REDUCING CARBON EMISSIONS FROM CEMENT PRODUCTION
Masonry construction has been around for centuries, predating the emphasis on being sustainable or green. Its many attributes have always been environmentally friendly. New technology is making the masonry industry even more so.
Sustainable development is defined by the World Commission on Environment and Development as development that meets the needs of the present without comprising the ability of future generations to meet their own needs. Masonry construction has always met this definition because of its energy efficiency, by reducing the heat island effect, by its thermal mass properties, by reducing its carbon footprint, by lowering life cycle costs and being recyclable. Most masonry products are made with regional materials, saving on transportation costs. Masonry construction, when designed properly, is resilient, an added benefit to help resist natural disasters or extreme weather events such as fire, tornados, hurricanes and earthquakes, minimizing loss of life and property.
History shows that builders from the time of the Romans to today have been constructing buildings to take advantage of masonry’s thermal mass, improving comfort for occupants by the material’s ability to absorb energy and slowly release it. Depending on climate zone, masonry cavity wall construction, with room for insulation, and inherent thermal mass, can reduce energy use by up to 50% over the lifetime of the building.
Changes to ASTM and ANSI cement specifications allow the use of 5% limestone additions to portland cement, reducing CO2 emissions and saving energy
Masonry systems for buildings and hardscaping can help minimize the urban heat island effect – an increase in microclimate temperatures in urban settings due to human activity – and thereby help reduce energy usage for cooling. Light colored masonry with high albedo absorbs less solar energy, moderating heat gain and higher temperatures.
Innovative Solutions Better for Environment
In recent years, production of construction materials and building practices have focused on profitability from first cost construction. Embodied energy from initial construction accounts for only 3-13% of the building’s lifetime energy consumption. Rising energy costs and demands necessitated that the construction industry change its ways. The US Green Building Council (USGBC) was one of the first groups to rethink how the construction industry looked at new building. The USGBC, founded in 1993, has made promoting sustainable-focused practices its mission. With its flagship tool LEED (Leadership in Energy and Environmental Design), USGBC is pushing the green building industry further by its certification process designed to inspire project teams to seek innovative solutions that are better for the environment, building occupants and communities. In just 20 years, LEED has revolutionized this industry and set the international standard for design and construction. The latest version, LEEDv4, aims to push the green building boundaries further by tightening its certification and making the program easier to use, but making it harder to reach certification levels. USGBC and LEEDv4 are helping architects and engineers design masonry in more environmentally-friendly ways than in the past.
50 Years of Change
The portland cement industry has reduced energy consumption for production over the last 50 years. Improvements in manufacturing have led to 40% reductions in total energy used to produce cement since the early 1970s. As a result, products based on cement, like concrete, concrete block, grout and mortar, have become more environmentally friendly.
Process, Ingredients and Fuel
Modern dry process plants use considerably less energy than older wet process plants. A dry-process plant moves fine materials pneumatically and reclaims heat in various stages of production for use in other areas. Wet-process plants use water to move fine materials, which requires more energy to remove the water before materials can be pyroprocessed (burned) in a kiln.
In an effort to reduce and conserve virgin materials, cement companies are using industrial by-products, or waste, in two ways:
- as a replacement for virgin materials in the raw mix as a supplemental fuel
- and by-products from other industries used as raw supplementary cementitious materials (SCM) in cement clinker production.
Typical materials include Taconite (an iron bearing, high silica rock used in steel manufacturing), fly ash (by-product of coal combustion in generating electrical power), granulated blast furnace slag cement (byproduct of the steel industry), foundry sand (generated by the metal casting industry) and mill scale (ferric oxide formed from hot rolling steel). Incorporating these waste products into cement saves valuable landfill space.
Industrial by-product materials used as supplemental fuels in the production of cement clinker are petroleum coke (a coal-like substance produced in the petroleum refining process), shredded tires, and automotive paint waste and solvents. Cement manufacture requires temperatures over 2700°F. High temperatures and long burn time ensure complete combustion of any byproduct fuel. Non-traditional fuels not only help save natural resources like coal and oil, but also dramatically cut down on emissions. Certain changes to ASTM and ANSI cement specifications allow 5% limestone additions to portland cement, which further helps to reduce CO2 emissions and saves energy. European and Canadian specifications allow even higher limestone additions.
Occurring during the kiln process, calcination of the carbonate material (limestone) results in the emission of CO2. Around 0.90 tons of CO2 is released into the atmosphere for each ton of clinker produced. The CO2 footprint of masonry and mortar cements is lower than portland cement and lime mortar. This is due to the clinker factor, the amount of clinker per ton of masonry, mortar or portland cement produced. The CO2 footprint is then approximately, 0.38, 0.56 and 0.90 tons per ton of material used in making mortar with masonry cement, mortar cement and portland/lime cement respectively.
Supplementary cementitious materials (SCM) can be used in the production of mortar for masonry construction. SCM may possess hydraulic or pozzolanic properties that contribute strength when used with portland cement as an ingredient in concrete and mortar. SCM can be added to the cementitious portion of the mortar or interground or blended into masonry, mortar or blended cements used in the production of mortar. SCM, when used in mortar production, give the added benefit of reduction in the clinker factor of the mix. Reducing the clinker factor lowers demand on limestone extraction reducing energy usage and lowers CO2 emissions, which reduces the carbon footprint even further. Two common SCM are granulated blast furnace slag and fly ash. If these products are not used by the cement industry, they likely end up in landfills.
