How Long Should Concrete Cure Before Removing Forms
Concrete is one of the important building materials used in construction. For making good concrete that lasts a long decade, it has to be properly produced, placed, and most importantly cured after casting.
So, In this article, we will cover When to Remove Concrete Forms or How Long Should Concrete Cure Before Removing Forms from them.
What Is Formwork?
Formwork is a type of casting mold or box, like a container into which fresh concrete is poured and compacted. When the concrete is hardened, the formwork is removed and a solid mass is produced in the shape of the inner face of the formwork.
What Is Removal of Formwork
The removal of formwork is also called a strike-off of forms in which concrete is poured. The formwork should be removed only after when concrete component achieves sufficient strength.
Care should be taken during the removal of formwork to ensure the stability of the remaining formwork.
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Factors Affecting Concrete Formwork Striking Times
The time of removal of formwork depends on how quickly concrete members gain sufficient strength and it depends on the following factors.
Grade of concrete:
As the rich grade of concrete, the rate of development of strength is higher, and thus concrete gains strength in a shorter time.
Grade of cement:
A Higher grade of cement offers a quick setting and it gains strength in a shorter time. Type of Cement – The cement type used in concrete also affects the strength development of concrete.
For example, Compare to ordinary Portland cement rapid hardening cement has higher strength gain in shorter. Low-heat cement requires more time for setting compared to OPC.
A high temperature of concrete and surrounding at the time of placing concrete makes it achieve higher strength in shorter times. During winter, the strength-gaining process becomes slower.
Size of the concrete member:
The size of the concrete member also matters in the strength-gaining process. Large-sized concrete section members gain strength in a shorter time than smaller sections.
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When to Remove Concrete Form
Time of Removing Formwork as per ASTM
|Type of Cement||Time of De-shuttering|
|1||Type I cement||7 days|
|2||Type II cement||10 days|
|3||Type III cement||3 days|
|4||Type IV or V cement||14 days|
|5||ASTM C 1157 C 595, C 845 types of cement||Varies|
Generally, the American Concrete Institute recommends the following
|Type of Formwork||Minimum Period Before Striking Formwork|
|1||Walls and columns vertical Supports||24-48 hours|
|2||Slabs, with their props left under them||3-4 days|
|3||Soffits, with their props left under them||7 days|
|4||Props supporting slabs under 15 feet||7 days|
|5||Props supporting slabs under 15 feet||14 days|
|6||Props supporting arches& beams over 20 feet||21 days|
Formwork Removal Time Period | DE shuttering Time
|Sr. No.||Type of Formwork||Minimum Period Before Striking Formwork|
|1||Vertical formwork to columns, walls, beams||16-24 h|
|2||Soffit formwork to slabs (Props must be re-fix immediately after removal of formwork)||3 days|
|3||Soffit formwork to beams (Props must be re-fix immediately after removal of formwork)||7 days|
|4||Props to slabs: 1) Spanning up to 4.5 m 2) Spanning over 4.5 m||7 days & 4 days|
|5||Props to beams and arches: 1) Spanning up to 6 m 2) Spanning over 6 m||14 days &21days|
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How to Properly Remove Formwork
- Formwork removal is one of the most hazardous jobs on the site. If not properly done it not only affects the structure but also can result in high risk for the laborers working at the site.
- Therefore following important points should be kept in mind while removing the formwork.
- Conduct proper tests (mostly NDT) on concrete to ensure its strength is developed.
- Removal of formwork should be started from vertical members are removed first.
- The supports of the slab or soffits should not remove until it is ensured to bear their self-weight and external stresses effectively.
- The crowbars should not fix on the side to remove the formwork as it can damage the edges of the concrete.
- Loose concrete or any other material found in the edges and corners is to be removed.
- The safety engineers should inspect the site before the removal of formworks to ensure suitable conditions.
- For workman safety, inspect the formwork position so that sufficient bracings and work platforms are provided to remove the formwork at higher elevations.
- The team removing formwork should know about risk and rule regulation of safety on the construction site.
The curing process of concrete is crucial for its durability, strength and overall performance, the duration for it concrete should cure before removing the formwork depends on various factor such as ambient condition, specific mix design, and types of projects.
Usually it is recommended to wait at least 3 to 7 days for horizontal surface like pavement and slabs, and 24 hours to 48 hours before removing the vertical structure formwork.
During curing period, the concrete gradually gains its strength as the chemical reactions between water and cementitious materials take place and adequate curing allows for the development of the desired compressive strength and it help to prevent shrinkage, cracking and other potential issues.
What is the curing process for concrete?
Curing is the process of maintaining favorable moisture and temperature conditions for freshly placed concrete to ensure optimal hydration and strength development.
How long does concrete need to cure before removing forms?
The time required for concrete to cure before removing forms depends on several factors, including the type of concrete, ambient conditions, and project specifications. However, as a general guideline, forms are typically removed after the concrete has gained sufficient strength, which is usually around 24 to 48 hours.
What factors influence the curing time for concrete?
Several factors can affect the curing time for concrete, including temperature, humidity, concrete mix design, cement type, admixtures used, and the size and complexity of the concrete element. Warmer temperatures and higher humidity generally accelerate the curing process.
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