It is a naturally available metal in the form of ores which contain small amount of iron and sulphur. After removing impurities, it is processed electrolytically to get purest metal. This metal is almost indestructible. Copper scrap can be processed to get original copper. Properties of Copper 1. It is having reddish brown colour. 2. Its structure is crystalline. 3. It is highly ductile and malleable. 4. It resists corrossion. 5.
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
It is a light weight concrete produced by introducing large voids in the concrete or mortar. Its density varies from 3 kN/m3 to 8 kN/m3 whereas plain concrete density is 24 kN/m3. It is also known as aerated, foamed or gas concrete. Properties of cellular concrete It has the following properties: 1. It has low weight. 2. It has good fire resistance. 3. It has good thermal insulation property. 4. Thermal expansion
Plain concrete possesses deficiencies like low tensile strength, limited ductility and low resistance to cracking. The cracks develop even before loading. After loading micro cracks widen and propagate, exposing concrete to atmospheric actions. If closely spaced and uniformly dispered fibres are provided while mixing concrete, cracks are arrested and static and dynamic properties are improved. Fibre reinforced concrete can be defined as a composite material of concrete or mortar with discontinuous and uniformly distributed fibres.
Strength of concrete in tension is very low and hence it is ignored in R.C.C. design. Concrete in tension is acting as a cover to steel and helping to keep steel at desired distance. Thus in R.C.C. lot of concrete is not properly utilized. Prestressing the concrete is one of the method of utilizing entire concrete. The principle of prestressed concrete is to introduce calculated compressive stresses in the zones wherever tensile stresses
It is the combination of reinforcement, brick and concrete. It is well known fact that concrete is very weak in tension. Hence in the slabs, lintels and beams the concrete in the portion below the neutral axis do not participate in resisting the load. It acts as a filler material only. Hence to achieve economy the concrete in tensile zone may be replaced by bricks or tiles. Dense cement mortar is used to
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,
1. As bed concrete below column footings, wall footings, on wall at supports to beams 2. As sill concrete 3. Over the parapet walls as coping concrete 4. For flagging the area around buildings 5. For pavements 6. For making building blocks. However major use of concrete is as a major ingradient of reinforced and prestressed concrete. Many structural elements like footings, columns, beams, chejjas, lintels, roofs are made with
Appropriate quality and quantity of cement, fine aggregate, coarse aggregate and water should be used so that the green concrete has the following properties: (a) Desired workability (b) No seggregation in transporting and placing (c) No bleeding and (d) No harshness. Hardened concrete should have (a) required characteristic strength (b) minimum dimensional changes (c) good durability (d) impermeable (e) good resistance to wear and tear
The following are some of the important tests conducted on concrete: 1. Slump test. 2. Compaction factor test. 3. Crushing strength test. Slump Test This test is conducted to determine the workability of concrete. It needs a slump cone for test (Fig. 3.3). Slump cone is a vessel in the shape of a frustum of a cone with diameter at bottom 200 mm and 50 mm at top and 300 mm high.
Strength The characteristic strength of concrete is defined as the compressive strength of 150 mm size cubes after 28 days of curing below which not more than 5 per cent of the test results are expected to fail. The unit of stress used is N/mm2. IS 456 grades the concrete based on its characteristic strength as shown in Table 3.3. Till year 2000, M15 concrete was permitted to be used for reinforced
Workability This is defined as the ease with which concrete can be compacted fully without seggregating and bleeding. It can also be defined as the amount of internal work required to fully compact the concrete to optimum density. The workability depends upon the quantity of water, grading, shape and the percentage of the aggregates present in the concrete. Workability is measured by (a) The slump observed when the frustum of the
Concrete has completely different properties when it is the plastic stage and when hardened. Concrete in the plastic stage is also known as green concrete. The properties of green concrete include: 1. Workability 2. Segregation 3. Bleeding 4. Harshness. The properties of hardened concrete are: 1. Strength 2. Resistance to wear 3. Dimensional changes 4. Durability 5. Impermeability
Curing may be defined as the process of maintaining satisfactory moisture and temperature conditions for freshly placed concrete for some specified time for proper hardening of concrete. Curing in the early ages of concrete is more important. Curing for 14 days is very important. Better to continue it for 7 to 14 days more. If curing is not done properly, the strength of concrete reduces. Cracks develop due shrinkage. The durability of concrete
The following steps are involved in the concreting: 1. Batching 2. Mixing 3. Transporting and placing and 4. Compacting. 1. Batching: The measurement of materials for making concrete is known as batching. The following two methods of batching is practiced: (a) Volume batching (b) Weight batching. (a) Volume Batching: In this method cement, sand and concrete are batched by volume. A gauge box is made with wooden plates, its volume being equal
Cement is the binding material. After addition of water it hydrates and binds aggregates and the surrounding surfaces like stone and bricks. Generally richer mix (with more cement) gives more strength. Setting time starts after 30 minutes and ends after 6 hours. Hence concrete should be laid in its mould before 30 minutes of mixing of water and should not be subjected to any external forces till final setting takes place. Coarse aggregate consists