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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


•  Grade « 1 »


-‐ CORE GRADING -‐


•  Grade « 5 »


-‐ 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

ICH Capacitación

Early age compressive

strength

Bernard & Geltinger, 2007



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”


Fiber Reinforced Shotcretes


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

ICH Capacitación

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



absorption

Movement of water resulting from a pressure gradient



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)


mechanisms – Permeability – Water diffusivity –  Ionic diffusivity – Capillary absorption

Movement of ionic species resulting

from a concentration gradient

RCPT test!


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)

ICH Capacitación

ICH Capacitación

Marc JOLIN, prof. Dep of Civil Eng. Laval University

[email protected]

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