presentation-sprayed concrete qc issues (customer)

7/27/2019 Presentation-Sprayed Concrete QC Issues (Customer)

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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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6

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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