Reinforced concrete

Reinforced concrete

What is reinforced conrete?

R.C.C is a simple concrete with a addition of reinforcement (rebars). Reinforced conc is one of concrete type widely use around the world.

What is the difference between concrete and reinforced concrete? Its the most commonly asked question. Reinforced concrete is same as plain concrete but there’s a use of steel bars, wires, steel mesh etc.

Why is reinforced concrete better than concrete? Reinforced concrete is far more better than concrete because it has two properties, its has high tensile strength and high compressive strength, where plain concrete only have compressive strength.

These two properties make it much more stronger than typical concrete. One the most used products is reinforced concrete pipe. It is sometime called precast reinforced concrete pipe.

Reinforced concrete pipe:

The sewerage pipe, that made up of reinforced concrete. It is most durable and stronger than its alternative PVC or UPVC pipes. RCP can last upto 50 to 75 year or more.

Mostly RCP are used in city and town sewerage lines because of it life time and mantainance cost which is almost nil. But there should be much care taken while handling RCP, because its more heavier.

Reinforced concrete pipe
Reinforced concrete pipe

How to make reinforced concrete?

Reinforced concrete or reinforcement concrete is full form of R.C.C. Mostly M15 concrete mix grade or (1:2:4) mix ratio is used in R.C.C with steel. Reinforced concrete density is 2500 kg/m3.

What is ferroconcrete? Reinforced concrete is called ferroconcrete. Ferro is a Latin word which means “iron”. Reinforced concrete is used in slab, beams, column and many other structural elements.

What is reinforcement?

Reinforcement is commonly steel bars, wires, mesh etc. It is provided with covers all sided, and then poured strong concrete mix.

Why steel/rebar/reinforcement is used in concrete? Or what is use or reinforcement in concrete? Concrete itself is weak in tension but strong in compression, that’s why rebar is used in concrete to provide tensile strength. Structural steel has 400-550 MPa ultimate tensile strength.

These mild steel bars should be according to specification and SI codes. At the time of use, the surface of rebar shouldn’t have dust, oil, paint etc. That surface will not let them make a stronger joint between steel & concrete.

what is reinforced concrete?
Reinforced concrete

Bar bending:

Its the process of bending steel bars to make stirrups or bending the corner of bars to provide strength against shear. Bar should be bend in cool condition.

It should be bend according to size & shape mentioned in detail drawing. Edges of the bars should be bend to semi circular hook. If the deformed bars are being used, there is no need of providing hooks.

Overlapping of steel bars:

Try to use the full lengths of steel bars, but if there is a need to join two bars, then it should be overlap according to mentioned in detail drawing or engineering’s advice.

The bars joint shouldn’t be inline, but scattered. Joint should be at the point where shear force and bending moments are minimum. The overlap of steel bar should be done with binding wire.

What should be overlapping length of steel bars? The length of joint of steel bar is called overlapping length? Overlapping length of steel bar is calculated with the simple formula.

60d where (d is diameter of steel bar)

The joining of steel can also done by welding, but it isn’t better way to do so, but if it is needed, it can be done according to engineer’s instructions.

Placing the bars in position:

Steel bars should be placed on form work according to design and mentioned in drawing. The point should be tie up with binding wire, where two bars intersect each other. So it will not move while concrete placement.

In different cases following are the methods used to positioned the bars.

Simple beam and slab:

In this case, cover blocks are provided below the steel bars at different points according to designed concrete cover. These cover blocks are called Chairs. These chairs are made up with cement mortar ratio (1:2).

Double reinforcement beam:

To positioned the bars in case of cantilever beam & cantilever slab, the chain spacers or support bars are used.

Reinforcement column or wall:

In this case, vertical bars are positioned with help of wooden templates/mould. There’s holes on wooden template according to the position of bars.

Placing of concrete:

The ingredients in R.C.C are same as in plain concrete. The coarse aggregates size used in R.C.C is 20 mm (0.75 inch). Concrete proportioning, mixing of concrete and curing is same as in plain concrete.

It should be good quality concrete, it shouldn’t segregate at the time of placing. In case of use of vibrator, water quantity should be little less. Slump test and workability test should be done before placing.

Compaction of reinforced concrete:

Concrete should be compacted on form work as soon as possible. Use vibrator for compaction. If it is not possible to use vibrator then compaction can be done with tamping rod.

Compaction should be done till the corner of form work filled up. After compaction, cement slurry filled up the aggregates voids and the concrete surface become smooth.

Compaction should be done before starting of initial setting time of concrete.

Construction joints:

There shouldn’t be joints in construction work, or it should be minimum. If its compulsory to provide joint, the joint should be at point where there is minimum shear force and bending moment.

Finishing of reinforced concrete:

In case of building slab, make the surface of reinforced concrete smooth with the help of wooden float. After removing of form work, let the engineer inspect, and clear the exceptional errors.

If there is a major error, demolish the defected elements by which structure becomes unsafe. R.C.C work should be done with caution, so the plaster thickness on it don’t exceed by 6 mm ( 0.25 inch).

Concrete testing:

To insure the required strength, test the concrete on site intermittently. Following are test should be done e.g. work test and slump test. These test measures the workability and consistency of concrete.

These test help to insure the desired strength and help to correct the fluctuation values on site.

What are the advantages of reinforced concrete?

Now a days reinforced concrete is used widely such as residential construction, commercial construction, dams, bridges etc. It is because R.C.C has more advantages. Some of them are followings.

  1. R.C.C is higher in compressive strength.
  2. It is good in tensile strength.
  3. It has resistance against fire and weather affects. R.C.C can bear high temperature and atmospheric affects.
  4. It can bear the seismic effect. (Advantage that consider mostly)
  5. It is monolithic, which make it more resistant against rigidity.
  6. It is really good against wear and tear, impact load & abrasion.
  7. R.C.C is durable.
  8. Maintanance cost of R.C.C. is zero almost.
  9. R.C.C provide cover to steel against rusting, corrosion & buckling.

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