Guniting: Applications, Techniques, and Differences Between Dry-Mix and Wet-Mix Processes for Concrete Repair and Construction

This presentation explores the process of "Guniting," a specialized concrete spraying technique for structural repair and surface strengthening. It begins with the history of guniting, including its origins and technological evolution, and examines both dry-mix (traditional guniting) and wet-mix (shotcrete) processes. Key topics include equipment, procedures, reinforcement options, and essential quality measures for effective application. The presentation also highlights real-world applications, from swimming pools and tunnels to fireproofing and rock slope stabilization, as well as a comparison of properties and benefits of each method. Perfect for civil engineers, architects, and construction professionals focused on innovative concrete repair methods.

1. Presentation on
“Guniting”

Presented by:- Kartabya Regmi

2. 2
INTRODUCTION
HISTORY
PROCEDURE
QUALITY FINISH
PROPERTIES
DIFFERENCES BETWEEN DRY-MIX AND WET-MIX
PROCESS
APPLICATIONS
Contents

3. General Introduction
❏Most effective process of repairing
concrete work which has been damaged
due to inferior work or other reasons

❏Gunite is a mixture of Portland cement,
sand and water, shot into the place by
compressed air

❏Used for providing an impervious layer

❏Also known as pneumatically applied
mortar


3
Pic:- Guniting being done

4. History in Guniting process
4
Invented by American
taxidermist Carl Akeley to
repair the crumbling façade
of the Field Columbian
Museum in Chicago
The Cement Gun
Company in Allentown,
PA trademarked the word
“gunite”
1907 1914 1950s
First reported use of
guniting in underground
works in North America in
the Brucetown
Experimental Mine
Wet-mix process was
introduced
1930s1912
Method of spraying
concrete under
compressed pressure and
high velocity was started
1975
Incorporation of silica
fume as a cementitious
material in gunite
brought huge changes

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Pic:- The first Guniting Machine designed by Akeley Pic:- Guniting Machine used in old times
Machines Used Back Then

6. Is it called Guniting or Shotcrete?
❏"Guniting" term was coined in 1907 after
it's invention
❏The term "Shotcrete" was adopted by
American Railway Engineering Association
in the early 1930s
❏After invention of wet-mix process,
“Guniting” was used for dry-mix process
and “Shotcrete” for wet-mix process
❏The core principle is the same


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7. Procedure
➢Mixture
➢Spraying Process
➢Reinforcement

8. Mixture (Dry-Mix Process)
8
PORTLAND
CEMENT AND
SAND

➢Cement-sand mixture
should be in the ratio
of 1:3
➢Cement requirements
are similar to those for
conventional concrete
➢Low-alkali cement
must be specified

AGGREGATES

➢Lightweight aggregate is
most practical for the
dry-mix process
➢The size of fine aggregate
used in the mix is 10mm
CHEMICAL ADMIXTURES

➢The use of admixtures in
guniting is not the same as in
conventional concrete
because of equipment
limitations
➢Should comply with the
appropriate requirements


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01 02

9. Spraying of Cement
9
Pressure of about
20-30 N/cm
2

●Distance of about 750 mm to 850 mm
from the surface to be treated
●Velocity varies from 120 to 160 m/sec

Fig:- Schematic Figure of Guniting Process

10. 10
Shotcrete (Wet-Mix Process)
❏All the ingredients, including water are
mixed before entering the chamber of
delivery equipment
❏Additional air is injected at the nozzle to
increase the velocity and improve the
running pattern
❏Sticks to the surface of application with
less rebound than Guniting

Fig:- Detailed Figure of Shotcrete

11. 11
Comparative Diagram of Dry-Mix and Wet-Mix Process
Fig:- ShotcreteFig:- Guniting

12. 12
Flowchart Representation

13. Reinforcement
13
Two types of reinforcement are generally used:-

1) Steel Mesh Reinforcement

➢4 inch by 4 inch mesh and 3 inch by 6 inch mesh of 8 gauge
or 9 gauge wire
➢Use of bars larger than 16 mm diameter or heavy
concentrations of steel are not practical
➢Increase the strength of the finished job
➢provide the necessary degree of support for the mix

