Formwork is a temporary mould which is used to hold freshly placed and compacted concrete so it will gain sufficient strength to be self-supporting. Formwork is very important in the construction industry because when concrete is still fresh and in its liquid state, it needs to be restrained to acquire its required shape, size and the desired finish.
Formwork is fabricated from timber, steel, glass fibre reinforced plastics, and other materials. While still in its liquid state, concrete imposes considerable forces on the formwork used to restrain it. Hence, a good formwork must have enough strength to carry the load it is expected to carry during casting operation for the concrete to get hard and gain the required design strength.
The formwork is allowed to stay in position until the concrete achieves enough strength to resist the stresses coming on it without the assistance of the formwork. After this, the formwork is removed.
Due to its importance and its enormous purpose it serves in construction, a formwork should certify some requirements, ranging from technical, quality, safety and economic requirements to be adjudged good.
- It should produce the required shape and size
- Easy removal
- Minimal leakage
Formwork should be constructed to meet to form the desired shape and size required of the concrete. It should also fit properly at the location of the member in structure according to the drawings, as well as produce the required concrete surface.
The formwork should be rigid enough and efficiently popped and supported in order to be able to withstand the pressure of fresh concrete and working loads. Its rigidity will also help it to hold its shape and not deflect from its position during the concrete placement operation.
The framework should be designed in such a way that it can be easily removed with less hammering. The edge or surface of the concrete and the framework itself should not get damaged in the process of removal.
The formwork should be arranged properly in order to prevent leakage through the joints. The joints at the adjacent sections of the formwork should be tight enough to make minimal leakage of cement paste possible.
- Smooth surface
The formwork should be strong enough to withstand all the dead and live loads coming on it during pouring, compaction and curing. The loads may be self-weight, weight of wet concrete, weight of reinforcement, loads of workers, construction and wind loads, incidental loads caused by placing and compacting the concrete, and horizontal pressure of the wet concrete against vertical formwork. To achieve this, the loads should be estimated carefully, as over-estimation of loads leads to expensive formwork while under-estimation causes failure of formwork.
It should be easily lifted and moved from one place to another and from one construction site to another, and be easily dismantled.
Crude oil or soft soap should be applied to the surface of the formwork so as to make it smooth and easily stripped.
The formwork units should be interchangeable so they can be used to form different members.
It should be as lightweight and simple as possible without any strength reduction.
- Adherence to safety regulations
- Stability of the structure
- Creation of emergency route
Formwork should be designed and managed with adherence to safety and health standards. This will help construction workers handle them without any safety issue.
The stability of the formwork should be adequately checked to avoid any undesired events such as loss of life, delay construction, and increase cost.
While designing and constructing the formwork, there should be provision for emergency escape route in case such is needed at any point.
- Cost-effectiveness and minimum energy consumption
- Easy dismantling and maintenance
Formwork does not contribute to the stability of the construction when it is finished so it should be cost effective. Quality but low-cost materials should be used. Its energy consumption and labour cost should also be low.
Based on the reason stated above, the framework should be reusable for several times without losing its shape.
The whole structure of the formwork should be easy to design and dismantle either with skilled, semi-skilled and unskilled labour. Whenever it requires maintenance, it should be conducted with strict adherence to established standards.
Formwork, though often temporally built, is very important as it helps hold freshly placed and compacted concrete until it gains enough strength to be self-supporting. Hence, the above parameters must be taken into consideration when fabricating it, so that it will serve its purpose effectively.