Displaying items by tag: Fly Ash

Cement and concrete products with sustainability credentials have increased in recent years as societies start to demand decarbonisation. In spite of the recent drop in the European Union (EU) Emissions Trading Scheme (ETS) price, there has been a trend in recent years in the construction industry towards offerings with better environmental credentials. Indeed, this week’s position paper from Cembureau on a carbon border mechanism concerns directly the growth of these kinds of products within Europe. Typically, the higher profile projects have been slag cement or concrete implementations such as Hanson’s use of its Regen cement substitute in a London sewer project or David Ball Group’s Cemfree concrete in a road project also in the UK. In this short review we’ll take a selective look at a few of the so-called low carbon cement and concrete products currently available.

Table 1: Some examples of methods to reduce embodied CO₂ in cement and concrete. Note - the product examples are selective. In some cases many other products are available.

Looking at cement first, the easiest way for many producers to bring a lower carbon product to market has been to promote cements made using secondary cementitious materials (SCM) such as granulated blast furnace slag or fly ash. These types of cements have a long history, typically in specialist applications and/or in relation to ease of supply. For example, cement producers in eastern India often manufacture slag cements owing to the number of local steel plants. However, cement producers have more recently started to publicise their environmental credentials as they reduce the clinker factor of the final product. Alongside this though, in Europe especially, a number of so-called low carbon cement producers have appeared on the scene such as EcoCem and Hoffman Green Technologies. These newer producers tend to offer SCM cement products or other low carbon ones built around a grinding model. It is likely that their businesses have benefitted from tightening EU environmental legislation. How far cement producers can pivot to SCM cement products is contentious given that slag and fly ash are finite byproducts of other industries that are also under pressure to decarbonise. Although it should be noted that other SCMs such as pozzolans exist.

As will be seen below a few of the methods to reduce embodied CO₂ in cement and concrete can be used in both materials. SCMs are no exception and hold a long history in concrete usage. As mentioned above David Ball Group sells Cemfree a concrete product that contains no cement. Harsco Environmental, a minerals management company, invested US$3m into Carbicrete, a technology start-up working on a cement-free concrete, in late 2019.

Limestone calcined clay cements are the next set of products that are starting to make an appearance through the work of the Swiss-government backed LC3 project, more commercial offerings like FutureCem from Cementir and H-EVA from Hoffman Green Technologies and today’s announcement about ThyssenKrupp’s plans to fit the Kribi cement plant in Cameroon with its Polysius activated clay system. They too, like SCM cements, reduce the clinker factor of the cement. The downside is that, as in the name, the clay element needs to be calcined requiring capital investment, although LC3 make a strong case in their literature about how fast these costs can be recouped in a variety of scenarios.

Calcium silicate cements offer reduced process emissions by decreasing the lime content of the clinker lowering the amount of CO₂ released and bringing down the temperature required in the kiln to make the clinker. Solidia offers its calcium silicate cement as part of a two-part system with a CO₂ cured concrete. In the US LafargeHolcim used Solidia’s product in a commercial project in mid-2019 at a New Jersey paver and block plant. Solidia’s second core technology is using CO₂ to cure concrete and reducing water usage. They are not alone here as Canada’s CarbonCure Technologies uses CO₂ in a similar way with their technology. In their case they focus more on CO₂ mineralisation. In Germany, Schwenk Zement backed the Celitement project, which developed a hydraulic calcium hydro silicate based product that does not use CO₂ curing. Celitement has since become part of Schwenk Zement.

Solidia isn’t the only company looking at two complementary technologies along the cement-concrete production chain. A number of companies are looking at recycling concrete and demolition waste. Generally this splits into coarse waste that is used as an aggregate substitute in concrete and fine waste that is used to make cement. LafargeHolcim has Evopact for the coarse waste and Susteno for the fine. HeidelbergCement has EcoCrete for the coarse and is researching the use of fines. Closing the loop for heavy building material producers definitely seems like the way to go at the moment and this view is reinforced by the involvement of the two largest multinational producers.

