Shotcrete is a process where concrete or mortar is pneumatically projected at high velocity onto a surface. It can be placed using dry or wet mixes through pneumatic guns onto difficult surfaces like vertical walls. Shotcrete provides compaction during placement and is used in tunnels, dams, pools and for repairs. When placing concrete underwater, the tremie method involves placing concrete at the bottom of a form through a pipe to displace water without washing out cement. Choosing the best concrete placement method depends on factors like the job location, size, and amount of concrete needed above, at or below ground.

1. PROPERTIES OF CONCRETE
Lecture No.03

2. Lecture Contents
Placing of Concrete
 Shotcrete
 Pneumatic guns
 Tremie
 Choosing the Best Method for Placing of
Concrete

3. shotcrete
What is shotcrete?
The term “shotcrete“ is a derivate of two
English words “shoot“ and “concrete“.
The term “shotcrete“ refers to pneumatic high
pressure spraying of concrete or mortar using
a spraying jet onto a surface.

4. Shotcrete

5. Shotcrete
Shotcrete is concrete (or sometimes mortar)
conveyed through a pipe (pneumatic guns) and
pneumatically projected at high velocity onto a
surface, as a construction technique.
Pneumatic guns
Pneumatic guns are used where concrete is to be
placed in difficult locations and where thin sections
and large areas are needed

6. Shotcrete
Shotcrete undergoes placement and compaction at
the same time due to the force with which it is
projected from the nozzle. It can be impacted onto
any type or shape of surface, including vertical or
overhead areas.

7. shotcrete
History of shotcrete
 Shotcrete was invented in the early 1900s by
an American citizen.
 He used the method of blowing dry material
out of a pipe with compressed air and then
wetting this material as it was released. This
was later used to patch weak parts in old
buildings.

8. shotcrete
History of shotcrete
 In 1911, his invention was named as "cement gun",
because of the equipment used, and this process
was named as guniting.
 In the 1960s, the alternative method for gunning by
the dry method was devised with the development
of the rotary gun, with an open hopper that could be
fed continuously.

9. shotcrete
Gunite (dry process)
Gunite is a process involving a “mixture of
Portland cement and sand thoroughly mixed
dry, passed through a cement gun and
conveyed by air through a flexible tube,
hydrated at a nozzle at the end of such
flexible tube and deposited by air at the
place of final repose”.

10. shotcrete
Difference b/w Shotcrete and Gunite
Shotcrete and Gunite both are thought of the
same but the difference is:
 Shotcrete is used for both dry mixture and
wet mixture.
 Gunite is used only for Dry mixture.

11. shotcrete
Shotcrete Technologies
 Dry mix Shotcrete.
 Wet mix Shotcrete.
 Steel fiber reinforced micro silica Shotcrete.
 Mesh reinforced Shotcrete

12. shotcrete
Dry Mix Shotcrete
 Pre-mixed dry or damp materials are placed
into the delivery equipment.
 Compressed air conveys material through a
hose at high velocity to the nozzle, where
water is added.
 Material is consolidated on the receiving
surface by the high-impact velocity.

13. shotcrete
Process of dry mix shotcrete

14. shotcrete
Wet Mix Shotcrete
• All ingredients, including water, are
thoroughly mixed and introduced into the
delivery equipment.
• Wet material is pumped to the nozzle where
compressed air is added to provide high
velocity for placement and consolidation of
the material onto the receiving surface.

15. shotcrete
Process of wet mix shotcrete

16. shotcrete
Steel fiber reinforced micro silica
shotcrete
• Steel fiber reinforced shotcrete was introduced in
the 1970s.
• Silica fume or micro silica is a by product of the
ferro silicon metal industry and is an extremely
fine.
• Quantities of 8 to 13% of micro silica by weight
of cement, allow shotcrete to achieve
compressive strengths , increased resistance to
alkali and chemical attack, improved resistance to
water .

17. shotcrete
Mesh reinforced shotcrete
 In very poor quality, loose rock masses, where
adhesion of the shotcrete to the rock surface
is poor, the mesh provides a significant
amount of reinforcement for shotcrete.

18. shotcrete
Meshes for reinforced shotcrete

19. shotcrete
Advantages
 Perfect adhesion of the sprayed material onto
the base.
 Reliable filling of all cracks and uneven places .
 High initial strength using suitable hardening
agents .
 High water proofing given by perfect compaction
and a low ratio of W/C .
 Easy selection of the thickness of the sprayed on
layer depending on the requirements and
situation.

20. shotcrete
Advantages
 Formwork savings of 50 to 100% over
conventional cast-in-place construction
 Complex shapes require very little, if any,
formwork.
 Crane and other equipment savings or
elimination.
 Better bonding to the substrate, which
enhances durability.

21. shotcrete
Disadvantages
 Handling dry concrete mixture carries the
problem of dust.
 Due to the high speed of discharge and other
factors, the dry technology has a higher
impact on the material and results in falling
off of the material (up to 30% of the gravel
aggregate).
 The pneumatic transport of the dry concrete
mixture places higher demands on a more
efficient source of air pressure.

22. shotcrete
Disadvantages
 In wet mix ,Only a limited period of time is
available between mixing and application
of the wet concrete.
 In case of any longer delays, the entire
system must be emptied, cleaned and filled
up again before renewing the work.

23. shotcrete
Applications Of Shotcrete
 Tunnels
 Channels
 Seismic reinforcing
 Dams
 Pools
 Grouting
 Plastering bigger concrete areas

24. shotcrete
Applications Of Shotcrete
 Repairing
Shotcrete can be used to repair the damaged
surface of concrete.
The following examples indicate a few ways in
which shotcrete can be used in repairs:
Bridges ,buildings, marine structures
 Underground excavations
For the most part, shotcrete is used in underground
excavations in rock such as tunnel, basement.

25. Shotcrete In Tunneling
shotcrete

26. Shotcrete In Pools
shotcrete

27. Conclusions
 shotcrete is one of the very efficient
construction technique
 It is a time saving and we can get required
thickness
 It is durable as compared to the other
techniques
 We can get more strength in our constructions
by using shotcrete.
shotcrete

28. Tremie
 This method is used for placing concrete
under- water level.
 In this method, concrete is placed below water
level through a pipe, the lower end of which is
kept immersed in fresh concrete so that the
rising concrete from the bottom displaces the
water without washing out the cement content.

29. Tremie
 The tremie concrete method is often used in
bridges that span bodies of water.
• It can be used to funnel concrete down
through the water into the foundation or
other part of the structure being cast.

30. Tremie

31. Laying of Concrete by using Tremie

32. Laying of Concrete by using Tremie

33. Choosing the Best Method
 The first thing to look at is the type of job, its
physical size and the total amount of concrete to be
placed.
 Studying the job details further will tell how much of
the work is below, at, or above ground level. This
aids in choosing the concrete handling equipment
necessary for placing concrete at the required levels.

34. Choosing the Best Method
Work Above Ground Level
 Conveyor belt, crane and bucket, hoist, pump, or the
ultimate sky-hook, the helicopter, can be used for
lifting concrete to locations above ground level.
 The tower crane and pumping boom are the right
tools for tall buildings.

35. Choosing the Best Method
Work At and Below Ground Level
The largest volumes of concrete in a typical job
usually are either below or at ground level and,
therefore, can be placed by methods different from
those employed on the superstructure.
Concrete work below ground can vary enormously—
from filling large-diameter bored piles or massive
mat foundations to the complicated work involved in
basement and subbasement walls. A crane can be
used to handle formwork, reinforcing steel, and
concrete.