De-shuttering Time

The de-shuttering time is related to the maturation of concrete and is temperature-dependent.

Formwork must not be hammered until the concrete has reached a strength at least twice that of the stress to which the concrete may be subjected during formwork clearance.

In this article you’ll learn:

• What is de-shuttering time?
• Purpose of de-shuttering time.
• Merits and Demerits of de-shuttering time.
• Lots more.

So, if you’re ready to go with a de-shuttering time., this article is for you.

Let’s get started!

What is De-shuttering Time?

The de-shuttering period is determined by the maturity of the concrete, it is defined as a function of curing time and air temperature at the time of curing.

Practically, the de-shuttering period is the time during which a structure or part of a structure can withstand at least twice the number of stresses that may be applied to the structure during removal.

As a result, the de-shuttering period is determined by the ambient temperature, curing time, and structural component.

Purpose of De-shuttering Time:

• While de-shuttering time OPC cement is employed.
• Curing is completed properly then only de-shuttering is a must.
• The temperature must not fall below 15° Celsius.

According to IS 456-2000 De – Shuttering Time:

De-shuttering time, also referred to as strike-off or stripping of formwork, should be performed only after the concrete has gained appropriate strength, at least twice the stress that the concrete may be subjected to when the reinforcing is eliminated.

During formwork elimination, it is also vital to assure the stability of the residual formwork.

The de-shuttering duration or stripping time for the RCC construction is detailed in IS-456 (2000), and let us explain it with the necessary drawings for a clear understanding.

De-shuttering of a concrete section should not cause the structural member to:

• Under self-load or design load, collapse.
• Unduly deflect the structural part in the short or long term.
• When the formwork is eliminated, it physically damages the structural part.

The following considerations must be made during formwork removal, regardless of whether the building will be subject to:

• Damage from freezing and thawing.
• Thermal contraction of concrete causes fractures to develop.

Following formwork striking, If there is a considerable chance of any of the foregoing hazards, it is preferable to postpone formwork removal.

 If formwork must be removed to optimize concrete building activities, these structures must be effectively insulated to avoid such harm.

According to IS 456, the De-shuttering time for various parts of Structural Construction is as follows:

De-shuttering Time:

• Columns, walls, and beam sides: 16-24 hours.
• Soffit formwork to slabs: 3 days.
• Soffit to the beams: 7 days props to refix after removal.
• Props to slab:  7 days span up to 4.50m.
• Props to slab:  14 days spanning over 4.50m.
• The elimination of supports under beams and arches took 14 days and spanned up to 6 meters.
• Over 6 m span: 21-28 days.
• Footing: 16-24 hours.
• Staircases with waist slab minimum:  7 days is required to avoid deflection.

Factors Affecting De-shuttering Time:

The hitting time of concrete formwork is influenced by the strength of the structural part and the growth of concrete member strength is determined by:

Concrete grade:

The greater the grade of concrete, the faster the strength develops, and so the concrete acquires strength in less time.

Cement grade:

A higher cement grade allows the concrete to reach greater strength in less time.

Cement Type:

The cement type influences the strength development of concrete.

Rapid hardening cement has a faster strength growth than ordinary Portland cement.

Low heat cement takes longer than OPC to reach appropriate strength.

Temperature: 

When concrete is placed at a higher temperature, it achieves more strength in less time.

Across the wintertime, the time it takes for concrete to reach strength rises.

A greater ambient temperature causes the concrete to build strength more quickly.

Formwork insulates the concrete from its surroundings, therefore the longer the formwork remains with the concrete, the less heat is lost during hydration and the rate of strength increase is great.

The size of the concrete component also has an impact on the increase of concrete strength. Members of larger concrete sections increase strength faster than smaller parts.

Accelerated curing is another approach for increasing the pace of strong growth with heat.

Advantages of De-shuttering Time:

1. It will have a stronger strength than regular curing because the shuttering material creates more heat and prevents water from evaporating, causing the chemical process to function quicker.
2. The only thing to keep in mind is that the top surface of the concrete should be cured with water at the same time.
3. This is good because removing the shuttering material after the curing period will allow the concrete to reach its desired strength and will not cause any harm to the concrete.

Disadvantages of De-shuttering Time:

1. It is reduce shuttering material used at the same time.
2. If the concrete is not completely dry under shuttering and curing within the period. Concrete may have flaws such as cracks, strength, and so on.
3. As a result, either the concrete should be completely enclosed with shuttering material or the open area of the concrete should be cured.

Also read: Concrete Slab | Grade Beam | Formwork

Conclusion:

It is important to consider the environment and design mix while de-shuttering any concrete construction after it has been poured.

The size of columns and beams is critical, the addition of fly ash also helps with the settling time.