A building framework gives the shape to a building but also underpins or supports the main structure. Sometimes referred to as the “skeleton of the building” the framework is subsequently clothed by the cladding and other external finishes to give the desired architectural or aesthetic effect.
Without the framework, the building may not be strong enough to complete its designated functions (ie carry floor loads) or withstand the forces of nature such as high winds or major storms.
Yet, as with many parts of modern buildings, until relatively recently, when selecting the most appropriate materials to meet the required functions of the framework, little heed was given to the effects of such materials on the environment. Little or no regard was had to the CO2 emissions or their overall contribution to global warming.
What’s currently used for a building framework?
Before we look at how things are changing, it’s worth reviewing the two major materials currently used for building frameworks:
Steel
Before 1800, metals played an ancillary role in building construction. They were mainly used for fixing masonry together or strengthening domes or arches and for roofing, doors, windows, and decoration.
The first metal used for traditional structural materials was cast iron which was used in bridge building around 1779, but the evolution of steel frame construction in the 20th century significantly changed how a building framework was designed and built.
Steel is uniformly strong, elastic, and workable, and its high resistance to all stresses can be calculated in detail. Steel structural members come in a variety of shapes, the commonest of which are plates, angles, I-beams, and U-shaped channels. These members can be joined by steel bolts or rivets or welded to produce fused joints.
The joints are as firm as the member and help distribute stresses between beams and columns. This was a fundamental change but had a major change to architectural design and building techniques.
Steel is usually protected against corrosion by surface coverings, although alloys such as stainless steel have been developed for exposed surfaces.
Concrete
Concrete is a manufactured mixture of cement and water, with aggregates of sand and stones. It hardens rapidly by chemical combination to a stone like solid of great compressive but low tensile strength.
Concrete was first used in ancient Egypt and then further developed by the ancient Romans. However, the technique of manufacture declined in the Middle Ages but became popular again in the18th century. Yet concrete had only a limited importance in architecture until reinforced concrete was introduced in the 1860s.
Reinforced concrete was developed to add the tensile strength of a steel mesh embedded before pouring the concrete to the compressive strength of mass concrete. The combination is much more versatile than either individual products of steel or non-reinforced concrete. It is ideal not only for constructing rigid frames but also for foundations, columns, walls, floors, and a wide variety of coverings.
What is the estimated CO2 contribution of frame materials both globally and within the UK?
On the downside, and this has been well-known for some years, but concrete currently accounts for about 8% percent of the CO2 being emitted into the atmosphere. This is far more than, say, the 2.5% of the aviation industry. Indeed, concrete’s contribution of CO2 is comparable to the entire agriculture industry, which stands at 9%.
Steel also is up there with concrete, with every ton of steel produced in 2018 emitting on average 1.85 tons of CO2, or about 8% of global CO2 emissions.
Clearly, if the construction industry is serious about working on global warming issues, alternative materials need to be found. These need to have a lower negative impact on climate change yet still meets the primary functions of concrete and steel and the minimum statutory requirements.
What are the key performance measures do framework materials need to adhere to?
Following are some of the main performance measures which building framework materials need to company with. Each of the items has its own performance standards and methods of measurement, methods of testing for compliance, and acceptability criteria.
Structural frame members need to:
- support own weight and transfer lateral loads to building frame;
- resist water penetration and excessive air infiltration;
- accommodate differential movement;
- resist thermal transfer through radiation, convection and conduction;
- limit sound transmission;
- provide rated resistance to heat and smoke;
- be durable as well as looking attractive for the long term;
- be cost effective
What other materials for building frames are being used around the world to improve sustainability?
Ferrock
This is a new material that uses recycled materials to create a concrete-like building material.
It is said to be up to five times stronger than concrete. Ferrock actually absorbs and traps carbon dioxide as part of its drying and hardening process which makes it not only less CO2 intensive than traditional concrete, but actually carbon neutral.
Ferrock can withstand more compression before breaking and is far more flexible, thereby resisting earth movements caused by seismic activity or industrial processes. One of the unique properties of Ferrock is that it becomes even stronger in salt water environments, making it ideal for marine-based construction projects.
Pre-cast concrete slabs
Pre-cast concrete slabs commonly are used for walls and building façades because they hold up well to all kinds of weather, but certain types can be used for floors and flat roofs, especially roof decks.
This type of concrete slab is formed at a manufacturer’s site and shipped in whole sections to construction sites. The outer layers often enclose a lightweight filler, such as foam insulation. Other versions are made entirely of concrete but have large, hollow air spaces, like concrete blocks.
The sustainability factor of pre-cast concrete slabs is higher than many traditional poured concrete options because the slabs often take much less energy to produce and assemble. Plus, pre-cast concrete can be properly cured in a controlled environment, instead of potentially exposing it to a variety of unfavourable conditions whilst being cured on a construction site.
Reclaimed or recycled metal or wood
Steel and aluminium are highly embodied energy materials due to the energy required to produce them. Energy is needed to mine the ore, heat and shape it and then transport it.
However, each time the metal is properly and efficiently reused or recycled into new products, its embodied energy is lowered, and the material becomes sustainable because the whole raw extraction and processing steps are eliminated.
Recycled metal is a long-lasting material that does not need frequent replacement. It tends not to burn or warp, making it a viable option for roofing, structural supports and building façades. It’s also water and pest resistant.
Reclaimed metals, such as plumbing components, can sometimes be used in their existing forms instead of having to be recycled and manufactured into a new product.
Wood also uses its embodied energy, which already is lower than metals because of its light and reclaimed wood can be used for a wide variety of building purposes, including structural framing, flooring, siding and cabinetry.
Final thoughts
In the ongoing processes of re-thinking construction techniques and materials, looking at the framework of buildings is an important part of the exercise. This is especially so given the high CO2 emissions of two of the more favoured materials, namely concrete and steel.
Alternative, new more sustainable materials are coming into greater use, as well as adaptations of or bi-products from existing materials such as Ferrock.
A good place to learn more about eco-friendly building materials is here, and this might stimulate some thoughts on how the construction industry needs to do more to combat global warming and better protect the environment.
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