Displaying items by tag: Slag

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.

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.

There is lots to mull over for the cement industry from last week’s Global Slag Conference that took place in Prague.

One striking map from Michael Connolly, TMS International, showed the status of slag and steel products in the US. It was a multi-coloured patchwork of different regulatory statuses from approval to be used as a product to regulatory exclusion. This won’t come as a surprise to many readers but even within one country the way slag can be used legally varies.

As this column reported last year after the Euroslag Conference, the European Union can be presented in a similar way. The irony here is that increased use of slag and other secondary cementitious materials (SCM) is exactly the kind of change the cement and concrete industries need to make to decrease their carbon emissions. Constant quibbles over whether slag is a product or a waste undermine this. Happily then that Connolly was able to report progress in the US as lobbying by industry and the US National Slag Association have led to more states legally accepting slag as a product.

However, cement producers have other concerns in addition to environmental ones when it comes to slag usage as Doug Haynes from Smithers Apex explained. Haynes, a former UK steel industry worker turned consultant, spoke around a market report on the future of ferrous slag. His take on Basic Oxygen Furnace (BOF) slag was that despite fuel savings, decreased CO₂ emissions and the benefits of embodied iron when it is used as a raw material for clinker production, it is in the interests of cement producers for slag to be a waste because they then get it for free or at a reduced rate. It’s a similar story to the use of waste-derived fuels powering cement plant kilns where producers want lower fuel costs but waste collectors want value for their product. Unsurprisingly, Haynes wanted cement producers to accept the value embodied in BOF slag.

Charles Zeynel of ZAG International, an SCM trader, then laid out the situation where global SCM supplies are remaining static but cement demand is growing. Coal-fired power station closures are reducing supplies of fly ash, another SCM, placing pressure on existing granulated blast furnace slag (GBS) slag supplies. The message was very much in a slag trader’s favour but instructive nethertheless. If slag is in demand then the price will rise. Anecdotally, the increased number of cement producers at the conference seemed to indicate increased interest of the cement industry in the product.

Lots more speakers followed on topics such as slag beneficiation, grinding advances and new innovations. On grinding, one surprise that popped up was that Spain’s Cemengal has sold a Plug & Grind Vertical mill to CRH Tarmac’s cement plant at Dunbar in Scotland. It is the first such sale of this product in Europe. The last speaker, Jürgen Haunstetter of the German Aerospace Centre, stuck out particularly with his presentation on using slag as a thermal energy storage medium in a concentrated solar power (CSP) plant. This may not seem connected to the cement industry but it is along similar lines to Italcementi’s project at the Aït Baha cement plant in Morocco, which uses a CSP process that can be used with the plant’s waste heat recovery unit.

The Global Slag Conference will return in April 2019 in Aachen, Germany.

Read the full review of the 13th Global Slag Conference 2018

Putting two speakers from the European Commission front and centre at the start of this year’s European Slag Association Conference (EuroSlag) in Metz, France was always going to cause a ruck. Once Coal and Steel Research Unit head Hervé Martin and steel sector policy officer Gabriele Morgante said their pieces and the panel opened up then the verbal punches started flying. Okay, this may be slightly exaggerated, but after a bunch of policy-heavy presentations, suddenly the situation became crystal clear. Was the agricultural use of ferrous slag going to be allowed to continue? What would be the classification of the slag? And so on. One Russian delegate commented afterwards, “I thought we had environmental problems in Russia.”

Jérémie Domas, Centre Technique et de Promotion des Laitiers Sidérurgiques (CTPL) explained in a later presentation that the heart of the current debate goes back to the European Waste Framework Directive (2008/98/EC). This legislation created an ambiguity over the status of slag between classifying it, as a waste or as a by-product, that the European industry has been battling over ever since. A multi-coloured map in Aurelio Braconi of the European Steel Association’s (Eurofer) presentation depicted the disarray this has caused with the varied legal statuses of slag across Europe. To add to this, Braconi’s home country of Italy, for example, is split into designating slag as both a product and a waste. His response was to say that the ‘human factor’ was important back home for utilising slag. The European Union (EU) is now working on its Circular Economy Package, which includes revised legislative proposals on waste, and it has been consulting on various issues throughout the year. It is this process is that been making slag producers twitchy.

