How to Stop Concrete Formwork from Failing

Have you ever wondered how concrete is shaped into perfect beams, columns, or staircases? The answer is formwork. Formwork is used extensively in construction and are temporary or permanent moulds into which concrete is poured until it hardens. Formwork is used to create any concrete shape, so naturally the foundations, walls, columns, suspended slabs, and almost every aspect of a concrete structure is made using formwork. Formwork is typically constructed from steel, aluminium, wood, or pre-fabricated modules such as glass reinforced plastics (GRP).

The success of any project is greatly dependent on formwork which represents approximately 35 – 40% of the overall concrete costs. Most formwork that is used in today’s construction is modular to maximise accuracy, efficiency, and speed. When compared with traditional wood formwork, modular formwork has two key advantages in speed and costs. Modular formwork can generally be reused hundreds of times before it needs to be replaced, and the need for skilled labour is also significantly reduced.

Formwork requirements

The success of any construction project requires formwork to fulfill the following requirements:

• Successfully propped and braced both vertically and horizontally to ensure its shape is preserved.
• Capable of supporting the weight of concrete during pouring and vibration together with any other loads such as workers or equipment.
• Has a secure base or foundation.
• Allows for stripping without damaging the concrete.
• Eliminates any leakage through properly tight joints.
• Stable in any form of weather – it should not distort or warp when exposed to the elements.
• Capable of being handled safely using the available equipment.

Common reasons why formwork fails

Formwork failure can be brought on by a range of reasons, however the most challenging aspect is when the concrete is being poured. The following lists several of the most common sources of formwork failure.

1. Improper inspections – Many formwork failures result from a lack of inspections or inspections conducted by inexperienced or unqualified personnel.
2. Flawed design – When the formwork design is flawed (generally resulting to the structures stability), it’s common for formwork to collapse due to excessive loads. On top of that, each time formwork is reused its load capacity is lessened and this variable is challenging for engineers to calculate.
3. Premature removal – A common reason for formwork failure is when formwork is removed before the concrete has hardened properly usually.
4. Defective components – Where proper maintenance isn’t performed on formwork components, they can easily become faulty after multiple uses. Substandard bolts, nails or splicing, faulty wedges, and poor weld quality can jeopardise formwork integrity.
5. Substandard foundations – Where formwork foundations are put on weak soil or when the foundations fail to transfer the load to the ground, formwork can collapse as it has a reduction in carrying capacity.

Preventative measures

To minimise the risk of formwork failing and causing injuries, the following preventative measures should be employed.

Before concrete pour

• Inspect all formwork components before use and replace or repair any faulty components.
• A qualified person must inspect the formwork before any concrete is poured to ensure it has been effectively erected.
• The formwork design should be undertaken by a qualified person with experience formwork design.
• The expected dynamic and static loads should be easily supported.
• Where formwork doesn’t adhere to the original design, adjustments should be made with the designer examining the formwork to validate the structural integrity.
• Always assemble formwork systems according to the manufacturer’s guidelines.

During concrete pour

• During the concrete pour, ensure the formwork is never overloaded.
• A boundary zone should be established to restrict workers from accessing areas under the formwork until the concrete has cured properly.
• During the early stages of the concrete pour, observe the formwork to identify any signs of failure. If workers require access to the area under the formwork, a risk assessment should be carried out to ensure its safe to do so.

Stripping stage

• Ensure the concrete is given enough curing time (as stipulated in the formwork design) before stripping.

There’s no doubt that construction sites are dangerous and proper care should be taken to ensure one’s safety. When using formwork, contractors must ensure that all health and safety measures have been complied with to ensure the safety of all workers. If you have any queries about formwork or any methods used to prevent formwork failure, call the experts at Uni-Span by phoning 1300 882 825.