2) Synthetic Fibre Reinforcement

➢Microfibres and Macrofibres are used
➢Microsynthetic fibers can be used in both wet- and dry-mix
process
➢Macrosynthetic fibers are mainly used in wet-mix process
➢Allows for a uniform thickness and uniform density for the
contours of the receiving face

Pic:- Steel Mesh
Pic:- Synthetic Fibre

14. 14
Pic:- Nozzle Pic:- Guniting Machine
Pic:- Hose or pipe
Pic:- Wet Shotcrete Machine
Equipments Used

15. Practical Example of Guniting
15
Link for the video:-
https://www.youtu
be.com/watch?v=z
2_Cj25sXNk

16. 16
High quality mortar is necessary in order to reduce permeability and increase the
resistance to weather and chemical attack
Conducting sand blasting on the surface of application will help in removing rust
on the reinforcement before spraying.


The surface of application must be cleaned by high pressure water jet or by air
blast
If the surface of treatment has high absorption, then it must be kept wet for a time
period of 6 hours before undergoing guniting
The distance between nozzle and the surface of treatment should be around 0.8m
Should be performed by careful and skillful control of nozzle for high quality
guniting
Angle of spraying should be perpendicular to the treatment surface
Skilled
Manpower
Distance
Angle
Clean Surface
Rust Removal
High Quality
Mortar
Surface of
Treatment
Quality Finish

17. Properties of Guniting
17





Adding
fibres to
gunite can
produce
significant
load carrying
capability





Bond
Strength
with other
materials is
generally
higher
Bond
Strength




High
compressive
strength of
56-70 n/mm2
at 28 days is
achievable
CS
Strength





High
impermeabi
lity can be
achieved
Pores




It should
enhance
durability in
most cases
Durable





Water-cemen
t ratio should
be between
0.33 and
0.50
W-C
Ratio




Small
maximum
size
aggregate
used and
cement
content is
high.
Content
Load
Carry

18. Dry-Mix Process and Wet-Mix Process
18
Dry-Mix Process Wet-Mix Process
Bonding ability is excellent because of the low
water-cement ratio and high impact velocity
Bond strength and tensile strength is less
Applied at a rate of 1 or 2 cubic yards per hour Applied at a rate of 7 or 8 cubic yards per hour
Low Investment More Investment
Experienced nozzleman required to control the
water content varied through nozzle adjustment
The water content is controlled more precisely
Rebound is comparatively more, thus high dust
emission
Lesser Rebound because of the mixture
Applicable for places where transportation is
difficult
Transportation facility is required
Less Wastage More Wastage of Materials

19. ❏Used in different construction such as thin overhead
vertical or horizontal surface, particularly the curved or
folded sections, canal, reservoir, and tunnel lining.
❏Used in swimming pools, water retaining structures, and
prestressed tanks.
❏Used in the stabilization of rock slopes and temporary
protection of freshly excavated rock surfaces.
❏Utility for protection against long-term corrosion of
pilling, coal bunker, oil tanks, steel building frames, and
other structures, as well as in encasing structural steel for
fireproofing.
❏Developed for high-temperature applications, such as the
refractory lining of kilns, chimneys, furnaces, etc.


Applications
19
Pic:- Guniting in Tunnels
Pic:- Guniting in Swimming Pools

20. Bibliography
http://totalfoundation.in/grouting-and-guniting.php
https://civilblog.org/2014/06/29/what-is-guniting/
https://shotcrete.org/wp-content/uploads/2020/05/2017Fal_Morgan-Bernard.pdf
https://abcpolymerindustries.com/fiber-reinforced-shotcrete/
https://theconstructor.org/concrete/what-is-guniting-procedure-uses/17702/#:~:text=Guniting%20is%20a%20process%20used
,of%20the%20concrete%20repair%20works.
https://www.civilknowledges.com/guniting/
https://www.civilknowledges.com/what-is-shotcrete/
https://civiljungle.com/what-is-guniting/
https://www.ques10.com/p/48054/note-on-guniting-1/#
https://buildtechindia.com/what-is-guniting/
https://www.designingbuildings.co.uk/wiki/Shotcrete_technology#Properties_of_shotcrete
https://knowledge4civil.wordpress.com/2017/02/06/gunitting/
https://www.concreteconstruction.net/how-to/materials/the-gunite-technique_o
https://civilblog.org/2014/06/29/what-is-guniting/






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