Offshore hydrogen storage system made of UHPC concrete

Standard concrete can suffer various problems due to hydrogen, especially in special applications such as
hydrogen storage or hydrogen pipelines. The main problems are:

1. Micro-cracking due to hydrogen pressure

• Problem: hydrogen is a small molecule that can enter pores and micro-cracks in concrete. When hydrogen is under high pressure in these pores, it can expand the pores and enlarge cracks.
  
• Consequences:
  
• weakening of the mechanical strength of the concrete.
  
• Progressive damage due to cyclic loading.

Due to its very high density, UHPC has significantly fewer problems with this issue and its consequences.

 

2. Damage due to hydrogen embrittlement (indirect)

• Problem: Hydrogen does not chemically attack concrete, but it can embrittle steel reinforcement elements embedded in the concrete. This is referred to as hydrogen embrittlement.
  
• Consequences:
  
• Reduction in load-bearing capacity due to cracking and failure of the reinforcement steel.
  
• Shortening of the service life of the concrete structure.
  

Due to the very high material density, possible hydrogen embrittlement occurs after aconsiderably longer period of time and to a small extent. 

 

3. Reaction with free ions and moisture

• Problem: Hydrogen can react with moisture and chemical compounds in the concrete (e.g. calcium hydroxide), creating by-products such as water or hydroxide ions.
  
• Consequences:
  
• Alteration of the chemical composition of the concrete, which can lead to a reduction in alkalinity.
  
• Accelerated corrosion of the reinforcement due to the loss of the passivation effect.

Occurs to a much lesser extent in UHPC

4. Pore structure and permeability

• Problem: Hydrogen can easily diffuse through the pore structure of concrete due to its small molecular size, especially in porous or poorly compacted concrete.
  
• Consequences:
  
• Loss of tightness, which is critical for hydrogen storage tanks or pipes.
  
• The ingress of hydrogen causes pressure build-up and damage.

Hydrogen can only penetrate UHPC concrete very slowly and under high pressure because UHPC concrete is an extremely dense material.

5. Increased risk of a hydrogen fire

• Problem: If hydrogen escapes from the concrete (e.g. through diffusion or crack formation), there is a risk of a hydrogen fire, as hydrogen is highly flammable.
  
• Consequences:
  
• Safety risk for the surrounding area.
  
• Additional thermal stress on the concrete.

Due to its high material density and strength, the risk is only present to a very limited extent
with UHPC concrete.

Ultra-high performance concrete offers many advantages, but requires careful planning and adaptation when exposed to hydrogen, especially in demanding applications such as hydrogen storage or transport lines.

UHPC 3D printing

It is interesting to see today what printing results universities and printer manufacturers achieve.

The results are an interplay between printer technology and material technology. In my opinion today, very good results are achieved in the design areas with the printers, but many problems still have to be solved in professional architectural building construction.

There are

Compressive strength

The standard concrete reaches its maximum compressive strength after 28 days. For the printing technology unacceptable, here must be helped with accelerator. Printing speed and strength development must be matched and optimized without loss of strength.
UHPC Ultra High Performance Concrete can be a solution. Strengths of over 200 MPa can be achieved here. Already during the UHPC binder production, we can adjust the strength development, as well as the flow characteristic. The addition of commercially available additives is no longer necessary.

Print speed

Of course you want an optimum speed, you want to process a large amount / weight of concrete in a very short time. The concrete should be able to support itself after a very short time and be load-bearing for ceiling elements.
With UHPC materials, large amounts of material are already processed in a short time using the wet and dry spraying process. The consistency of the UHPC print material can be adapted to the printer characteristic. UHPC materials already develop high strength values in short time in the standard qualities. However, this time can be extremely reduced by changing material production.

Statics

The print heads are usually small in diameter and the applied wall thicknesses compared to a masonry or a finished concrete wall are very thin. Static load-bearing walls can be printed for several floors, or double-skin walls must be printed in order to achieve a structurally stable construction. Do I have to print double-shelled?

Heat / cold insulation

If I print with a standard concrete I do not achieve any insulating properties. So I have to print double-shelled and fill the cavity with insulation material or retrofit an insulating layer from the inside.
At the moment we are the only ones who are able to combine a high pressure resistant material with an insulating material. This combination material is also pumpable.

Steel girders, reinforcements

Even with 3D printing, you can not ignore reinforcements and support structures, or you can remain eternally restricted to small, simple and low-rise building constructions. How can I optimally combine carrier structures, steel reinforcements with a single printing process?

Last but not least interesting design

So far I have seen the obligatory pressure bulges on all prints. For the beginning, this may be fine but soon you should have printing technologies that ensures a sharp-edged pressure even on the wall corners. A rework of the walls in the flat areas to get is cost and time consuming. Of course, when I use the printing technology, I also want to print exceptional geometry and thin-walled constructions.

I have a note at the end

If all my misgivings can be wiped out the question remains if I want to print a large building, I need a fairly large printer technology which is not even built and dismantled and I need a very fast continuous flow of material to the printer when the printer should work quickly.

I do not want to know misunderstood. I think 3D printer technology is very interesting for the future and I know that some engineering companies are working on technical solutions. As part of our material development, we also work on a flexible, extreme fast-curing, high-compressive strength material for the printer producer. In close technical agreement with the respective printer manufacturer, we can adapt our UHPC materials to the requirements and provide test material to the printer manufacturer.

Corrosion problems at offshore wind turbines solved with UHPC concrete

You have the solution already built in your
wind turbine system UHPC Ultra High
Performance concrete material was already
used in the first wind turbines and has been
stable to date and not replaced.

UHPC is absolut seawater resistant and you
can cast it into the seawater if necessary. No
elaborate preparation is necessary and the
corrosion protection will last for at least 100
years without having to be repaired.
Most system suppliers for offshore wind
turbines have known this for a long time.
 
The UHPC material would have to be
modified a bit, that's all.
We modifed it and it work together
with a simple installation system perfect.

The assembly costs and the operating costs
for a complex anode/cathode system is
several times higher and this electrical
system must be monitored regularly.

Well, there are several ways to tackle the
corrosion problem
- You let it rust because the system is already

   so old
- You can apply an extremely complex anti-
   corrosion paint system. Very expensive and
   the durability is extremely limited.
- UHPC is applied to the steel structure as a
   protective layer.
   A relatively simple and safe installation with
   a durability of more than 50 years
- UHPC is used as a constructive measure to
   improve or stabilize the load-bearing capacity
   of the foundation
- UHPC is brought up as a constructive measure
   in connection with the design of an artificial
   reef around the foundation in order to improve
   the situation of the marine fauna.