Plain cement concrete is used to provide a rigid impervious bed to RCC in the foundation where the earth is soft and yielding. It can be used over brick flat soling or without brick flat soling. The short name of plain cement concrete is PCC. It is also defined as Cement Concrete (CC) or Blinding Concrete. When we say reinforced cement concrete, we know that there are reinforcements inside that concrete. when we don’t use any reinforcement inside the concrete, that is the plain cement concrete. It’s just a mix of concrete ingredients.
Materials Used to Produce PCC
Cement: We generally use Portland cement as bonding material in PCC.
Fine Aggregate: Sand is used as fine aggregate. The FM of sand should be 1.2 to 1.5.
Coarse Aggregate: We normally use brick chips for producing PCC. Stone chips can also be used for this purpose. The size of the coarse aggregate is 20mm downgrade.
Water: Pure drinkable water should be used in PCC.
Main Purpose of PCC
1- It is used as a protective layer for the RCC above so that water from the RCC is not absorbed by the earth below.
2- Moisture available in soil should not absorbed by R.C.C footings which causes corrosion of reinforcement.
3- Provides a base for the concrete and also helps workers to set out the structure above in a easier way. It provides a flat base for upcoming foundation rather than undulated base.
4- The effective depth of RCC member is achieved as the form-works can be easily and sturdily fixed.
5- As the Grade of comcrete of PCC and Foundation is different it also provide material difference for ground bactrial effect on foundation.
6- Act as a cover to reinforced cement concrete i.e. resist corrosion of steel bars in footings.
7- Some time it can decrease the stresses to the soil.
Proportioning of Plain Cement Concrete
1- The proportioning is done based on the requirement or given specification. Generally 1:2:4 or 1:3:6 mix is used.
2- The measurement of material can be done by weight batching or volume batching.
3- In volume batching, coarse aggregate and sand shall be measured by measuring box of 30cmx30cmx38cm of a suitable size equivalent to one bag cement of 1/30 m3or 0.035 m3.
4- Sand shall be measured on the basis of its dry volume.
5- While measuring the aggregate, sacking, ramming or hammering shall not be done.
Limitations
PCC remarkably strong in compression, But it is equally remarkably weak in tension. It’s tensile ‘strength’ is approximately one tenth of its compression strength. Hence use of plain concrete as a structural material is limited to situations where significant tensile stresses and strains do not develop.
