Cement pavers
INTRODUCTION
Cement Concrete tiles and paving blocks are pre-cast solid products made out of cement concrete. The product is made in various sizes and shapes viz. rectangular, square and round blocks of different dimensions with designs for interlocking of adjacent tiles blocks. The raw materials required for manufacture of the product are Portland cement and aggregates which are available locally in every part of the country.
MARKET POTENTIAL
Cement concrete tiles and paving blocks find applications in pavements, footpaths, gardens, passenger waiting sheds, bus-stops, industry and other public places. The product is commonly used in urban areas for the above applications. Hence, the unit may be set up in urban and semi-urban areas, near the market. A lot of face-lift is being given to roads, footpaths along the roadside. Concrete paving blocks are ideal materials on the footpaths for easy laying, better look and finish. Whereas the tiles find extensive use outside the large building and houses, lots of these materials are also used in flooring in the open areas of public offices and commercial buildings and residential apartments.
BASIS AND PRESUMPTIONS
Efficiency: It is envisaged that the unit will run on one shift a day for 25 days in a month or 300 days in a year. 75 percent efficiency of machinery and manpower is considered.Time Period: Full capacity utilization is expected to be achieved within 12 months of commencement of commercial production. Labour Wages: Minimum applicable wages are considered. Interest Rate: An interest rate of 14% per annum on the total capital investment has been considered. Margin Money: Promoter is expected to bring in 25% of the total capital investment. Pay Back Period: The project will have a payback period of about 3-4 years. Land and Construction Cost: Land cost is considered at Rs. 500 per square meter, and Construction cost for office and stores at Rs. 2000 per square meter, and work shed at Rs. 1500 per square meter.
TECHNICAL ASPECTS
Process of Manufacture Cement concrete is a mixture of portland cement, aggregates (sand and stone chips) and water. Aggregates passing through 4.7 mm IS sieve are known as fine aggregates and the aggregates retained on this sieve are coarse aggregates.
The process of manufacture of cement concrete paving blocks involves the following steps:
a) Proportioning
b) Mixing
c) Compacting
d) Curing
e) Drying
A concrete mix of 1:2:4 (cement: sand: stone chips) by volume may be used for cement concrete paving blocks with water to cement ratio of 0.62. The concrete mix should not be richer than 1:6 by volume of cement to combined aggregates before mixing. Fineness modules of combined aggregates should be in the range of 3.6 to 4.0. All the raw materials are placed in a concrete mixer and the mixer is rotated for 15 minutes. The prepared mix is discharged from the mixer and consumed in the next 30 minutes. Vibrating table may be used for compacting the concrete mix in the moulds of desired sizes and shapes.
Diffrent shapes and sizes of moulds are available in market
.
Filling the mould
Demodulled the block
After compacting the blocks are demoulded and kept for 24 hours in a shelter away from direct sun and winds. The blocks thus hardened are cured with water to permit completemoisturisation for 14 to 21 days. Water in the curing tanks is changed every 3 to 4 days. After curing, the blocks are dried in natural atmosphere and sent for use. The concrete paving blocks gain good strength during the first 3 days of curing and maximum gains in strengths are secured in the first 10 to 15 days of curing. After curing, blocks are allowed to dry in shade so that the initial shrinkage of the blocks is completed before they are used in the work. A drying period of 7 to 15 days would normally complete the drying shrinkage after which they can be used. The concrete tiles are similarly produced with the help of semi-dry pressing of the mixture and allowed to set for 24-36 hours. It is cured in the tanks for 15 days. If need be water can also be sprinkled to gain maximum physical strength in 15-21 days.
Quality Control and Standards
a) Indian Standard Specification There is no Indian Standard Specification specifically on cement concrete paving blocks. However, the specifications laid down in IS 2185 (Part 1) Specification for concrete masonry units: Part 1 for Hollow and Solid concrete blocks, may be used as general guidelines for meeting the quality parameters, since the paving blocks are also essentially solid cement concrete blocks.
b) Quality Requirements Proportioning of raw materials, mixing, compacting, curing and drying are the important stages of manufacture. Quality parameters like actual proportion of the individual raw materials, ratio of coarse aggregates to fine aggregates, water to cement ratio, good finish, accuracy in size and shape and compression strength after curing are the some of the important parameters that should be checked periodically to ensure good quality of the product.
Production Capacity (per annum) Quantity: 800 tonnes Value: Rs. 22, 00, 000 Motive Power 10HP.
Pollution Control Dust collecting unit is required to be installed at the mixing and raw material handling section. The workers may use dust masks. Energy Conservation General maintenance of the machine and drive system can be employed for saving energy.