Aug 14, 2015 - the creation of new green, or sus- tainable, chemical products. Researchers are increasingly adopting gre
Green Chemistry Impacts Construction Industry New sustainable non-toxic chemicals are gradually replacing hazardous substances in concrete, steel and asphalt production
By Paul Fournier
T
he ways that basic construction materials are manufactured and utilized are being transformed by the creation of new green, or sustainable, chemical products. Researchers are increasingly adopting green chemistry principles to design new non-toxic products that are harmless to humans and the environment, help prevent or reduce pollution, and even reverse the effects of accumulated hazards caused by centuries of industrial activities. At the governmental level, the Environmental Protection Agency (EPA) is strongly encouraging these efforts since they can reduce or eliminate the use or generation of hazardous substances and result in source reduction. While developments in green chemistry affect most industry sectors, from agriculture to mining, transportation, communications, and manufacturing, their impacts on the construction industry are especially far-reaching. And to some degree, green chemistry research and development has been underway for a number of years in the design and manufacture of concrete, steel and asphalt -- staples of the heavy, highway and building sectors of construction. These developments have been driven by the need to reduce the amounts of toxic substances being generated and the quantities of energy being consumed during manufacture of these materials.
Green chemistry additives are increasingly being blended with raw binder and aggregates at asphalt plants.
Federal Laws Prompt Changes Historically, changes in design and manufacture of chemicals to counteract pollution in the U.S. were prompted by enactment of federal pollution control laws. For instance, The Air Pollution Control Act of 1955 was the first United States Clean Air Act enacted by Congress to address the national environmental problem of air pollution. Later amendments (1970 and 1990) granted significant N14 August 2015
Cement Production’s Greenhouse Gasses
Employing green chemistry principles, the asphalt industry in 2013 produced 106 million tons of warm-mix asphalt and used nearly 74 million tons of recycled pavement and shingles in mixes.
more authority to the Feds including the establishment of The National Emission Standards for Hazardous Air Pollutants program. Passage of these laws and regulations led to the inventing of new chemicals and chemical processes to clean up air emissions from industrial and municipal activities. Similarly, discharges of pollutants into the waters of the U.S. began to be regulated under the Clean Water Act of 1972 (CWA). Under the CWA, EPA has implemented pollution control programs such as setting wastewater standards for industry, and has also set water quality standards for all contaminants in surface waters. This legislation sparked a flurry of activities by scientists and engineers to create new chemicals and treatment systems – primary, secondary and even advanced tertiary processes – enabling industrial, municipal and other facilities to meet the new water quality standards. It also led to the construction of billions of dollars’ worth of treatment plants throughout the country. Solid waste and hazardous waste were targeted by the Feds in 1976 when Congress approved the Resource Conservation and Recovery Act to address the increasing volume of municipal and industrial wastes. RCRA set national goals for protecting human health and the environment from the hazards of waste disposal, and also for energy conservation, source reduction and recycling, and managing waste. RCRA was the catalyst for developing entirely new chemical molecules to help industry and municipal facilities meet the new standards. But the Pollution Prevention Act of 1990 may ultimately turn out to be the most
influential environmental legislation. This Act established a national policy to have pollution prevented or reduced at the source wherever possible, and also expanded the Toxics Release Inventory. EPA notes that the Pollution Prevention Act focused industry, government, and public attention on reducing the amount of pollution through cost-effective changes in production, operation, and the use of raw materials.
From Renewable Feedstocks to End-of Life Although significant progress has taken place in making chemicals and chemical processes safe for the environment over the past 60 years, primarily due to various federal laws, much more remains to be done to solve the growing problem of toxic substances poisoning the planet’s land, water and air. And this is where green chemistry is seen by many as providing the solution to these vexing problems. To this point, the 158,000-member American Chemical Society says that scientists and engineers using principles of green chemistry in the design, development and implementation of chemical products and processes can protect and benefit the economy, people and the planet by finding innovative ways to reduce waste, conserve energy, and discover replacements for hazardous substances. Furthermore, the group notes that the scope of green chemistry and engineering principles go beyond concerns over hazards from chemical toxicity, and includes considerations such as using more sustainable or renewable feedstocks, and designing for end-of-life, or final disposition, of products.
