Table – 2: Formwork Stripping Time (When Ordinary Portland Cement is used): –

Type of Formwork	Formwork Removal Time
Sides of Walls, Columns and Vertical faces of beam	24 hours to 48 hours (as per engineer’s decision)
Slabs (props left under)	3 days
Beam soffits (props left under)	7 days
Removal of Props of Slabs:
i) Slabs spanning up to 4.5m	14 days
ii) Slabs spanning over 4.5m	14 days
Removal of props for beams and arches
i) Span up to 6m	14 days
ii) Span over 6m	21 days

Important Note: It is important to note that the time for formwork removal shown above in Table -2 is only when Ordinary Portland Cement is used. In normal construction process Portland Pozzolana cement is used. So, the time shown in Table-2 should be modified. For cements other than Ordinary Portland cement, the time required for formwork removal should be as:

Portland Pozzolana Cement – stripping time will be 10/7 of the time stated above (Table-2) Low heat cement – stripping time will be 10/7 of the time stated above (Table-2) Rapid Hardening Cement – stripping time of 3/7 of the time stated above (Table-2) will be sufficient in all cases except for vertical sides of slabs, beams and columns which should be retained at least for 24 hours.

Should formwork be removed when removing concrete?

Step-by-Step –

1. Begin by stripping the face of walls and the sides of beams and columns first. These pieces of formwork are not load-bearing; their purpose is simply to hold the concrete in place. This process can typically begin at around 48 hours,
2. Second, begin to remove the soffit, or underside, of slabs. This can begin around day 3 or 4, Props should be left under the slabs at this time.
3. The beam soffits can be removed at around day 7,
4. At around day 14, the props supporting the slabs can be examined for removal. Whether or not the props can be removed will depend on the size of the slab.
5. Props for beams and arches should always be removed last. For spans under 20 feet, the recommended wait time is 14 days, For spans 20 feet or greater, wait at least 21 days,

All of the times above are estimated based on Ordinary Portland Cement usage. Always follow the advice of the engineer. Once the concrete formwork is removed, the structure should be able to withstand twice the stress it may be subjected to at the time of formwork removal

What is the purpose of formwork on a concrete slab?

Formwork are temporary models in which concrete is poured and compressed to lay concrete according to the design. The formwork is set up in the correct position to cast the members onto the concrete structure. The formwork is held in place until the concrete hardens and gains strength.

Removing the formwork is only recommended when the concrete has its dead weight and is strengthened without the formwork or any props. Before dealing with the precautionary measures to be taken when removing formwork or props, it is always necessary to know the exact time to remove the formwork. The formwork must be removed after the concrete structural elements supported in the formwork have been removed.

Here is a brief description of the exact time and precautions to be taken to remove the formwork. Correct Time of Removal of Formwork The time from which the concrete is placed in formwork till the time the formwork is removed is called as supporting period.

This time period will vary, based on different factors like: TYPE AND GRADE OF CONCRETE • Type and grade of concrete • Admixtures used in concrete mix • Formwork designs • Temperature • Type of structural element (Columns / beams / slabs) • Quality of content • Curing conditions The process of removing the formwork occurs after the concrete has turned and gained sufficient strength, which is called formwork striking time.

This can cause stress on the structural dimension due to loss of support on or below all sides, which is now the responsibility of a support structure. Properly hardened concrete element can withstand these external stresses when removing formwork. Formwork is left for a long time to aid in the healing process of concrete components.

Concrete Strength	Structural Member Type and Span
2.5 N/mm2	Lateral parts of the formwork for all structural members can be removed
70% of design strength	Interior parts of formwork of slabs and beams with a span of up to 6m can be removed
85% of design strength	Interior parts of formwork of slabs and beams with a span of more than 6m can be removed

Formwork Stripping Time (When Ordinary Portland Cement is used)

Type of Formwork	Formwork Removal Time
Sides of Walls, Columns and Vertical faces of beam	24 hours to 48 hours (as per engineer’s decision)
Slabs (props left under)	3 days
Beam soffits (props left under)	7 days
Removal of Props of Slabs:
i) Slabs spanning up to 4.5m	14 days
ii) Slabs spanning over 4.5m	14 days
Removal of props for beams and arches
i) Span up to 6m	14 days
ii) Span over 6m	21 days
Type of Formwork	Formwork Removal Time

Must read: Know the Difference between Formwork, Shuttering, Centering, and Staging Structured members are structured based on designed loads. But before a structure is completed and subjected to all the loads considered during structural design, the structural elements will be subjected to its own weight and construction loads during the construction process.

