Types of Formwork

Introduction

Formwork is the term used to create a temporary mold in which concrete is poured and formed. The formwork traditional is made of wood, but it may also be constructed of steel formwork, plastic reinforced with glass fibers and other materials.

Although formwork is a broad term used in the forming process using a wide variety of materials, the term formwork is a term often used to refer to the process of using plywood to form the mold.

The casing may be the type of shuttering the most popular. It is usually built on-site using wood and plywood. Special grade plywood is required for the formwork and must be water-resistant. It is easy to produce, although it may take a long time for larger structures. It is used when labor costs are lower than the cost of producing reusable forms from materials such as steel or plastic. It also has the advantage of being able to pour a large quantity of concrete.

The simple formwork of planks can be used for the construction of a path or a stand. Planks should be cut to the same level as the top surface of the slab, resulting in a tidy concrete finish.

Formwork specifications

When choosing the formwork , the type of concrete and the casting temperature are important considerations as they both affect the pressure exerted.

The sides of the formwork must be able to withstand the hydrostatic pressure of the wet concrete, which will disappear after several hours depending on the setting and hardening speed.

The base or soffit of the formwork must be able to withstand the initial permanent load of the wet concrete and the permanent load of the dry concrete.

Once the concrete has acquired sufficient strength, the formwork can be struck (removed). A minimum value of 5 N / mm2 is recommended in all cases when producing vertical formwork in order not to damage the permanent concrete during the process.

A high quality finish and inspection is required to ensure a high level and appearance of the resulting concrete structure.

Formwork and formwork, in their various forms, will be supported by false work. This applies to poles, stabilizers or other units that hold the formwork or formwork in place during concrete drying. For more information, see False job.

Beam formwork

The formwork for the beams is in the form of a three-sided box that is supported and wedged in the correct position and at the desired level. The shrinkage time of the formwork will vary according to the air temperature, humidity and the resulting polymerization rate. Typical typing times are as follows (with an air temperature of 7 to 16ºC):

Beams: 9-12 hours.

Beam soffits: 8-14 days.

Beam props: 15-21 days.

Column formwork

It is a vertical mold of the desired shape and size of the casting column. To reduce to a minimum the thickness of the material formwork, of steel or wooden horizontal clamps are used to centers equal to the filling batch and on different centers for filling in a single casting.

The head of the column formwork can be used to support the formwork of the beam, but if it offers good lateral restraint, it can make the formwork complex. Alternatively, the column may be cast on the underside of the beams. Later, a formwork collar can be clamped around the cast iron column to complete the pouring and support the incoming beam formwork .

Plastic formwork

The formwork reusable plastic is generally used for quick concrete castings. The formwork is assembled from nested panels or a modular system and is used for relatively simple concrete structures. Due to prefabrication requirements, it is not as versatile as wood formwork and is ideal for costly repetitive structures such as community housing projects.

The formwork structural remaining on site is generally assembled on site using prefabricated fiber-reinforced plastic. It is used for concrete columns and pillars and remains in place, acting as permanent axial reinforcement and shear for the structural element. It also offers environmental damage resistance for both concrete and rebar.

Exclusive systems are used to support vertical forms during concrete hardening , consisting of a series of tubes and fasteners.

Requirements of a good formwork

Good formwork must meet the following requirements:

Strong enough to support dead and alive charges.

Able to maintain its shape by being effectively wedged and wedged horizontally and vertically.

The joints must prevent leakage of cement grout.

Must be removable in various parts without damaging the concrete.

The materials used must be reusable.

Should be fine tuned to the desired line.

As light as possible.

The material should not warp or warp when exposed to the elements.

Should rest on a firm basis.