Curing of the concrete structures and stripping time for striking formwork in structural construction

Curing of the structural components like beams, columns, slabs, foundation will give better compressive strength as per the assumed grade of the concrete. Basically after casting the concrete structural members (Beams, columns, slabs, foundation or other) we need to apply the water for the curing purpose with minimum water standards. Depending upon the curing periods the values of the compressive strength varies and the optimal value of the compressive strength was obtained at the 28 days curing period.

Compressive strength for various curing period of concrete

The compressive strength of the concrete increases with increase in the curing period after casing the concrete members. The below table shows the percentage of strength obtained at 1day, 3days, 7days, 14days and 28 days curing period.

S. No	Curing period	Percentage of compressive strength
1	1 day	16.66%
2	3 days	40.00%
3	7 days	66.66%
4	14 days	90.00%
5	28 days	99.00%

For 1day curing approximately 16.66% compressive strength is obtained. In the similar process at 3days approximately 40.00%, at 7days approximately 66.66%, at 14days approximately 90.00%, and finally at 28days approximately 99.00% strength is obtained in the selected grade of concrete.

In general condition the props under slabs, beams are removed in the sequence to effect the same type of structural action and support condition. In other words example for beams the props under the cantilever are removed initially at the free end and then removed at the fixed end.

Minimum curing of the concrete time period for structural members and stripping time for removing of form work

Curing of the concrete Walls and other vertical faces of structural members

Walls are the constructed in the building structures to divide or separate the rooms to form the closed structure. In the general condition building structures the walls are two types based on the thickness of the members. One is external wall and other is internals wall, the eternal walls are used in the exterior structure and which is consisting of 9 inches thickness approximately 230 mm and internal wall are used as partition walls generally used at 5 inches thickness which is approximately 120 mm to 125 mm thick.

The either external or internal walls in the structure are cured at 16 hours to 24 hours as minimum curing period from the end of the construction time.

Curing of the concrete columns

The columns are the vertical components in the building and they are the most important members to transfer the loads from the beams to foundations. As per the IS 456: 2000 code standards the minimum of 9 inches is considered as the dimensions of the column with minimum of four reinforced bars. For the columns the minimum curing period and removing of the formwork is taken as 16 hours to 24 hours.

Soffit form work to the slab

In this condition the props to be refixed immediately after removal of formwork at the time period of minimum 3 days.

Soffit form work to the beams

In this condition also the props to be refixed immediately after removal of formwork at the time period of minimum 7 days.

Removal of props under the slabs

In this condition the members are classified two types which are given below

1. Spanning up to 4.5 meter
2. Spanning over 4.5 meter

Spanning is the center to center distance between the columns or the distance between the slab members. For the spanning up to 4.5m the props are removed at the time period of 7 days, in the same process spanning over 4.5m the props are removed at the time period of the 14 days from the end of the construction time.

Removal of props under beams and arches

In this condition also the members are classified two types which are given below

1. Spanning up to 6 meter
2. Spanning over 6 meter

For the beams and arches, for the spanning up to 6 meters the props are removed at the time period of q4 days, in the same process spanning over 6 meters the props are removed at the time period of the 21 days from the end of the construction time of the beams and the arches.

Summary of minimum curing period and stripping time for striking formwork

The complete summary of minimum curing period and stripping time for striking formwork is shown in the below table in detailed.

S. No	Members	Time period
1	Columns, walls, other vertical faces	16 hours to 24 hours
2	Soffit formwork to slabs	3 days
3	Soffit formwork to beams	7 days
4	Removing of props under slabs a.      Spanning up to 4.5 meters b.     Spanning over 4.5 meters	7 days 14 days
5	Removing of props under beams and arches c.      Spanning up to 4.5 meters d.     Spanning over 4.5 meters	14 days 21 days

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Conclusions of minimum curing period and stripping time for striking formwork in structural construction

Well now the above explained concepts are related to the complete basic concepts of structural construction. Which are related to columns, walls, other vertical members, Soffit formwork to slabs, soffit formwork to beams, removing of props under slabs, removing of props under beams and arches

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