Of the rest of the other low carbon cement methods detailed in table 1 these cover other non-Ordinary Portland Cement (OPC) such as geopolymer and calcium sulphoaluminate cements. The former are a type of alkali activated binder and generally lack common standards. The latter are similar to slag cements in that they are established specialist products with lower CO₂ emissions than OPC.

With concrete when trying to make a low carbon product the first choice is whether to choose a low-carbon cement as the binder or even not to use cement at all in the case of Regen or Cemfree. From here the next step is to simply use less cement in a concrete mixture. There are a number of ways to do this from optimising aggregate gradation, following performance specifications more closely, using strength tests like maturity methods and generally adhering to quality control protocols better to deliver more consistency. Read the Mineral Production Association (MPA) publication Specifying Sustainable Concrete for more detail on this. Using concrete admixtures can also help make concrete more sustainable by improving quality and performance at construction sites through the use of plasticisers and accelerators, by decreasing embodied carbon through the use of water reducers and by improving the whole life performance of concretes. The use of locally-sourced aggregates is also worth noting here since it can reduce associated transport CO₂ emissions.

More novel methods of reducing embodied CO₂ emissions in concrete include the use of geopolymer concrete in the case of Zeobond Group’s E-Crete or adding graphene as Concrene does. Like geopolymer cements, geopolymer concretes are relatively new and lack common standards. Products like Concrene, meanwhile, remain currently at the startup level. Finally, if all else fails, offsetting the CO₂ released by a cement or concrete product is always an option. This is what Cemex has done with its Vertua Ultra Zero product. The first 70% reduction in embodied CO₂ is gained through the use of geopolymer cement. Then the remaining 30% reduction is achieved through a carbon offsetting scheme via a carbon neutral certification verified by the Carbon Trust.

As can be seen, a variety of methods exist for cement and concrete producers to reduce the embodied CO₂ of their products and call them ‘low-carbon.’ For the moment most remain in the ‘novelty section’ but as legislators promote and specifiers look for sustainable construction they continue to become more mainstream. What has been interesting to note from this short study is that some companies are looking at multiple solutions along the production and supply chain whilst others are concentrating on single ones. The companies looking at multiple methods range from the biggest building material producers like LafargeHolcim and HeidelbergCement to smaller newer ones like Solidia and Hoffman Green Technologies. Also of note is that many of these products have existed already in various forms for a long time like SCM cements and concretes or the many ways concretes can be made more sustainable through much simpler ways such as changing aggregate sourcing or working more efficiently. In many cases once markets receive sufficient stimulus it seems likely that low carbon cement and concrete products will proliferate.

Global Cement is researching a market report on low carbon cement and concrete. If readers have any comments to make please contact us at This email address is being protected from spambots. You need JavaScript enabled to view it.

Sri Lanka: Norochcholai Coal Power Plant (NCPP) is courting buyers for its fly ash, of which it says it produces US$5.5m-worth annually. In 2019 NCPP sold US$3.3m to Sri Lankan cement producers. Daily News Sri Lanka has reported that the company has undertaken measures to increase the value of the fly ash to cement producers, in order to obtain a higher price. NCPP manager Indrasiri Gallage said, "By selling fly ash to cement producers the plant has also helped to free the country from reliance on clinker imports."

An expansion, including the installation of a new 300MW coal-fired power plant, will eventually bring the NCPP’s capacity to 1200MW. The plant is currently working to increase the value of its bottom ash for paving block production.

US: Charah Solutions has been awarded an extension to its contract to provide byproduct sales and material handling operations for Luminant’s Miami Fort Power Plant and Zimmer Power Plant in Ohio. Charah Solutions will continue to manage and market coal combustion products produced by these two units. It currently sells and markets grade Class F fly ash from the two power plants via its materials network to concrete product manufacturers and ready mix concrete producers in the Midwest, Northeast and South regions of the country.