Other delegates on the first session’s panel provided a bit more context, with Thomas Reiche of the German Technical Association for Ferrous Slag (FEHS) saying that the waste legislation didn’t need to be changed but that public procurement laws did. Eric Seitz of the French Association of the Users of industrial By-products (AFOCO) added that slag products had been sold for decades without any problems. However, he definitely wanted ‘strong’ support from the EU on the issue.

Moving on, Craig Heidrich of the Australasian (Iron & Steel) Slag Association (ASA) provided some interesting figures in his presentation on worldwide slag production that differ from the data often reported by trading companies. Heidrich reckoned that 567Mt of slag was produced in 2015 with a breakdown of 347Mt blast furnace (BF) slag and 220Mt steel slag.

Andreas Ehrenberg of the FEHS presented research on converting electric arc furnace (EAF) slag into a hydraulic material that could be used in cement or concrete production. Given that, using Heidrich’s figures for example, about a third of ferrous slag production is steel slag often created in an EAF, the potential implications of this line of inquiry are important. Unfortunately, the main disadvantages of the original EAF slag analysed in Ehrenberg’s work compared to BF slag are the lower CaO and SiO₂ contents and the higher MgO and Fe oxide contents. Laboratory-scale tests confirmed in principle the feasibility of forming clinker or ground blast furnace slag-like materials based on EAF slag. But the reduction and treatment steps in the process require a lot of effort and the economical value of the recovered metal is low. Taking the research further will require much more work on the semi-technical scale.

The other paper with particular relevance to the cement industry was Chris Poling of SCB International unveiling his company’s ground blast furnace slag (GBFS) micro-grinding mill, the Nutek Mill 2. The new mill is intended to allow slag grinding to take place in a much wider range of locations, along similar lines to the modular clinker grinding mills made by Cemengal or Gebr. Pfeiffer’s Ready2Grind line. The pilot project is being installed now in New York State, US. The mill has a GBFS capacity of 10 - 12t/hr with a target of 40 – 45kWh/t when fully optimised. Further units at the same location are planned for early 2018 with approval sought from the New York State Department of Transportation.

The 10th European Slag Conference is expected to take place in 2019. With more clarity expected from the EU on its Circular Economy Package there will be much to discuss.

Tata Steel put up its UK business for sale last week. The Indian multinational declared that enough was enough having reported losses of over Euro2.5bn in the territory over five years. Non-UK readers may well wonder what the fuss is about. UK crude steel production comprised 10.9Mt in 2015 or about 0.7% of global production according to World Steel Association data according to World Steel Association data. By contrast the country produced 9.3Mt of cement in 2014 or about 0.2% of world production according to CEMBUREAU data according to CEMBUREAU data.

The UK’s flailing steel industry is worth discussing here for two reasons. Firstly, any decline in the local iron and steel industry will have implications for the supplementary cementitious materials (SCM) market as slag levels vary. Secondly, the cement industry in Europe may have lessons for a fellow heavy industry facing capacity rationalisation.

UK ground granulated blastfurnace slag (GGBS) production levels are low compared to total world supply. However, the UK Competition Commission certainly took note of the GGBS market in 2014. It was worried by LafargeTarmac’s and Hanson’s prominence in both the local GGBS supply chain and local cement production. At that time it ordered the HeidelbergCement subsidiary Hanson to sell one of its slag grinding plants to increase competition in the supply chain for GGBS. A GGBS plant in Scunthorpe was eventually sold to Francis Flowers in July 2015.

