Showing posts with label Concrete. Show all posts
Showing posts with label Concrete. Show all posts

Tuesday, October 31, 2017

FERRO-CEMENT

October 31, 2017 Concrete , 0 Comments


The term ferro-cement implies the combination of ferrous product with cement. Generally this combination is in the form of steel wires meshes embedded in a portland cement mortar. Wire mesh is usually of 0.8 to 1.00 m diameter steel wires at 5 mm to 50 mm spacing and the cement mortar is of cement sand ratio of 1:2 or 1:3. 6 mm diameter bars are also used at large spacing, preferably in the corners. Sand may be replaced by baby jelly.
The water cement ratio used is between 0.4 to 0.45. Ferrocement reinforcement is assembled into its final desired shape and plastered directly. There is no need for formwork. Minimum two layers of reinforcing steel meshes are required. According to American Concrete Institute “Ferrocement is a thin walled reinforced concrete construction where usually a hydraulic cement is reinforced with layers of continuous and relatively small diameter mesh.
The mesh used may be metallic or any other suitable material.” Ferro-cement is fast emerging as an alternate material for timber. The history of ferro-cement
goes back to 1843 (even before RCC). Joseph Louis Lambot constructed several rowing boats, plantplotsand garden seats using ferro-cement. In early 1940’s noted Italian engineer and architect Pier Luigi Nervi carried out scientific tests on ferrocement and used it to replace wood wherever possible.
He built small tonnage vessels, the largest being 165 tons motor sailor. Nervi also pioneered the architectural use of ferrocement in buildings. Ferro-cement can be given the finish of teak wood, rose wood etc. and even for making tables, chairs and benches it can be used.

Properties of Ferro-cement

1. Its strength per unit mass is high.
2. It has the capacity to resist shock laod.
3. It can be given attractive finish like that of teak and rose wood.
4. Ferro cement elements can be constructed without using form work.
5. It is impervious.

Uses of Ferro-cement

It can be used for making:
1. Partition walls
2. Window frames, chajjas and drops
3. Shelf of cupboards            
4. Door and window shutters
5. Domestic water tanks
6. Precast roof elements
7. Reapers and raffers required for supporting roof tiles.
8. Pipes
9. Silos
10. Furnitures
11. Manhole covers
12. Boats.
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Thursday, October 12, 2017

SOLID AND HOLLOW CONCRETE BLOCKS

October 12, 2017 Concrete , 0 Comments

Solid and hollow concrete blocks are manufactured in factories to meet the requirements of buildingblocks in cities and towns. These blocks may be called as artificial stones, since they replace the stones in the masonry construction. They are manufactured with lean mixes of cement, sand and aggregates of sizes less than 12 mm. Instead of sharp edged aggregates, round aggregates are professed in the manufacture of these blocks.
 The properties and uses of these blocks is given in this article.
(i) Solid Concrete Blocks: Solid concrete blocks of size 400 mm × 200 mm × 150 mm are
commonly manufactured. To reduce the weight of the block no fine concretes are preferred. No fine concrete is the concrete in which fine aggregate is not used, but round aggregates of size less than 12 mm are used.
 IS:2185 (part I) 1983 covers the requirement, for such blocks.The blocks should satisfy the strength requirement of 4 N/mm2. Their density should be as lowas possible, so that handling is not difficult. They should have sharp edges which are at right angles to each other. These blocks are used for load nearing wall construction also.
(ii) Hollow Concrete Blocks: To reduce the weight of concrete blocks, they may be made hollow as shown in Fig. 5.1. Hollow blocks of sizes 400 mm × 200 mm × 190 mm (nominal size 400 × 200 ×200 mm) and also of sizes 400 mm × 300 mm × 190 mm (nominal size 400 × 300 × 200 mm) are manufactured. IS:2185 (part I) 1983 covers the specifications for these blocks.These block need richer mixes. Fine aggregates upto 60% and coarse aggregates upto40% are used.These blocks also should satisfy the strength requirement of 4 N/mm2. They should have truely right angled corners.
Advantage of using concrete blocks is that the construction activity is fast. Mortar requirement for finishing the surface is less. Pointing alone is sufficient, in other words plastering is not necessary.
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Monday, October 9, 2017

REINFORCED CEMENT CONCRETE (R.C.C.)

October 09, 2017 Concrete , 0 Comments


Concrete is good in resisting compression but is very weak in resisting tension. Hence reinforcement is provided in the concrete wherever tensile stress is expected. The best reinforcement is steel, since tensile strength of steel is quite high and the bond between steel and concrete is good. As the elastic modulus of steel is high, for the same extension the force resisted by steel is high compared to concrete. However in tensile zone, hair cracks in concrete are unavoidable. Reinforcements are usually in the form of mild steel or ribbed steel bars of 6 mm to 32 mm diameter. A cage of reinforcements is prepared as per the design requirements, kept in a form work and then green concrete is poured. After the concrete hardens, the form work is removed. The composite material of steel and concrete now called R.C.C. acts as a structural member and can resist tensile as well as compressive stresses very well.
Properties of R.C.C./Requirement of Good R.C.C.
1. It should be capable of resisting expected tensile, compressive, bending and shear forces.
2. It should not show excessive deflection and spoil serviceability requirement.
3. There should be proper cover to the reinforcement, so that the corrossion is prevented.
4. The hair cracks developed should be within the permissible limit.
5. It is a good fire resistant material.
6. When it is fresh, it can be moulded to any desired shape and size.
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