Waffle Mold and Its Importance in a Waffle Slab

Waffle mold is the main element for implementing the waffle slab. This type of slab is very popular in large construction projects due to its technical and economic advantages. In the following, types of waffle molds and their dimensions, application, and the price will be presented.

What is a waffle mold?

Waffle molds are made from plastic and available in different standard sizes. Utilizing these formworks will omit the unused part of the slab. Since the tensile strength of concrete is mainly satisfied by the steel bar reinforcement, only the ribs containing the reinforcement are kept where the remaining unused concrete portion below the neutral axis is removed, to reduce the self-weight of the slab. Removing the unused part of the concrete will provide lighter and more economic slabs than an equivalent flat slab.

In the last decade, various ideas have been proposed to remove this unused part of the concrete, but only a few of them have been implemented. One of the most widely used solutions is the plastic waffle mold which is made of polypropylene and can be used several times. The name waffle comes from the grid pattern created by the reinforcing ribs.

Differences between waffle formworks and U-boot and Cobiax molds

As mentioned before, many other solutions such as U-boot, Cobiax, and Bubble Deck molds are used to remove the un-working part of concrete. The main difference between these types of molds and waffle formworks is being reusable. Uboot and Cobiax molds are buried inside the slab and they can’t be used anymore. Whereas, waffle formworks are designed in such a way that they could be removed after the concrete is hardened, and reused elsewhere. This feature makes the waffle molds more economical.

Here are some of the advantages of the waffle formworks over the Uboot and Cobiax molds:

Low-quality materials that are sensitive to sunlight are often used in producing Ubot or Cobiax molds to make them more cost-effective. This attribute makes them vulnerable against and they could be easily damaged during transportation and implementation. The appearance of cracks in the formworks may lead to concrete entrance into the formwork and increase the dead load of the roof.

In the execution of hollow slabs such as Uboot and Cubiax, the middle part of the slab is removed, but tensile concrete remains. By using waffle mold, in addition to the middle concrete, parts of the tensile concrete are also removed. For this reason, waffle slabs need about 20% less concrete compared to other hollow slabs. In other words, 200 kg less concrete is used per square meter, which is very important from an economic and technical point of view.

Waffle formworks, as they could be used multiple times, impose a lower cost per square meter of roof compared to other molds.

Types of waffle molds due to their performance

Waffle mold plays an important role in the implementation of waffle slabs. Their shapes and dimensions specify the slab’s performance in load carrying. For example, in one-way and two-way slabs, one-way waffle molds and two-way waffle molds are implemented, respectively. In the following, more details of these two types of formworks will be presented.

One-way waffle molds

One-way waffle mold is used to execute a slab that is supposed to transfer dead and live load in one direction, and its performance is similar to the slabs with blocks and joists, but in waffle slabs in contrast to joist and block slabs, prefabricated joists are not used and the molds themselves create ribs.

One-way waffle molds’ dimensions

One-way waffle molds mainly consist of a series of U-shaped plastic parts with end pieces that are connected at the site with the help of special clamps and form an integrated rectangular cube mold. In this case, distance between ribs are typically 60 to 70 cm with 25 to 30 cm depth. The width of the ribs are varied between 12 and 14 cm.

Price of one way waffle molds:

The price of one-way waffles is quantified by price per square meter and many lateral such as quality of molds. In addition, the construction cost of the waffle slab is calculated separately.

Two-way waffle molds

Two-way waffle molds, as its name suggests, are used in the construction of two-way slabs, which results in transferring the load in both directions. In other words, the live and dead loads of the roof and ceiling are transferred to all around a beam. The two-way waffle slab uses cube-shaped formworks in which the load distribution is optimized due to the existence of precise dimensions and square shape.

Mainly, two-way waffle formworks could not connect to adjacent formworks like one-way waffle formworks, but Zagros Bana Company makes it possible for the first time. In the waffle formworks of this company, adjacent formworks could be connected by fasteners (some type of locks) to ensure accuracy and increase the quality of construction.

Two-way waffle molds, like the one-way molds, could be removed after the concrete hardened and final strength was achieved. These removed formworks could be utilized in other slabs and buildings. This advantage helps to reduce the cost of constructing the slab.

Two-way waffle formworks’ dimensions

Two-way waffle formworks are made of polypropylene and designed in a semi-cubic shape with holes for fastening with adjacent formworks. Two-way waffle formworks are very suitable for wide spans. These formworks are designed in a way that they could be transported easily. Two-way waffle molds are usually available in different sizes from 60 * 60 to 90 * 90. The height of these types of molds are 18, 25, 28, 33, 35, and 40 cm.

Price of two-way waffle formworks

The price of two-way formwork is usually quantified per unit which depends on various factors.

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