How much better is the CO2 balance of Celitement than that of Portland cement?

This is one of the most frequent questions that we are asked. It does sound very simple but is not at all as simple to answer as it may seem at first glance. We are not using this statement to try to wriggle out of an important discussion. However, the journalistically understandable but sometimes very abbreviated “only one figure please” and the eye-catching “better” or “much better” as well as the frequently exaggerated polarization between “grey cement” and “ecocement” simply do not do justice to this important question. Let us go a little further before a figure is mentioned … It starts with the basis for comparison, Portland cement. Which one should be considered? Currently there are 27 types of cement in the European cement standard and in the future this figure will exceed 30. These differ mainly in the quantity of Portland cement clinker, which represents the largest source of CO2 in cement production. EN197 covers a very wide range of compositions between the main types, from a CEM III/C cement with only 5 % clinker to CEM I cement with at least 95 % clinker. But even within one type of cement the clinker content is still allowed to vary. This means that there is no such thing as “the Portland cement”. In most cases this is commonly taken to be CEM I Portland cement containing a minimum of 95 % clinker. At least this would be a clearly defined basis for a comparison with Celitement but even here it is still necessary to agree precisely how the calculation is to be made. Is the comparison to be made with a so-called generic cement, e.g. the average of all CEM I products from an entire country or only the products from a selected producer? There are three quality or strength classes of CEM I Portland cement, so which strength class is to be taken as the basis? A CEM I of the 32,5, 42,5 or 52,5 strength class? One with high early strength (R) or one from a slower class (N)? Also, will the average cement be weighted in accordance with the quantities sold (i.e. market relevance) or not? For which country is the comparison being made? Germany, Europe, China or the whole world? This is definitely significant, especially for the CO2 contributions from the average electricity mix of a country. Because a very energy-intensive process is involved the power consumption has a strong influence on the CO2 balance for production of a binding agent. France, for example, with its high proportion of atomic power has a very much lower specific quantity of CO2 per kWh of industrial electricity than Germany. How will the secondary fuels used in the rotary tube kiln and their contents of biogenic fuel be taken into account in the calculation of the CO2 intensity? Are the gross emissions (all CO2 emissions) to be compared or the net emissions (CO2 from the secondary fuels not included)? This all sounds horribly complicated and unfortunately that is the case. The comparison is also aggravated (for Celitement) by the fact that the production process for Portland cement clinker has been greatly optimized over many decades with respect to energy consumption and emissions. The size of modern cement plants (about 1.0 million t/a) facilitates great economies of scale that cannot be achieved so quickly at first with rather small industrial Celitement plants (planned initially for 0.05 million t/a). In earlier comparisons and publications we have therefore made the comparison with ground Portland cement clinker from rotary kilns without secondary fuels. We have then based the amount of CO2 from electricity consumption on the national electricity mix published by the Federal Environment Agency. Even though there are no reliable figures from measurements on an industrial Celitement plant we are of the opinion that with pure Celitement we are 30 % better than a European average clinker ground with industrial electricity. The further the process is optimized, and depending on the initial raw material mix formulation, it may be possible to achieve even greater savings up to about 50 %. In contrast to Portland cement, which was developed from low efficiency to ever greater efficiency over more than 150 years in a “bottom up” approach. On market entry, Celitement must compete with the most efficient and best Portland cements in a “top down” process. This applies both technologically and ecologically. To be successful in the market we have initially concentrated on product technology aspects. The CO2 efficiency will certainly be greatly improved, except for the main advantages that are explained really strikingly in the example with Lego blocks (see homepage and film clip), by the experience gained with an industrial plant. In the end it is not how much CO2 is emitted per tonne of an individual binding agent that counts but the extent of the CO2 loading of the structures or building products produced with it. Efficiency and technological performance come into play in this situation and the “green” cements and special binding agents like Celitement can demonstrate some further advantages.

If a tonne of Portland cement is replaced by a tonne of Celitement where is the ecological benefit of the claimed resource efficiency?

Good question, it is necessary to differentiate here between (at least) two aspects. The efficiency arises from the performance in the building element that is achieved with different binding agents. If, with a tonne of a new type of binding agent, one can produce more concrete of the same performance or a concrete that has a better performance and therefore less of it is required then resources have been saved. This, of course, applies in general and not just in the comparison of Celitement and Portland cement. Our approach with Celitement is to provide “the pure glue”. A general route to better climate compatibility of cements is to utilize their maximum performance. This can be achieved by very fine grinding and various concrete technology measures. However, it is a fact that in modern concretes with their sometimes very greatly reduced w/c ratios through appropriate superplasticizers a relatively large amount of the cement clinker in the μm size range is still incorporated in the matrix in completely unhydrated form as purely mechanical support particles even after decades. This is very good for the mechanical properties and the durability. However, the question arises as to whether, from the ecological point of view, cement clinker is the right material for this. When different, if possible CO2 neutral, fines are used here and correctly “glued” together with the aggregate (gravel, sand, interground additions) then the system has been made more ecologically efficient. This is particularly possible with Celitements which do form a pure C-S-H phase. Another question is the type and quantity of the resources that are consumed. Celitement requires less limestone but more sand, so there is no change in the total of mineral raw materials consumed. However, not having to calcine as much limestone, which releases CO2 and requires substantial energy resources, is naturally an advantage.

