By Johan van Wyk
I feel that the way that structures are currently designed for durability (and even the way the design code is written) is opposed to achieving a reduction in the carbon footprint of a structure.
The reason for this is that the current design methodology of durability concretes, calls for minimum cement contents (more cement), an increase in cover (more concrete) and the use of specific SCM’s (Supplementary Cementitious Materials, like fly ash and slagment) and aggregates, that sometimes have to be transported over large distances (increase in prices and use of more fossil fuel).
It is true that concrete is a dominant factor in embodied carbon, but reinforcing steel and structural steel has a minimum of 40% higher carbon footprint than concrete. In addition, the conventional waterproofing measures are PVC (plastic polymer), Bitumen (petroleum based hydrocarbon) and EPDM (synthetic rubber) based, which has a much higher carbon footprint than integral crystalline waterproofing systems. These conventional systems also comes at a higher cost, carries a shorter warranty time and needs a more frequent maintenance schedule.
It is important to note that the embodied CFP (carbon footprint) of a building is the sum of:
- CFP of all construction materials
- CFP of all construction operations
- CFP of all maintenance operations
- CFP of demolishing operations and disposal of used materials
By using a durable concrete mix with self-healing properties, the service life of a structure can be extended by 60 years and more. At the end of its service life, a building may either stay in service as is, or receive a new façade, monitoring and evaluation upgrades and be re-purposed to serve a similar design life. As a result, the total embodied carbon footprint, are either dramatically reduced or done away with entirely, effectively providing two structures with the CFP of a single structure.
Moreover, the cement and concrete that is “saved” becomes available for the construction of more infrastructure.
After all, the International Concrete Repair Institute Committee 160 notes that the most effective sustainability strategy for concrete and masonry structures is to avoid the need for repairs.
- This put’s the responsibility on the whole value chain on a construction project, to cooperate:
- Designers to design infrastructure with all the factors contributing to CFP in mind and to design structures that are easier and faster to build, using the latest technology available and with full, lifetime cost of ownership in mind
- Project managers to design the project with efficiency in mind, less individual operations and people on site will have less chances of things going wrong and less repairs
- Concrete technologists to design concrete mixes that are able to self-heal, that negate the need for repairs and maintenance, but with less cement
- Contractors to ensure that infrastructure is constructed right, first time
The skills, technology and knowledge is available, but it is clear that the current philosophy of “this is the way it has been done for years” will have to change.
