Dr' Wolfgang Aldrian

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Dr. Wolfgang Aldrian
Sprayed concrete for rock support
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Index

• Introduction
• Sprayed concrete
• Application
• Modern composite shell solutions
• Conclusion

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Introduction
Sprayed concrete was invented in 1907, and is
today widely used for rock support world wide,
both in mining and tunnelling
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Introduction
For a long time dry mix application was the only
way of applying sprayed concrete, but in the late
seventies the wet mix method was introduced The
development in sprayed concrete has gone a long
way since 1907, both in terms of equipment and
concrete technology. Especially since the wet mix
method started to get implemented, large
technology steps have taken place
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Sprayed Concrete
In the dry mix method, a premix of sand and
cement is fed into the hopper of a machine.
Compressed air conveys the mix through the hose
to the nozzle where water is added
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Sprayed Concrete
For the wet mix method, sand, aggregate, cement,
water and admixture are premixed in a concrete
plant Application of wet mix sprayed concrete is
mainly performed by the use of piston pumps, that
convey the concrete through the hosing system,
and at the nozzle a set accelerator and air is
added
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Sprayed Concrete
Wet vs. Dry Analyses done in Germany 1999 31
projects under progress at 3 different new
alignments in Germany (railway Frankfurt - Köln
and Nuremberg - Ingolstadt, road tunnels across
Thuringia mountains) have been analysed. The
total length of these tunnels is 75km, the total
sprayed concrete consumption close to 2 million
m³ Outcome Within short time it changed from 60
to 80 wet method Today more or less all bigger
tunnel sites use the wet system Rest of
presentation is about the wet system
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Sprayed Concrete

• Typical wet sprayed concrete mix design
• Batching plant
• 420kg CEM I 42.5 R cement
• 200kg total water
• 3kg super plasticizer
• 1700kg graded aggregates(0 8mm)
• Total fines (lt0,125mm), cement sand, about 500
  - 550kg
• At the nozzle
• 30kg accelerator

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Sprayed Concrete

• Batching plant more information
• W/C ratio lt 0.5
• Non retarding plasticizer typically
  Polycarboxylates
• If required hydration control additives
• Spread 55-60cm
• Workability / open time 2-3h, if required even
  more
• Concrete temperature gt 15 C

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Sprayed Concrete
At the nozzle to be looked at Alkali free
accelerator not Aluminates negative influence on
the long term strength development often
problems with leaching dangerous pH value
(about 13 14) not Silicates flash set with
lousy strength development often problems with
leaching problems with final strength
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Sprayed Concrete
Check the spread the total water
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Sprayed Concrete
Check the cohesion, fill boxes
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Sprayed Concrete
Measure early strength and plot the results (J
Austria),Penetration Needle
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Sprayed Concrete
Continue with strength measurements,Hilti
Equipment
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Sprayed Concrete
You may even drill cores for evaluation, 28d
typically 45- 50MPa - Check for layering
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Sprayed Concrete

• Is there any difference in between temporary and
  permanent sprayed concrete (sc)?
• Requirements
• Temporary sc has to temporarily stabilize the
  ground to enable a safe excavation
• Permanent sc has to permanently stabilize the
  ground, to be durable and watertight, typically
  substituting the concrete inner lining
• Application
• Temporary sc is applied in cycles at the face,
  reinforcement has to embedded and lapped, rebound
  not entrapped
• Permanent sc can be applied in a much better
  environment

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Sprayed Concrete

• Loading
• Sprayed concrete shells are only loaded through
  ground deformations! (except water pressure,
  concrete shrinkage, extra design loads)
• Temporary sc has to absorb the ground movement
• With little cover it is normally several
  centimetres only, which the shell can easily
  take
• With high cover and difficult rock conditions it
  may be up to 1 metre deformations with a partly
  destroyed shell
• Permanent sc has is usually installed after all
  deformations have levelled off
• It is therefore loaded only to a very small
  extent if at all!

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Application
How is the sprayed concrete applied at Site?
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Application
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Application
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Application
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Application
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Application
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Application
Is this first sprayed concrete layer watertight?
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Application
Water gets mostly through where the girders are!
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Application
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Application
Sprayed concrete as smoothening layer
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Application
What is the conclusion to be drawn? The first
sprayed concrete layer, mostly seen as temporary
only, is placed in a difficult environment and ?
gets reasonable strength, even system strength
? is very unlikely to be watertight The second
(inner) sprayed concrete layer has a by far
better chance to fulfil designers durability and
water-tightness expectations. This layer is
mostly seen as permanent
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Modern composite shell solutions
B O N D
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Modern composite shell solutions
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Modern composite shell solutions
Escape Tunnel Giswil, Switzerland
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Modern composite shell solutions
After 5 years ..
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Modern composite shell solutions
Ammunition Caverns Hirtenberg, Austria
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Modern composite shell solutions
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Modern composite shell solutions
Subway Station Puente Alto, Santiago, Chile
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Modern composite shell solutions
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Modern composite shell solutions
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Modern composite shell solutions
f
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Modern composite shell solutions
All projects shown did they fully benefit from
the chances provided by a composite structure? Is
the first sprayed concrete layer seen as
temporary only, partly permanent or even as
permanent? What are the design criteria for the
first and the second sprayed concrete layer? Did
I talk about substitution of cast in place inner
lining through sprayed concrete only, because for
the ease of application? Is there more to gain?
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Modern composite shell solutions
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T. Viret, Metro M2 Lausanne, CH
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T. Viret, design change
Detail design tender stage Sheet membrane 30cm
concrete
Alternative design proposal Sprayed, fully
bonded membrane 144cm sprayed concrete
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T. Viret in operation
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Modern composite shell solutions
Is the first sprayed concrete layer seen as
temporary only, partly permanent or even as
permanent? ? This is one key question for
potential savings. High quality sprayed
concrete can at least partly being seen
as permanent that statement gets more and
more acceptance What are the design criteria for
the first and the second sprayed concrete
layer? ? Goal is to fully benefit from the
composite structure, which requires a minimum
interaction in-between the layers
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Modern composite shell solutions
Did I talk about substitution of cast in place
inner lining through sprayed concrete only,
because for the ease of application? ?The ease
of placing sprayed concrete in complicated
geometries, compared to cast in place
concrete, is an additional benefit ? Through
spray application of concrete it is possible to
build thinner inner linings
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Conclusion
Sprayed concrete as used today can be seen as
permanent in most cases but hardly as being
watertight To ensure high sprayed concrete
quality knowledge and tests are essential, the
details make the difference! Sprayed membranes
can help to get the sprayed concrete support
system watertight, enabling the use permanent
sprayed concrete as lining There exist many
references with sprayed concrete as permanent
ground / rock support, some of which in
combination with sprayed membranes Were possible,
try to benefit from a real composite structure!
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