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QC Issues - Contents
Comparison on Cube vs Cored samples
QC issues on Spraying Application
Curing
QC issues on Pre-Application
Test Methods
Calculation on Accelerator Dosage
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EUROPEAN SPECIFICATION for SPRAYED CONCRETE
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Good Spraying Technique ?
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Spraying Technique Hand Spraying
Spot the mistake ???
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If you value your
hands
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State of the Art - Robotic Spraying
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Application Nozzle AngleNozzle angle
Nozzle should always point 90 to the receiving surface
For spraying onto steel arch / lattice girder exceptions will be required
90
90
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Application Nozzle Distance
Nozzle distance For Robotic application the distanceshould between 1 2 m
Influence Incorrect nozzle angel and distance
has significant influence on concrete
quality like poor compaction,
strength etc, and will dramatically
increase rebound
90
90
1-2m
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QC issues on Application -Layering
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The surfaces must be cleaned before
spraying to guarantee bond
Consistent high quality concrete isessential throughout the different layers
Thin passes guarantee continuity inthe quality of the sprayed concrete
throughout the different layers. This is
essential for final linings
Consistent Sprayed Concrete quality through out
the different layers
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In case of bad spraying, spray shadows form behind the
reinforcement bars
Water migrates into these voids, allowing corrosion of the
reinforcing bars
Corrosion reduces the diameter of the bars and there fore
there strength. The lining looses its lode bearing capacity
No spray shadows behind reinforcement bars
QC issues on Application - shadow
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QC issues on Application - shadow
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Same concrete mix from one truck, sprayed 10 minutes apart!
Sprayed by two different nozzlemen during training
Compaction is important for durability
Application technique can be dramatic
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Shotcrete Applicator Training Programs
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Recognized Standards
Trial Panel Spray Training Basic & Advanced Concrete Technology
Training
Robotic operator training
Hand Spraying applicator training
Shotcrete Application Techniques
Equipment Calibration and Instruction
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Shotcrete & Nozzleman Certification
The American Concrete Institute conducted the first ShotcreteNozzleman Certification Scheme in Asia
Kah Fai Lee ( Tam Singapore ) Alve Rutgersson ( Tam Singapore )
and Ritchard Hood ( Tam Hong Kong ) successfully completed the
course, and examinations, and are now ACI certified shotcrete
nozzlemen.
Alve Rutgersson is to be accedited with ACI Assessor certification
Alve Rutgersson , Ritchard Hood, Kah Fai Lee of Normet have
recently obtained the EFNARC Shotcrete Nozzlemen Assessor
certification for Robotic Shotcrete Application
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Curing is essential in sprayed concrete
As with conventional concrete, permanent
sprayed concrete structures need to be curedor the following may occur:
Rapid moisture loss and dryingresulting from the tunnel ventilationsystems
Relatively high cement content in mixand early reaction temperatures due toaccelerated mix may cause rapid dryingand shrinkage cracking
Without proper curing, we get poorbonding, low strength and poor
durability
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So why is curing important? The term hydration of cement means the
reaction between the cement and the waterwhich makes calcium silicate hydrates(CSH)
The CSH is the gel or binder that givesconcrete its strength
If the water in the concrete evaporates tooquickly, then these important hydration
processes are not given a chance to createa dense, strong matrix between theaggregates
Curing is needed to keep the water in thesprayed concrete as long as possible tohelp hydration of the cement
Good curing gives: Higher compressive strengths
Higher bond strengths
Increased durability
Less shrinkage cracking
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(Cement + water = CSH)Original cement particle
Hydration products
( CSH )Water to complete
the hydration
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Pre-Application - Ordering of Concrete
The Nozzlemen should be informed about:
General mix design, w/c ratio, slump, with or withoutfibres, etc.
The use of special admixtures for control ofhydration (open time), etc
The quality/performance requirements of theapplied concrete
Result from pre test, type and dosage of setaccelerator
Location and orientation of the area to be applied
Details of reinforcement and concrete thickness tobe applied
Total amount of shotcrete to be applied at thelocation
The timing for the application and supply rate for theconcrete
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Pre-Application Delivery Acceptance
Control of concrete on arrival at the spraying location should be
according the contract requirements Check delivery note of each truck mixer if according to order, and note
any exceptions
General visual assessment of the supplied mix before transferred into thehopper
Visually check presence of fibre and possible fibre balling (if applicable)
Check visually for any separation of the concrete mix Measure slump or flow for each delivery
Never add water to the mix for correction of slump
Spraying of test panels and sampling as required according to contractQC requirement
In case of interruptions longer than 15 minutes, slump to be observed
and re measured
In case of exceptions, or any doubt, report to responsible site engineerfor approval prior to start of application
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Vicat Test testing the reactivity of cement with accelerator
Interpretation of results:Initial set < 2 min 4 min
Final set < 5 min < 8 min > 8 min
Rating Good Acceptable Not acceptable
E l St th T ti P t t
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Early Strength Testing Penetrometer
Penetrometer Needle For testing of early strength
from 0.2 to 1.0 MPa
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Early strength testing -Hilti Pull Out Tester V
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Early Strength Testingusing stud driving from
3 to 12 MPa
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Compressive Strength Testing
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Test Spray Panels Coring of Spray Panels
For Compressive Strength > 10 MPa
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Pre-ApplicationDelivery Acceptance 1 Litre Test
1 2
3 4
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Calculation of Accelerator Dosage
What we need to Know ?
Weight of cement in kg per m3 (Cementkg )
Weight of Silica Fume / PFA / Slag (
Binder kg)
Output of concrete pump ( Qc m3 / hr)
Density of Accelerator ( D = kg /L)
Dosage of Accelerator in % by weight of
cement ( %)
Formula is :
( Cement kg + Binder kg ) x (m3/ hr) x (%) / 60 min/hr / D
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