- Posted on October 8, 2018
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If you read my earlier post: "The Path to Net Zero - Part 1" (linked below) you would have noted that the following are major sources of CO2, the primary greenhouse gas (GHG):
- Electric production (16 Gt)
- Mobility (11 Gt)
- Iron & steel production (3 Gt)
- Cement production (2 Gt)
I have written on the first two subjects extensively, including renewable electric generation, electric vehicles, and impacts decarbonization might have on these in the future. I also posted a paper on the metals industry a few months ago: "I Like Smoke and Lightning, Heavy Metal Thunder" (linked below).
Now it's time for number four to receive some attention, and I've decided to include the (closely related) concrete industry, for a number of reasons. One reason may surprise you – self-mitigation, and with a little work, the cement and concrete industry may become a net-minus greenhouse gas (GHG) emitter.
2.Cement and Concrete Industry Energy Use
The cement and concrete products industry group (NAICS 3273) has annual revenue of $41 Billion (2012). Note that the referenced source only collects economic data every five years, and the 2017 data is not yet available.
Regarding the industries in this group, they share the main factor driving their sales – construction. Thus the Great Recession caused a downturn that they, as of 2012, had not recovered from. Thus between 2002 and 2012 this group shrank by an average of 0.8% per year.
The industries in this group are detailed below.
- Cement manufacturing (32731, $6 Billion/Yr. (2012), shrank by an average of 5.5% per year (2002 to 2012)) needs limestone feed-stock, so the manufacturing tends to be where limestone deposits are. This is mainly in Midwest, Mid-Atlantic, Southeast states, plus Texas and Oregon. As a result only 15% of this industry are located in high energy-cost states.
- Ready-Mix Concrete (32732, $21 Billion/Yr., shrank by an average of 0.5% per year) needs to be close to construction, and thus is near metropolitan areas in high growth states. Since these states are primarily in the Sun Belt, only 15% are in high energy-cost states.
- Concrete Block & Pipe (32733, $4 Billion/Yr., shrank by 0.2% per year): Given the value of each item, these products tend to be bulky and heavy resulting in high transportation costs. Thus, like the Ready-Mix these facilities tend to be close to their customers, but are less driven by new construction, thus 18.5% are in high energy-cost states (also note that shrinkage is less).
- Other concrete products (32739, $8.6, Billion/Yr., shrank by 0.4% per year): Similar to the Concrete Block & Pipe Sector. 18.4% are in high energy-cost states.
There are a large number of smaller facilities compared to other manufacturing categories. In 2015 there were 100 firms with more than 500 employees, but these firms had a total of 2,664 facilities with an average of just 24 employees each. In order to have a facility large enough to support an advanced energy system, it is estimated that 150 employees would be required, and it is estimated that there would be 300 of these facilities.
The energy consumption per year is a complex picture. Although the production of any industry is affected by the health of the economy, the cement and concrete industry is tightly tied to construction and can swing dramatically from year to year. The table below shows the production of the U.S. cement industry from 2007 to 2017.
Production (Million Metric Tons / Year)
Also there are two processes for making cement kiln feed material: wet and dry. The dry process is much more energy-efficient. When the demand for cement decreases, wet process facilities are mothballed, resulting in an overall reduction of energy use per ton of cement. In 2014 the energy use of the U.S. cement industry was 0.3 Quad, compared to over 0.382 Quad in 2006. Note that a Quad is a quadrillion (1015) BTUs or about 293 million MWh.
The market dynamics for the concrete products industries is similar to that described for the cement industry. Ready-mix concrete accounts for about 75% of the overall annual concrete production, followed by the production of concrete blocks and precast concrete (13%). Energy use for 2007 in various segments is shown in the table below. Units are Trillion BTUs.
One unique factor in the ready-mix concrete industry is that the delivery trucks (concrete trucks) are considered part of the production process, and thus their fuel consumption is considered part of production energy consumption. See the table and chart below for the breakdown of this consumption and cost per unit product for the ready mix sector.
The Concrete block industry follows similar energy consumption in the front-end of their process, except after the blocks are cast there is a curing process in a kiln. Typical kiln temperature is 90˚C. Kiln firing is the highest energy consumption for this process – see table below. Note that a “CMU” (concrete masonry unit) is the industry term for a concrete block.6
Other concrete products have energy metrics similar to blocks, with the specifics varying with product size, shape and composition (which are widely varied).
