Emissions from the Cement Industry
A single industry accounts for around 5 percent of global carbon dioxide (CO2) emissions. It produces a material so ubiquitous it is nearly invisible: cement. It is the primary ingredient in concrete, which in turn forms the foundations and structures of the buildings we live and work in, and the roads and bridges we drive on. Concrete is the second most consumed substance on Earth after water. On average, each year, three tons of concrete are consumed by every person on the planet.
Concrete is used globally to build buildings, bridges, roads, runways, sidewalks, and dams. Cement is indispensable for construction activity, so it is tightly linked to the global economy. Its production is growing by 2.5 percent annually, and is expected to rise from 2.55 billion tons in 2006 to 3.7-4.4 billion tons by 2050.
Manufacture of Cement
Though “cement” and “concrete” are often used interchangeably, concrete is actually the final product made from cement. The primary component of cement is limestone. To produce cement, limestone and other clay-like materials are heated in a kiln at 1400°C and then ground to form a lumpy, solid substance called clinker; clinker is then combined with gypsum to form cement.
Cement manufacturing is highly energy- and emissions-intensive because of the extreme heat required to produce it. Producing a ton of cement requires 4.7 million BTU of energy, equivalent to about 400 pounds of coal, and generates nearly a ton of CO2. Given its high emissions and critical importance to society, cement is an obvious place to look to reduce greenhouse gas emissions.
The production of cement releases greenhouse gas emissions both directly and indirectly: the heating of limestone releases CO2 directly, while the burning of fossil fuels to heat the kiln indirectly results in CO2 emissions.
The direct emissions of cement occur through a chemical process called calcination. Calcination occurs when limestone, which is made of calcium carbonate, is heated, breaking down into calcium oxide and CO2. This process accounts for ~50 percent of all emissions from cement production.
Indirect emissions are produced by burning fossil fuels to heat the kiln. Kilns are usually heated by coal, natural gas, or oil, and the combustion of these fuels produces additional CO2 emissions, just as they would in producing electricity. This represents around 40 percent of cement emissions. Finally, the electricity used to power additional plant machinery, and the final transportation of cement, represents another source of indirect emissions and account for 5-10 percent of the industry’s emissions.
Opportunities to Mitigate
Indirect emissions from burning fossil fuels to heat the kiln can be reduced by switching to alternative fuels, including natural gas, biomass and waste-derived fuels such as tires, sewage sludge and municipal solid wastes. These less carbon-intensive fuels could reduce overall cement emissions by 18-24 percent from 2006 levels by 2050.
Alternatively, efficiency measures can reduce the demand for fuel by addressing the production process itself (such as switching from inefficient wet kilns to dry ones) or through technical and mechanical improvements (such as preventative maintenance to repair kiln leaks). While some estimate that energy efficiency improvements could achieve emission reductions of up to 40 percent, some industry analyses suggest that producers may have already exhausted this potential. Without additional financial incentives (such as subsidies or a tax on carbon), further breakthroughs could be difficult.
Reducing emissions from the calcination process means looking to a material other than limestone. Blended cement replaces some of the limestone-based clinker with other materials, primarily coal fly ash and blast furnace slag. It could reduce CO2 emissions by as much as 20 percent, but its widespread use is limited by other environmental regulations (these substitutes can contain toxic heavy metals); the limited availability of substitute material; and some building code restrictions (blended cement can take longer to set).
Finally, CO2 emissions can be captured after they are produced through carbon capture and storage (CCS). In addition to traditional CCS methods, which are already employed in some power plants, concrete producers can actually use their own product as a sink for CO2. Through the process of accelerated carbonation, CO2 penetrates concrete and reacts with calcium hydroxide in the presence of water to form calcium carbonate; the result is stable, long-term CO2 storage. As a mitigation technology, accelerated carbonation can be achieved by exposing freshly mixed concrete to flue gases with high CO2 concentrations.
Adapted from a factsheet published in the GNCS Factsheet Series, available here.
[…] Madeleine Rubenstein noted in a recent post at the Earth Institute, one of the hidden killers of the industrial world, as well as a major point-source of CO2 […]
I am assisting a waste to energy technology company to enter into the cement industry.
The plant requires waste input such as municipal garbage, including construction waste of a large volume. It outputs heat and electricity that can be used in the production of cement.
Any input you have to offer would be appreciated!
how bout this instead. We can actually absorb more CO2 than we create by producing HEMPCRETE rather than concrete. plus, it;s a better material, in every way. Look into it mates,
The automotive industry produces cars/trucks. The primary final assembly plant, and all the sub-supportive facilities, belch polluting emissions in response to ad driven demand (usually television). From there, the final product begins a new layer of pollution that is far more devastating than the birthing plant emissions from whence it originated. One can only begin to list coughing tail pipe emissions, spent tires piling up, windshield glass/dashboard plastic/seating foam/doors, body, and frame steel/ electronics copper wiring, and floor carpets- all insisting upon recycling attention. The same is true of the cement/concrete industry where the real pollution begins AFTER the slab concrete parking lot is no longer in use, AFTER the grain storage structure becomes obsolete, AFTER the cement bags are sent to the batch plant. Belching implosions, removals, and recycles are, many times, more in need of environmental consideration than originating production. And the real defeat is when the cement bags are sent to the batch plant for concrete slab end use. Please, not another earth smothering/heat generating parking lot. Madeleine’s stage one is a very alerting and informative article- we just need an equally alerting stage two article, because concrete is very hard to remove and very earth smothering. When there is high CO2 at the onset, and the end use stifles natures ability to make adjustments, a losing situation prevails.