In addition, Charah Solutions will continue all other coal combustion residuals material handling and disposal operations at both locations, including landfill management and byproduct loadout, as well as the operations and maintenance of the plant flue gas desulphurisation (FGD) system at Miami Fort.

UK: A study by the University of Dundee has dispelled the myths of substantial performance differences between concretes made with cement containing dry or wet-stored fly ash, with comparable reinforcement corrosion between the two.

Vertical News has reported that the research, whose backers included the Department for Environment, Food & Rural Affairs and Heathrow Airport Holdings, was aimed at “quantifying moisture effects, which indicate agglomeration of fly ash and a tendency for this to increase with free lime content, storage period and temperature.”

Researchers tested five moistened fly ashes and samples from two power station stockpiles, and further investigated different material and storage variables, comparing the concretes at 75mm slump and 28 day strength. Air permeability and water absorption of moistened fly ash proved greater with high free lime (up to 0.9%) and lower with low free lime (to under 0.1%). What benefits there were improved with longer storage. The moistening of low-free-lime fly ash generally yielded similar, or slightly higher, carbonation and chlorine diffusion. The moisture caused little change in high-free-lime ash’s carbonation, while increasing chloride diffusion. Furthermore, high storage temperature equated to greater carbonation.

In spite of these intriguing chemical differences, the study concluded, "these didn't seem to have a noticeable effect on concrete resistance.”

Charah Solutions has been steadily building up its fly ash distribution business in recent years with an eye on the supplementary cementitious materials (SCM) market. This week it opened the third of its new series of SCM grinding plants, at Oxnard in California, US. The unit sticks out because it is focusing on grinding natural pozzolans. The plant will receive natural pozzolan by truck and rail and then use Charah’s patented grinding technology to produce pozzolan marketed under its MultiPozz brand. The previous plants in this series mentioned natural pozzolans but this is the first to promote it explicitly.

The change is potentially telling because global demand for granulated blast furnace slag (GBFS) outstrips supply. Both performance benefits and environmental regulations are pushing this. It’s a similar situation for fly ash, also driven by trends to close coal-fired power stations in some countries. As Charles Zeynel of SCM trading firm ZAG International explained in the March 2019 issue of Global Cement Magazine, “...volcanic pozzolans are a potential SCM of the future. This is gaining traction, but it’s slow progress at the moment. This will be the answer for some users in some locations.”

The problem though is that natural pozzolans are down the list of preferred SCMs for their chemical properties after silica fume, GBFS and fly ash. The first is expensive but the latter two were traditionally cheap and easy to obtain if a cement or concrete producer had access to a source or a distribution network. Natural pozzolans are very much subject to variations in availability.

It’s no surprise then that Charah is promoting natural pozzolans in a Californian plant given that state’s environmental stance. It’s unclear where Charah is sourcing their pozzolan from but they are not the only company thinking about this in the US. Sunrise Resources, for example, is working on the environmental permits for a natural pozzolan mine near Tonopah in Nevada. As it described in its company presentation, California and Nevada are the most affected states in the fly ash supply crisis because they are, “...at the end of the line when it comes to rail deliveries from power stations in central and eastern USA.” It also estimated that California used 0.9Mt of pozzolan in its cement production of which about 90% is fly ash. The state produced 9.6Mt in 2015. Other companies are also mining and distributing natural pozzolans in the US as the website for the National Pozzolan Association (NPA) lists. Although, if this line-up is comprehensive, then the field is still fairly select. Most of these companies are based in the west of the country.

One last thing to consider is that various groups are tackling a potential future lack of SCMs for the cement industry by making their own pozzolanic materials through the use of calcined clay. These groups include the Swiss-government backed LC3 project and Cementir’s Futurecem products. Using clay should bypass the supply issues with natural pozzolans but the cost of calcining it requires at the very least an investment to get started.

