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. CMU offers 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. The product also natural sequesters 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. The mix will have a high slump rate. 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 going on 80 years. In that time ORCO has created improvements not only in 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). Even by the Carbon Leadership Forum’s standards for concrete block, ORCO’s average carbon impact is well below the baselines. 

All ORCO Concrete Block, including non-load-bearing units like breeze block and wall caps, are manufactured to the ASTM C90 Specification Standard. This means consistent performance, look and sustainability.  

Understanding the CMU Lifecycle 

The emissions savings of CMU’s composition – and therefore, its low embodied carbon output – set the stage early for long-lasting life and continual carbon emission reductions throughout its lifespan. While this discussion has focused on the choice of material on the front end, that choice impacts every other factor in a building’s longevity, functionality, and maintenance needs – all which factor into emissions.  

Consider how the choice to build with CMU affects these other components of life cycle costs beyond the initial build: 

  • Energy Use – Strong natural insulation (and options for additional support through pre-insulated block types) regulates temperature and cuts down on energy usage. 
  • Wear & Tear – With no maintenance requirements beyond aesthetic changes like painting, CMU doesn’t get replaced in a matter of years, but many decades – and less replacement and refurbishment means less emissions through the production of those replacement components. 
  • Environmental Hazards – CMU withstands harsh impacts from wind and pressure, is non-combustible, and can be easily repaired – all lending itself to greater resiliency and less waste 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 reclaimed and reused for future construction. 

In short, concrete pays for itself over the course of its lifetime, offering savings that other materials simply cannot match – both financially and environmentally. 

When considering the types of structures commonly built with CMU – structural and aesthetic walls, public works such as schools and city halls, and critical infrastructure such as water pump stations – it makes sense that the system with the longest lifespan and least amount of required maintenance is the standout choice. And by understanding how CMU also combats carbon emissions, bringing those benefits even further in a consistent environment has never been easier.  

Sources: