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Roller Compacted ConcreteEmbankments and Spillways
Coal Refuse Disposal Facility SeminarApril 10, 2014
Jonathan Pittman, PE
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.
1982: 433,000 CY of RCC Placed for USACE Willow Creek Dam in Oregon
1978: Japan Uses RCC for Shimajigawa Dam
1975: Emergency Repair of Tarbela Dam Outlet Tunnel in Pakistan
1970 to 1973: TVA and USACE Research
1964: Alpe Gera Dam in Italy
1951 to 1977: Number of New Mass Concrete Dams Experiences Significant Drop-off ($$$)
A little bit of history on RCC…
Most Common Applications
Water Dams
Pavements
What about coal refuse disposal impoundments?
STABILITY
DURABILITY
SEEPAGECONTROL
What Are The Major Performance Requirements/Objectives for Dams?
BALANCING COST AND
LONG-TERM PERFORMANCE
…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
Factors Affecting RCC Mix Design
Durability / Long Term Performance Size of Project Materials Available Cost Thermal Requirements Bond / Bedding Aesthetics
RCC Ingredients…that looks familiar!
Cement Pozzolans
Fine Aggregate Coarse Aggregate
Admixtures
Ingredients…Conventional vs. RCC
Well, what about all that aggregate we already have?
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
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
Wet Unit Weight Typically 145 to 155 pcf
Uniformity Compactability / Workability
RCC On-Site Mixing and Batching
Continuous Flow-Through Pugmill
Bowen, 2011
Batch Plant
Options Trucks Loaders Trackhoes Scrapers Conveyor Belts Crane and Bucket Combination
RCC Transportation
Considerations Freefall Height Pile Height Handling Technique for
Depositing Contamination
Goal is Prompt, Non-Segregated Delivery…
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
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
Unit Costs Aggregate availability and gradation Cement / Fly Ash
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 SpillwayRequirements and Objectives
1) Capacity2) Durability3) Stability
4) Cost5) Seepage Losses6) Aesthetics
Open Channel Spillway ExampleMix and Design Details
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 ExampleCost Estimate
RCC Quantity = 5,000 CY Relatively small quantity results in higher up-
front 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 ExampleSchedule Estimate
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
Lots of Great Info Out There!
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