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In terms of greenhouse gas emissions, cement production is the third most polluting industry, second only to chemicals/petrochemical products and steel.

Last month, a study published by the University of East Anglia showed that once concrete is in place, an average of 42% of the greenhouse gas emissions associated with cement production are actually recovered from the atmosphere.

This is good news, if it is true, but efforts are still needed to reduce the carbon footprint of cement to prevent catastrophic global warming, and there is an opportunity to turn cement from a climate change villain to a climate change hero by making it carbon-negative-namely In other words, more carbon dioxide is absorbed from the atmosphere than used to produce carbon dioxide.

This article explores the properties of cement and concrete, ways to reduce the impact of their current production processes, and new alternatives and production methods that, if successful at scale, will eliminate greenhouse gas emissions during their life cycle.

All in all, there are about 63 ways to reduce the impact of cement on global warming.

Concrete is made by bonding different proportions of coarse aggregates with cement that hardens over time. Most of the concrete used is lime-based concrete made of calcium silicate, such as Portland cement. The main ingredient is limestone or calcium carbonate (CaCO3).

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Portland cement is made by heating raw materials including limestone to above 600°C and then to about 1450°C for sintering. This emits carbon dioxide and produces calcium silicate ((CaO)3·SiO2). When it becomes liquid cement by adding water and exposed to the air, it will absorb carbon dioxide again, regenerate calcium carbonate (CaCO3) and harden.

This material is essential to modern architecture and is ubiquitous; the large ready-mixed concrete industry is the largest segment of the cement market (annual production of up to 4.3 billion tons), with an annual output value of more than 100 billion US dollars.

Most of the greenhouse gas emissions associated with cement production are due to the very high temperatures required for its production, but there are also large amounts of emissions associated with mining and transportation.

The International Energy Agency (IEA) estimates that by adopting best-practice commercial technologies, the global cement industry can save 28% to 33% of total energy use. So what are these?

Best practices involve energy efficiency savings in production and supply chains. According to the International Energy Agency, this may result in annual savings of 60 Mt CO2 (low-end) to 520 Mt CO2/year.

One of the most effective technologies is heat recovery and reuse, but this is still relatively untapped. Waste heat power generation is a form of heat recovery and reuse. The high temperatures associated with cement production can also be used to generate steam, which can then be used in steam turbines. This method has been widely used in China, which has more than 700 installations in the cement industry.

This web-based tool is based on MS-Excel and was developed to analyze the environmental impact of the production of concrete and its components (such as cement, aggregates, admixtures and supplementary cementitious materials).

This tool is not a traditional database that only considers directly affected resources (materials, energy, and water) and manufacturing emission inventories. For example, it only considers exhaust emissions from the transportation of concrete materials or emissions from power generation.

In GreenConcrete, the impact of each process in the production of concrete and its materials on the supply chain is evaluated. This makes it possible to analyze where the most savings can be made and what technological improvements can be made.

The primary energy (in the form of fuel and electricity) used in the entire production and transportation process is one of the main environmental impacts analyzed in this study.

Material substitution, such as adding waste and geopolymers to clinker, can reduce carbon dioxide emissions during cement manufacturing and save energy.

Clinker can be mixed with alternative materials, such as blast furnace slag, fly ash from coal-fired power plants, and natural pozzolans. The use of granular slag in Portland cement may increase energy use in the steel industry, but it can reduce energy consumption and carbon dioxide emissions during cement production by approximately 40%.

This Energy Star Guide for Energy and Plant Managers, Energy Efficiency Improvements and Cost Saving Opportunities in Cement Manufacturing, outlines more than 50 specific energy efficiency opportunities applicable to all stages of different production processes for different types of cement. This includes the use of high-efficiency roller mills, energy management and process control, reduction of kiln shell heat loss, use of waste fuels, conversion to kiln preheating, precalcining kilns, better maintenance and optimization of parts and systems, oxygen enrichment, and high-efficiency motors And variable speed drives, steel slag used in the kiln and so on.

Costs can also be saved at the end of the service life of the concrete structure. Currently, only 50% of concrete is recycled for use in new construction projects (compared to the 99% recycling rate for steel structures).

The downgrade cycle does help reduce the use of aggregate, but it does not help reduce the material supply required for new concrete.

There are also several alternatives to Portland cement that have less impact on global warming.

"Limestone-free cement can be achieved by chemical'activation' of by-product materials or by producing a series of magnesia-based cementing compounds," said Jenny Burridge, head of structural engineering at the British Concrete Centre. The following are the main ones:

This involves accelerating the carbonation of magnesium silicate instead of calcium carbonate at high temperatures and pressures, and then heating the resulting carbonate at low temperatures to produce magnesium oxide, and the produced CO2 is recycled in the process.

The use of magnesium silicate eliminates carbon dioxide emissions during the processing of raw materials. In addition, the required low temperature allows the use of fuels with low energy content or carbon intensity (biomass), making it possible to further reduce carbon emissions.

Like Portland cement, the production of carbonates absorbs carbon dioxide by carbonating part of the manufactured magnesium oxide using atmospheric/industrial carbon dioxide.

