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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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