Therefore, in order to proceed with construction activities at a rapid rate, it is necessary to calculate the behavior of the structure under self-load and construction load. This can be done and if the configuration member finds it safe, the formwork can be removed. If these calculations are not possible, the following formula can be used to calculate safe formwork strike times: Characterization of the cube of equal maturity to the structure required at the time of removal of the formwork = (Dead load + Construction load) / ( total design load) = Grade of concrete This formula was presented by Harrison (1995), which describes in detail the background that determines the time it takes to remove the formwork.

Another method of determining the strength of a concrete structure is to perform non-destructive tests on the structural member. Important Note: It should be noted that the time to remove the formwork shown above in Table-2 is only when ordinary Portland cement is used.

Portland Pozzolana cement is used in the normal construction process. Therefore, the time shown in Table-2 should be modified. For cement other than ordinary Portland cement, the time required to remove the formwork is: 1. Portland Pozzolana Cement – Removing time will be 10/7 of the time specified above (Table-2) 2.

Low heat cement – the transfer time is 10/7 of the time mentioned above (Table-2) 3. Rapid Hardware Cement – 3/7 of the time mentioned above (Table-2) The transfer time is sufficient in all cases except the vertical sides of the slabs, beam and columns, which must be maintained for 24 hours at least an hour.

• Reference: ACI (1995) In-place methods to estimate concrete strength.
• ACI 228.1R-95.
• ASTM (1987) Standard practice for estimating concrete strength by the maturity method.
• ASTM C1074–87 BS 8110 – code of practice for the structural use of concrete IS-456 – Plain and Reinforced Concrete – Code of Practice What Happens If The Formwork Removed Early? (A) Early Removal Of Side Support if you remove formwork immediately, the columns and beams sides may bulge if the concrete has not hardened.

And sides may go out of plumb or line. (B) Early Removal Of Support If you do not get enough strength, the system may be distracted or collapse. Please note that if deviations occur at such times it will be permanent and difficult to repair. So be careful. ALSO READ: INSPECTION CHECKLIST FOR COLUMN CONCRETING Must read: What Is Beam | Uses | Types | Loads On Beam If you find This information helpful please share it. Thanks! For reading the article.

What is the striking time of concrete formwork?

Factors Affecting Concrete Formwork Striking Times – The striking time of concrete formwork depends on the strength of structural member. The strength development of concrete member depends on:

Grade of concrete – higher the grade of concrete, the rate of development of strength is higher and thus concrete achieves the strength in shorter time. Grade of cement – Higher cement grade makes the concrete achieve higher strength in shorter time. Type of Cement – Type of cement affects the strength development of concrete. For example, rapid hardening cement have higher strength gain in shorter period than the Ordinary Portland Cement. Low heat cement takes more time to gain sufficient strength than OPC. Temperature – The higher temperature of concrete during placement makes it achieve higher strength in shorter times. During winter, the concrete strength gain time gets prolonged. A higher ambient temperature makes the concrete gain strength faster. Formwork helps the concrete to insulate it from surrounding, so longer the formwork remain with concrete, the less is the loss of heat of hydration and rate of strength gain is high. Size of the concrete member also affects the gain of concrete strength. Larger concrete section members gain strength in shorter time than smaller sections. Accelerated curing is also a method to increase the strength gain rate with the application of heat.

Generally following values of concrete strength is considered for removal of formwork for various types of concrete structural members.

What is formwork in civil engineering?

Formwork are temporary models in which concrete is poured and compressed to lay concrete according to the design. The formwork is set up in the correct position to cast the members onto the concrete structure. The formwork is held in place until the concrete hardens and gains strength.

Removing the formwork is only recommended when the concrete has its dead weight and is strengthened without the formwork or any props. Before dealing with the precautionary measures to be taken when removing formwork or props, it is always necessary to know the exact time to remove the formwork. The formwork must be removed after the concrete structural elements supported in the formwork have been removed.

