What is concreting process?
Concrete is used to construct different structures like buildings, bridges, concrete roads, irrigation canals or drains, etc. To prepare concrete, we have to mix different ingredients like cement, sand, aggregate, and water in one place.
Concrete is firstly prepared in a plastic form which is then cast to the required shape using formworks and then cured (Spread water) to allow for hydration to get the proper strength of the concrete in construction.
This goes through different stages of concreting like Batching, Mixing, Handing, Placing, Compaction, Curing, and Finishing. These all activities are known as concreting process.
Stages of Concreting Process
Let us describe the activities above in brief.
The mixing of different concrete ingredients in the right proportion to get the required strength of dry concrete is known as batching. This is the first step of Concreting Process. It can be done by two methods.
- Volume Batching
- Weight Batching
a) Volume Batching
In this method, the proportioning of materials is done by measuring their volume. Volume batching is an Easy method. It is done for less important or minor projects.
- 1 bag of cement (50 kg) is taken as 35 liters.
- The volume of aggregate is measured by a measuring box.
- 25 liters of water is required per bag of cement.
For higher strength, volume batching should not be used. The water-cement ratio should be around 05-0.55
The common proportion of volume batching
a) Weight Batching
In this method, the proportioning of materials is done by measuring the weight of individual materials. It is the correct method for volume batching.
- It requires a weighting arrangement
- Moisture content in aggregate shall be adjusted in proportion.
- Most common method and is done for any type of construction.
The concreting process of mixing the ingredients like cement, sand, and aggregate with water is known as mixing. The mixing of materials is essential for uniform & homogeneous concrete.
Methods of mixing
- Hand mixing
- Machine mixing
a) Hand mixing
- Mixing is done by using tools but with the power of the hands of workers.
- Suitable for small works.
- Additional 10% cement is required to compensate for the loss of strength to machine mixing.
b) Machine mixing
- In this method, the power of the machine is used for mixing concrete.
- It is used for medium to large works.
- It is economical for large constructional works.
- Give a more homogeneous & uniform mix at a lower water-cement ratio.
Concrete shall be moved from the mixing site to the construction site with the help of a vehicle or by carrying with human efforts if the distance is less.
Proper care and attention should be given to avoid loss of homogeneity & workability during the transportation of mixed concrete.
Some methods of transportation
- Pump pipeline
- Motor pan
- Bucket &rope, skip & hoist
- Truck mixer /transit mixer
- Belt conveyor
After transportation, the concrete shall be placed in the right shape and size with the help of formwork and shuttering. Transportation plays very important roles in concreting process.
Depending upon the site, different procedures and precautions and should be applied for different structural members like beam, column, slab, etc. during placing.
a) For foundation One worth
Before placing concrete for the foundation, any vegetation or organic matter should be removed from the ground. Loose earth should be removed or compacted and earth should be damped.
b) For slab
Concrete should be dumped not dragged during the placing of concrete. For high thickness, concrete shall be done in two layers compacting each layer
For RCC works thickness of each layer should be between 15-30 cm but for the mass concreting, the thickness of each layer should be between 35-45cm.
c) Concreting in the previous layer
While placing concrete for joining two old and new layers, the cold joint should be avoided. The joint should be well-cleaned with a wire – brush & Water jet.
The surface should be thoroughly wetted & a thin layer of cement slurry or binding chemicals should be applied to the joining surface before placing concrete.
If further concreting is necessary the top surface shall be left rough for proper bonding.
d) For RCC
- The correct placement & cover block of the rebar should be checked before placing concrete.
- Mold rebar signs agent (plastic, grease, or another chemical) can be applied on the surface of formwork for easy removal of shuttering or formwork after the concrete dries.
e) For Column
Before placing concrete in the column check whether the column is standing in a completely vertical condition. Formwork should be checked whether there is leakage or not. Concrete should be placed and compacted with the help of a vibrator and shaking column reinforcement gently.
The concrete shall be appropriately compacted in place right after placement.
- The primary objective of compaction is to remove the air voids that might be trapped during the mixing transporting or placing of concrete.
- As the air/voids drastically reduce the strength of concrete compaction is very necessary to achieve the desired strength.
- During the compaction of layered concrete vibrator needle shall penetrate the previous layer too.
Method of compaction
There are two methos of compaction in concreting process. According to volume of concrete required to compact, both methods are used.
a) Hand compaction
Hand compaction can be done for concrete of up to 15-20cm layers. Concrete of high consistency is required for hand compaction. Hand compaction can be done in three ways.
b) Compaction by vibrator
Compaction by vibrator is suitable in general propose concreting. It can impact concrete with an even lower water cement ratio. Vibration set particles in motion reducing the friction and causing temporary live faction –it makes the particle settle well.
Types of vibrator
- Needle Vibrator
- Surface Vibrator
- Vibrating Table
- Shutter Vibrator
The process of spreading water on concrete after certain time (Approximately after 24 hour) after placement of concrete to gain strength in desired time without harmful changes is called curing. The strength of concrete is achieved by the hydration of cement.
The water required for curing is greater than required because it is evaporated from the surface, leaving a dry top layer of concrete that may cause rapid shrinkage & insufficient hydration.
Without curing concreting process is incomplete. Curing is done to keep the concrete moist & warm enough so that the hydration of cement continues at an optimum level for the best gain in strength without any adverse effects.
Method of Curing
- Immersion – for precast concreting
- Ponding – for slabs pavements concreting
- Sprayings – plasters, and Vertical concreting
- Wet – covering (saw-dost, sand, jute bags, etc)-vertical surface concrete in a difficult position.
Concrete can be given the desired finishing during casting, during a partially hardened state, or after a fully hardened state. This is the last stage of Concreting Process. Finishing can be given to concrete in major three ways by work finish, Surface finish, and Applied finish.