After doing excavation, the surface of earth is uneven, to make it level the PCC is done.
It helps you on following;
Avoiding contamination of rebars.
Avoid possibilities of concrete getting contaminates and further attacks on concrete.
It provide plane base for footing, it help to ensure uniform cover to rebars, uniform transferring of loads to base and avoid wastage of concrete.
PCC have less strength compare to any grade of concrete use for RCC, basic purpose of it is to provide the level base for footing.
Once the structure above PCC begins to get constructed, settlement at footing level starts as the loads on top gets increased.
The total settlement generally happens within a year or two.
There may be possibility that, base have voids and it is getting compressed or the PCC crumble down or sink into earth.
All structure experience the settlements and the design of footing (Size) made by considering the properties of base material.
A compaction of soil / fill need to be ensured correctly, in order to avoid a settlement / failure of structure.
A building collapsed at Pune during monsoon.
There was a water well inside that plot which was filled haphazardly. Due to water and voids in soil, building started to sink on one side and ultimately fall down.
Base is important for any structure, an Engineer should do work by taking utmost care at footing level.
