Products for UHPC and UHPFRC/BFUB
NANODUR® Compound 5941
Nanodur Compound is a binder premix for self-compacting concretes in precast plants. The grey or white binder is made from 59% standard and ultrafine components actuated by synthetic silica and 41% fine grinded quartz sand. Pit sand and aggregates diameter 2mm to 5mm can be procured locally as well as the PCE superplasticizer.
Technically the high tensile strength of the cement paste matrix (limit of elastic behavior) is remarkable. Economically, the great advantage is the uncomplicated and robust processing, where all critical components are included in the binder premix.
VARIODUR®
Variodur premium cements are standard cements according to Eurocodes and do not require additional procedures for approval. Single separated components of standard cements with different particle sizes were mixed with a base cement to achieve extraordinary properties. No additional silcafume or metakaoline is necessary. Pit sand and aggregates diameter 2mm to 5mm can be procured locally as well as the PCE superplasticizer.
The resulting concrete mixes need to be compacted but can also be poured with slope e.g. for pavings.
Technically the high compressive strength is remarkable. Economically, the great advantage is the use of only one silo , so these UHPC-binder is also used in ready-mix plants.
UHPC-Additive
UHPC-Additive: For the simple production of UHPC durcrete and Dyckerhoff have developed an innovative puzzolanic, mineral concrete additive. It is a pozzolanic ultra-fine cement powder, which substitutes silica fume and meta-kaoline at a significant lower dosage and less water demand. It enhances density, durability and especially the flexural strength. The concrete remains pumpable and sprayable, the mixture is not sticky and no special mixers are required. It is used in precast and ready mix concrete as well as dry mortar mixes. UHPC-Additive is classified as cement CEM III/C 52.5 N. Durcrete delivers UHPC-Additive in all countries outside Europe.
Notes About Fibers
The best concrete is without fibers. Fibers are a major cost item in the cost break down, make the concrete difficult to work with because of less viscosity, and are often visible on the surface.
Fibers are more effective the longer and thicker they are and the more they are directed in such a way that they follow the path of the tensile force. The most effectice fiber is therefore a reinforcing bar, but it requires sufficient concrete cover.
Textile fabrics significantly increase the post-cracking tensile strength and allow very thin slabs. The decisive factor for the load-bearing capacity of these systems is the fabric; high strength of the concrete is less important. The mixes used must be very liquid to penetrate the fabric, then the mesh tends to float up and must be fixed adequatly in the formwork. Therefore, very often special production methods are used.
Short fibers or micro fibers made of glass, plastic, basalt or carbon have a positive effect on cracks that form at an early stage, but have only a minor influence on the structural behavior and the strain hardening. Since short fibers increase the water demand of the mix very strongly, they are not used in concrete mixes with a low water to cement ratio, such as UHPC.
Our products have not yet been used in sprayed glassfiber concrete -GRC- and therefore we do not have any experience for this application.
The best and simplest fibers for structural UHPFRC/BFUB are straight steel fibers with a length of 15mm to 25mm. High amounts up to 275 kg/m³ of steel fibers increase the compressive strength as well as the tensile strength after cracking (strain hardening behaviour). Be aware, that steel fibers can protrude from the concrete and injure someone. When exposed to the weather, they create small rust spots on the surface.
Macro-plastic fibers are a suitable alternative, but do not perform as well as steel fibers. They are up to 55mm long, flexible and have a light color. Check with the authorities the fire protection requirements and note that the fibers can deform plastically under long-term static stress. We have had good experience with plastic fibers which, when used in sufficient quantities, produce strain-hardening behavior. We use them both for facade panels and for thin overlay layers on bridges. Although they have a lower performance level than steel fibers, they do not rust and do not hurt anyone.
The concrete of UHPC is so dense that in the event of a fire, the water below the surface cannot evaporate but small parts spall off from the surface. If reinforcement is used, the positive effect of the concrete cover is reduced, the steel can heat up faster and the component can fail prematurely. Therefore, thin and short PP fibers (2kg/m³] are used here. They melt at temperatures around 150°C, and create relief channels for the water vapor, effectively preventing the risk of spalling. The short fibers increase the water requirement and reduce the strength. The viscosity and therefore the workablity of the mixture is reduced.
Note About PCE Superplasticizers
Good superplasticizers suitable for self-compacting concretes as well as vibrated concretes with a low w/C-ratio are now available all over the world. Ask your local distributors, there is no need to import such products from Germany.
When comparing Superplasticizers, note that even if the name is identical to a product in another country like Germany, the contents may not be identical. Mixing tests must be carried out with the intended local product.
Many PCE lose their effectiveness above 30°C concrete temperature and do no longer liquefy sufficiently. The colder the mixture the better. However, use only cold water and not ice for cooling. With ice, it is very difficult to assess if the ice has already melted or if there is some other problem why the mix is not yet liquid.
With all high quality superplasticizers, the mixing time is about 8 to 12 minutes, depending on the temperature of the mix and the mixer. The superplasticizer needs this time to work.
Technical Equipment and Mixers
In order to precisely maintain the w/c ratio of the mixtures, the moisture content of the aggregates must be taken into account when adding water. Sand and aggregates must be stored under roof so that they do not constantly change their moisture content due to rain.
There is no need for a fully automated mixing plant if careful workers are available. Volumetric dosing, e.g. via wooden boxes, is sufficient.
