Placing and compacting Mass Concrete (massive pours of reinforced concrete)
With mass concrete, the volume of concrete being placed at a time will usually be high and may take several hours to complete. One of the problems, therefore, is to avoid the formation of cold joints. The following figure illustrates the proper method and sequence of placing and compaction. The main aims are to restrict the area of exposed concrete and to make sure that the fresh concrete is not cast against concrete which has already hardened. When using skips, discharge them as quickly as possible and from a height –usually about 1 or 2 m – so that the concrete does not form cone-shaped heaps but is made to slump and spread under its own weight.
Layer Thickness to be maintained as 400 to500mm per layer and the length of the pour can be taken as 3m to 5m (approx.) and can be calculated based on the placement capacity of concrete per hour.
Concrete to be poured to the full width of the structure or foundation.
Sequence of pours as mentioned to be maintained to have full joint stitching to avoid cold joint formation.
Calculation:
Dimension of foundation is 40 x 20 x 2.0 m = 1600 cum
No of batching plants deployed : 2 Nos
Production capacity of batching plant 30 cum/hour plant = 80 % of rated capacity = 30 cum x 80%= 24 cum / hr
Total quantity produced / hour : No of plant x cum / hour = 2 x 24 = 48 cum/hr
Quantity effectively compactable / hour = 20 cum (max) No of pump required = 2 Nos
Quantity required per metre length of 400 mm thick = 1.0 x 20 x 0.40 = 8 cum
Maximum Layer length to be poured = 48 / 8 cum = 6.0 M
As initial setting time of concrete is generally 5 to 6 hours considering that the length can be maintained as 4 to 5 m then we need 32 to 40 cum / hour which also matches with the vibratable quantity of 40 cum with 2 pumps.
So, we can plan initial length of 5.0 m as layer 1 and 4 m length as layer 2 which will have one meter thrust and concrete will be in steps. Successive layers can be planned with in initial setting time of concrete.
In the above example the concrete pumps can be placed as mentioned below and concrete can placed in layers as mentioned above.
With mass concrete, the volume of concrete being placed at a time will usually be high and may take several hours to complete. One of the problems, therefore, is to avoid the formation of cold joints. The following figure illustrates the proper method and sequence of placing and compaction. The main aims are to restrict the area of exposed concrete and to make sure that the fresh concrete is not cast against concrete which has already hardened. When using skips, discharge them as quickly as possible and from a height –usually about 1 or 2 m – so that the concrete does not form cone-shaped heaps but is made to slump and spread under its own weight.
Layer Thickness to be maintained as 400 to500mm per layer and the length of the pour can be taken as 3m to 5m (approx.) and can be calculated based on the placement capacity of concrete per hour.
Concrete to be poured to the full width of the structure or foundation.
Sequence of pours as mentioned to be maintained to have full joint stitching to avoid cold joint formation.
Calculation:
Dimension of foundation is 40 x 20 x 2.0 m = 1600 cum
No of batching plants deployed : 2 Nos
Production capacity of batching plant 30 cum/hour plant = 80 % of rated capacity = 30 cum x 80%= 24 cum / hr
Total quantity produced / hour : No of plant x cum / hour = 2 x 24 = 48 cum/hr
Quantity effectively compactable / hour = 20 cum (max) No of pump required = 2 Nos
Quantity required per metre length of 400 mm thick = 1.0 x 20 x 0.40 = 8 cum
Maximum Layer length to be poured = 48 / 8 cum = 6.0 M
As initial setting time of concrete is generally 5 to 6 hours considering that the length can be maintained as 4 to 5 m then we need 32 to 40 cum / hour which also matches with the vibratable quantity of 40 cum with 2 pumps.
So, we can plan initial length of 5.0 m as layer 1 and 4 m length as layer 2 which will have one meter thrust and concrete will be in steps. Successive layers can be planned with in initial setting time of concrete.
In the above example the concrete pumps can be placed as mentioned below and concrete can placed in layers as mentioned above.
