Page 36 - 2020 Sustainability Report

ENVIRONMENTAL STEWARDSHIP

Our Cement Business

Cement and aggregates are critical components of building materials, such as concrete, and in the construction and
maintenance of roads, buildings, bridges and other infrastructure assets that are vital to economic growth and quality of life.
While it is well known that the cement sector is a significant contributor to global GHG emissions, a holistic approach that
takes into account the environmental impacts of embodied carbon during the entire life cycle of cement and concrete
building materials (including materials sourcing, distribution, use, productive reuse, recycling and disposal) means that
cement and concrete products can play an important role in a sustainable low-carbon economy.
Emerging research suggests that up to 25 percent of the CO originally emitted during cement production can be captured
2
over the lifecycle of concrete through the process of “recarbonation”. According to Cembureau, the European Cement
Association, recarbonation is a slow process that occurs in concrete where lime (calcium hydroxide) in the cement reacts with
carbon dioxide from the air and forms calcium carbonate. At the end of their useful life, buildings and infrastructure
(reinforced concrete structures) are demolished. If the concrete is then crushed, its exposed surface area increases and this
further increases the recarbonation rate. The amount of recarbonation is even greater if stockpiles of crushed concrete are
left exposed to the air prior to reuse. 2

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 fact, our GHG footprint is largely driven by the operation of our two cement
kilns and, in particular, the calcination process that is chemically necessary to transform the raw materials used in
manufacturing cement.

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 2 is emitted from the plant. In a modern kiln, more
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. 3

2 https://lowcarboneconomy.cembureau.eu/5-parallel-routes/downstream/recarbonation/
3 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.

34 2020 SUSTAINABILITY REPORT