 20 4. 150/200 mm Stone block masonry' Random rubble masonry 30-20

5. Stabilised mud blocks Burnt brick walls 20

6. FaL-G Block masonry Clay brick walls 20

7. Fly ash brick walls Gay brick walls 25

8. Rat trap bond walls . English/Flemish bond 25

9. Hollow blocks walls Solid masonry 20

III. ROOFING

1. 85 mm thick sloping RCC 110 mm RCC 30

2. Tiles over RCC rafters Tiles over timber rafters 25

3. Brick panel with joists RCC 20-25

4. Cuddapah slabs over RCC rafters CS over timber rafters 20

5. L-panel sloping roofing RCC 10

6 RCC planks over RCC joists RCC 10

7. Ferrocement shell roofing RCC 40

8. Filler slab roofing RCC 22

9. Waffle roofing RCC 15

10. RCC channel units RCC 12

11. Jack arch brick roofing RCC 15

12. Funicular shell roofing RCC 18

13. Brick funicular shell roofing RCC 30

14. Precast blocks over inverted T-beams RCC 25

15. Micro-concrete roofing tiles Clay tile roofing AC sheet roofing 20-15