A normal compulsory mixer, a pan mixer or a ring trough mixer is perfect. A rotary drum mixer is unsuitable because it discharges self-compacting concrete with great difficulty. The mixer should be filled with only half its usual volume so that the engine is not overloaded by the sticky material. A higher mixing energy of a heavy duty mixer does not help, but only increases the temperature of the mixture and is therefore counterproductive.
Testing is possible in local laboratories.
Where to Buy Binders for UHPC
The products described above are distributed by Dyckerhoff either directly or through durcrete. There is no regional dealer network. Sales and exports are made directly from Germany.
No license fee for patents or long term delivery contracts are required for this UHPC technology.
Dyckerhoff and durcrete only cooperate with professional business partners such as precast plants. Therefore, the binders are only delivered in silo trucks, as BigBags or paper bags in whole containers. In exceptional cases, the delivery of whole pallets is possible for sampling or testing.
durcrete is only active in B2B relationships. This is the reason, why consumer protection laws and the German BFSG law is not applicable.
A reference source for small quantities is the webshop in english language www.moertelshop.eu. The web-shop offers small amounts of the special UHPC-binder TEGNO, which is similar to Nanodur Compound. In the web shop you can buy small quantities of superplasticizer, dry mortar, pigments, reinforcements, fibers, release agents, etc.. The CEO Dr. Backstein, saying 'concrete makes you happy' and offers books, seminars and sample videos on YouTube.
FAQs
What is the secret behind the binders?
We deal with a special concrete Ultra High Performance Concrete -UHPC-. Dyckerhoff do not use silica fume or metakaoline, they add special grinded slag cement in a defined grading curve to achieve a dense and strong cement paste.
Do I need a mixing plant?
The concrete has to be mixed in a professional prefab plant with local available aggregates (sand and natural
stone). All products are not suitable for Do-It-Yourself purposes.
Does a dry concrete premix exist there?
There is no dry premix available, where only water has to be added. If you have professional equipment, fresh mixed concretes with local aggregates are always cheaper than dry concrete mixes.
Can we buy ready-made façade panels or structural elements in Germany?
No German prefab plant is willing to export prefab elements for construction purpose. Main problem is the fact that there is no possibility of replacement in case of damage during transport or erection within a short time. Further it is more economical to ship the binder alone rather than the finished product
Economic advantage?
UHPC is an expensive product for special applications, where the special characteristics are essential. If you can solve your technical challenge already with ordinary concrete or with GRC-Panels, UHPC or UHPFRC/BFUB concrete is no more competitive.
Can I adjust the recipe to fit my needs?
The binder is available in grey or white. Recipes can be individually adapted, e.g. recipes only with sand (maximum diameter: 2 mm). Colorful aggregates, pigments, plastic fibers, steel fibers etc. can be added to meet your individual requirements. The surface can be washed-out concrete, sand blasted concrete, photo print and so on. Please note that the
amount of cement paste represents about 50 % of the visible area, the size of aggregates is limited to a maximum diameter of about 8 mm.
Surface quality?
With self compacting mixes -SCC- the surface is identical to the formwork or mould. Special attention has to be given to dark shades on the surfaces, caused by special ingredients e.g. ultrafine slag cement. Most applications use a painting or light coating for surface finishing of architectural concrete surfaces.
Real white color?
The binders contain grinded slag or Super-GGBS (ground granulated blastfurnace slag), which is why a certain gray shading is unavoidable even with white cement. In order to avoid permanent green or blue discoloration, the surface must be quickly deformed and kept dry for at least two weeks.
Steel Fibers?
In some applications, steel fibers are required for ductility. Also some codes recommend using steel fibers. Common fiber content is between 60 kg/m³ ordinary steel fibers up to 280 kg/m³ of microfibers. Steel fibers cost between 2.00 to 4.00 €/kg and influence the price of the final product. Fibers have also an effect on the viscosity and workability of the fresh concrete.
Security Applications?
We have special recipes and test reports for very thin elements which are resistant to bullets, blast waves and burglary. If there are no restrictions to weight or space, Nanodur concrete is no more competitive as well as any other UHPC.
Application in GRC?
NANODUR Compound is not used as a binder in glass fiber reinforced concrete (GFRC). Fiberfree recipes are preferred due to the high strength of the cement paste. Glass fibers and textile fabrics are difficult to work into the stiff mixture with low viscosity. A high amount of fibers stiffens the fresh concrete and destroy the self-compacting characteristics of the SCC. The high portion of fine Portland cements and the dense structure allow nearly no carbonation, so give special attention to the long-lasting alkaline attack on the glass fiber.
Which panel thickness is possible?
For unreinforced, fiberfree cladding systems the following sizes are applicable.
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Panels with thickness of 8 mm max size 0.5 m x 0.8 m. No fibers, fixing with nails or screws
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Panels with 30 mm to 50 mm max size 2.0 m x 4.0 m. No fibers, strainfree fixing with anchor pins like natural stone or fixing with undercut anchor on a rail system.
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Panels with 40 mm to 70 mm max size 4,0 m x 6,0 m. Reinforced or steel fibers fixing with anchorage systems e.g. Halfen.
Disclaimer to Products
The data provided are of a general nature and may therefore not be suitable for a specific application. As a result, tests, calculations, and experiments on a case-to-case basis are required prior to use of the products. The data provided in these information sheets do not constitute a guarantee of quality. Defects and claims for restitution and damages are excluded by virtue of this statement. Proprietary rights of third parties must be observed.