What is PCC in Construction?

Cement, fine aggregate (sand), and coarse aggregate without steel are combined to create plain cement concrete. In order to prevent direct contact between the reinforcement of concrete and the soil and water, PCC, a crucial building component, is laid out on the soil’s surface.

Materials used in PCC

The general requirements for materials used in PCC are as follows:

Coarse Aggregate

The coarse aggregate for the PCC must be made of hard, shattered stone that is similar to granite and free of dust, grime, and other extraneous materials. The stone ballast must be no larger than 20 mm. All of the coarse material must be kept in a 5 mm square mesh that is carefully graded to keep the void percentage under 42%.

Fine Aggregate

The fine aggregate must go through a screen with a mesh size of 5 mm and be composed of coarse sand with hard, sharp, and angular grains. Sand must meet specified requirements and be clean, devoid of organic matter, dust, and filth. You must not use sea sand.

Cement

 For plain cement concrete, pozzolana cement (P.P.C.) is typically utilised. It should meet the requirements and have the necessary tensile, compressive, and fineness stresses.

 Water 

The water that is utilised must be clear and reasonably devoid of harmful substances including oils, acids, alkalis, salts, and vegetative growth. In general, drinking water must have a pH level of at least 6. 

Methods of Mixing PCC

PCC can be combined manually or with the aid of machinery.

1. Hand Mixing 

• Only small-scale projects are permitted to use hand-mixing for PCC.
• A clean, watertight slab or steel platform must serve as the foundation for mixing the concrete.
• Crushed aggregate is added after completely combining sand and cement. In order to achieve a uniform tint and consistency, water is lastly added and thoroughly blended into the mixture.

2. Machine Mixing

• Cement, dry coarse aggregate, and fine aggregate must all be weighed out and poured into the appropriate hoppers.

• The dry ingredients must be blended for at least four spins in the mixing drum before the necessary amount of water is added gradually while the drum is still in motion.
• Before 25% of the mixing time has passed, the complete amount of water must be added, and it must be controlled to reach the desired water-to-cement ratio.
• To produce a plastic mix with a consistent tint, the mixing must be thorough.

The procedure of Machine Mixing of Concrete includes the following steps:      

3. Add one or two buckets of water to wet the mixer’s interior surface.
4. Next, coarse aggregate, sand, and cement are added.
5. The components should not be added all at once; they should be added in turn.
6. The mixture needs to be stirred for two to three minutes while it is dry.
7. Pour the necessary amount of water while monitoring the consistency of the concrete mixture; if the concrete is too watery, the strength may be lowered.
8. Pour the mixture onto a clean sheet or debris-free surface after properly combining the ingredients for two minutes.

Laying of PCC

• Dense concrete is generated by extensively vibrating the PCC using mechanical vibrators as it is placed out in layers no thicker than 150mm.
• Concrete must be hand-compressed whenever necessary with the aid of wooden tamping rods to ensure that it is fully compacted and packed into the formwork’s corners.
• Within 30 minutes of adding water to the dry mixture, compaction must be finished before the initial setting.

Curing of PCC

• Freshly constructed concrete must be covered appropriately to protect it from the elements.
• One to two hours after it has been laid, when the concrete has started to firm, it must be covered with wet gunny bags, sand, or other materials to prevent it from drying out too quickly.
• After the concrete has been laid for 24 hours, the surface must be cured by being submerged in water that is approximately 25mm deep or by being covered with weight-absorbent materials.
• The minimum time for curing is fourteen days.

Dos and Don’ts of PCC Work

Dos

• PCC shuttering needs to be the exact thickness and size.
• A determined amount of water should be added to a bucket of cement in accordance with the w/c (water/cement) ratio.
• Pour concrete where there is more depth using a chute or extra labour.
• To prevent soil or other materials from collapsing in the pit during concreting, remove any loose material from the pit’s sidewalls.
• De-watering should be done concurrently with concreting if the water table is high.

Don’ts

• Never combine the components on bare ground.
• The PCC must not be used without formwork.
• Concrete must be levelled and compacted before being poured.
• Concrete should not be poured into the hole from a height of more than 1.5 metres.
• For a smooth finish, don’t allow more cement mortar to be applied to PCC.