The general point here is that a Tata sale of its UK operations could have ramifications for the UK GGBS sector as existing deals are renegotiated following the shakeup. It would be even worse for the local slag market if any of the plants closed. No doubt the Competition Commission would also want to have its say to maintain some sort of competition in an already concentrated market. The UK cement market has been the bright spot in the multinational cement producers’ European regions in 2015. However, construction growth is starting to slow again with hints that the looming European Referendum in June 2016 may be having a negative effect. Uncertainty over GGBS supplies is not helpful in this atmosphere.

A wider lesson for other national cement industries looking in is that if Chinese steel continues flood the world market it will also hit the cement industry. Tata’s woes have been squarely blamed on China dumping its steel on the world market. Various jurisdictions promote the use of SCM cements and concrete for their low-carbon and sustainability properties. If local or existing GGBS supplies are hit then the cement industries may be penalised while the lawmakers and competition bodies play catch-up.

The wider point about heavy industry reducing its production capacity is one that the European cement industry will be well used to. Spain, for example, has seen its cement production drop from 55Mt in 2007 to 15Mt in 2014 according to Oficemen data. Alongside this, demand for cement has dropped to levels not seen since the 1960s. The European response has been to shut plants, sell assets and to merge companies.

The big question following the 2008 recession is whether ‘this’ is the new normal for mature construction markets. Eight years later global interest rates are still lagging and China’s economy is slowing down. All of the European infrastructure was built long ago meaning that steel and cement will only be required to maintain it. Luckily it looks likely that demand for SCMs should stay buoyant as industries are encouraged to decarbonise. The problem though is where the slag comes from. Oversupply in the short term in areas like Europe might be great for cement producers but as the iron and steel industries readjust to market reality there might be a hangover in store.

Well, it seems like they were serious.

The UK Competition Commission has provisionally decided that Lafarge Tarmac should sell off one of its cement plants in the Midlands. The Commission also wants the sale to exclude buyers from any pre-existing UK cement producer. The door is open from Holcim or CRH downwards to enter the UK market. Although if the enforced Lafarge sale of Hope to Mittal Investments in 2012 is indicative, it may well be to an industry outsider.

If the move goes ahead it will open up the Midlands and north of England from four cement producers - Hope Cement, Lafarge Tarmac, Hanson and Cemex - to five. Lafarge Tarmac's cement production capacity lead of nearly 4Mt/yr will be knocked down to nearer 3Mt/yr, putting it level with Hanson Cement's production capacity.

Unsurprisingly Lafarge Tarmac is not best pleased, putting out the following in response to the commission's announcement. "The Commission's assumptions and reasoning have serious flaws and the biggest loser in this process will be the customer. There is strong evidence to demonstrate there is effective competition in the sector – with new players having recently entered the marketplace."

The Commission also wants to increase competition in the supply chain for ground granulated blast furnace slag (GGBS). According to the Commission findings Hanson dominates the UK GGBS market and Lafarge Tarmac controls the market for its precursor, granulated blast furnace slag (GBS). So production facilities may need to be sold by both Hanson and Lafarge Tarmac.

As an aside it's worth noting that the Belgian Competition Council recently imposed fines due to anti-competitive practices also related to GGBS. Also, elsewhere in the news this week Irish GGBS cement producer Ecocem is aligning itself with the EU carbon roadmap to 2050, partly at least because its product produces less CO₂ per tonne of cement. Whoever or whatever controls the supply of GGBS in the UK has implications for how emissions are lowered in the cement sector.

Other suggested measures from the Commission such as restricting the publication of UK cement market data seem problematic. Although it may make it more difficult for UK cement producers to collude it will also make it harder for related businesses (including press and industry analysts like Global Cement) to understand what is happening at any given time.

Finally, we have to ask what the effects of the Commission's suggestions might be at the start of an uncertain recovery in the UK construction market might be. According to the Minerals Production Association cement production fell from 8.5Mt in 2011 to 8Mt in 2012, the first decrease since 2009. 2013 seems set for modest growth on 2012. The implications of Commission's plans - if they happen – could be huge.