Abstract the fine surface irregularities and results in good

Abstract

Shotcrete
is a concrete conveyed through a hose and sprayed pneumatically at a high
velocity onto a receiving surface. Pneumatic application ensures proper
compaction of shotcrete. It helps in achieving high strengths and low
permeability. It has immense applications in slope-stabilization, tunneling and
domes. In this paper, the use of shotcrete as slope-stabilizing agent in USBRL
project(J&K) of Br. No. 87 A1-P1 is practically accomplished.

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Keywords:
shotcrete, pneumatic, hose, high velocity, compaction, low permeability,
slope-stabilization, tunneling, domes.

 

Introduction

Shotcrete
is a structurally durable and long-lasting construction material which exhibits
eminent bonding characteristics to an existing concrete, rock, steel, and various
other materials. It usually has high strength, low absorption, good resistance
to weathering, and resistance to chemical attack. Many of the physical properties
of shotcrete are comparable or superior to those of conventional concrete
having the same composition. Improperly applied shotcrete may lead to
conditions much worse than the untreated condition.

 Shotcrete is used in place of conventional concrete,
in most cases, for reasons of cost and convenience. Shotcrete has merits in situations
when formwork is cost prohibitive and where form work can be  eliminated, access to the construction area is
difficult, thin layers or variable thicknesses are required, or normal casting
techniques cannot be engaged. Shotcrete with rockbolting can be employed for
immediate slope stabilization where the soil mass encountered is loose, seepage
is prominent and cutting depth is large.

The
excellent bonding of shotcrete to other materials is an important design parameter.
The force of the impact of this pneumatically spurred material on the surface
causes compaction of the shotcrete  matrix into the fine surface irregularities
and results in good adhesion to the surface and cohesion between the particles.
Within limits, the material is capable of supporting itself in vertical or
overhead applications.

The
selection of shotcrete for a particular application depends on knowledge,
experience, and a vigilant study of required material performance. The
performance of the shotcrete for that application is contingent upon proper
planning and supervision, and also the skill and cautious attention provided by
the shotcrete applicator.

In
bridge repairs, shotcrete can be used for bridge deck rehabilitation, but it
has generally been

Uneconomical
for major full-thickness repairs. It however is advantageous for beam repairs
of variable depths, caps, columns, abutments,flywalls and underdecks from the
standpoint of technique and cost.

In
building repairs, shotcrete is mostly used for repair of fire and earthquake
damage

and
deterioration, strengthening walls, and encasing structural steel for
fireproofing. The repair works of structural members such as beams, columns,
and connections is common for structures that are damaged by an earthquake.

In
underground excavations in the rock shotcrete is effectively used in the
advancement of tunnels through altered, cohesionless, and loose soils. Typical
underground shotcrete applications range from supplementing or replacing
conventional support materials such as lagging and steel sets, sealing rock
surfaces, channeling water flows, and installing temporary support and
permanent linings.

Shotcrete
is mostly used for temporary protection of exposed rock surfaces that will
deteriorate when exposed to air. Shotcrete is also used to permanently cover
slopes or cuts that may erode in time. Slope protection must be properly
drained to prevent damage from excessive uplift pressures.

In
this paper slope stabilization using shotcrete-reinforced with steel fiber
having low aspect ratio (L/D) is discussed in detail which is being employed in
the USBRL project at Bridge 87 A1-P1 site. The steel fiber used is 35kg per
cum. The effect on compressive strength with varying cement content is studied
for 3day,7 day and 28 days. Analysis of results depict a gradual increase in
compressive strength of shotcrete with increase in cement content keeping the
water-cement ratio constant. It was seen that compressive strength increases by
7% for every 10kg increase in cement. 

 

 

 

Images showing the
application of shotcrete at Br. No. 87 A1-P1 site (USBRL Project J&K )

 

 

 

 

 

 

 

 

 

 

 

 

 

Proportioning of Shotcrete
materials.

The
various ingredients of shotcrete mix are as follows:

 

1.
Cement: Ambuja cement of 43grade was used with varying contents ranging from
460kg to 480kg per cum as show in table1.

 

2.
Aggregates: Crusher sand (dust) was blended with 10mm aggregates in ratio of 68%:
38% respectively.

 

3.
water-cement ratio: The water cement ratio of 0.37 was kept constant in all the
three mixes.

 

4.
Steel fiber: 35kg steel fiber of low aspect ratio was used per cum.

 

5.
Admixture: 0.7 % of AT-PlAST-260 was used as an accelerator.

 

 

 

Grade of Shotcrete

W/C Ratio

Steel Fibre (kg)

Cement Content(kg)

Crusher Sand(dust)

Coarse aggregate (10mm)

Compressive Strength(Mpa)

3Days

7Days

28Days

M25

0.37

35

460

68%

32%

10.13

27.46

32.98

M25

0.37

35

470

68%

32%

11.86

29.11

35.23

M25

0.37

35

480

68%

32%

13.24

37.67

45.21

                                                             
TABLE 1                

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Conclusion

 

Three
trial mixes were conducted at a constant water cement ratio of 0.37 and effect
on compressive strength with varying cement content was evaluated. The cubes at
3days, 7days and 28 days were tested which proved that with increase in cement
content the compressive strength increases .The graphs of compressive strength
versus cement content were also plotted.

 

References

1.  Shotcrete
Handbook by sika 2013.

2.  www.fhwa.dot.gov/bridge/tunnel/pubs/nhi0901.

3. Harbour,
Dock and Tunnel Engineering -R.Srinivasan .

  
Charotar Publishing House Pvt.Ltd. 22nd edition 2008.

4.
http://web.iitd.ac.in/~tanusree/courses_files/02Standard%20Practice%20for%20Shotcrete.pdf