There appears to be some potential for CHP, especially in sectors that use kilns. Since kilns require relatively low temperatures, these can be heated by steam that is also used to generate electricity via steam turbines. Nine installations with a total capacity of 150 MW were noted in the CHP database.
Below we look at two time horizons: Short-term reductions are already being used, but have limited impact on GHG. Long-term solutions are required for complete decarbonization of this industry, but most are not currently being widely used.
3.1.Short Term Reductions
Portland cement is made by grinding and calcining (heating to high temperature) a mixture of clay and limestone. The resulting material, known as clinker, is ground to a ﬁne powder with 3–5% gypsum added to make Portland cement. The chemical reaction produced by calcining generates on average 842kg CO2/ton of clinker, and this represents about 60% of the total GHG by cement and concrete industry. The remainder is produced by combustion to produce process heat and provide transportation.
3.1.1.Substituting Other Materials for Portland Cement
Given the high percentage of GHG produced by the chemical reaction that produces Portland cement, reducing the amount of Portland cement in concrete products would reduce the GHG emitted in producing those products, if such a process can be done without reducing the quality of the products. The eliminated Portland cement is replaced by supplementary cementitious materials (SCMs) in mix designs, and this actually can improve the quality of the resulting concrete. 
The above is not a new development, "pozzolanic" materials were used in ancient times. Mixtures of calcined lime (Portland cement) and finely rounded, active alumino-silicate materials were pioneered and developed as inorganic binders in the Ancient world. Architectural remains of the Minoan civilization on Crete have shown evidence of the combined use of slaked lime and additions of finely ground potsherds for waterproof renderings in baths, cisterns and aqueducts. The use of volcanic materials such as volcanic ashes (tuffs) by the ancient Greeks dates back to at least 500–400 BC, as uncovered at the ancient city of Kameiros, Rhodes. In subsequent centuries the practice spread to the mainland and was eventually adopted and further developed by the Romans. The Romans used volcanic pumices and tuffs found in neighboring territories, the most famous ones found in Pozzuoli (Naples), hence the name pozzolanic.
Go through the link below to the Portland Cement Association's site for SCHs for more information on this.
3.1.2.Optimizing Transport of Ready-mix
Ready-mix concrete is the primary product in the cement and concrete products industry group, and virtually all of this is delivered to construction sites using concrete trucks. Delivered concrete frequently has a less than optimum consistency. For that reasons construction managers perform a concrete slump test. This test measures the consistency of fresh concrete before it sets. It is performed to check the workability of freshly made concrete, and therefore the ease with which concrete flows. If the concrete fails the slump test, the load is rejected.
Recently In-transit Concrete Management Systems have been developed that greatly improve the odds of the concrete arriving with the proper consistency. One such system is the VERIFI System. VERIFI is composed of sensors and devices that manage the flow rate (slump) of a concrete shipment from the ready-mix plant to the job site. While in transit, the system performs several key functions. It controls concrete mixing, using only the necessary number of drum rotations and harnessing excess energy from the truck’s engine whenever possible. It also measures the flow rate of the concrete, and can provide precise injections of water and water-reducing admixtures to achieve the specified slump upon arrival at the job site. Finally, VERIFI software tracks the movement of the truck along its route, identifying opportunities for improved fleet efficiency.
The following are the primary GHG reduction benefits of systems like VERIFI:
Cement Reduction: Various stakeholders in the production of concrete often add water to achieve the specified slump, but this can weaken the concrete – in some cases leading to concrete placement that eventually fails testing and must be torn out. To avoid such costly scenarios, concrete mixes are routinely “overdesigned” to include more cement than truly needed, in order to compensate for the addition of water. A conservative estimate is that 5% of the cement included in the design of a concrete mix is included only to hedge against these issues. Through precise and reliable quality control, VERIFI can reduce the overdesign needed to consistently meet a given performance specification. Reduction in concrete equals reduction in CO2 emissions.
Waste reduction: The National Ready Mixed Concrete Association estimates 5% of ready-mix concrete deliveries in the U.S. are rejected at the job site, typically because they fail to meet the specified slump at the time of delivery. The returned concrete is either crushed and used as road base, made into blocks, or simply discarded. All these scenarios require additional time, fuel use, and a duplication of the load of concrete. Because VERIFI software monitors and controls concrete consistency in transit, and the concrete is delivered more consistently within performance specifications. Early data indicates that this could reduce rejection rates from 5% to 3.8% – saving time, money, and materials. Since a typical concrete load represents 2.75 tons of carbon dioxide emissions, reducing concrete waste also benefits the environment.
