Unit:-3
Concrete works
Introduction
It is a work in which concrete is used in construction and it is the mixture of sand, cement, water, aggrerate and sometimes admixture in a fixed ratio to give a diquet trength to the tructure is known as concrete. They are use for binding and fointing purpose. Concrete resist compressive strength.
Types of concrete
1.Plain concrete coment (P.C.C)
2.Reinfoerced concrete cement (R.C.C)
3.Pre-stressed concrete cement
Properties of concrete
1.It is strong and durable.
2.It has high compressive strength resisting capacity.
3.Excellent to resist water.
4.Density of concrete varies around 2400 kg/m3.
5.Elasticity of concrete relatively low.
Formwork
It is a set of implace to hold very well concrete unit itself on the structure of boards. It is support to concrete work. The structure of board that makes for holding concret in the construction is known as formwork. Example timber, plywood, iron plate etc are used for formwork.
Requriment of formwork
1.It should be strong enough to support the weight of fresh concrete during placing and compacting and any other load if may be requried.
2.The materials of formwork should be cheap and suitable foe using several time.
3.The face of formwork should be smooth.
4.The surface of formwork should be leveled and desire line.
5.The formwork used in construction should be of light weight.
6.The joint in the formwork should be tight to prevent leakage of cocnrete.
7.Formwork should be easy removeable.
8.It should be stiff enough so that defflection is minium.
9.The formwork should resist on non-yelding support.
Characteristic of steel
1.High tensile strength
2.Compressive strength
3.Difficut to mould
4.Relatively expensive
Characteristic of concrete
1.Tensile strength
2.High compressive strength
3.Easy to mould
4. Relatively inexensive
Advantage of reinforced concrete
1.High compressive strength
2.High tensile strength
3.Fire and weather resistance
4.Durability
5.Economy to mould shape
6.low maintainance cost
7.Echonomy as construction materials
8.less deflaction
9.Used as precast structure component
10.Less skilled labour requried
Disadvantage of reinforced concrete
1.Tensile of reinforced is about 1/10th of its compressive strength.
2.Uncertaninty of final strength.
3.High maintance cost
4.Larger column section
5.Shrinkage
Reinforce placing
Placing reinforced onto layer of freshly concrete or adjusting the position of bars or teo yelding where reinforcement during concrete placement should be permited. The ill-advice pratice is slap construction or placing reinforcement on a sub-grade and pulling it up during concrete placement is called hooking.
Compaction of concrete
Compaction is a process which entraped from freshly placed concrete and pack the aggregate partical together so as to increase the density of concrete.
Curing of concrete
It is the most essential process foe gaining early strength ofo concrete in which concrete is kept continously for certain days by the following method:-
1.Water curing (Ponding cover with wet burlap speikling water)
2.Mechanical curing
3.Steam Curing (Applicable in cold region)
4.Chemical Curing (Sodium silicate)
Factor affecting strength of concrete
The sterngth of concrete is defined as resistance developed by concrete to resist rapture (break) sprites, sterngth of concrete primarily deponds upon the strength of paste depends upon th edilution of paste. The strength of concrete also deponds upon the following factod:-
1.Quality of raw materials
2.water cement ratio
3.Coarse/fine aggregate ratio
4.Age of Concrete
5.Aggregate/cement ratio
6.Compaction of concrete
7.Relative humadity
8.Curing
9.Mix proportion
10.Admixture
11.Shape, size, strength of aggregate
12.Gel space ratio
13.Temperature
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