Here is a brief description of the exact time and precautions to be taken to remove the formwork. Correct Time of Removal of Formwork The time from which the concrete is placed in formwork till the time the formwork is removed is called as supporting period.

This time period will vary, based on different factors like: TYPE AND GRADE OF CONCRETE • Type and grade of concrete • Admixtures used in concrete mix • Formwork designs • Temperature • Type of structural element (Columns / beams / slabs) • Quality of content • Curing conditions The process of removing the formwork occurs after the concrete has turned and gained sufficient strength, which is called formwork striking time.

This can cause stress on the structural dimension due to loss of support on or below all sides, which is now the responsibility of a support structure. Properly hardened concrete element can withstand these external stresses when removing formwork. Formwork is left for a long time to aid in the healing process of concrete components.

Concrete Strength	Structural Member Type and Span
2.5 N/mm2	Lateral parts of the formwork for all structural members can be removed
70% of design strength	Interior parts of formwork of slabs and beams with a span of up to 6m can be removed
85% of design strength	Interior parts of formwork of slabs and beams with a span of more than 6m can be removed

Formwork Stripping Time (When Ordinary Portland Cement is used)

Type of Formwork	Formwork Removal Time
Sides of Walls, Columns and Vertical faces of beam	24 hours to 48 hours (as per engineer’s decision)
Slabs (props left under)	3 days
Beam soffits (props left under)	7 days
Removal of Props of Slabs:
i) Slabs spanning up to 4.5m	14 days
ii) Slabs spanning over 4.5m	14 days
Removal of props for beams and arches
i) Span up to 6m	14 days
ii) Span over 6m	21 days
Type of Formwork	Formwork Removal Time

Must read: Know the Difference between Formwork, Shuttering, Centering, and Staging Structured members are structured based on designed loads. But before a structure is completed and subjected to all the loads considered during structural design, the structural elements will be subjected to its own weight and construction loads during the construction process.

Therefore, in order to proceed with construction activities at a rapid rate, it is necessary to calculate the behavior of the structure under self-load and construction load. This can be done and if the configuration member finds it safe, the formwork can be removed. If these calculations are not possible, the following formula can be used to calculate safe formwork strike times: Characterization of the cube of equal maturity to the structure required at the time of removal of the formwork = (Dead load + Construction load) / ( total design load) = Grade of concrete This formula was presented by Harrison (1995), which describes in detail the background that determines the time it takes to remove the formwork.

Another method of determining the strength of a concrete structure is to perform non-destructive tests on the structural member. Important Note: It should be noted that the time to remove the formwork shown above in Table-2 is only when ordinary Portland cement is used.

Portland Pozzolana cement is used in the normal construction process. Therefore, the time shown in Table-2 should be modified. For cement other than ordinary Portland cement, the time required to remove the formwork is: 1. Portland Pozzolana Cement – Removing time will be 10/7 of the time specified above (Table-2) 2.

Low heat cement – the transfer time is 10/7 of the time mentioned above (Table-2) 3. Rapid Hardware Cement – 3/7 of the time mentioned above (Table-2) The transfer time is sufficient in all cases except the vertical sides of the slabs, beam and columns, which must be maintained for 24 hours at least an hour.

• Reference: ACI (1995) In-place methods to estimate concrete strength.
• ACI 228.1R-95.
• ASTM (1987) Standard practice for estimating concrete strength by the maturity method.
• ASTM C1074–87 BS 8110 – code of practice for the structural use of concrete IS-456 – Plain and Reinforced Concrete – Code of Practice What Happens If The Formwork Removed Early? (A) Early Removal Of Side Support if you remove formwork immediately, the columns and beams sides may bulge if the concrete has not hardened.

And sides may go out of plumb or line. (B) Early Removal Of Support If you do not get enough strength, the system may be distracted or collapse. Please note that if deviations occur at such times it will be permanent and difficult to repair. So be careful. ALSO READ: INSPECTION CHECKLIST FOR COLUMN CONCRETING Must read: What Is Beam | Uses | Types | Loads On Beam If you find This information helpful please share it. Thanks! For reading the article.