Fuel efficiency: In ready-mix concrete delivery, fuel use is a significant source of cost and environmental impact. Approximately 23% of fuel in a concrete delivery is used for high-speed drum rotations that mix the concrete. The timing of these rotations is typically controlled by the truck driver – based on minimal information about concrete consistency or fuel efficiency. In contrast, VERIFI software gives the driver instructions on the optimal number and timing of rotations. Early data suggests that the number of high speed revolutions can be reduced by 10%, representing significant cost reductions and associated reductions in GHG.
The author did not perform an extensive survey of the above systems, and it could be that there are other systems equivalent to VERIFI. However, the manufacturer of verify did provide very good information on the operation of this systems and its GHG benefits. The link below is to the manufacturer of the VERIFI system, GCP Applied Technologies.
3.2.Long Term Solutions
3.2.1.Sequestration via CO2 Admixtures
This technology is approaching implementation vs. the solutions below that are years away from this stage. A Canadian firm, CarbonCure Technologies has developed this technology, and this firm is well funded via well-known "breakthrough" environmental venture capitalists, including Breakthrough Energy Ventures with the participation of GreenSoil Building Innovation Fund, BDC Capital, Pangaea Ventures, 350 Capital, Innovacorp, Brightpath Capital Partners, Neo Ventures, the Shaw Group, Power Generations, and Carmanah Management.
This technology adds CO2 to concrete as it is being mixed. Although the percentage is rather low (25 lbs of CO2 per cubic yard of concrete), given the huge quantities of concrete that is used in construction, this technology can sequester a significant quantity of CHC. CO2 injected into concrete chemically converts to a mineral and will never re-enter the earth’s atmosphere.
The mechanism of carbonation of freshly hydrating cement was systematically studied in the 1970s at the University of Illinois. The main calcium silicate phases in cement were shown to react with carbon dioxide, in the presence of water, to form calcium carbonate and calcium silicate hydrate gel. Further any calcium hydroxide present in the cement paste will react, in the presence of water, with carbon dioxide. 
An admixture is a chemical that is added to concrete to enhance its consistency when pouring and/or other characteristics when hardened. Adding a CO2 admixture to a ready mix truck is described below. CO2 can also be added to a batch process and used for concrete blocks, bricks, pipes and other precast products.
The injection of CO2 varies depending on whether the customer has a central mixer operation or a dry-batch operation. In the case of a central mixer operation, a fixed CO2 outlet is positioned to inject the CO2 into the discharge hopper as the concrete is being dumped from the mixer into the truck. In the case of a dry-batch operation, the injection device is an extendable flexible abrasive resistant hose housed inside a fixed position steel tube positioned next to the cement pipe. The hose is extended and retracted from the ready mix truck chute using an air cylinder controlled by the CarbonCure Technologies system and injects the CO2 after the other dry components have been batched. 
Strength Testing: Five batches of concrete were tested: a reference mixture, a reference mixture that used a proprietary non-chloride accelerating admixture, and three batches that were treated with increasing doses of carbon dioxide.
Concrete treated as described above were used to cast 100 to 200 mm cylinders for compressive strength testing at ages of 1, 3, 7, 28, 56, 91 and 182 days.
The concrete containing the non-chloride accelerator was 9% stronger than the reference at 1 day, ranged between 2 and 3% up to 56 days, and was 14% stronger at later ages.
Compressive strength measurements of the CO2-injected concrete batches revealed that the best results came from the lowest dose, which provided a 14% improvement of the compressive strength for the cylinders tested at 1 day and 10% at 3 days. It was functionally equivalent to the reference at ages beyond 7 days where the benefit varied between 1 and 8%.
At all ages, except for 91 days, the strength decreased as the CO2 dose was increased. The ranges of dosages used in the different batches indicates that an optimal dose of CO2 for strength development would be lower than 0.30% and likely on the order of 0.05% to 0.15%.
August 21, 2018 (from CarbonCure Technologies Web Site referenced above): Following an extensive year-long testing procedure at the U.S. Concrete National Research Laboratory in San Jose, CA, Central Concrete, a northern California business unit of U.S. Concrete, Inc. (NASDAQ: USCR), committed to a first phase roll-out which includes installing the CarbonCure Technology in its seven West Bay Area plants.
