Concrete Block Technology (CBT)

Concrete Block Technology (CBT) (fig 1a) offers a speedier alternative to conventional materials, since it is typically equivalent to 4.5 bricks.

They are compatible with other materials like fired bricks, CEBs and dressed stone for composite wall construction, as shown below.

The most common sizes are 30 x 20 x 15 cm; its weight about 18-19 kg. The basic raw material is cement. Very little water is used. CBTs are produced using a semi-mechanized stationary type machine. The other production systems are:

§     Manual Moulds, which require hand tamping

§     Mobile Semi-Mechanized 'egg-laying' machine

§     Fully Mechanized system, which combines compression and vibration.

High quality machines provide optimum vibration in the mix, so that the ratio of cement used can be reduced substantially, without compromising on the strength of the blocks.

The blocks are cured for a minimum period of 14 days, before use. On average, a skilled and 6-8 semi-skilled workers can make 600 - 800 blocks in 8 hours.

Ferrocement Roofing Channels (FRC)

The Ferrocement Roofing Channels (FRC) developed by DA uses state-of-the-art design principles to manufacture reinforced shells, commonly called channels, as shown below:

They have high density and are impervious to penetration of water and provide high structural strength. FRCs can be used for intermediate floor applications as well and offers a viable alternative to conventional flat roofing systems.

FRCs have a uniform segmental profile of 2.5 cm thick and 83 cm wide. Maximum length of mechanically produced channels can be 6 meters. Longer spans of roofs can be built with intermediate support. FRCs can be safely transported after a curing period of 14 days. FRCs are prefabricated elements. The mechanized system of production uses a vibrating table and profiled steel shell moulds.

The production yard, as shown above, consists of a vibrating table positioned under a gantry system 6.5 meters in width. A production team consisting of 2 masons, 6 semi-skilled workers and a supervisor can produce upto 5 channels of 4.6 meters length each, in 8 hours of operation.

Buildings

The current cost of buildings made with Sankalp/TARA technology varies from Rs.150 to Rs. 250 per sq. ft. The buildings shown below were designed for Latur earthquake victims, which cost Rs 221 per sq. ft.

Cost of buildings

The estimated cost of a bare single (10' x 12') dwelling unit including a verandah space is about Rs. 20,000 (US$412), which means that the gross building cost is going to be about Rs 170 per sq.ft (US$3.50 per sq.ft.) only. This compares very well with current rates of between Rs 350 to 500 per sq.ft, using conventional building materials. The basis of these cost estimates are given below:

A. COST OF ROOFING = Rs. 3,000 (US$62)

Assumptions:

a)       Cost of one tile is Rs. 6.

b)       Cost of understructure of bamboo and labour cost of making understructure and tile laying is Rs. 10 per sq. ft. (US$0.20 per sq.ft.);

c)       Cost of construction of sloping roof using MCR tile and understructure of bamboo is Rs. 25 per sq. ft. (US$0.52 per sq.ft.)

B. COST OF WALLS = Rs. 4,000 (US$83)

Assumptions:

a)       Cost of each CEB (Balram) brick is Rs. 1.20

b)       Cost of labour and mortar is Rs. 2,500.00

C. COST OF FOUNDATION = Rs. 5,000 (US$103)

Assumptions:

a)       Same as that for fired bricks.

D. COST OF DOOR AND 3 WINDOWS = Rs. 3,000 (US$62)

Assumptions:

a)       Cost of Door = Rs. 1,200.00

b)       Cost of Windows = Rs. 800.00

E. OVERHEAD CHARGES = Rs. 5,000 (US$103)

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TOTAL COST (A+B+C+D+E) = Rs. 20,000 (US$412)

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Notes:

1.        Finishing operations (whether on interior or exterior walls, or on floor) will cost extra.

2.        These are estimated costs. Precise cost estimates can be made when we gather cost of local material and labour costs, in situ.