SEMINARIOINTERNACIONAL - ICHich.cl/.../uploads/...shotcrete_07_JOLIN_DurabilityEvaluation.pdf ·...
Transcript of SEMINARIOINTERNACIONAL - ICHich.cl/.../uploads/...shotcrete_07_JOLIN_DurabilityEvaluation.pdf ·...
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SEMINARIO INTERNACIONAL “Diseño y Durabilidad del Shotcrete”
Durability & Evalua.on of Shotcrete
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Plan
• Evalua)on & Durability of Shotcrete – Specifica)ons – Tes)ng & Evalua)on – Cer)fica)on
• Shotcrete service-‐life modeling
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Tes)ng & Specifica)ons
• What tests can be run on shotcrete? – Shotcrete IS concrete… so: everything we do for regular concrete !
• What should be part of a good specifica)ons ? – THAT… is the ques)on!
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Quality Control + Before-Construction +
• Qualify shotcrete crew using proposed materials and equipment
• Crew knowledgeable of the specification requirements
• Use approved shotcrete mixtures • Use of qualified nozzlemen
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Qualified Nozzlemen
• A lot can be said about this item! The qualification and experience of the nozzle-man are KEY to the success of a shotcrete job ! • ACI Certified Nozzleman and/or • Preconstruction mock-ups
…are the two most popular approaches used.
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ACI SHOTCRETE NOZZLEMAN CERTIFICATION
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• Consists of: – WriLen examina)on (75% passing grade) – Performance examina)on
• Checklist • Test Panels
– Dry-‐ and Wet-‐Mix Shotcrete • Ver)cal only (Mandatory) • Ver)cal and Overhead
– Cer)ficate valid for 5 years
ACI Shotcrete Nozzleman Cer)fica)on
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ACI SHOTCRETE NOZLEMAN
CERTIFICATION -‐ PANEL
LAYOUT -‐
750 mm
ref.: CP60-‐09
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ACI Shotcrete Nozzleman Cer)fica)on
• Grade « 1 »
ACI SHOTCRETE NOZZLEMAN CERTIFICATION
-‐ CORE GRADING -‐
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ACI Shotcrete Nozzleman Cer)fica)on
• Grade « 5 »
ACI SHOTCRETE NOZZLEMAN CERTIFICATION
-‐ CORE GRADING -‐
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Observa)on
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Pre-Construction Qualifications • Shotcrete mixture design*
– Test panels for shotcrete performance tes)ng (compressive strength, absorp)on voids, air void distribu)on, toughness, etc.)
• Mock-‐up test panels with appropriate reinforcement and geometry* – Evaluate with core grading, saw cuang and visual examina)on
* If necessary
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Pre-Construction Qualifications
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Quality Control + During-Construction +
• For fresh wet-‐mix shotcrete: • Slump, temperature (& air content)
• For hardened concrete – Samples for the delivery truck (QC) – Shoot test panels at required intervals and test for:
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Specifications Typical Performance Requirements
Test Description Test Method Requirement
Early age compressive strength (15 minutes +)
See Bernard & Geltinger, 2007 ; Shotcrete Mag.
Ask your ground support engineer!
Compressive Strength of Cores (28 days)
ASTM C1604 Min 4000 psi (28 MPa) to 5800 psi (40 MPa)
Boiled Absorption
ASTM C642
Max 8% - 10%
Bond Strength Min 1 MPa at 28 days
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ICH Capacitación
Early age compressive
strength
Bernard & Geltinger, 2007
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Specifications Typical Performance Requirements
Test Description Test Method Requirement
Early age compressive strength (15 minutes +)
See Bernard & Geltinger, 2007 ; Shotcrete Mag.
Ask your ground support engineer!