Additional case studies are on the CarbonCure Site.
A primary target for electrification would be the concrete truck. Although the author could not find any electric concrete trucks (or even prototypes), One Italian firm appears to make most of the drum and drive components required for this application (link below).
Bonfiglioli Riduttori S.p.A., https://www.bonfiglioli.com/en/mobile/products/electric-solutions/
Since several manufacturers have shown prototype Class-8 Semi-Trucks, and at least one (Tesla) plans to ship product in the next few years, cement trucks are not a great leap. Since these are mostly used in urban environments, I would think they would have a ready market.
3.2.3.Synergies with other Carbon Capture and Sequestration (CCS) Processes
There are probably 10 to 15 different processes for CCS, but two of the primary methods appear to be Amine Scrubbing and Calcium Looping. The latter process uses a revisable variation of the chemical process used to make Portland cement (see section 3.1). This is:
Calcination: Solid calcium carbonate is fed into a calciner, where it is heated to 850-950 °C to cause it to thermally decompose into gaseous carbon dioxide and solid calcium oxide (the main ingredient of Portland cemment). The almost-pure stream of CO2 is then removed and purified so that it is suitable for storage or use.
Carbonation: The solid CaO is removed from the calciner and fed into the carbonator. It is cooled to approximately 650 °C and is brought into contact with a flue gas containing a low to medium concentration of CO2. The CaO and CO2 react to form CaCO3, thus reducing the CO2 concentration in the flue gas to a level suitable for emission to the atmosphere.
A main problem with the above process is that the calcium oxide sorbent degrades as it is cycled. However, even though it is no longer suitable for the above proves it does appear to be suitable for use in Portland cement.
3.2.4.CCS in Clinker Production
The manufacture of cement consists of four major functions, described as follows:
- Mining: The raw materials used to prepare cement are primarily limestone, clay, shale, and silica sand. These materials are quarried, crushed, and transported to a nearby cement plant.
- Kiln feed preparation: Raw materials are proportioned to the correct chemical composition and ground to a fine consistency. Hot gases from the pyro-processing system (kiln) are used to dry the raw materials before they are fed into the kiln.
- Clinker production: The finely ground raw meal is fed into large rotary kilns where it is heated to about 1,500°C (2,700°F). The flame in the hottest part of the kiln can reach up to 1,870°C (3,400°F). This high temperature causes the raw meal to react and form complex mineral compounds which exit the kiln as small, dark gray nodules called “clinker.”
- Cement milling of clinker: The clinker is cooled and ground with approximately 5% content by weight of gypsum and other additives to produce cement.
Note that the document referenced above is from a DOE study by CEMEX, Inc. for the retrofit of a real plant (CEMEX's cement plant in Odessa, TX) to capture a majority of CO2 produced by the cement manufacture process (including coal combustion) as described above. The plant was to be retrofitted to reduce air-infiltration and increase the CO2 percentage at the stack to 21.7% by volume. The process selected was a Calcium Looping Process using RTI International’s Dry Carbonate CO2 Capture Process. The Calcium Looping process is described in the prior subsection. The calcium-based sorbent is was to be used as raw material for clinker production when depleted (see prior subsection). The following conclusion is in the referenced report.
CEMEX USA believes that the Odessa plant, production line #2, can be retrofitted to operate at commercial scale a proposed CO2 capture technology to capture >75% of CO2 from the cement kiln flue gas comprised of about 20%vol. CO2 for a total capture amount in the range of 160,000 to 180,000 metric tons of CO2 per year.
What about the remaining CO2? See section 4, Self-Mitigation.
3.2.5.Biomethane for Process Heat with CCS
Biomethane comes from biogas, which is generally produced by anaerobic digestion of bio-waste and also includes landfill gas. Biomethane is produced by purification of biogas to a composition that meets the specifications of a pipeline transmission system. In other words it’s no different in composition than any other “natural gas”.
There are a set of recently-defined regulations (at least in California) that allow biomethane to be delivered via the public gas transmission pipeline network. This will greatly expand the number of sources of biomethane and destination-consumers that can use biomethane.
The process for pipeline delivery will consist of the purchaser buying the biomethane. The biomethane will be injected at the production site, and withdrawn at the consumer’s site. The consumer will also pay a transmission charge to the pipeline company.
