SHOTCRETE ADVANCEMENTJANUARY 15, 2019
Lihe (John) Zhang, Ph.D., P.Eng.,
LZhang Consulting & Testing Ltd, Vancouver, BC, Canada
Email: [email protected] Tel: 7787067198
LZhang Consulting & Testing Ltd, Vancouver, BC, Canada 1
Contents
Shotcrete Basic and Industrial Overview
Recent Development: structural shotcrete
Recent Development: shotcrete for ground support
New Technology: fiber reinforcement with hemp-basednatural fiber
New Technology: durability
Code and Standard: ACI, ASA, etc
Future Development
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Shotcrete 101– Wet-mix Shotcrete: Concrete is pumped through a hose and air is
added at the nozzle to accelerate the mixture to a high velocity.Most widely used in US and Canada, Australia, Europe, Singapore,Japan, Korea, and started to be used in China. Applied by eitherhand nozzlling or robotic sprayer nozzlling.
– Dry-mix Shotcrete: The dry concrete mixture is conveyed through a hosein an air stream at high velocity; water is added at the nozzle to produceplastic material on impact. Mixing of water and the dry material occursat the nozzle and on the receiving surface. Materials normally requirepredempening, either by hydro nozzle or predempener. Most widelyused in US and Canada, China. Applied primarily by hand nozzlling.
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Shotcrete 101 Rebound: Shotcrete material which ricochets off the receiving surface
Rebound for wet-mix: > 8-15% Rebound for dry-mix: : > 13-18% or
even higher
Shotcrete 101 Overspray: Shotcrete material deposited remote from the intended receiving area
Overspray must be removed
Shotcrete 101: Mix DesignWet-mix Mass per m3 SSD Agg
[kg]Cement Type GU 410Silica Fume 40Coarse Aggregate (12.5-5 mm, SSD) 430Fine Aggregate (SSD) 1320Estimated Water, L 185Superplasticizer, L 1.00Hydration Control Admixture, L 1.0Air Content, (3.5-5.5% as-shot) -Total 2387
High cementitious content: fly ash, silica fume, slags, metakaolin, natural pozzalan, etc
Structural shotcrete: 50-100 mm slump; Underground shotcrete: 150-200 mm slump
Air content: entrained air to have higher as-batched air content, after shooting, as-shotair content will be 2.0-6.0%
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Shotcrete 101
Pumpability: mixture must be pumpable without plugging thepump, hose and nozzle
Shootability: mixture comes out from the nozzle and stay onthe wall
Stackability: when shooting structural wall, shotcrete will stackup without sloughing and sagging
Infrastructure Application John Hart Hydro Dam, Campbell River, BC. Underground headrace tunnel and underground
powerhouse completed on 2017
Upper Lillooet (Pemberton, BC) and Big Silver (Harrison Lake, BC) Hydroelectric project, 2014-2017
Ruskin dam spillway resurface, started 2012, and have 2 bays to complete
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Infrastructure ApplicationRock Support: WAC Bennett Dam, Hudson Hope, BC
Steel fiber reinforced dry-mix shotcrete
Infrastructure Application
Hwy 97 Stone Creek
Retaining Wall Stage I shotcrete
Prince George, BC
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Infrastructure ApplicationPort Mann Main Water Tunnel North Shaft Isolation Liner - Shotcrete
• Dry-Mix shotcrete appliedfrom a floating deck
• Dewater Shaft• Install Screed Rails• Commence Shooting
Shotcrete Quality Control• Mix design• Oversize aggregate, shotcrete balling, chunks of hardened
shotcrete• Nozzlemen qualification• Accelerator dosing pump calibration (if used)• Batching, mixing and delivery• Slump loss• Temperature control• Rebound• Construction QC test panels shooting & testing• Nozzlemen skills and shooting technique• Construction Monitoring
Structural Shotcrete:Pre-Construction Test Panels
Job specific pre-construction test panels
The most congested area
The section of structural shotcrete is based onpresentation from Mr. Chris Zynda (1949-2017)
Coring Pre-Construction Test Panels
Coring Pre-Construction Test Panels
Inspector evaluating cores
Coring Panel
Shotcrete with Embeds
Air lance (blow pipe) helper
Small vibrator
Typical ShotcreteApplication
Picture #1 Typical liftPicture # 2 Man LiftPicture # 3 Scaffolding
