SEMINARIOINTERNACIONAL - ICHich.cl/.../uploads/...shotcrete_07_JOLIN_DurabilityEvaluation.pdf ·...
Transcript of SEMINARIOINTERNACIONAL - ICHich.cl/.../uploads/...shotcrete_07_JOLIN_DurabilityEvaluation.pdf ·...
SEMINARIO INTERNACIONAL “Diseño y Durabilidad del Shotcrete”
Durability & Evalua.on of Shotcrete
Plan
• Evalua)on & Durability of Shotcrete – Specifica)ons – Tes)ng & Evalua)on – Cer)fica)on
• Shotcrete service-‐life modeling
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!
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
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.
ACI SHOTCRETE NOZZLEMAN CERTIFICATION
• 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
ACI SHOTCRETE NOZLEMAN
CERTIFICATION -‐ PANEL
LAYOUT -‐
750 mm
ref.: CP60-‐09
ACI Shotcrete Nozzleman Cer)fica)on
• Grade « 1 »
ACI SHOTCRETE NOZZLEMAN CERTIFICATION
-‐ CORE GRADING -‐
ACI Shotcrete Nozzleman Cer)fica)on
• Grade « 5 »
ACI SHOTCRETE NOZZLEMAN CERTIFICATION
-‐ CORE GRADING -‐
Observa)on
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
Pre-Construction Qualifications
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:
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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Early age compressive
strength
Bernard & Geltinger, 2007
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
Compressive Strength Standard compressive strength, and many other tests, are measured on cores taken
from panels
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”
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
Toughness of FRS ASTM C1550 Round Panel Test
Other samples need to be cut-out from panels (e.g.: all beam tests)
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.
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)
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
DURABILITY
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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
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
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
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 !
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 ?
• 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
Which parameters influence BWA?
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
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 (%)
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
– 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
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
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, ...
Transport properties • Transport
mechanisms – Permeability – Water diffusivity – Ionic diffusivity – Capillary
absorption
Transport properties • Transport
mechanisms – Permeability – Water diffusivity – Ionic diffusivity – Capillary
absorption
Movement of water resulting from a pressure gradient
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)
Transport properties • Transport
mechanisms – Permeability – Water diffusivity – Ionic diffusivity – Capillary absorption
Movement of ionic species resulting
from a concentration gradient
RCPT test!
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!
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
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
Service life modeling
A multiphase transport and reaction model that can predict the degradation of cement-based materials exposed to a wide range of aggressive environments
STADIUM®
Service Life Prediction
• Simulation example (STADIUMTM)
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
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
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
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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