Another waste of energy is making plastic bottles for drinking water – to make just ONE plastic bottle takes the equivalent of 2.5 times the volume of the plastic bottle in water.
Unfortunately, going from my own experience in the construction industry, very few firms would even consider spending extra money on these alternative solutions. I’ve worked with both great firms and shady cowboys and one thing they share is the desire to maximise profit, going green is normally the last thing on their mind.
Exactly why a carbon tax must happen.
Its a fact that most of the cement industry experts know that this industry emit huge CO2 and also also they have found some alternative fuels also, but still lot of natural resources are wasted which can reduce clinker percentage of a cement, We have to address general public in a simple language which we can educate them about cement types which have developed with less clinker.
does cement only emit co2 as a by product
I did a cement in room temperature no (CO2, power consumption & Electrical consumption). The produced cement is more higher in compressive strength and acid and fire resistance than ordinary Portland cement.
I am a student, currently learning about Trump’s solid concrete wall proposal and the DHS contractor bid hunt taking place which is now approaching Phase 2. I am trying to understand the dynamics of a 30 foot under ground and 50 foot over ground, totaling 80 foot concrete US Southern border wall and its effects to the environment. I do not agree with the idea, and I am interested in learning further just how insane this dream of Trump’s division really stands.
Stop. There is no answer to this problem. Cement has been developed over thousands of years. Portland cement is the strongest most cost effective material to use. Short of coming up with a whole new binder, ie a polymer, epoxy, nothing is going to change. Go after the other 95% of CO2 emissions. Large power plants can and are being replaced with wind turbines and solar farms. Transportation is next. Large consumers of energy are typically located near hydroelectric dams, ie aluminum manufacturing.
Don’t say there is no solution. Have a look at this: https://www.kapre.com/resources/contractor/is-green-cement-the-future-of-sustainable-construction/
I like Chad’s comment above about using hempcrete. Hemp is also replenishable and sustainable in near perpetuity. We have not utilized this amazing plant near enough.
I heard about cement emissions but did not know the exact impact on this world.
I am listening to a program from the Netherlands and am astounded about their historical impact on the world and their country since the 1700’s. (TV program: Buitenland), every Sunday. Of course America is getting the blame and Trump the worst.
The Netherlands, China, Japan, etc. are the worst in producing and using cement.
They do not look at the problem of excess water in their country caused by drying the lakes and building more landmasses, building houses, roads etc.
I am going to send a letter to this program with the same type of remarks. I am Dutch, came here in 1964 and am I glad to live here with my family.
7 billion pounds. Each ton of cement produces almost a ton of CO2. Most from the fossil fuel used to heat the kilns. Try Several billion tons per year.
How about the use of Geopolymer with Coal Power Plant by products such as Bottom Ash as an alternative to production of concrete? it has proven its use in low end applications.
what are the byproducts of cement industry?please can anyone help me with this?
How about this:
Visit Padang factory in West Sumatra
You will want to turn around before you get there
I couldn’t see down the Main Street near the complex
Thousands of people wandered around on their daily business
I am appalled by the standards Portland Cement operates under
It is killing people directly whilst capitalists go on their merry way
Visit factory in Padang West Sumatra
Appalling pollution in the main thoroughfare. Can’t see down the road
Portland has no respect for human life
Profane comments are subjective so hope comments don’t offend- We the people are killing our selves off through concreting over earth and blocking off air to survive. Building houses is killing us off just as are roads, anything concrett, versus letting the natural waters flow with growth to earth. Global warming is too late to save earth as technology and building will kill us all. Susan
If I understood this correctly the emissions are created in the process of producing the material. Not the excretion of co2 once the structure is erected. Heating the limestone releases co2 and the burning of fuel to heat the limestone produces more. So, work the fuel burning problem first. Wind, solar, nuclear produced electricity to heat the ovens. Then work the emissions from heated limestone problem. Recapture. Scrubbers. Or, switch to hempcrete like the other fellow said. But, keep in mind growing hemp requires vast areas of farmland. If we switch to quickly and the demand creates too much incentive farmers will grow hemp rather than food and I like to eat, so that’s a problem. Also, we already know some crops are devastating to the soil, corn for instance. Before we start growing large amounts of hemp we should ask some questions about its effects on the environment.
Solar furnaces could be the answer, there has been one working in France for many years and it can get to the required temperature to produce cement. I would have thought that putting these in the deserts of North Africa where the sun is hottest would make sense. Solar panels can’t work there because they overheat, but it would be ideal for a solar furnace. Cement ovens are tubular in shape and you could focus the suns rays using huge curved mirrors and direct the beam down the tube.
Great article! None of the links are working for sources, could you update them?