ShotcreteApplications
Structural
Architectural
ConcreteStructures
Limited only to
Application
Forming
Imagination
Forming Shotcrete
Fast easy lay-out
One sided
Less material
(use of recyclematerial)
Forming is the Key
Structural Shotcrete: Forming for Shotcrete
Tall single sided forming
Congested Rebar detail
Structural Shotcrete: Forming for Shotcrete
Ensure formwork is stable
Bracing may be needed to prevent over turning
Structural Shotcrete:Forming of Shotcrete
Large Formwork
Pre-fabricated
Crane set
Forms will be re-used
Structural Shotcrete:Sliding/Jump Forms
Single Form Design
Jump Form - Both SidesAre Finished
Structural Shotcrete: Forming Straight or Radius
Structural Shotcrete: Form Material
Foam FormingSystem – InsulatedSheet metal
StructuralShotcrete: Form Liner’s
Wood - Inlay Reveal
Plastic - Inlay Reveal
Structural Shotcrete: Face of Wall Patterns
Structural Shotcrete: Heavy Congested Rebar
May need Smaller Nozzle’s Special Mixes High Pressure Equipment Sufficient Air Volume Very Experienced
Nozzleman / Crew
Structural Shotcrete: Reinforcement
No end-of-wallforming
This will allowfull encasementof the rebar
Structural Shotcrete: Structural Shotcrete Walls
16 inch Walls
CongestedRebar
Pilasters
Stanford Bing Concert HallStanford University, CA
Structural Shotcrete: Structural Shotcrete Projects
Structural Shotcrete: Shotcrete Walls
Single Form Design
Re-used Plywood
Trowel Finish Face
Structural Shotcrete: Sand Float Finish
StructuralShotcrete:Parking Structures
Structural Shotcrete: Trowel Entry Walls
Structural Shotcrete: Freeform Shapes
Structural Shotcrete:Landscape Features
Structural Shotcrete: Stairway Walls
Structural Shotcrete: Curved Walls
Fiber Reinforced Shotcrete
Figure 2: The Q-Chart published in 1993 with classes of energy absorptionFiber Reinforced Shotcrete for Ground Support
Flexural Toughness
Energy absorption after shotcrete cracks
Fiber Reinforced Shotcrete
Flexural Toughness: Performance Requirements based on FlexuralToughness Tests (Closed loop testing equipment is required)
Beam Flexural Toughness based on ASTM C1609: Third Point BendingLoad of the Beams
42
Fiber Reinforced Shotcrete
42
Fiber Reinforced Shotcrete
LEVEL IV
LEVEL III
LEVEL II
LEVEL I
LEVEL V
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Flex
ural
Str
ess
(MPa
)
Deflection (mm)
STRESS-DEFLECTION DIAGRAM TO ASTM C1609
A
Span Length : 300 mmSample Width : 101 mmSample Depth : 102 mm
Macrosynthetic Fiber Reinforced Wet-Mix Shotcrete Flexural Toughnes Test Report
May 7, 2015
ASTM C1609 Beam Flexural Toughness Test for Macrosynthetic Fiber Reinforced ShotcreteClosed loop testing equipment is requiredTypical performance requirement:Toughness Performance Level: Minimum Level III
0
100
200
300
400
500
600
700
0
5
10
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0 10 20 30 40
Ener
gy [J
]
Load
(kN
)
Central Deflection (mm)
ASTM C1550 Round Panel Test
Load
Energy
Fiber Reinforced ShotcreteASTM C1550 Round Panel Flexural Toughness Test (Closed-Loop testing machine is required)
250 Joules at 3 days350 Joules at 7 days450 Joules at 28 days
Flexural Toughness based on ASTM C1550 Round Panel Test
Fiber Reinforced Shotcrete
ASTM C1550 Round Panel Test(Closed-Loop testing machine is required)
Performance Requirements based on Flexural Toughness Tests
Residual Tensile Strength based on BS EN 14651 / RILEM-TC-162-TDF
Fiber Reinforced Shotcrete
• Beam test to RILEM-TC-162-TDF: notched beam test• Dimensions: 6x6x22 “ (150x150x550 mm)• Used in UK and other European countries, closed-loop machine is required
Fiber Reinforced Shotcrete
Sequential Excavation Method (SEM), also called New Austrian TunnelingMethod (NATM)
Three biggest SEM caverns in North America:
1. Beacon Hill Station, Seattle, WA, completed on 2007. Steel fiberreinforced wet-mix shotcrete
2. New York Metro Transportation Authority (MTA) East Access, New YorkCity, completed on 2014. Steel fiber reinforced wet-mix and dry-mixshotcrete
3. San Francisco Chinatown subway station, San Francisco, CA, May 2016-February, 2018. Macrosynthetic fiber reinforced dry-mix shotcrete
Underground Shotcrete
Natural fiber, waste of agriculture, treated and coated.
