Are there any examples where Celitement has already been used successfully in building practice?

We have not yet produced any large structural elements or buildings with it. The quantities from the existing pilot plant are just not adequate. After all, a cubic metre of concrete contains about 300 kg cement and at the moment we only produce about 100 kg Celitement per day in our pilot plant. This means that the production from three whole days would be needed to make just one cubic metre of concrete. This would be prohibitive. However, we have naturally already carried out some fairly large practical trials, such producing concrete products in the plants. There is in fact a sample from the production of paving stones in front of our main building that also houses the pilot plant. More than a tonne of material was needed for these trials. Therefore, yes, we have successfully used Celitement, but unfortunately only in initial “exploratory trials” industrially due to the very limited quantities available so far. However, this will change when the extension has been completed.

Can Celitement be used for producing reinforced concrete?

Yes, Celitement can also be used like entirely normal cement for producing reinforced concrete. The background to this question is probably the pH of the pore solution of Celitements that is lowered because of the reduced calcium content. The worry is often expressed that, with a low-calcium binding agent like Celitement, the pH is too low to ensure reliable passivation of the reinforcing steel. The pH of the pore solution in Celitements, with values of between pH 11.5 and 12.5, is admittedly lower than with Portland cement but is still sufficient for passivation. The pH can vary somewhat depending on the amount of the raw material portlandite [Ca(OH)2], which is not always completely converted. If required it can also be raised to any desired value by the simple addition of quicklime or alkali hydroxides. However, we believe that this is not at all necessary. The carbonation responsible for depassivation of reinforcing steel is actually a concrete technology durability factor. If a concrete is sufficiently dense and therefore only slightly permeable to gases and water then no CO2 can penetrate to the reinforcing steel. However, concretes that are extremely dense, and therefore very durable with respect to carbonation, can be produced with Celitements. This can, where appropriate, be compared with UHPC concretes in which as much surplus Ca(OH)2 as possible is converted to the C-S-H phase by the addition of highly reactive silicon dioxide in the form of, for example, silica fume. This also lowers the pH of the pore solution to low values similar to those with Celitement. Celitements form a great many, very pure, C-S-H phases which are also only slightly distorted by the morphologies of other phases, so with correctly chosen w/c ratios the pore system can be made extremely impermeable. This is shown by numerous electron microscope recordings. Thanks to a pH value that is still adequate and to good concrete technology we can therefore see absolutely no restrictions for Celitements with respect to use in reinforced concrete. According to recent research the passivation of reinforcing steel and the formation of a protective oxide layer also depends very substantially on the nature of the hardened cement paste matrix that surrounds the steel in the early stages and on the morphology of the C-S-H phases. In this case Celitement may possibly even have similar advantages to those that can be achieved by the addition of silica fume. Comparative electrochemical investigations into the passivation of reinforcing steel are still being carried out. Quite apart from this, a somewhat lower pH of the pore solution can even be definitely positive for alternative reinforcing systems. Wood- and cellulose-based reinforcement systems and also the less expensive variants of glass fibre reinforcement could be achieved more simply and durably with Celitements than with highly alkaline (pH > 13) Portland cement.

Does Celitement also function with classical superplasticizers like PCEs? To what extent, in general, can conventional PCE superplasticizers be used with pure C-S-H phase cements?

Yes, Celitements can be plasticized and adjusted with well-known brand-name products from various producers. However, in most cases these products have been optimized for classical Portland cements so the addition levels needed are sometimes higher than usual.

How many tonnes of Celitement have been produced so far?

Since the mill in the pilot plant came into operation at the end of 2013 we have produced about 10 tonnes of the various Celitements or their intermediate products every year. However, this was over a very long period and with a great many different process parameters and variants of the formulation. In normal operation in which we attempt to produce the same material very uniformly over a fairly long period we usually make about 2 tonnes “at a go”.

Is it now possible to use Celitement in building practice on a fairly large scale?

It depends on the application. If building practice is taken to mean the concreting for a house, a load-bearing floor or a concrete girder then unfortunately no. Celitement is not a standardized binding agent, i.e. not a cement complying with EN197. The legislature has introduced strict building regulations where life and limb is involved or where there are tough requirements for long-term durability. These regulations are normally based on standard cements. However, there are numerous other applications in which there are fewer or even no normative requirements on the binding agent or that do not explicitly require Portland cement as the binding agent. This includes concrete products, tile adhesives, fibre-reinforced cement slabs, aerated concrete, etc. We have identified a total of 20 areas or fields of application where Celitement could be used immediately. When the first industrial plant is in production it will then be possible to obtain building authority approvals for other applications for the product produced there. This can take place at a national or European level and lasts for at least 2-3 years from the application.

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