roller compacted concrete embankments and spillways
TRANSCRIPT
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Roller Compacted ConcreteEmbankments and Spillways
Coal Refuse Disposal Facility SeminarApril 10, 2014
Jonathan Pittman, PE
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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.
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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…
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Most Common Applications
Water Dams
Pavements
What about coal refuse disposal impoundments?
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STABILITY
DURABILITY
SEEPAGECONTROL
What Are The Major Performance Requirements/Objectives for Dams?
BALANCING COST AND
LONG-TERM PERFORMANCE
…RCC is a great option!
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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 Pozzolans
Fine Aggregate Coarse Aggregate
Admixtures
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Ingredients…Conventional vs. RCC
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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 ↓
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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
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RCC On-Site Mixing and Batching
Continuous Flow-Through Pugmill
Bowen, 2011
Batch Plant
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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
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Segregation
Clute, 2011
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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
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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
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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…
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Lift Joint Treatment – Fresh, Warm or Cold?
Clute, 2011
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Steps – Unformed or Formed?
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QA/QC
Visual Inspection / Observation
Field & Lab Testing Instrumentation
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QA/QC
Nichols, 2011
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Let’s Talk About Cost!?
Hansen, 2011
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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
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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?
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Saddle Dike
I’m at this little saddle in the ridge and I’ve got no room to build a dike!
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Open Channel Spillway
So, let’s take this example a little further…
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Open Channel SpillwayRequirements and Objectives
1) Capacity2) Durability3) Stability
4) Cost5) Seepage Losses6) Aesthetics
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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
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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.
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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.
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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!
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