Compressive Strength of Cores (28 days)
ASTM C1604 Min 4000 psi (28 MPa) to 5800 psi (40 MPa)
Boiled Absorption
ASTM C642
Max 8% - 10%
Bond Strength Min 1 MPa at 28 days
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Compressive Strength Standard compressive strength, and many other tests, are measured on cores taken
from panels
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Shotcrete Test Panels
“Proper handling of freshly applied specimens requires they be protected from damage due to extremes of temperature and vibraCng movements, shaking, or shock during the hydraCon process”
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Specifications Typical Performance Requirements
Fiber Reinforced Shotcretes
Test Description Test Method Requirement
Flexural Strength ASTM C1018
Min 580 psi (4MPa) at 7 days
Toughness – Beam Tests • Toughness factor, MPa • Toughness performance levels • Residual load
ASTM C1399, C1609
* * *
Toughness - Round Panel Test (Joules) ASTM C1550 150 – 400 J
Square panels (all supported - Joules) EFNARC 300 – 1000 J
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Toughness of FRS ASTM C1550 Round Panel Test
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Other samples need to be cut-out from panels (e.g.: all beam tests)
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Elements of a good specifica)ons
What is needed in a spec is closely linked to the type of job at hand
• Intended purpose: mechanical strength, durability, water )ghtness, etc.
• The shotcrete process and the mixture design: – Wet-‐mix or Dry-‐mix – Presence of fibres, presence of accelerator, etc.
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Example: Shotcrete for ground support in mining
• “Regular” shotcrete – Maximum amount of rebound – Early age compressive strength (4, 8, 12h) – Compressive strength (3, 7, 28d) – Boiled absorp)on
• Fibre reinforced shotcrete + Toughness tests (C1550)
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Specifica)on & Tes)ng
• Be careful and don’t go crazy on QA & QC, it’s very costly! – Establish what you need technically, validate it at the beginning
– Run regular QC checks for the simpler (cheaper) tests: compressive strength and absorp)on (and fibre content).
– Less ooen, run the more complex and costly tests
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DURABILITY
ICH Capacitación
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Durability
• There is a definite trend in the concrete industry toward sustainability and design of green structures
• This has brought concepts such as service life and design life in the concrete industry
• Unfortunately, there is very little information available on service life of shotcrete specifically
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Challenge
• Predict long term durability of various types of shotcrete
• … which is the same problem we find in practice with regular cast in-place concrete – past experience, QA/QC, etc.
• Same approach: low w/cm, good aggregates, proper consolidation and curing
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Durability
• Shotcrete shows more voids than regular concrete – Absorption values and volume of permeable
voids are higher than that generally found for similar concrete
– however…
• Shotcrete is generally reported as having an excellent durability
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Durability
• Specification often refers to absorption (ASTM C642) and to RCPT (ASTM C1202) of shotcrete
• The industry now often relies on the boiled water absorption (BWA) or RCPT to estimate the durability of shotcrete!
[Morgan et al., 1987]
Which is the source of animated
discussion both around the construction site and technical committee meetings !
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Challenge
• Considering that the placement process changes the in-place composition and has an impact on the consolidation level,
• and apart from compressive strength (and toughness), what else should we be controlling shotcrete quality for:
• Boiled water absorption ? • Rapid chloride permeability test ? • Air void parameters ?
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• Shotcrete characterization Fresh Shotcrete Hardened Shotcrete
In-place mixture composition
Rebound
Consistency (dry)
Slump (Wet) Air Content (Wet)
Compressive strength (ASTM C1604) Air void system (ASTM C457)
BWA (ASTM C642) RCPT (ASTM C1202)
In-‐house test procedures performed to predict the service life of shotcrete with the STADIUM™ sooware
Experimental program
Migration test Drying test
Pore solution extraction and analysis
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Which parameters influence BWA?
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Aggregate gradation • Influence of the aggregate gradation
– Cast mixtures – Air content, W/B, binder, paste volume are
kept constant
4
5
6
7
8
50 65 80
BW
A (%
)
Sand / Coarse aggregate
65/35 80/20 50/50
3000
4000
5000
6000
7000
8000
9000
50 65 80
RC
PT (C
oulo
mbs
)
Sand / Coarse aggregate 50/50 65/35 80/20
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Paste (cement+water+air) • Influence of the paste volume
– Cast mixtures – Air content, W/B, binder, agg. gradation are
kept constant
4
5
6
7
8
35 40 45
BW
A (%
)
Paste volume (%)
4000
5000
6000
7000
8000
9000
35 40 45 R
CPT
(Cou
lom
bs)
Paste volume (%)
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W/Cm ratio
– Dry- and Wet- Shotcrete
4
6
8
10
0,3 0,4 0,5 0,6 0,7
Abs
orpt
ion
(%)
W/Cm
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– Dry- and Wet- Shotcrete
4
6
8
10
0,3 0,4 0,5 0,6 0,7
Abs
orpt
ion
(%)
W/Cm
Mortiers Voie sèche Voie humide Lineal (Mortiers) Lineal (Voie sèche) Lineal (Voie humide)
ACI #1 - Mortar
W/Cm ratio
Vpaste∈ [37.9%, 39.1%] Vpaste∈ [33.2%, 35.2%]
Vpaste∈ [29.6%, 30.2%]
In-between
ACI #2 - Concrete
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Discussion – Durability criterion
0
1000
2000
3000
4000
5000
6000
0 2 4 6 8 10 12
RC
PT (C
oulo
mbs
)
BWA (%)
Marginal Excellent Good Fair
High
Moderate
Low
Very low
Silica fume
Fly ash
OPC
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Durability • Concrete durability
– Chemical attack • Soft water attack (leaching) • External sulfate attack • Acid attack
– Reinforcement corrosion • Carbonation • Chloride ingress
– Alkali-Aggregate Reaction – Frost attack
• Freezing-thawing cycles • Scaling
– Thermal effects, erosion, ...
