Roller Compacted Concrete Embankments and Spillways

Roller Compacted Concrete
Embankments and Spillways
Coal Refuse Disposal Facility Seminar
April 10, 2014
Jonathan Pittman, PE
schnabel-eng.com
What is RCC?
Roller compacted concrete (RCC) is a
concrete of zero slump consistency in its
unhardened state that is transported,
placed, and compacted using earth and
rockfill construction equipment.
A little bit of history on RCC…
1951 to 1977: Number of New Mass Concrete
Dams Experiences Significant Drop-off ($$$)
1964: Alpe Gera Dam in Italy
1970 to 1973: TVA and USACE Research
1975: Emergency Repair of Tarbela Dam Outlet
Tunnel in Pakistan
1978: Japan Uses RCC for Shimajigawa Dam
1982: 433,000 CY of RCC Placed for USACE
Willow Creek Dam in Oregon
Most Common Applications
Water Dams
What about coal refuse
disposal impoundments?
Pavements
What Are The Major Performance
Requirements/Objectives for Dams?
BALANCING
COST AND
LONG-TERM
PERFORMANCE
STABILITY
SEEPAGE
CONTROL
DURABILITY
…RCC is a great option!
Use the Following Strategies to Achieve
These Requirements / Objectives
Mix Proportions
 Material Quality / Aggregate Production
 Batching / Mixing Operations
 Placement
 Compaction
 Verification
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Factors Affecting RCC Mix Design
Durability / Long Term Performance
 Size of Project
 Materials Available
 Cost
 Thermal Requirements
 Bond / Bedding
 Aesthetics
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RCC Ingredients…that looks familiar!
Cement
Fine Aggregate
Pozzolans
Coarse Aggregate
Admixtures
Ingredients…Conventional vs. RCC
Well, what about all that aggregate
we already have?
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Potential advantage
Base course gradations typically result in a
more well-graded, workable mix that requires
less cementitious material and water
Fines content ↑ - Water ↑ - Strength ↓
Mix Properties
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Strength (fc’ and lift joints)
 fc ’
typically ranges from 2,000 to 4,000 psi
 Lift Joints: Φ = 40-45 deg; c = 50-100 psi
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Wet Unit Weight
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Typically 145 to 155 pcf
Uniformity
 Compactability / Workability

RCC On-Site Mixing and Batching
Continuous Flow-Through Pugmill
Batch Plant
Bowen, 2011
RCC Transportation
Goal is Prompt, Non-Segregated Delivery…
Options
 Trucks
 Loaders
 Trackhoes
 Scrapers
 Conveyor Belts
 Crane and Bucket
 Combination
Considerations
 Freefall Height
 Pile Height
 Handling
 Technique for
Depositing
 Contamination
Clute, 2011
Segregation
Clute, 2011
RCC Placement

Typically spread in lifts by a bulldozer

12” thick compacted lift is typical
Placement rates vary (100 – 1,000 cy/day)
 “Continuous” operation – typ. and preferred

Thermal Considerations
Influenced by individual mix materials
 Cooling requirements or seasonal
placement restrictions are common
 Delicate balance of ensuring long-term
performance vs. increased costs

RCC Compaction
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98% of Apparent Maximum Density (AMD)
Determine no. of passes and equipment
required to achieve density in test section
Start compaction within 10 min of spreading
Take Care Not to Over-Compact…
Lift Joint Treatment – Fresh, Warm or Cold?
Clute, 2011
Steps – Unformed or Formed?
QA/QC
Visual Inspection /
Observation
 Field & Lab Testing
 Instrumentation

QA/QC
Nichols, 2011
Let’s Talk About Cost!?
Hansen, 2011
What Drives the Cost of RCC?
Economy
 Fixed Costs

Plant
 Test section
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Unit Costs
Aggregate availability and gradation
 Cement / Fly Ash
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Production
Placement complexities
 Specified restrictions

Main Dam
Can’t go upstream or downstream, but I need
more storage or it’s time to build the cap!
What about RCC for this guy?
Saddle Dike
I’m at this little saddle in the ridge and I’ve
got no room to build a dike!
Open Channel Spillway
So, let’s take this example a little further…
Open Channel Spillway
Requirements and Objectives
1)
2)
3)
Capacity
Durability
Stability
4)
5)
6)
Cost
Seepage Losses
Aesthetics
Open Channel Spillway Example
Mix and Design Details
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Total RCC Volume of 5,000 CY (20’ Raise)
Pugmill On-Site
Deposited by Conveyor
No – Trial Mix Design / Yes – Test Section
50/50 Cement and Fly Ash
Off-Site Aggregate
Less Stringent Thermal Requirements
Lift Joint Preparation
Thorough Cleaning
 Typically No Bedding Mortar

Open Channel Spillway Example
Cost Estimate
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RCC Quantity = 5,000 CY
Relatively small quantity results in higher upfront costs per CY
Simple, mass placement (no joints, etc.)
Less stringent mix design, thermal, and lift
joint requirements result in lower cost
Reasonable cost might be $110/CY
Cost of RCC = 5,000 CY x $110/CY = $550k
Need to also consider foundation prep, etc.
Open Channel Spillway Example
Schedule Estimate
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Production estimate considers small quantity and
placement area versus simple, mass placement
Reasonable production rate may be 200 cy/day
Assume production schedule of 10 hrs/day
RCC Schedule ~ 25 days
Need to consider time for mobilization, setup,
trial mix design (not required), uniformity testing,
test section, foundation prep, etc.
Why RCC?
Flexibility in Design and Construction
 Much Smaller Footprint
 Readily Available Equipment
 Potential On-Site Aggregate Source
 Durability and Erosion Resistance
 Rapid Placement
 Relatively Low Cost
 Proven Performance
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Lots of Great Info Out There!
schnabel-eng.com

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