R&D process for natural fiber to be used in the shotcete:1) Laboratory trial batch with fiber reinforced concrete, tested plastic
shrinkage, compressive strength, workability, beam flexuraltoughness.
2) Shotcrete trial batch and shooting. Wet-mix shotcrete was trial shotand tested for pumability, shootability, rebound, plastic shrinkage,finishability.
3) Shotcrete trial batch and shooting. dry-mix shotcrete was trial shotand tested for pumability, shootability, rebound, plastic shrinkage,finishability.
4) Field project trial. A pilot project was used to apply the fiber to thestructural shotcrete. Shootability, pumpability, and finishability weresatisfactory. Contractors, in particular, nozzlemen were very satisfiedwith it.
5) This fiber is now being widely used in the wet-mix and dry-mixshotcrete. The fiber has been specified to be used in the 2022Beijing Winter Olympic Bob Luge Track shotcrete construction.
New Technology: hemp-based natural fiber
Control of plastic shrinkage
ASTM C1579 Evaluation of Plastic Shrinkagefor Restrained Fiber Reinforced Concrete
Plain wet-mix shotcrete (WP) developed an average crack width of 0.63mm(0.025 in), which satisfies the ASTM C1579 requirement.Microsynthetic fiber wet-mix shotcrete (WSF) developed an average crackwidth of 0.10mm (0.004 in)Natural fiber wet-mix shotcrete (WNF) developed an average crack width of0.05mm (0.002in).
New Technology: hemp-based natural fiber
MixtureFiber Content Crack Reduction
Ratio (CRR), %(kg/m3) (% volume)
WP 0 0 N/A
WNF 2 0.15 92
WSF 1.35 0.15 84
Thickness buildup at vertical orientationEnhance overhead thickness buildup
New Technology: hemp-based natural fiber
Microsynthetic fiber reinforced wet-mixshotcrete sloughed off plywood panelafter being disturbed by cutting
Cutting and trimming natural fiber mixnatural fiber reinforced wet-mixshotcrete with no sagging or sloughing
Pumpability: with 50-100 mm (2-4”) slump,mixture is sticky and in favor of pumping
Finishability
Megnsium finish
Fibers were not pulled out to the surfaceAs they are Hydrophilic, not Hydrophobic
Refer to: Shotcrete magazine, 2017 Fall,“New Hemp-Based Fiber Enhances Wet-Mix Shotcrete Performance”
New Technology: hemp-based natural fiber
Challenges of Shotcrete:Is shotcrete durable ?
Will shotcrete be as durable as cast-in-place concrete ?
Durability
-Chemical resistant: use sufficient supplementary cementitiousmaterials
-Freeze-thaw resistant: air entrainment
--Transport properties: permeability, porosity, chloride ionmigration, tortuosity
Designed service life and durability requirements will overrideminimum structural strength requirements
Research Program on TransportProperties of Shotcrete
Absorption (liquid uptake in a porous medium)
Diffusion (liquid, gas or ion movement under a concentration gradient)
Permeability (resistance to flow of a liquid under a pressure gradient)
Sorbtivity (absorption of a liquid by capillarity)
Wicking (capillary transport through a porous medium to a drying surface)
Lower porosity -> lower coefficient of diffusion ->
longer time for ions to diffuse to the reinforcement
-> durable structure
Research carried out by LZhang Consulting & Testing,
Sponsored by Canadian National Science & Engineering ResearchCouncil (NSERC): Industrial Post-Doc Fellowship 2013-2016
Sponsored by American Shotcrete AssociationL. Zhang, D. R Morgan, S. Mindess “Comparative Study of Transport Property of Shotcrete vs. Cast-in-PlaceConcrete ” ACI Materials Journal, V. 113, No. 3, May-June 2016, pp 373 – 384.