As concrete enthusiasts often point out, a variant of pozzolanic concrete was used by the Romans to build many of their iconic structures, some of which survive to the present day. To give the last word to the NPA, “What is old is new again: natural pozzolan is back!” If environmental trends continue and steel and coal plants continue to be shut then it might just be right.

UK: Aggregate Industries has launched its Lafarge Endure SR, a CEM II blended cement product that uses fly ash. It says that the product has a lower embodied CO₂, has improved plastic and hardened properties when used in concrete and has enhanced suitability for all ground types. Lafarge Endure SR is resistant to sulphates, allowing contractors and suppliers to scope a wider variety of projects. It also uses 10% less water than CEM I products to reach a workable consistency and offers improved pumpability and mixing efficiency.

“As its name suggests, Lafarge Endure SR is designed to dramatically increase the longevity of the concrete it forms a part of. It is a great solution for contractors that want to reduce the environmental impact of their build while simultaneously improving its life span,” said Steve Curley, Commercial Director at Aggregate Industries.

Canada: Lafarge Canada plans to develop and demonstrate a full-cycle solution to capture and reuse CO₂ from a cement plant. Project CO₂MENT will demonstrate and evaluate Inventys' CO₂ capture system and a selection of CO₂ utilisation technologies at Lafarge's Richmond cement plant in British Colombia over the next four years. This project is being led by Inventys in partnership with Lafarge Canada and Total. It also received financial support from CCP (CO₂ Capture Project), the Province of British Colombia and Canada's federal government through the National Research Council of Canada Industrial Research Assistance Program (NRC IRAP).

"At Inventys, we see a real opportunity to build a CO₂ marketplace where tonnes of CO₂ are traded between emitters and users," said Inventys president and chief executive officer (CEO) Claude Letourneau.

Phase I of Project CO₂MENT, the Contaminant Program, will attempt to reduce harmful organic and inorganic substances, such as sulphur dioxide, dust and soot, as well as nitrogen oxides, from cement flue gas. Phase II, the CO₂ Capture Program, will separate the CO₂ from flue gas using a customised-for-cement version of Inventys' carbon capture technology at pilot scale. Phase III, the CO₂ Reuse Program, will prepare post-combustion CO₂ for reuse and support the economical assessment and demonstration of CO₂ conversion technologies onsite, such as CO₂-injected concrete and fly ash.

Funding for the first two phases is complete and development of Phase I is underway. Phase I will begin operation in 2019 followed by Phase II and III in 2020.

US: Charah Solutions has opened a terminal for fly ash in Hopedale, Massachusetts. The unit has railway access and is connected to local road networks. It is intended to serve customers in New England.

Charah Solutions says that the terminal will increase the availability of fly ash from its MultiSource materials network locations in the South, New England, the Midwest, the Rocky Mountains and California. These locations supply Class C and Class F fly ash for ready mix concrete producers and other customers.

Bangladesh: The Bangladesh Cement Manufacturers Association (BCMA) has asked for import tariffs on clinker to be reduced. In a letter to the National Board of Revenue (NBR) it requested that the duty be cut to either US$2.40/t or a fixed rate of 5%, according to the Dhaka Tribune newspaper. Importers pay around US$6.00/t at present. The BCMA argues that the cement industry is paying more than other industries for its imports.

The association has also called for value added tax (VAT) on raw materials to be cut to 5% from 15%, reducing advance income tax to 2.5% from 5% and exempting regulatory duties for fly ash and import duties for cement bulk carriers.

Serbia: Elektroprivreda Srbije, a government-owned power company, has completed a Euro14m terminal on the River Danube for its Kostolac B coal-fired power plant. The unit will be use to transport 105,000t/yr of synthetic gypsum and 157,000/yr of fly ash. It will also process limestone. The terminal was built as part of the first phase of a credit arrangement between Serbia and China.