Process heat is required for both cement production and curing cast products in the concrete industry, and in the latter about half of this heat is currently furnished by natural gas.
In cement production facilities the exhaust of the process heat combustion can be combined with the CO2 from the Calcination process that produces clinker, and CCS can be performed as described in the prior subsection.
In concrete product production, a CCS process will need to be added to the exhaust of the process heat combustion. Calcium looping as described in the prior (and earlier) subsection is recommended for this, as the depleted calcium oxide can be used in the concrete production. The CO2 can be sequestered in the concrete as described in subsection 3.2.1.
The mortar, concrete, and rubble from demolished buildings can gradually absorb CO through a process called carbonation (as used in calcium looping CCS). As CO2 from the air enters tiny pores in the cement, it encounters a variety of chemicals and water trapped there. The ensuing reactions convert the CO2 into other chemicals, including water. Still, just how much CO2 the world’s cement soaked up had never been estimated until recently.
So a team of Chinese scientists, including physicist Zhu Liu, now at the California Institute of Technology in Pasadena, set out to do just that. Those researchers eventually teamed up with Steve Davis, an earth systems scientist at the University of California, Irvine, and other U.S. and European researchers. Together, they compiled data from studies of how cement is used around the world.
That included everything from the size range of concrete rubble and how long it was left in the open air, to how much cement was used in thick concrete versus thin layers of mortar spread on walls, where it’s exposed more readily to CO2.
Then they took things to the laboratory. Here, they calculated the carbonation rate in mortar and concrete in different settings—buried, in the open air, and enclosed in a room. The information formed the underpinnings of a computer model that the scientists ran 100,000 times to see how the final estimates changed as different variables were tweaked.
The results cast a different light on the cumulative impact cement has on the climate. The researchers estimate that between 1930 and 2013, cement has soaked up 4.5 gigatons of carbon or more than 16 gigatons of CO2. This is 43% of the total carbon emitted when limestone was converted to lime in cement kilns.
 U.S. Census Bureau, American Fact Finder, Advanced Search, Dataset: 2012 Economic Census, All available Codes.
 U.S. Census Bureau, 2013 SUSB Annual Datasets by Establishment Industry, U.S. & states, NAICS, detailed employment sizes (U.S., 6-digit and states, NAICS sectors), https://www.census.gov/data/tables/2015/econ/susb/2015-susb-annual.html
 “Cement Statistics and Information”, National Minerals Information Center, U.S. Geological Survey,
 U.S. DOE, Energy Information Administration, Manufacturing Energy Consumption Survey, Consumption of Energy for All Purposes, 2014, https://www.eia.gov/consumption/manufacturing/data/2014/
 Katerina Kermeli, Ernst Worrell, Eric Masanet, “Energy Efficiency Improvement and Cost Saving Opportunities for the Concrete Industry, An ENERGY STAR® Guide for Energy and Plant Managers”, Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA, LBNL-5342E, 2011. https://www.energystar.gov/ia/business/industry/downloads/Energy_Efficieny_Improvement_Cost_Saving_Opportunities_Concrete.pdf
 Lura Schmoyer and Miranda Intrator, West Main Consultants, National Precast Concrete Association, "Concrete Producers Paid to Reduce Greenhouse Gas Emissions by Substituting Supplementary Cementitious Materials for Portland Cement", 2010, https://precast.org/2010/07/concrete-producers-paid-to-reduce-greenhouse-gas-emissions-by-substituting-supplementary-cementitious-materials-for-portland-cement/
 CarbonCure Technologies, "Properties and durability of concrete produced using CO2 as an accelerating admixture", 2016, http://info.carboncure.com/white-papers/properties-and-durability-of-concrete-produced-using-co-2-as-an-accelerating-admixture
 CarbonCure Technologies, "Ready Mixed Concrete Technology System", 2016, http://info.carboncure.com/white-papers/ready-mixed-technology-system
 Simon Hadlington|, Chemistry World, "Putting the cement industry in the calcium loop", 2011, https://www.chemistryworld.com/news/putting-the-cement-industry-in-the-calcium-loop/3003350.article
 Warren Cornwall, Science, "Cement soaks up greenhouse gases", Nov. 21, 2016, http://www.sciencemag.org/news/2016/11/cement-soaks-greenhouse-gases