If Celitement functions well in principle and is environmentally friendly then why doesn’t the cement industry convert rapidly to this new process?

Because it is not just a matter of a simple “conversion” but of the construction of new plants. The scale-up step from the pilot plant (150 t per year) to the first industrial reference plant (50,000 t per year) is itself enormous. The next jump, to the plant sizes that are usual in the cement industry ranging from about 1 million tonnes per year for cement plants in Germany to the world’s largest plants of up to 5 million tonnes per year, is then even greater. The technical and economic risks are simply too high at first for very large plant capacities. We are of the opinion that the market will wait to see how the first 50,000 t/a Celitement plant holds up. If this can show that the process can produce a high-grade binding agent uniformly and without problems then the process may well spread rapidly. However, it should be borne in mind that one of the central challenges of the pending transformation of the primary industries is the long investment cycles of most production plants. For cement plants this lies in the region of 50 years or more.

Is there an ecobalance, an Environmental Product Declaration (EPD) or a Life Cycle Assessment (LCA) for Celitement yet?

If this means a certified official document drawn up by independent third parties then unfortunately the answer is no. There is still no industrial plant with a defined location so there is a lack of much important data and basic information needed for compiling a certified EPD or an LCA. The specific values from the small pilot plant are only suitable for preliminary assessments. However, there are numerous publications and reports that compare the different approaches of alternative binding agents, including Celitement. This means that although there are no full EPDs the publications do permit qualified ecological assessment of products or applications that are produced with Celitement.

What is the climate-damaging problem with conventional cements and why is Celitement better for the climate and environment?

The majority of cement is needed for producing concrete. And concrete is, after water, mankind’s most used “artificial” substance. Cement and concrete are produced worldwide with raw materials that are available in large quantities and are relatively cheap. The two building materials are comparatively easy to handle and are characterized by an unbelievable variety of possible uses. Their outstanding technological properties, at comparatively moderate costs, are the basis of their immense success. However, the colossal worldwide demand, especially in the growth regions of Asia and Africa, and a quite significant “CO2 footprint” mean that cement makes a globally substantial contribution to the greenhouse gas problem. The problem with conventional cement is therefore simply the enormous amount of it that is required and produced. Nowadays cement is produced in the almost unbelievably large quantity of over 4 billion tonnes per year! This corresponds to a cube with edge lengths of about 1.7 km. And the weight of concrete produced with it is even greater. A cubic metre of concrete weighs about 2.4 tonnes and contains, on average, about 300 kg cement while the remainder, approximately seven times the weight of the straight binding agent, is made up of gravel, sand and water.

On a global scale it is the shear mass of cement and concrete that is processed annually that has now become a problem. And the demand for our building materials is rising ever further due to population growth, urbanization and the requirement of developing economies for modern infrastructure in the form of roads, bridges, tunnels, sewage systems, water reservoirs and housing.

The most important constituent of cement, namely cement clinker, is required for its production. The clinker is produced in a high temperature process with a gas temperature of about 2,000 °C and a material temperature of about 1,450 °C in rotary tube kilns from, in the simplest case, limestone, clay, sand and iron ore. This process releases large quantities of CO2 – between 750 and 850 kg per tonne of cement clinker, depending on the plant and the raw material basis. About 2/3 of this CO2 released directly at the cement plant comes from the limestone required (CaCO3 → CaO + CO2). This is therefore an emission resulting from the raw material so it can hardly be avoided. About 1/3 of the CO2 emitted during the clinker production comes from the fuels needed to generate the high process temperatures. On top of this must be added the indirect CO2 emissions, e.g. from the high power consumption of a cement plant as well as the quantities of CO2 released by the transport involved in the logistics of mass building materials. However, the majority of cements nowadays do not consist just of cement clinker. The proportion of clinker in the cement end product can be reduced by the addition of inert or reactive interground additions (limestone meal, granulated blastfurnace slag from steel production, fly ash from coal-fired power stations, natural pozzolans, rock meal, etc.). This makes it possible to reduce the specific CO2 emission per tonne of cement (not of clinker, which we unfortunately often confuse!) to average values of between 600 and 700 kg CO2/t cement. The actual level is, however, very specific to the country involved but even at 0.6 t CO2 per tonne of cement (the approximate average in Germany) it is, with a worldwide production of 4,000,000,000 t cement per year, enormous! Celitement does not claim to be able to provide a rapid replacement for this colossal amount of classical cement. However, we will at the very least indicate an innovative and completely new way of at least reducing the CO2 emissions due to the raw materials during the production of cement. We have explained the basic principle in our LEGO video clip on YouTube or our homepage.

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