What is Formwork? What are the requirements of Ideal Formwork? Discuss various types of Formwork material?
The formwork is also known as temporary structure used in the construction work. The term ‘formwork’ refers to a temporary mould for the structure into which concrete is placed and formed so that it can harden and mature to the required shape. In building work, the cost of formwork is upto 20 to 25% of the cost of the structure, and in bridges the cost of formwork may be higher. In order to decrease this expenditure, it is important to design economical types of formwork.
A formwork designer must attain the basic objective that to construct a mold (form) correctly so that the size, shape and finishing of the concrete are obtained. He should also ensure that the mold is capable of supporting live load, dead load and other lateral loads on the casting of concrete.
What are the requirements of an ideal formwork?
Requirements of an ideal formwork are:
(i) The material used for formwork should be cheap.
(ii) The material used for formwork must be reuse many times.
(iii) Formwork should be lightweight as much as possible.
(iv) Formwork should be waterproof so that it cannot absorb water from concrete and also its swelling and shrinkage properties should be minimum.
(v) Formwork should be sufficiently strong so that it can withstand all loads coming on it, like dead load of concrete and live load during pouring, compaction and curing.
(vi) Formwork should be stiff to get minimum deflection.
Types of Formwork materials:-
(i) Timber Formwork: It is the most commonly used material for formwork. Timber logs, lumber, etc. are used as bracing members from ancient times. So, the timber formwork is also called as traditional formwork. It is the most economical material used for formwork. For many years, this material is used as formwork.
(ii) Plywood Formwork: Plywood which is a manufactured product of timber is also used for formworks. It consists a number of veneer sheets in layers. Nowadays, the use of plywood formwork increases, especially for facing panels. The reason behind it is that the plywood formwork provides smooth finish when compared to normal timber formwork. Hence, finishing cost may reduce by the use of plywood.
(iii) Steel Formwork: Steel can also be used as formwork material. It is very costly but can be used for more number of times than others. They provide excellent finish to the concrete surfaces. For mass structures like dams, bridges, etc. steel formwork is strong and safe.
(iv) Aluminum Formwork: Aluminum formwork is usually used for pre-fabricated formworks. It is getting more popular because of its light weight and good strength. It requires fewer supports and ties.
(v) Plastic Formwork: Plastic is another type of formwork material which is used for small concrete structures or for complex portions of the structures. It is lightweight and durable for long periods. For complicated concrete structures, glass reinforced plastics (GRP) and vacuum formed plastics are used.
(vi) Magnesia Formwork: Magnesium is another metal element which is used for formwork. Magnesium is not directly used for formwork and is used with the combination of oxygen atoms which forms magnesium oxide, usually called magnesia or MgO. MgO boards are available in required sizes and grades.
(vii) Fabric Formwork: Fabric formwork is a modern technology that employs geotextile fabrics as the formwork material for concrete construction. Fabric can be molded into any required shapes, which makes it more famous formwork for architectural purposes.
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