In recent years, it has been hoped that the manufacturer Novacem (a spin-off company of Imperial College London) claims that using this method to make a ton of cement absorbs 100 kilograms more carbon dioxide than it emits, making it a carbon-negative product – which could revolutionize the industry. However, problems arose in trying to expand production, and the company went bankrupt in 2013.

Calera's process involves capturing raw flue CO2 gas from industrial sources and converting it into calcium carbonate cement-based building materials. By converting the gas into solid form of calcium carbonate, it can permanently sequester carbon dioxide.

Commercial demonstrations include capturing flue gas from power plants and burning coal without concentrating carbon dioxide. The flue gas is in contact with the alkaline aqueous solution in the scrubber, which can effectively remove CO2 and calcium sources to form a special calcium carbonate product, which is then dried into a free-flowing powder.

It needs alkalinity and a source of calcium. Some industrial waste streams contain both, such as calcium hydroxide (Ca(OH)2). Another option is a separate stream, one for alkalinity, such as sodium hydroxide (NaOH), and another for calcium, such as calcium chloride, which can be naturally present or in the waste stream of existing chemical processes.

The result is a high-strength material that can be used to make concrete products without any other cement or adhesive systems, from countertops, plant supports and benches to fiber cement boards on commercial production lines, exceeding strength requirements but weight It is lighter than many existing cement board products.

SOLIDIA cement is a related product and process that can use carbon dioxide (for example from flue gas) to solidify concrete and is currently in the commercialization stage. Therefore, it requires less limestone, so it can be fired at a lower kiln temperature. Compared with ordinary Portland cement, it requires less energy and produces about 30% less greenhouse gas.

Celitement is a kind of cement substitute, which adopts the process developed by KIT of Karlsruhe Institute of Technology, Germany, and is produced at a temperature below 300°C. Therefore, it will require less energy and emit fewer greenhouse gases.

Celitement is calcium silicate, a raw material that already contains calcium (CaO) and silicon (SiO2), but the ratio is incorrect. It must be processed in an autoclave under saturated steam conditions, ground and added water.

All of these emissions are about 50% less carbon dioxide than Portland cement. But it is still in the research and development stage.

Alkali-activated cement and "geopolymer" cement gain strength through a chemical reaction between an alkali source (a soluble alkali activator) and a material rich in aluminate.

The source of alumina-rich materials will be other wastes-fly ash, municipal solid waste incinerator ash (MSWIA), metakaolin, blast furnace slag, steel slag or other slag, or other alumina-rich materials.

Their implied energy/carbon footprint is often lower than Portland cement (up to 80-90%, but this depends on the source of the aluminate-rich material).

Now the standard covers production: PAS 8820:2016 building materials.

It was created by David Stone and is partly composed of iron dust recovered from steel mills and is currently sent to a landfill. Stone applied for a patent for Ferrock and established a company called IronKast. The company is in the early stages of commercialization of the patent. The University of Arizona is testing and benchmarking the pilot implementation in the marine environment.

It does not emit carbon dioxide during the production process, and in order to solidify it, just like Portland cement, it needs carbon dioxide as a catalyst, making it carbon-negative.

When carbon dioxide dissolves in water, it forms carbonic acid. If iron powder is present, it will combine with carbonate molecules and precipitate out of solution as solid iron carbonate. The resulting material has higher compressive strength than mortar made of Portland cement.

However, due to the limited availability of iron powder, it will never completely replace all uses of Portland cement.

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Another alternative to concrete is Hempcrete, which is made of hemp and lime. Cannabis absorbs carbon dioxide from the atmosphere as it grows. Lime applied in this way will also absorb carbon dioxide in the atmosphere, making the material carbon negative.

Although it does not have the structural strength of concrete (its typical compressive strength is about 1MPa, which is more than 20 times lower than low-grade concrete, and its density is 15% of traditional concrete), the k value is between 0.12 and 0.13 W/mK, which provides some insulation value.

It can be used in many situations where concrete is currently used.

It also attracts attention for its breathability, which allows it to be used with building materials from other countries to create buildings with a pleasant internal atmosphere that are not affected by moisture or condensation.

Aether is a partner of Lafarge, a world leader in the field of building materials, and has two technical centers, BRE (UK) and the Institute of Ceramics and Building Materials (Poland).

Technically, this is a Belite-Calcium Sulfo-Aluminate-Ferrite compound. Tests have found that compared with pure Portland cement (CEM (I) type), ether produces 20% to 30% less carbon dioxide per ton of cement and has a compressive strength similar to Portland cement. A European standard is currently being developed.

However, this is still in the research and development stage; the key issue is that its hydration rate is very slow.

It has shown good prospects in the implicit CO2 substitution of cement, but lacks experience, lack of norms and standards, and some concerns about the availability and durability of raw materials.

Research on the recent start-up attempts in this field, low-carbon alternatives to OPC, concluded that these technologies are still in the early stages: "High-end cement science using new analysis techniques and modeling has just begun, marking the methodology Breakthroughs on the market."

