3.14 Sustainable Materials



2.14 Sustainable Materials

In some cases, materials can be replaced by sustainable substitutes. Factors affecting a material choice are usually material properties, suitability for the job, availability and cost. In choosing sustainable material substitutes it may be that you have to compromise with one of the parameters for selectionsuch as strength, life of the materials, or cost. Below is an outline of materials and suggestions for alternatives.

Masonry can be used in place of concrete; it can be as strong and it releases lower emissions during its manufacture. However, must be still be bonded with cement, and it cannot be moulded or reinforced. The concrete industry is aware of the environmental effects of its actions, and in recent years that has been a move to to reduce the emissions and other detrimental effects of concrete.

Steel can sometimes be used as a substitute for concrete columns, beams, foundation piles. Although steel can be recycled, and you can do the same job with much less steel than concrete, it is more expensive and produces more emissions per unit mass or unit stiffness than concrete.

Timber can be used as a replacement for steel and concrete, it has a higher strength and stiffness per unit of embodied energy, but it is not nearly as durable. Also, it must be protected from fine rot. Timber will be looked into as a potential material for buildings in the next chapter.

Figure 2.14.1 Stiffness of various materials and embodied energy per stiffness

Source: MIT Opencourseware [see reference 3]

Figure 2.14.1 sourced from MIT opencourseware under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License

As shown in Figure 2.12.1 above figure, for a relatively similar stiffness there is a greatly reduced embodied energy for wood and brick compared to concrete, steel and aluminium. Note however that the stiffness is measured in compression only, and in many application compression and tension are required.

Bio-ethylene from sugar can be used as substitute for crude oil. Ethylene is less energy intensive, and has the advantage of being biodegradable. This conserved oil supplies and will offer less of a problem with waste issues. However, land is required to grow sugar cane and there are social and environmental problems with taking land away from growing food to growing plastics for consumer goods

It has been demonstrated that materials with a lower environmental impact can replace traditional materials, and should be considered in the design process by engineers. However, issues such as cost and lifetime of materials will be important factors in the decision making process.