One industry that contributes damaging materials to the planet is the manufacture of portland cement – the most common type of cement in general use around the world for making concrete and mortar. Cement is manufactured by heating limestone and other raw materials in a kiln at temperatures approaching 3,000 F to produce clinkers, then grinding the clinkers, and adding small amounts of other materials such as gypsum, fly ash or slag, depending on the type of cement desired. Cement manufacture requires immense quantities of energy, and releases harmful gasses, in particular, carbon dioxide, said to be the primary greenhouse gas contributing to recent climate change. Every metric ton of ordinary portland cement that is produced releases on average about 0.9 tons of carbon dioxide into the atmosphere. In 2014, world cement production was approximately 4.08 billion metric tons, according to the U.S. Geological Survey. The amount of carbon released into the atmosphere from this production is roughly 5 percent of all man-made carbon emissions. A scientific paper published in the International Journal of Sustainable Built Environment warns of the issues facing the cement industry. Co-authored by M. Imbabi, C. Carrigan and S. McKenna, “Trends and Developments in Green Cement and Concrete Technology” observes that the two most important challenges facing the cement industry are reducing carbon dioxide emissions and improving energy efficiency. The paper
Concrete is relatively non-toxic if proper work clothing is worn, but the manufacture of Portland cement, a key ingredient, emits huge amounts of carbon dioxide each year.
examines a number of remedies being researched and applied, and concludes that the most effective methods of producing environmentally and economically sustainable cements are the use of alternative, low carbon fuels and development of novel cement formulations and production methods. In other words, applying green chemistry principles.
Researchers are inventing new molecules in labs that can be applied to industrial processes to reduce the amount of greenhouse gasses contributing to global warming.
Steel Production Makes Green Progress The production of steel is another major consumer of raw chemicals and energy. More than 1.3 billion metric tons of steel is being produced annually worldwide, with most steelmaking facilities employing either the basic oxygen furnace (BOF) or the electric arc furnace (EAF) processes. In BOF processing, liquid pig-iron (molten iron) from a blast furnace and scrap steel are used as the main feed stock. Pig iron is the intermediate product from the blast furnace created by smelting iron ore with a high-carbon fuel such as coke, usually with limestone as a flux. In the EAF process scrap steel or direct reduced iron (DRI) are the main feed materials. According to the American Iron and Steel Institute (AISI), BOFs make up approximately 40 percent of today’s steelmaking in the U.S., and they use 25 to 35 percent old steel (scrap) to make new steel. The EAF process uses virtually 100 percent old steel to make new steel. EAFs make up about 60 percent of today’s steelmaking in the U.S. Globally, these percentages are reversed, with BOF processes taking the lion’s share. Both processes generate toxic byproducts. However, AISI says that during the last two decades the North American steel industry has invested billions of dollars in new technologies resulting in reductions in energy consumption, reduced carbon dioxide emissions, a reduced life cycle impact and increased volumes of steel scrap being recycled. Worldwide, green programs are making progress with more than 80 mil-
lion tons of steel recycled annually. In North America over the past 25 years, advances in steelmaking have cut energy consumption per ton of steel by 28 percent and carbon dioxide emissions by 35 percent per ton of steel shipped.
