CNC Report 08.26.24 8.5x11 - Flipbook - Page 50
USE SMART CARBON MATERIALS
What materials are both durable and low in embodied carbon for integration in the public realm of use?
Material selection is critical to road, sidewalk, and bike lane design, directly impacting environmental
footprint. Choosing the right materials ensures longevity, sustainability, and user comfort while
minimizing maintenance requirements and resource usage.
1. Construction Phase Emissions
CO2 emissions mainly arise from the energy usage of construction machinery and equipment, along
with transportation of materials from manufacturing sites to construction areas. Cement and asphalt
are significant contributors to emissions in this phase, particularly cement. Cement production is
highly energy-intensive due to its limestone calcination manufacturing process, resulting in high CO2
emissions. Asphalt produces approximately 55% less CO2EQ compared to concrete.
2. Emission Reduction Strategies
Using recycled materials and implementing lower-temperature mixtures helps decrease emissions
during material production and construction. Some examples:
• Utilizing fly ash and blast furnace slags as cement replacements.
• Developing bio-based methods for bitumen further reduces carbon emissions.
• Adding crumb rubber from end-of-life tires to asphalt mixtures.
• Recycling asphalt pavement reduces the need for new aggregate extraction.
• Using recycled steel for reinforcement decreases emissions compared to traditional steel
production.
• Reusing construction and demolition wastes in the sub-base gravel road construction.
• Stabilizing fine soils with lime instead of dumping reduces emissions by decreasing the need for
virgin materials in embankment construction.
• Rubberized asphalt concrete (RAC) and reclaimed asphalt pavement (RAP) show significant
potential in reducing carbon emissions in asphalt mixtures.
Emerging solutions like carbon capture and storage, carbon sink, and renewable energy sources offer
promising avenues for emission reduction in the road sector and merit further research.
3. Roads and Sidewalks Embodied Carbon Spectrum
Asphalt accounts for nearly 90% of the carbon footprint in the construction of streets and sidewalks.
Depending on the material and thickness used, they are categorized as either low or high carbon
intensity. High-carbon asphalt emits 190 kgCO2/m3, while low-carbon asphalt emits 102 kgCO2/m3.
Streets typically have a depth of 40cm, while sidewalks have 10cm. Street replacement, Stages B3-B5
(Reference Appendix p139 for more detailed information regarding each of these factors), is estimated
every 30 years, with the new infrastructure retaining 80% of the initial carbon value. Concrete is the
highest carbon emitter due to limestone calcination, followed by asphalt which has nearly half the
carbon intensity. Pavers typically measure below 5kg CO2e/m²; however, some fall within the concrete
spectrum as they are made of concrete. Bricks have the lowest carbon intensity, which varies based
on color, density type, and burning time.
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archimania
Transsolar
KlimaEngineering