Research Program on TransportProperties and Durability of Shotcrete:Analysis & Modeling ProgramSTADIUM program, specifiedin US Navy (UFGS) 03 31 29USACENASA
Transport properties
Service life prediction
Research Program on Transporties ofShotcreteA total of 3 mixes were cast and 15shotcrete mixes were shotOver 50 test panels were shot, over500 shotcrete cores were extractedand tested
Durability – Transport PropertyPermeability
Permeability of shotcrete is lower than concrete
0
2
4
6
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10
12
Concrete(Cement)
Concrete (FlyAsh)
Concrete (SilicaFume)
Shotcrete(Cement)
Shotcrete (FlyAsh)
Shotcrete (SilicaFume)
K, P
erm
eabi
lity
, e-2
2 m
2
LZhang: Transport Property of Cast-in-Place Concrete vs ShotcreteK, Permeability, e-22 m2 from Drying Test
Durability – Transport PropertyCoefficient of Diffusion of Ions to US Navy (UFGS) Specification 03 31 29 Marine Concrete
Shotcrete process produces lower chloride penetration
0.0
0.5
1.0
1.5
2.0
2.5
CIP Cast C CIP CastFA
CIP Cast SF Wet Cast C Wet CastFA
Wet CastSF
Wet Shot C Wet ShotFA
Wet ShotSF
Effe
ctiv
e C
oeff
icie
nt o
f Dif
fusi
on, D
if[O
H-]
x V
PV,
(10-
11 m
2/s)
Effective Coefficient of Diffusion from Ionic Migration Test
Durability – Transport PropertyResults show that the transport properties for properly applied shotcrete areequal to better than cast CIP concrete and cast shotcrete.
Shotcrete Service Life Modelling by STADIUM: Marine Dock, Tampa, Florida
Service Life Modelling by STADIUM:Chicago Parking Structure, 300 mm thick
Shotcrete with Fly Ash
American Concrete Institute ACI 506.R-16 Guide for Shotcrete ACI 506.E-13 Specification for Shotcrete ACI 506.6T-17 Visual Shotcrete Core Quality Evaluation ACI 506.5R-17 Guide for Specifying Underground Shotcrete
On 2018 October 17, ACI 318 passed the addition of shotcrete to the ACI 318-19Code.
It is a very significant milestone for the shotcrete industry and will allow shotcreteplacement to be more widely accepted in structural concrete. Several of youwanted us to get the word out (press release, WITM, etc) which we will do.However, I wanted to point out the overall ACI 318 approval process isn’t quitecomplete, so I think it is a bit premature to start spreading the word.
Yes, the ACI 318 committee approved shotcrete provisions, and completed theirwork on the 318-19 version of the Code. But there is still some “process” left. Thecompleted version is sent early next week to the ACI Technical ActivitiesCommittee (TAC) for review.
• ACI C660 ACI Certified Shotcrete Nozzleman (Started from 1999)• ACI Shotcrete Inspector Program (in progress)
ACI Certified Shotcrete Nozzleman• ACI C660 ACI Certified Shotcrete Nozzleman (Started from 1999)
• wet-mix vertical• wet-mix overhead• dry-mix vertical• dry-mix overhead
Useful Reference for ShotcreteAmerican Shotcrete Association:
Shotcrete magazine (published quarterly)
it is FREE Subscribe to www.shotcrete.org
Shotcrete forUnderground Support Publications by Dr. Rusty Morgan
Shotcrete book contains 10 publications on fiber reinforcedshotcrete/shotcrete for underground support in US, Canada& other countries
Norwegian Concrete Association: International Symposium onSprayed Concrete Modern Use of Wet-Mix SprayedConcrete for Underground Support 2014 – Sandefjord, Norway; 2018 – Treidham, Norway
Future for ShotcreteRefer to “Shotcrete magazine, 2019 Winter President Message”
Sophisticated complex concrete structures with complicated reinforcement details are nowbeing constructed with shotcrete. Examples: thick structural walls are being constructedusing shotcrete as a final lining method in subway station structures.
-Contractors really need good experience with shotcrete materials and mixturedesigns, equipment and competent shotcrete crews.
-Rigorous construction monitoring/inspection/QC testing needs to be provided fromthe owner’s side.
-Collaboration with the structural design engineer.
Durability of shotcrete structures: Ongoing research and engineering projects are beingconducted to assess the durability of shotcrete. Durability aspects being evaluated includechloride penetration, ionic migration, heat of hydration and service life prediction andvalidation.
Repair and rehabilitation: ACI 562 is proposing code changes of concrete structures repairand rehabilitation. Shotcrete is considered as a construction method to meet theperformance requirements for repair projects.
New materials to enhance workability, pumpability and shootability of shotcrete
Equipment advancement
In summary, the future for the shotcrete industry is bright.