It advocates "the cooperation of long-term research projects between interested industry partners and basic research institutions and resources as a necessary prerequisite for the progress of radical invention."

This is exactly the approach that LEILAC, the new collaboration between European and Australian partners, is taking.

The LEILAC (Low Emission Intensity Lime and Cement) project is experimenting with a new type of carbon capture technology called direct separation. To this end, it is about to build and operate a pilot plant at the Heidelberg Cement plant in Lixhe, Belgium.

This aims to capture about 60% of the total carbon dioxide emissions of the two industries without significant energy or capital losses, with a daily production capacity of up to 240 tons of cement, and to prove that the technology is strong enough to start expansion plans.

This technology has been proven on a commercial scale in Australia for processing magnesite-an ore similar to limestone, albeit at lower temperatures (760°C and 950°C exhaust temperature).

Calix, the company that runs the project, is the main partner of the project. It has partially calcined limestone, although about 70% is calcined in a 22-meter tube, there is no preheating. It uses catalytic steam calcination of limestone, dolomite and magnesite for cement and construction products.

As part of the European Union's Horizons 2020 plan, the project has received a grant of 12 million euros (A$17.3 million). Heidelberg Cement, CEMEX, Tarmac, Lhoist, Amec Foster Wheeler, Calix Limited, ECN, Imperial College, PSE, Quantis and Carbon Trust are all working hard to apply this key technology to the cement and lime industries.

All these partners recognize that the long-term future of the cement and lime industry, which is vital to many aspects of the European economy, depends on the reduction of its carbon dioxide emissions.

The independent elements of carbon dioxide capture, transportation and storage have been proven, but integrating them into a complete CCS process and reducing costs remains a challenge.

There are currently two large projects in Europe, Sleipner (operating since 1996) and Snøhvit (operating since 2008), which capture and store approximately 1.7 million tons of carbon dioxide.

However, this technology has not yet been applied to the cement or lime industries because traditional carbon dioxide capture methods are either too complicated or too expensive.

The new trial aims to do this by starting a complete front-end engineering design (FEED) phase. The results should be available in 2020.

When integrated into a new plant, or retrofitted to an existing plant that uses biomass or waste combustion, and uses the current best practices described above, by using "direct separation" technology, the total carbon dioxide emissions from cement production will be reduced by more than Compared with traditional fossil fuel burning lime and cement plants, 85%, there are no major operational problems, energy or capital penalties.

If you add 42% of the figure-the greenhouse gas emissions associated with the use of traditional methods to produce cement, which are now known to be absorbed by the concrete after the production of concrete-then this will mean that traditional concrete may actually be carbon negative .

This is undoubtedly a dream worth pursuing.

David Thorpe is the author of:

116 N. Matson Street, Kershaw, SC 29067. All of the above technologies have setbacks because they affect carbon content, do not increase PSI too much, do not have an internal heat generator, use corrosive, heavy metals or cannabis to break the company. The cost of finishing factories is too high. There is one main difference between geopolymer concrete and aluminum silicate concrete (no cement concrete). You can walk in 2 hours, drive in 4 hours, and land on Airbus in 6 hours. Add mica/glass beads and PSI 75,000. Fire resistant 3000 F. Do not add water or mud. Mica is an inert mineral. Manufacturing fiberboard, shingles, rubber, blocks, general catalysts, hydrogen, paper, cosmetics, medicines, medicines, paints, textile products, combined with Cs137 and toxic waste (landfills). Plastics, insulation, powder coatings, oil wells, muds and fracturing beads. Water filtration equipment. Both paddle mixers or concrete trucks on site need to be dumped. 1/3 of the cost of combined concrete and concrete blocks. Mesoporous inorganic polymer binders can combine organic and inorganic substances. Used as a filler for animal food and cat litter. Used for welding products. This mica is the only crystal that can be ground to less than 1%. It can be used to make anti-dirty bomb kits and control oil spills (used in combination with sawdust). It can be floated on the water and recycled or used alone. It can be deposited on the seabed and recovered from the environment or restrain damage. Compatible with a variety of waste products to make anti-microbial and anti-mildew construction products. Used to clean the room undergoing chemotherapy for immediate use. Used in the manufacture of bulletproof glass and vehicles. The mask, helmet, vest and door of the car can be removed by extension and pull down, which can be used as a police shield. Nanotechnology Global LLC. 116.N. Mason Street Kershaw, SC 29067

Calcined CCS works well, but still only reduces CO2 emissions by 60%. The existing technology of alkali-activated materials/geopolymers can reduce carbon dioxide by up to 80%, and can achieve 100% carbon dioxide-free emissions-examples of the use of geopolymer concrete include the University of Queensland Institute for Global Change Building and New Brisbane 30,000 tons of geopolymer concrete Wilkamp Airport in the west. VicRoads also includes geopolymer concrete in its specifications.

As I said in the previous article: Cement absorption of CO2 is a false economy, because it will lead to a decrease in the pH of the concrete and subsequent "concrete cancer". We design concrete to resist this carbonation to achieve a long life. If we want to include this 42% absorption, we need to consider the resources used to replace carbonated concrete.