Can the familiar design and dimensioning principles for classical concretes also be employed for concretes based on Celitements?

The dimensioning and design factors used by planners and structural engineers for concrete structures are based on factors that have been determined over decades, or sometimes centuries, in classical concrete mix formulations and then confirmed empirically. Every new binding agent, including Celitement, must therefore first prove in tedious tests that, for example, Celitement concretes are subject to the same design factors as those produced with Portland cement. This is actually not a problem as the end product of the hydration of Celitement is in fact the C-S-H phase, the glue in concrete, that is sufficiently well known from Portland cement. However, this proof requires intensive work and testing and costs a great deal of time and money. The development of completely new building materials for the construction mass market therefore also takes a comparatively long time. It is perhaps comparable in some ways with new drugs. Here again, tedious clinical studies are necessary after a successful laboratory and research phase so that the compatibility of a new active substance can also be securely statistically verified. This means that drugs can also easily take 10-12 years from active substance to finished medicine.

When can one assume that it will be possible to use Celitement universally as a standardized building material?

It is necessary to differentiate here between European and national standards. At the moment the European standardization work in the building materials sector has almost come to a standstill in most areas for purely formal legal reasons. Even the extension of EN197-1 to include new types of cement with low clinker contents has still not been completed after more than 6 years because of mandate problems between the European Commission and the CEN. If changes to the standards can take up to 10 years even for proven bulk building materials it cannot be assumed that completely new building materials will be available in the form of harmonized European standards in a shorter time. We therefore assume that national approvals (e.g. building authority approvals from the German Institute for Building Technology) or European Technical Approvals (ETA) will pave the way to regulating the building legislation for new building materials like Celitement.

Why are compressive strengths of Celitement usually specified with low w/c ratios of around w/c = 0.40 and not with the usual value of w/c = 0.50 stated in EN196?

Because Celitement is a hydraulic binding agent that already contains water and has a substantially lower chemical water demand than Portland cement. With CEM I Portland cement only about 15 % of the water that is needed for producing concrete or mortar is chemically incorporated in C-S-H phases. The rest is needed for the aluminate and aluminoferritic phases and for the rheology. The w/c ratio for the standard tests for Portland cements is based on this substantially greater water demand and is therefore actually too high for testing Celitements. As with classical cement, an oversupply of water leads to a drop in physical performance. There is therefore no sense in simply transferring the w/c ratios that apply to Portland cements. The optimum w/c ratio for Celitements is lower and must then also be relatively accurately adhered to.

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