RCC in construction stands for reinforced cement concrete.
In RCC buildings steel is used as a reinforcing material to increase the strength of concrete.
What is PCC and RCC in construction?
PCC stands for Plain cement concrete.
PCC consists of cement, sand, aggregates and water.
In the previous post, we have discussed workability, the importance of the water-cement ratio in concrete.
In this post, we shall discuss more RCC in construction and its ingredients of RCC in building construction.
RCC stands for reinforced cement concrete. In the tension Concrete is week but it is excellent in compression.
Steel is really good in tension. Steel is utilised as a reinforcing material to enhance the tensile strength of concrete and the coefficient of linear expansion for both steel and concrete is same.
IS code of RCC is IS:456
Important 6 ingredients of RCC in construction.
Reinforced cement concrete or RCC in construction consists of the following 6 ingredients:
- Fine aggregates
- Coarse aggregates
The cement consists of 60 % to 67% of lime.
Compounds responsible for the strength of concrete
1. Dicalcium silicate-C2S.
Later strength in concrete is responsible by C2S
2. Tricalcium silicate-C3S
The early strength of concrete is responsible by C3S.
Few types of cement
1.Ordinary portland cement
Ordinary portland cement (OPC) is used for general construction purpose.
IS code of OPC-IS 269-1976.
2.Low heat cement
In massive construction, this low heat cement is used. Low heat cement IS code is- IS 269
3.Rapid hardening cement
For removing formwork immediately this rapid hardening cement is practised in construction.
Rapid hardening cement IS code is-IS 8041.
For chemical resistance purpose, this pozzolana cement is practised.
Pozzolana cement, IS code is IS 1489
5.High strength cement
This cement is used in prestressed concrete.
IS code of high strength cement -IS 8112
This cement is used in a waterproof construction.
IS code of Hydrophobic cement -IS 8043.
Grades of cement
There are three grades of cement
a.33 grade OPC
b.43 grade OPC
c.53 grade OPC.
When tested after 28 days in N/mm2 the compressive strength of cement is represented by grade number.
In terms of fineness of cement this grades of OPC defers primarily which is expressed as specific surface area.
Specific surface area
The surface area of the particle in 1 gram of cement (unit cm2/gm) is termed as specific surface area.
In one gram of cement, all the particles surface areas cumulative sum is called sp.of cement.
By using Blain’s permeability apparatus specific surface area is estimated.
Specific surface area is not less than 2250 cm2/gm for 33-grade cement.
Specific surface area is not less than 3400 cm2/gm for 43-grade cement
Specific surface area is much larger than 3400 cm2/gm for 53-grade cement.
shrinkage is greater in 53 grade of cement compared to other grades, but earlier strength is higher.
Therefore in quality concretes 53-grade cement is preferred in general.
2.Fine aggregates and sand
Fine aggregates are the materials under 4.75 mm sieve.
In cement concrete, the sand selected in Zone II or medium sand.
Only river sand to be practised.Sea sand shall not be practised.
Robo sand (crushed rock fine) is practised in concrete nowadays.
Bulking of sand: If the moisture content is 4% by weight, then increase in volume is 25 to 30%.
This is called bulking of sand.
The coarse aggregates are the materials which are held on 4.75 mm sieve.
The maximum size of concrete should not be more than 1/4 of the minimum thickness of the member.
There are two types of Coarse aggregates
1.Round aggregates :
The round aggregates have fewer surface areas. The round aggregates have more excellent workability due to its fewer surface areas.
Due to a weaker bond, they have weaker strength.
They have higher surface areas as these aggregates are angular. The angular aggregates have smaller workability due to its higher surface areas.
Due to more reliable bond with angular interlocking, they have greater strength.
Sizes of coarse aggregates used for RCC in construction
The highest nominal size of coarse aggregates is 20 mm for RCC works and the smallest size of coarse aggregates is 12mm.
The highest size of coarse aggregates is 40 mm (M10, M15) for PCC works
For bed concrete course, the aggregate of size 40 mm to 60 mm.
pH value of Water used in concrete should not be less than 6 (6 to 8).
The permissible limits for solids in water are mentioned below.
I. The Inorganic solids should be less than 3000 mg/l
ii. Organic solids should be less than 200 mg/l
iii. Chlorides should be less than 2000 mg/l
iv. For RCC works Chlorides should be less than 500 mg/l
v. Suspended solids should be less than 2000 mg/l.
For improving workability, settings etc, the characteristics of concrete chemical compounds like admixtures are utilised.
Few types of admixtures practised in RCC in construction are given below.
iii.Water reducing admixtures
I Retarders :
Retarders delay the setting time of cement. This is used in hot weather.
To increase the rate of hardening or to reduce the setting time or to improve strength accelerators are utilised in concrete.
It is used in repairs work, precast exciting production, RCC in cold weathers.
iii Water reducing admixtures
Without increasing the water content to increase the workability of concrete these water-reducing admixtures are practised.
This water-reducing admixture used in case of congested reinforcement and in rich concrete mixes.
In the form of minute bubbles air to be combined in concrete during mixing to increase the resistance to freezing and thawing and workability.
Example: Vinsol Resin.
Steel is used in the reinforcement for reinforced concrete.
The strength of concrete is greater than the strength of steel.
The coefficient of expansion of steel is the same as of concrete.
Types of steel used in RCC in construction:
i.Mild steel-Plain bars (Fe 250)
ii.HYSD.High yield strength deformed bars (Fe 415, Fe 500, Fe 550)
In Fe 415,
Water Cement Ratio
It is the ratio of the volume of water to the volume of cement.
For any provided condition, the strength test of compacted concrete depends only on the water-cement ratio.
Setting time of Concrete
The least setting time of concrete should not be smaller than 30 min.
The final setting time of cement should not be more than 10 hrs.
To determine the final and initial setting time Vicats apparatus is practised.
Minimum Grades of concrete and Types of Construction
1.M 5, M 7.5 grades are utilised for Lean concrete bases.
2.M 10, M 15 grades are utilised for Plain cement concrete.
3. M 20 grade is used for RCC in construction of general buildings.
4. M 25 grade is practised for RCC in construction of Water tanks, domes, shell roofs.
5.M 30 grade is practised for RCC in construction of Post-tensioned concrete members.
6. M 40 grade is used for RCC in construction of Pre-tensioned concrete members.
The above mentioned 6 ingredients are utilised for RCC in construction and above mentioned different grades of concrete in different types of construction.