If you were hiking through the snow, and you knew that 40 per cent of your bodily heat loss was coming from your head, you’d wear a thick hat to stay insulated and warm. In this article, Laurent Morel, segment owner for building, construction & infrastructure (BCI) at global composites manufacturer Exel Composites, tackles historical misconceptions about composite materials and explains how they can help mitigate the 40 per cent of heat lost from modern homes through windows and doors.
Image Credit: Exel Composites
Composite materials, such as fiberglass and carbon fiber, are no longer new, unfamiliar resources for building and construction. After the invention of fiberglass in the 1930s, and carbon fiber in the 1960s, more and more uses for these lightweight, utility materials have been devised, from sporting goods and defense equipment to telecommunications and, of course, building, construction and infrastructure (BCI).
However, some concerns persist about the suitability of composites for use in construction. In the past, they have been perceived to lack long-term durability, to be too difficult to install and work with, and to have underdeveloped regulatory codes and standards. Before we tackle those concerns, though, why should we bother with composites at all?
Are Composites Really Better?
Composite materials have a unique combination of mechanical performance, thermal efficiency, stability, and longevity that make them perfectly suitable for BCI applications. Their inherent corrosion resistance can contribute to longer service lifetimes and lower maintenance costs. This invulnerability against corrosion by the salty, moist conditions of the seaside makes composites especially popular for coastline infrastructure.
Another advantage of composite materials is their strength-to-weight ratio. Particularly in large, complex structures, lightweight composites can provide great structural strength while reducing weight compared to steel or concrete. Steel rebar is approximately four times the mass of fiberglass rebar of equivalent size, yet has roughly 20 per cent less tensile strength.
However, one of the key characteristics of composites is their superb thermal insulating ability. The 40 percent heat loss figure from a building’s windows and doors, when using conventional metal frames, highlights the importance of properly insulating these spaces.
The difference in thermal performance between aluminum and glass fiber reinforced polymers (GFRP) is stark. Aluminum has a thermal conductivity value of 237 watts per meter-kelvin (W m-1 K-1) while GFRP’s value is generally accepted to be <5 W m-1 K-1, although it can sometimes vary based on resin type, volume fraction, and other factors. This insulating power is critical for the thermal barriers that keep houses, offices, and other populated buildings warm.
Another strength of fiberglass specifically is that its coefficient of thermal expansion is very close to that of the glass that makes up window panes, 4.43 × 10−6 °C-1 and between 5.9-10 × 10−6 °C-1 respectively. This creates a thermal barrier, rather than a thermal bridge through which heat can escape. Both the window frames and panes will expand or contract based on atmospheric conditions, so the proximity of these thermal expansion coefficients means that minimal gaps appear between them.
What has Held Composites Back?
It is unsurprising that architects and construction workers can be reluctant to use materials they aren’t familiar with. In most industries, the methods and information that decision-makers learn during training and education tend to stay popular until the next generation of decision-makers comes along.
In BCI applications, this might be using aluminum window frames for their thinness and durability or steel-reinforced concrete for industrial port berths for its strength and impact resistance. However, when more suitable materials become available, the attachment to traditional methods can hold back intelligent design and construction professionals.
A lack of national and international regulatory codes has also slowed the rise of composites as building materials. Standardized testing, and prescribed design guidelines and construction practices, are central to safe and reliable built environments.
Although the European Commission for Standardization (CEN) has published a second generation of the Eurocodes in 2023 that does advise on composite material use, this has not always been the case – and engineers over many decades have become accustomed to complying with standards that govern traditional materials like wood and metals.
Organizations like the International Conference of Building Officials (ICBO) and the Building Officials and Code Administrators (BOCA) in the US published guidelines on using wood and metals decades ago. Even further back, the Metropolitan Building Act was established in the UK in 1844. These standards have been around for many years and have allowed engineers to learn about, use, and grow comfortable with traditional building materials. Composites have some catching up to do.
Composite manufacturing processes determine the aesthetic properties of the product – they are ‘baked in’: the visual features of composites can come directly from manufacturing with no post-processing needed. But like wood, composite materials can also be sanded, painted and stained once machined.
Exel Composites is an expert in pultrusion and pull-winding. These are continuous manufacturing methods, suitable for volume manufacturing, that enable it to provide composite materials on a large enough scale to supply BCI projects with fiberglass, carbon fiber, and more.
What’s the Truth About Composites for BCI?
While all the concerns we’ve covered here were valid at one time or another, the outlook for composites is very different in 2024. Composites manufacturers have precise control over the aesthetic properties of their products, new legislation has been introduced in nations across the world to better regulate composites in construction, and continuous manufacturing techniques have enabled optimized, efficient production.
Among the aforementioned Eurocodes is the new CEN/TS 19101: Design of Fiber-Polymer Composite Structures. This technical specification, to be trialed for 2 to 3 years before verification, will guarantee that composite materials adhere to high standards in use for building, bridge, and other civil engineering project designs.
In the United States, the American Society of Civil Engineers (ASCE) Load & Resistance Factor Design (LFRD) aims to deliver similar assurances about the loads and resistances that various materials, including composites, can withstand. These are important foundational steps to increase confidence in composites as building materials.
Great progress has also been made in the quality and design flexibility of composite materials. As a continuous manufacturing process, pultrusion produces profiles of uniform aesthetic, dimensional and structural performance and is well suited to consistent, high-volume production. In the pultrusion process, fiber reinforcements are pulled together, saturated with resin, and then pulled into guides that feed into a heated die to cure the composite, which is then cut to the desired length and machined as specified.
Selection of fiber veils, mats, fabrics, and even functional thermoplastic coatings contribute to the appearance and surface texture of the final product and can be used to achieve the desired appearance. This is especially useful for exterior building components and reduces post-processing costs, as pultrusion can incorporate the target aesthetic in-line during manufacturing.
Exel Composites is focusing particularly on helping their construction partners upgrade their process towards energy- and carbon-neutrality. In the European Union, buildings account for 36 per cent of CO2 emissions and 40 per cent of energy consumption.
Ultimately, it’s clear that there are still some obstacles to the widespread adoption of composites in the building, construction, and infrastructure industries, such as unfamiliarity with the material performance and navigating newer regulatory codes that dictate how civil engineers and architects can use them.
However, advancements in manufacturing techniques have resulted in composite materials that can be produced in sufficient quantities, with tailored properties, that architects and civil engineers who ignore them run the risk of ignoring good material options for their products.
Nowhere is this truer than window and door frame design. In a geopolitical climate that has seen energy prices soar by 262 per cent between January 2021 and 2023, perhaps it’s time to pull that woolly hat on after all.
To read more about Exel Composites’ solutions for better insulated windows and doors, read these case studies from its website.