Page 62 - 2023 Sustainability Report

ENVIRONMENTAL STEWARDSHIP

Cement Manufacturing

Carbon dioxide (CO ) emissions are an unavoidable component of manufacturing cement due to the nature of the raw
2
materials and chemical reactions involved. In particular, the calcination process that is chemically necessary to transform the
raw materials used in manufacturing cement has the side effect of driving out the CO naturally found in the limestone
2
which is the main ingredient of cement. It is this CO that makes up the bulk of emissions from any cement plant.
2
1 Limestone and other raw
materials quarried

2 Raw materials are ground
and blended

3 Raw materials are heated
to 2,850° F in a kiln

4 Heat transforms the materials
into pellets of “clinker”
5 Clinker is ground with gypsum
1 5 6
cement

6 Cement is stored and shipped
via truck or rail

7 Primary end use consumption
is concrete

During the calcination process, limestone is heated in excess of 2,800 degrees Fahrenheit. This breaks down the molecular
structure of the stone into clinker (mainly comprised of calcium oxide (CaO) compounds) and CO gas. While the solid
2
clinker is subsequently ground and incorporated into cement, the CO is emitted from the plant. In a modern kiln, more
2
than 50 percent of the Scope 1 GHG emissions are a result of this calcination process, with the remaining emissions
coming from the combustion of fuels needed to heat the kiln and the on-site generation of electricity. 1
Cement producers have limited ability to abate or reduce process emissions resulting from calcination due to the fundamental
chemical composition of the limestone. While awaiting development of commercial-scale carbon capture and storage
technologies that may provide new, practical means of addressing the CO emitted from limestone, cement producers must
2
focus on opportunities to use lower-carbon fuel sources and improving energy efficiency in the manufacturing process.

Carbon Capture and Sequestration

As recognized by a number of international organizations (including the International Energy Agency) as well as various
industry associations, the cement sector’s ability to limit GHG emissions levels in a manner consistent with the goals of the
Paris Agreement depends on successful future development and implementation of carbon capture and sequestration (CCS)
and other innovative technologies on a commercial scale. In fact, the IEA in its September 2022 report on the cement sector
states that in order to achive net zero and alignment with the Paris Agreement: “(s)harper focus is needed in two key areas:
reducing the clinker-to-cement ratio (including through greater uptake of blended cements) and deploying innovative
technologies, such as carbon capture and storage and clinkers made from alternative raw materials.” However, the IEA notes
in discussing CCS and other technological changes that “(a)ligning with that scenario (the net zero scenario) will require the
development and deployment of technology that is not currently available.” Similarly, further acceptance of even lower
clinker content cements by Departments of Transportation and ASTM in the United States will also be critical in allowing the
cement sector to achieve carbon neutrality across the value chain by 2050. We are monitoring these developments closely.
1 Testimony for the Congress of the United States House of Representatives Select Committee on the Climate Crisis hearing on “Solving the Climate
Crisis: Reducing Industrial Emissions Through U.S. Innovation”, September 26, 2019. Jeremy Gregory, PhD, MIT on behalf of the PCA.

60 2023 SUSTAINABILITY REPORT