Composite materials are amazing engineering advancements that have revolutionised all kinds of industries. From ceramic composites used in the heat shield systems of rockets to more common uses of wood composites in buildings, they are highly effective materials with significant advantages over non-composites.
This guide will break down exactly what composites are and their use in an area that impacts all of us – construction.
What Is A Composite?
A composite material is a combination of two or more different constituent materials with dissimilar properties. However, unlike mixtures or solid solutions, the individual constituent materials remain separate and distinct. The composite, in turn, has different properties from its individual constituents.
Composites typically offer one or more advantages over common materials, such as being more lightweight or more robust.
History Of Composites
Combining materials to produce something with better properties is not a new idea. Human-made composites have been around for thousands of years. Construction is one of the oldest uses of composite materials, with straw and mud combined to form bricks. Wattle and daub is a composite building process used for making walls and buildings. This process involved covering a lattice of wooden strips (wattle) with a material consisting of wet soil, clay, sand, and animal dung (daub). Its use dates back over 6000 years. Around five and a half thousand years ago, the Mesopotamians created plywood by glueing wood together at different angles to produce something unique to natural wood.
We have detailed guides for producing concrete dating back more than two thousand years. In Ten Books on Architecture, Roman architect and military engineer Vitruvius wrote about the various types of aggregate in the preparation of lime mortar and identified different solutions for different uses. For instance, he recommended using the volcanic sand pozzolana with limestone in a ratio of 3:1 for cement used in buildings. For underwater lime mortar, he recommended a 2:1 ratio.
Modern Composite Examples
Composites in construction have a long history, and they are even more prevalent today. There are a staggering number of impressive composites that provide many great benefits that far outcompete those of their individual constituents. Composites are found throughout buildings and structures of all kinds. They are present in everything from the concrete in the foundation to the cladding on the outside of the building.
Here are just a few of the many composites you are likely to encounter: (materials with properties and examples)
Concrete
Concrete is the most widely used composite material and construction material. Its usage in construction (by weight) is double the combined usage of steel, aluminium, wood, and plastic. Cement consists of a cementitious binder and aggregate typically rocky materials, sand or loose stones). Cementitious material is combined with water to create a cement paste. The paste is then mixed with the aggregates, binding them together in a stone-like substance once hardened.
There are many cement options, each engineered for specific uses. The binder and aggregates combination determines the cement’s strength, density, and chemical and thermal resistances. Concrete is a strong and inexpensive material that can handle a large compressive force. However, it has relatively low tensile strength, which means it has low resistance to stretching and will break apart. You can mitigate this through reinforced concrete which adds steel bars (which have high tensile force resistance) to the concrete.
Fibre-Reinforced Plastics
Fibre-reinforced plastics (FRP) are also among the most common, versatile and effective composites used today. They have extensive uses in construction and many other areas. Fibre-reinforced plastics are also known as fibre-reinforced plastics and (as the name suggests) consist of a polymer matrix reinforced with fibres. The fibres are typically glass, carbon, aramid and basalt. Other fibres such as paper or wood can be used too.
Glass Reinforced Plastics (GRP)
Glass is one of the more common components of fibre-reinforced materials. Different glass fibres offer various unique properties. They are used in insulation materials such as glass wool to trap air. There is a range of glass-reinforced plastic products. In construction, they are most prevalent in fibreglass. Fibreglass is popular for a variety of reasons. It is stronger than many metals by weight, more flexible (and less expensive) than carbon fibre and can be moulded into complex shapes.
Fibreglass is lightweight, making it easier to handle. It is, therefore, easier and faster to install than its metal and wood counterparts. Combine its lightweight properties with vacuum lifting equipment to make fibreglass installations a breeze. Furthermore, fibreglass’ strength makes it an effective and resistant material. Its applications in construction include:
- Piping
- Roofing laminate
- Door surrounds
- Over-door and window canopies
- Coping
- Cladding
Carbon Fibre
Carbon fibre reinforced polymers are popular for their high strength to weight ratio. It is extremely rigid. However, carbon fibre composites can be brittle. Carbon fibre can be reinforced with materials such as graphite to produce new composites with further benefits. Reinforced carbon fibre composites typically provide high heat tolerance in addition to their strength. Carbon fibre sheets can be used in conjunction with concrete to strengthen preexisting structures for repair or to increase load tolerance.
The major drawback of carbon fibre is its high price compared to alternative composite and non-composite materials. Though occasionally used in construction, it is most common in aerospace and automotive industries. Other industries generally opt for more cost-efficient alternatives. However, as the comparative price of carbon fibre comes down, it is reasonable to expect an increased adoption across industries.
Aramid Fibre
The third common FRPs is a class of heat-resistant synthetic fibres called Aramid fibres (aromatic polyamide). They have applications in the aerospace and military industries. It is also used as an asbestos substitute. In construction, aramid fibres are utilised to reinforce concrete, asphalt and thermoplastic pipes.
Metal Composites
A metal matrix composite consists of fibres dispersed in a metal matrix. Most commonly, this is steel, copper, or aluminum combined with ceramics or a second metal. The reinforcement material in metal composites can be used to change a number of properties including structural integrity, wear resistance, and thermal conductivity.
The benefits of composites to the construction industry are not limited to building materials. Some of the most common applications of metal composites are for tools. Tungsten carbide cutting tools, for example, use a metal matrix (often cobalt) to cement the carbide particles.
Composite Wood
Composite wood comes in various forms, each boasting incredible benefits. This makes wood composites widely used across the construction industry. The many possibilities allow for hyper-specific solutions tailored to particular applications for optimal performance. In addition to the required shape and dimensions, composite wood can be created to alter various properties such as exposure durability, stability and structural strength.
They are also a great way to make use of small or otherwise defected wood. Plus, some composite boards can be easier to work with.
Wood composites are created by binding or fixing strands, particles, fibres, veneers or boards of wood together.
Examples of composite wood include:
- Plywood
- Densified wood
- Fibreboard
- Particleboard
- Oriented strand board
- Laminated timber
- Laminated veneer
- Cross-laminated
- Parallel strand
- Laminated strand
- Finger joint
- Beams
- Trusses
- Transparent wood composites
Ceramic Composites
The other composite category of note is ceramic composites. Ceramic composites consist of ceramic matrix and ceramic fibres (where carbon and carbon fibres are regarded as ceramic materials). They are less common in construction, though their high temperature resistance makes them highly effective in aerospace applications. They can also be found in everything from break disks to gas turbine components.
Sustainability
Among their many benefits, many composites are also highly regarded due to their sustainability. Not all composites fall into this category, however. The chemical process of manufacturing cement, releases a lot of CO2. Yet, some composites are great sustainable options. Wood composites can be used in place of steel. The processes in manufacturing steel also produce many greenhouse gases, making wood composites a more environmentally friendly option.
Composite materials are extraordinary engineering feats. They offer countless advantages over other materials leading to better, longer-lasting and more sustainable construction. (Plus, they help us go to space!)