Types of Mortars
Environmentally-friendly masonry mortars have been used since the turn of the 20th century. Modern masonry mortars for new construction are made from masonry cements, mortar cements and portland cement with hydrated lime. The Romans used lime and pozzolanic soils in their masonry construction thousands of years of ago. Hydrated lime was used in the 1800s. Portland cement was patented in 1824. Portland and lime mortars have been used for almost two hundred years. Masonry cements were invented in the early 1900s and mortar cements, the newest mortar in the industry, was invented in the 1990s.
In the US, between 10% and 15% of annual portland cement consumption is used in masonry construction
Using masonry cements and mortar cements to make mortar is environmentally friendly. They are formulated with ground limestone, which provides a lower environmental impact than portland cement and hydrated lime-based mortars. Masonry cements and mortar cements are produced with 25%-55% limestone and the balance clinker.
Chemistry of Mortar
Masonry cements, mortar cements, portland cement and hydrated lime mortars are all appropriate for use in mortar per American Society for Testing and Materials (ASTM) C270, Standard Specification for Mortar for Unit Masonry. Masonry cement must meet ASTM C91, mortar cement must meet ASTM C1329, and portland cements must meet ASTM C150. Blended hydraulic cements must meet ASTM C595 and hydrated lime must meet ASTM C207. ASTM C270 permits the use of each of these materials either by proportion or by property specification method. Proportion specification requirements state which materials to use in production of mortar and provides a recipe for each type of mortar. Property specification method permits the use of any of these materials as long as the mortar is demonstrated by testing to meet properties required by C270. For further explanation of proportion and property methods of specifying mortar, see Effective Mortar Specifications by Jamie Farny and Dan Zechmeister, PE, FASTM in SMART|dynamics of masonry v3.2 p 37, archived at dynamicsofmasonry.com.
Masonry Honors Sustainability
In the US, which is a mature masonry market, between 10%-15% of annual portland cement consumption is used in masonry construction. The US cement industry produced approximately 92 million metric tons (MMT) of portland cement last year and about 14 MMT of that is used in masonry construction. Selecting masonry and mortar cements helps make a difference in the environment by reducing CO2 emissions. But the CO2 savings related to mortar selection is only one aspect of the way that masonry benefits people and the environment.
Masonry remains among the most aesthetic, versatile, durable and low maintenance building systems in the world. When designed for wind resistance, masonry can withstand winds up to 250 mph and can help save lives. It can be used for safe rooms to protect occupants from tornados and hurricanes. It is fire-, wind- and blast-resistant. Masonry is non-combustible, does not give off toxic smoke fumes during a fire, and still maintains its structural integrity. Masonry is not a food source for mold and is easy to clean. When old masonry buildings come to the end of their intended use, they can be adapted for new uses or its components, like brick, block, and stone, can be recycled or reused in new construction, reducing effects of extraction and processing of virgin materials. Extending a historic masonry building’s life conserves resources, reduces waste, saves history and reduces the building’s life-cycle cost.
Most of the brick, block, sand and mortar used in masonry construction are produced from abundant raw materials that are locally available. This reduces the environmental impact of transportation and supports the local economy. The masonry crew is likely to be from the local labor force. Consequently, a majority of the money spent on masonry construction will go back into the local economy.
As one of the world’s oldest building materials, masonry continues to offer favorable attributes even today. New homes, schools and churches are built every day. Flexible unit masonry construction remains a preferred mode of construction for so many good reasons.
Masonry systems have proven themselves to be safe, comfortable and energy efficient over hundreds and thousands of years. Even better, next generation masonry materials continue to evolve to make these systems more sustainable.
William Barker is masonry manager at St Marys Cement, Inc. He is responsible for all package sales in Michigan. He is a member of the Board of Trustees of the Masonry Institute of Michigan and chair of the MIM's Cement Producers Standing Committee and Membership Committee and is active in the Michigan Mason Contractors Association and the Mason Contractors’ Association. Barker received a Bachelor of Business Administration from Western Michigan University. 313-849-4583 |[email protected]
Mortars and Grouts with 21st Century Cements. James Farny, Paul D. Tennis, and John M. Melander. 05/17/2015.
The Greening of Mortar – Story Pole Magazine 2008. William Barker
Masonry Cement: Setting the Standard for Mortar Materials for 75 Years. PCA, Jamie Farny, Summer 2007.
Masonry Power Point. Jamie Farny 2016.
USGBC – website, 09/2017.
LEED – website, 09/2017
Masonry Cement Mortars, A Laboratory Investigation, PCA, 1990. V.S. Dubovoy and J.W Ribar.
Masonry Cement: Product Data Sheet, PCA, 09/2002
Smart Dynamics of Masonry: Designing and Building Concrete Masonry Safe Rooms Using FEMA P-320. Jamie Farny 09/16/2017.
The Brundtland Commission Report, Our Common Future, (Oxford University Press 1987), The World Commission on the Environment and Development.