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Transport properties • Transport
mechanisms – Permeability – Water diffusivity – Ionic diffusivity – Capillary
absorption
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Transport properties • Transport
mechanisms – Permeability – Water diffusivity – Ionic diffusivity – Capillary
absorption
Movement of water resulting from a pressure gradient
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Transport properties • Transport
mechanisms – Permeability – Water diffusivity – Ionic diffusivity – Capillary
absorption
Movement of water vapour resulting
from a relative humidity gradient
– Crucial parameter in presence of wetting/drying cycles:
• Wetting: Concrete absorbs water • Drying: Water evaporates
from concrete (moisture transport)
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Transport properties • Transport
mechanisms – Permeability – Water diffusivity – Ionic diffusivity – Capillary absorption
Movement of ionic species resulting
from a concentration gradient
RCPT test!
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Transport properties • Transport
mechanisms – Permeability – Water diffusivity – Ionic diffusivity – Capillary
absorption
Suction of water resulting from the surface tension exerted in the capillary porosity
Surface tension BWA test!
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Discussion – Durability criterion
0
1000
2000
3000
4000
5000
6000
0 2 4 6 8 10 12
RC
PT (C
oulo
mbs
)
BWA (%)
Capillary Absorption
Marginal Excellent Good Fair
High
Moderate
Low
Very low
Silica fume
Fly ash
OPC
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Therefore… • Main transport properties
– Permeability è Pressure – Moisture diffusion è R.H. gradient – Ionic diffusion è Concentration gradient – Capillary Absorption è Surface tension
• Every mechanism refers to a distinct physical phenomenon (or driving force!)
• The environmental exposure should be considered to decide which test is relevant
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Service life modeling
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A multiphase transport and reaction model that can predict the degradation of cement-based materials exposed to a wide range of aggressive environments
STADIUM®
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Service Life Prediction
• Simulation example (STADIUMTM)
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Service Life Prediction • Comparison of 4 mixtures
1. Control concrete: W/Cm=0,45 – Type GU+8% SF
2. Dry-mix shotcrete: W/Cm=0,51 – Type GU+10% SF
3. Wet-mix shotcrete: W/Cm=0,40 – Type GU+8% SF
4. Dry-mix mortar: W/Cm=0,47 – Type GU+12% SF
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Service Life Prediction
BWA = 5%
BWA= 7.5%
BWA = 4.2%
BWA = 7.2%
Chlorid
e concen
traF
on
@ 25 mm dep
th
Time (year)
SUMMA Concrete – 0.45 Dry-‐mix Shotcrete – 0.51 Wet-‐mix Shotcrete – 0.40 Dry-‐mix Mortar – 0.47
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Conclusion • The aggregate gradation by itself does not
affect shotcrete transport properties • The placement process, through rebound,
will affects the in-place paste volume • Paste volume, W/Cm ratio, and the presence
of SCM affect shotcrete transport properties
• In shotcrete, BWA is not a reliable durability criteria; it is poorly correlated with tests that measure diffusion coefficients
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Comments
• However: – This study is for stable, homogeneous, well compacted shotcretes
– It does NOT take into account prac)cal situa)ons that can represent poten)al (durability) problems:
• excessive rebound • long transport )me • high usage of admixture (SP, stabilizers, accelerators)
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