Before we delve into the process of its removal, it is essential to understand what “formwork” means in the concrete sphere. As described by Hunker, formwork that is set prior to pouring concrete “serves as a frame for the shape of the concrete, holding the poured material in place as it cures”.
So why the question of removing formwork? During the conclusion of its curing stage, concrete reaches a desirable level of hardness which ensures its ability to support its own weight, thereby eventually rendering the formwork unnecessary. This level of hardness, measured in MPa or PSI depending on the country is set out in the project specifications by an engineer.
While formwork removal can be a laborious task, we have laid out a step-by-step plan that will guide you through a meticulous but vital procedure:
Step 1: Checking the concrete
- To ensure a firm surface, make sure to confirm that the concrete is cured, in that it is hard and dry to adequate measure.
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- Weather is a key element to factor in when checking if your concrete is ready because the required concrete removal time in winter is considerably higher than during summer.
Step 2: Tackling the top
- Form removal must always be approached from the top of a sloping slab.
- A hammer comes in handy when dislodging nails that hold the forms together.
- Slabs and beams usually undergo a live load whilst in the construction process, so ensure that the achieved strength is sufficient to manage such loads.
Step 3: Next come the ground and the sides
- The stakes that support the forms from the ground must be removed using a stake puller since this helps avoid any damage to the forms or the stakes.
- Forms can be pulled away from the sides of the concrete slab with the use of minimum strength, but if a form becomes challenging to remove then a pry bar helps to loosen the form in the concrete when pried upwards from the ground.
- Alternate the sides of the slab when removing forms as this helps to preserve the balance of the structure, and make sure to reuse the forms if they can be cleaned and dried, or dispose of them if necessary, instead.
In keeping these points in mind, it is pertinent to plan for contingencies or choose more optimal processes regarding numerous factors––whether they may concern the type of cement, the grade of concrete, or even accelerating the curing process.
Below, we have laid out some of the ways in which you may optimize your formwork stripping process or prevent undesirable outcomes during this procedure:
Tips for Formwork Removal Optimization
- Here are some resources, methods, standards, and practices that will help you determine if the concrete has reached the desired level for the formworks to be stripped:
- 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
- Here is a formula that will help you calculate safe formwork striking times:
(Dead load + construction load) / (total design load)
= Grade of concrete
- The following is a table obtained from LCETED Institute for Civil Engineers which provides formwork stripping times for reference:
Formwork Removal Time (Ordinary Portland Cement)
Tips for Damage Prevention During Formwork Removal
- Avoid using the force of tools such as crowbars whilst removing the formwork as this may damage the concrete, but a preferable alternative would be wooden wedges.
- There are several risks to removing the formwork too early and these may include: columns and beam
ssides could bulge or misalign if the concrete is not hard enough, or the structure could collapse without adequate strength.
- It is highly recommended to seek the approval, supervision, and/or expertise of the on-site engineer for matters concerning the organization (pattern/sequence) of formwork removal as well as to confirm the quality of hardened concrete.
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