Asphalt Recycling Success Perhaps more than any other construction-related industry, asphalt production over the past two decades has embraced such green chemistry principles as energy conservation, waste reduction, and life cycle considerations. The industry recycles asphalt pavements at a rate of over 99 percent, according to a 2014 survey conducted by the National Asphalt Pavement Association (NAPA). The report estimates total plant mix asphalt production for the U.S. in 2013 was 350 million tons, of which 106.4 million tons was warm-mix asphalt (WMA). The survey also indicates that about 72 million tons of recycled asphalt pavement (RAP) and 1.7 million tons of recycled asphalt shingles (RAS) were used in new asphalt pavement mixes in the U.S. WMA technologies allow significantly lower temperatures for producing and installing asphalt mix, thus consuming less fossil fuels and releasing less carbon dioxide and other greenhouse emissions, with increased health benefits for workers. What’s more, these technologies ease mix compaction and allow colder weather paving. In addition, the NAPA report points out that reclamation and reuse of asphalt cement in RAP and RAS conserved more than 68 million tons of virgin aggregate and saved about $2 billion in 2013 compared to the use of 100 percent virgin asphalt binder. One of the problems associated with using large amounts of RAP and RAS in new pavement mixes is the higher viscosity (stiffness) and lower ductility of the embedded asphalt due to long-term aging in the field. This diminishes new pavement resistance to rutting and cracking. A remedy for this is to use an asphalt rejuvenator. Rejuvenators can restore the original properties of the asphalt binder. However, traditional rejuvenators may contain lubricating oil extracts and extender oils, which may be derivatives of benzene, a substance toxic to humans and the environment.
Case Study: a Green Chemistry Solution Since one of the goals of green chemistry is to discover replacements for hazardous
Leadership team for Warner Babcock Institute for Green Chemistry (WBI) and Collaborative Aggregates (CA): standing, left to right, John Warner, WBI President and Chief Technology Officer; Steve Viviano, CA Vice President Business Development; Melinda Furse, WBI Director of Marketing and Business Development; Jay Bianchini, CA Vice President Operations and Technology Liaison with WBI; sitting, left to right, Joe Pont, WBI CEO; and James Babcock, CA CEO.
substances used in the manufacture of existing products, creating an asphalt rejuvenator that is completely non-toxic, safe for workers and environmentally friendly was thus a welcome challenge for scientist/entrepreneur John C. Warner, Ph.D., President and Chief Technology Officer for Warner Babcock Institute for Green Chemistry (WBI). The Wilmington, Massachusetts, company that he heads recently invented an entirely non-toxic asphalt rejuvenator called Delta S, which allows the use of higher RAP and RAS content in pavement mixes and in lower doses serves as warm mix technology alone. Such products as Delta S are developed by a staff of more than 35 scientists in WBI labs. Founded in 2007 by Dr. Warner and Jim Babcock, WBI is essentially an invention factory where sustainable technologies are created for all industries producing or employing chemicals. About 85 percent of the research at WBI is performed under contract with companies needing or wanting new sustainable products for their own operations. The other 15 percent of research is spent on finding new technologies for WBI’s proprietary purposes. In line with this, WBI affiliate Collaborative Aggregates LLC was founded in 2014 to manufacture, market and sell engineered construction products developed by WBI. Delta S is one of those products. Another, currently under late-stage development at WBI, is a non-toxic, formaldehyde- and isocyanate-free thermosetting resin that is effective as an adhesive in engineered wood products. A different
kind of scientist, Dr. Warner successfully treads two seemingly philosophically opposed career paths – that of a researcher employing green chemistry to invent environmentally beneficial products, and that of a businessman making profits while fulfilling customers’ product needs. A pioneer in green chemistry, Dr. Warner in 1998 co-authored Green Chemistry: Theory and Practice, with Paul T. Anastas, Ph.D., which established the 12 Principles of Green Chemistry. The textbook was written to make budding chemists aware of the need to study toxicology and consider the effect that the manufacture and utilization of existing and new substances could have on the environment. In recognition of his work with green chemistry, Dr. Warner was awarded the 2014 Perkin Medal by the American Section of the Society of Chemical Industry for “innovation in applied chemistry resulting in outstanding commercial development.”
Scientists are discovering new products to substitute for toxic substances currently employed in manufacturing such construction materials as cement, steel and asphalt.
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