COMPOSITE MATERIALS PART II

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By: Konstantin Gorchakov, General Manager, MRG-Composites

In the previous article, we covered ground on a brief background on the use of Composite Materials in history. Furthermore, we covered the major divisions (matrices and reinforcing elements) of the components of composites, and the way composite materials are classified or grouped – the zero-dimensional group, the one-dimensional group, and the two-dimensional group. Lastly, we described the main production technology of composites – the manual manufacture, manufacture by dusting, by pultrusion by winding, by compression and by RTM (resin transfer moulding).

We promised that in the next article, we would describe the applications in construction as well as the physical and mechanical properties of composites, and then discuss the pros and cons of these materials in today’s world. Thus in this article we will focus on the practical application of composites in civil and industrial construction.

The practice

Composites are new products in East Africa, although the technology of fibreglass reinforced bars (FRP-bars) has already established itself around the world.

This product – fibreglass reinforced bars (FRP-bars) – has more than 70 years’ history. During its existence, the technology has been greatly improved and has become available to a wide range of consumers. FRP-bars replace metal rebars, familiar to everyone, but they are cheaper and more durable, which reduces the cost of construction and increases the availability of housing.

At the moment there are tens of thousands of buildings around the world using FRP-bars, including more than 300 bridges in Canada, let alone skyscrapers there and in China and Japan. Even here in Uganda, there is a bridge in which renovation with this material was used and several buildings constructed.

Raw materials

Unlike metal counterparts, no recycled materials are used in the production of FRP-bars. All raw materials created specifically to produce products with high requirements for strength. The main materials are different types of resins and glass roving – the finest glassfibres, which are several kilometres long. The thinner the fibre’s diameter, the stronger the composite: at the moment, the most common fibre is one with a diameter of 0.024 mm and thinner.

If there is a task to increase the strength of the final product, glassfibre may be replaced with basalt or carbon fibres. It is important to note that in the production of this kind of material, only certified components are used.

Production process

In the previous article, we have already considered this method of manufacturing composites as pultrusion. It is this process that underlies the production of fibreglass reinforcement or FRP-bars. Starting from a special stack, the roving of the coils is passed through a bath containing a mixture of chemical components, where it is thoroughly impregnated. Next, passing through the calibration die, the excess resin is removed and returned to the impregnation bath. This phase  is extremely important, because the mechanical properties of the rod are dependent on the ratio of reinforcing material/binder. The formed cylindrical bar passes through the site of application of a periodic profile (rib). The necessary bonding with concrete is then achieved with further use in construction. Modern manufacturers apply from 1 to 4 ribs per rod, depending on the technology or customer requirements.

After that, a bar with ribs moves to a continuous furnace where, under high temperature, the glass transition process of the resin occurs and the reinforcement gains its strength. At the exit, a device designed to pull the rod through the entire technical process is installed and a cutting mechanism that measures the required length of the final product is in place to do its job.

The technology allows to produce a rod of any length, up to 5 km in one piece. Furthermore, the rebar is wound into coils which can be delivered in this form to the customer. If the rod is made more than 12 mm in diameter, then such products are delivered in the straight form.

After production, each batch of finished products must pass through a system of tests, according to international and local standards. Attention should be paid at this stage in order to avoid the use of substandard low-grade material.

Ecology

An important issue in the modern world is environmentally friendly production, operation and disposal of products. In this regard, the composites are really ahead in the industry. Around the world, a lot of research on the impact of composite materials on humans and the environment has been conducted. After the production, these materials are known to be completely safe and approved for use in medical institutions, schools and restaurants. During the production process, certain substances are emitted, but their concentration does not harm the environment. This is because, since these compounds are extremely unstable, they break down into environment-friendly substances, almost immediately, without harming the environment.

After the end of the life of the composites, the powders that have been produced in the process can be reused in the production or as a filler in concrete or other building materials.

The advantages and disadvantages

Every material has advantages and disadvantages when compared with the others. Here we shall consider only the major ones.

The advantages:

  1. The weight of fibreglass composites is 9 times lighter than metal counterparts, assuming both have the same strength.
  2. Their durability is 3.5 times higher than that of steel (compared with the brand of reinforcement A400).
  3. Their service life is up to 80 years.
  4. Fibreglass composite materials are cheaper than steel (assuming both have the same strength characteristics).
  5. Fibreglass composites can be produced in special lengths. This reduces the cost of construction and installation time.

The disadvantages:

  1. The modulus of elasticity for fibreglass composites is lower than that of steel.
  2. Fibreglass is dielectric, i.e. it is not designed for welding.
  3. Do not bend these composites. It is not possible to give the necessary shape on the construction site.
  4. Does not burn. However, after heating above 300ºС FRP-bars lose their properties of strength.

How to install them

Working with FRP-bars is easier than with metal. Due to low weight, transportation becomes easy and cheap. You can transport 100 rods of 12 metres each on a regular bodaboda, as rebars are delivered in rolls. It is possible to cut and install FRP-bars as well as metal. In cases when it is necessary to bend a corner, it is applied together with metal. When using, it is necessary to take into account the modulus of elasticity of this product.

FRP-bars can completely replace metal reinforcement. However, based on international experience and the level of construction in a particular region, the following recommendations can be made. Without recalculating the strength characteristics, it is easy to replace the metal with a composite in slabs, foundations and flooring, columns and load-bearing walls up to the 5th floor. Septic tanks, drainage systems, port and hydraulic structures, special concrete tanks for the storage and operation of chemicals. For example, when enriching gold-bearing ore, these are precisely the harsh conditions in which composites work perfectly.

For the floor slabs, beams and any suspended structures, special calculations are needed. In the world over several decades of exploitation of this material, enough research has accumulated and Design Codes have been created for designers with recommendations and calculation methods.

Safety of FRP-bars

By themselves, FRP-bars cannot harm health. However, when working with them, you should observe safety precautions as in any construction process. Since the material consists of fibres, they can cause splinters. When cutting the material, glass dust is formed. All these factors do not cause significant harm, but for comfort it is recommended to work in protective gloves, respirators and protective glasses.

The cost

Since the strength of this material is several times higher than that of the common steel, this allows the use of a smaller FRP diameter compared to the metallic counterpart. For example,  instead of using steel diameter Ø 12mm, FRP of diameter Ø 8 mm can be used , and for steel Ø 16mm,  FRP Ø 12 mm. The current cost of steel Ø16mm is Shs68 000 while FRP-bar Ø12mm costs Shs52,000.

 

 

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