Maximising sustainability in construction: what strategies to adopt ?
Posted on Jul 5, 2023Author(s)
Aïcha Besser
Communications Manager
CLIMACT
Expert(s)
Dr. Numa Bertola
ENAC, EPFL
The construction industry plays an important role in shaping our built environment, but it also contributes to various environmental challenges. Faced with the growing urgency of combating climate change and preserving natural resources, it is essential to rethink traditional building practices and adopt innovative strategies that prioritize sustainability.
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This article is a follow-up interview to the CLIMACT online seminar, in order to delve deeper into the topics discussed:
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Could you give some examples of innovative strategies that can be employed to maximise the sustainability of existing buildings?
Dr. Numa Bertola: The main degradation processes in reinforced concrete, wood and steel are due to the presence of water. It is therefore essential to prevent structural elements from coming into direct contact with water. This is why buildings (roofs, facades, etc.) are generally coated to protect them. Where bridges are concerned, it is often impossible to avoid contact with the elements. What's more, the deposition of de-icing salts in winter catalyses the degradation process. These structures are therefore more prone to deterioration over time. Two strategies can be implemented to significantly increase a structure's lifespan:
- Real-time measurement of structural behavior using sensors: these tools enable real-time monitoring of changes in structural behavior (as opposed to a visual inspection every 5 years at present!), so that action can be taken before deterioration becomes too serious. The data collected by this "monitoring" often enables us to certify that the structure has reserves of load-bearing capacity, and can therefore be used for longer than initially planned.
- Use high-performance cementitious fibrous composite (CFUP) to reinforce the structure: CFUP is a new material that is both highly resistant and waterproof, and was largely developed at EPFL. A thin layer of CFUP (generally between 3 and 5 cm) on the exposed concrete surface is enough to protect and reinforce it. In this way, degraded structures can be rehabilitated and their useful life extended, as the degradation processes are halted. In addition to benefiting the environment by preserving the existing structure, this strategy is also more economical than replacing the structure. These qualities explain why this technique is beginning to be used on a large scale in Switzerland, and increasingly abroad. The Chillon viaduct and, more recently, the Riddes viaduct were saved thanks to CFUP.
How can the concept of reusing materials contribute to a more sustainable construction industry?
Dr. Numa Bertola: At present, many concrete structures in good condition are being demolished to be replaced by more "modern" projects. During demolition, these structures are "crunched", i.e. they are reduced to rubble with concrete tongs. They return to the state of "raw material". All the structural properties and history of the structure are lost. This rubble is then used as is for road sub-construction, or mixed with other materials to make recycled concrete. However, this is an energy-intensive process, and recycled concrete offers no real reduction in CO2 emissions compared with conventional concrete, since at least as much cement must be used.
Reuse is a much less energy-intensive alternative that involves carefully cutting the structure into large elements rather than crushing it. Concrete blocks or modules are extracted in this way, preserving many of the properties of the existing structure. These re-used elements are then transported and reassembled into a new structure, without the need for major alterations. The Re:Crete footbridge and the RebuilT project are two examples of reused concrete structures. This avoids both the generation of waste and the production of new materials. The environmental benefits are therefore unequivocal. Thanks to the reuse of materials, it is possible to reduce the environmental impact of the conventional demolition-new-build solution by up to 90%.
How do new strategies for more sustainable construction improve the existing environment while promoting environmental conservation?
Dr. Numa Bertola: Concrete alone is responsible for 8.6% of CO2 emissions worldwide, and creates regional stresses on natural resources such as water and sand. In Switzerland alone, around 40 million tonnes of concrete are consumed every year. Solutions must therefore be found quickly to reduce these impacts.
The buildings demolished in Switzerland today are generally in good structural condition, and their demolition is often the result of real estate operations such as densification or reprogramming. To reduce the negative impact of construction on the environment, it is essential to give priority to transforming the built environment wherever possible, rather than demolishing and then rebuilding. The three strategies presented (monitoring, CFUP, reuse) enable us to make better use of existing built heritage and avoid unnecessary consumption of resources. By preserving an existing structure, we safeguard its history and that of its users.
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