What Is Embodied Carbon?
Embodied Carbon refers to the emissions from design and construction choices when building a facility, such as the materials used and their manufacture, transportation, and installation. This differs from Operational Carbon which refers to the emissions produced when that building is in operation, including energy consumption from lighting, HVAC, and maintenance processes. Simply put, Embodied Carbon is what’s emitted to construct the building, and Operation Carbon is what’s emitted to run the building.
The architects, building owners and contractors understand that intentional and strategic material choices can significantly impact these elements when designing for sustainability. Concrete Masonry Units (CMU) offer benefits in both Embodied and Operational Carbon reduction efforts.
CMU is a low Embodied Carbon product due to its dry cast manufacturing. Very little cement and water are used which greatly reduce emissions. Dry cast products also naturally sequester CO2, which we will speak to shortly.
When used as the building shell, CMU is a mass wall product that helps regulate energy usage saving on energy costs which reduce Operational Carbon. CMU is also a low maintenance product providing a long life cycle compared to many other building materials. Not bad for a block with origins dating back over 120 years!
Block Composition and Concrete Contents
Not all concrete products are created equally, which will have an impact on emissions.
We can best explain the differences by breaking out concrete into two product ranges – dry cast which is comprised of concrete masonry units, concrete pavers, segmental retaining wall products and wet cast which is made up of poured concrete, like tilt-up buildings, precast concrete wall panels, poured concrete parking and driveways and poured concrete retaining walls.
Wet and Dry cast products share many of the same raw ingredients: fine and coarse aggregates and cement and water. The key differences come from the ratio of these aggregates with a major difference coming from cement and water usage. In both cases cement is common binding agent.
Dry cast products are manufactured using a mix that is akin to brown sugar. The coarse and fine aggregates are combined with cement and just enough water to hydrate the cement. In CMU production cement is used sparingly, enough to create the strengths required by ASTM. For dry cast products, this typically ranges from 8-12% of the overall mix, yet it is also the biggest embodied carbon impact. The mix is put into a mold which is subject to vibration and pressure to consolidate the aggregates within, which makes more efficient use of its cement. Dry cast units require little water as it does not need to flow like poured or ready mix concrete which also reduces impacts on our potable water supplies.
Wet cast concrete must be poured into the form it will take – such as being molded for sidewalk or vertical walls. To make the concrete flowable, the mix must be very wet, – and it will require additional water, cement, and plasticizers to strengthen its structure and remain workable for builders.
ORCO has been producing concrete masonry units for 80+ years. In that time ORCO has created not only process improvements to our machinery but also aggregate gradations and most notably in cement. Limestone is the predominant material used in cement production and through a process known as calcination, it is also a source of CO2 emissions. ORCO worked with its cement producer to create a cement that would incorporate uncalcined limestone fines thus reducing the CO2 emitted during the calcining process. We did this well over 30 years ago. You can say we were producing a low embodied carbon product before LEED became a thing.
The impact is noticeable in our Global Warming Potential (GWP) score on our Environmental Product Declaration (EPD). ORCO’s average carbon impact is well below the baselines established by The Carbon Leadership Forum’s standards for concrete block.
Understanding the CMU Lifecycle
This discussion has focused on the the low embodied nature of dry cast CMU units. CMU has many other beneficial attributes that impact a building’s longevity, functionality, and maintenance needs – all which factor into emissions.
Consider how the choice of building with CMU affects these other components of life cycle costs beyond the initial build:
- Energy Use – Thermal mass regulates temperature and cuts down on energy usage. Options for additional support through pre-insulated block types, make CMU a versatile choice.
- Wear & Tear – CMU buildings achieve a service life of 100 years. The maintenance required is minimal to framed structures. Less maintenance and material reduce lifetime emissions.
- Environmental Hazards – CMU withstands harsh impacts from wind and is non-combustible. CMU structures possess an excellent inherent resilience and high likelihood of complete serviceability reinstatement in the aftermath of a disaster.
- End Of Life – Few building materials can claim to be fully recyclable after tear-down, and CMU’s components can be crushed and reused as aggregate, including new CMU production. Crushed CMU will continue to sequester CO2 in it’s crushed form.
In short, concrete masonry pays for itself over the course of its lifetime, offering savings that other materials simply cannot match – both financially and environmentally.
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