Concrete Masonry: An Optimized Low Carbon Wall

Angelus concrete masonry units and high SCM grout minimize carbon impacts compared to other systems.

Not All Concretes are the Same

Concrete block, or concrete masonry units (CMU) as cited in building codes, are not your typical concrete. The term "concrete" may evoke images of sidewalks, driveways, massive structures, and of course, buildings.

These are all forms of wet-cast, or poured-in-place (PIP), concrete and contain significant amounts of cement, cited so often as a major contributor to global CO2 emissions. While it isn't the only major culprit, or the largest emitter per product volume, it is the most recognizable and widely known. But is so practical and resilient that it's simply ubiquitous.

Not everything with "concrete" in its name is the same. CMU, though a type of concrete, has substantially less cement per volume compared to PIP concrete. Masonry grout, a type of concrete that fills the cells of CMU, is a very different concrete than PIP and can be altered to dramatically reduce its cement content with supplementary cementitious materials (SCM). (See Masonry Grout: Cement Replacement Studies.)

CMU Compared to PIP/Tilt-Up

As an example, let's examine a comparison of carbon impacts of tilt-up and concrete masonry. The flexibility of concrete masonry's components — CMU and masonry grout — offers exceptional low carbon potential.

Consider a structure with 100,000 square feet of wall area. This could be a large warehouse, industrial or office complex. We'll assume a 6-inch-thick tilt-up wall, and an 8-inch-thick concrete masonry wall. Of course, the tilt-up is all concrete; the concrete masonry wall consists of CMU and masonry grout.

System   Percent of Wall Mix Design
Cementitious Content
Impact: CO2
Cement Cement Replacement1
Tilt-up:   100% 7-Sack 15% Fly Ash 524 Tons -
Concrete Masonry: CMU 55% 2.5-Sack - 392 Tons 165 Tons
Less than Tilt
  Masonry Grout 45% 7-Sack 50% Fly Ash

The significant decrease in cement afforded by concrete masonry cuts 132 tons of cement. That equates to 165 tons LESS CO2 than tilt-up, or 2.6 pounds less CO2 per square foot of wall area.2

CMU have low cement usage and begin as a low-impact material. Masonry grout has enormous potential for cement and carbon reduction by using supplementary cementitious materials (SCM). Fly ash and fly ash/ground granulated blast furnace slag (or, slag cement) blends have been studied as SCM in high percentages, up to 80%. This research indicates high SCM masonry grout as a viable structural, sustainable, and economic alternative to conventional grout.1

There's More to Concrete Masonry

All of that is impressive and promising, yet Angelus Block has lowered the CMU-related CO2 even further with CarbonKind™ Low Carbon CMU.

The tremendous improvements offered with CarbonKind CMU provide a potent element to an optimized concrete masonry wall utilizing high SCM masonry grout. They're a powerful carbon-cutting combo. See Masonry Grout: Cement Replacement Studies.

And after its manufacture, CMU have exceptional carbon uptake potential, absorbing atmospheric CO2 at notable rates. See Carbon Uptake of Concrete Masonry

1 Bradfield, Maribeth, High Supplemental Cementitious Material (SCM) Grout Phase 2 and 3 Research, Masonry Chronicles, Winter 2010-11, Concrete Masonry Association of California and Nevada, Masonry_Chron_Winter_2010-11.pdf
As noted in this reference, page 6, certain levels of high SCM replacement should be tested at 42 days rather than 28 days. In most cases, this will not have a significant impact on the overall project schedule.

2 Siggard, Kurt, Less Cement - The Choice is Concrete Masonry, Concrete Masonry Association of California and Nevada.

Concrete Masonry: An Optimized Low Carbon Wall