Quality in the Concrete Paving · PDF fileQuality in the Concrete Paving Process CPU 6- 6 ......

Quality in the Concrete Paving Process

Module 2 CPU 6- 1

Workshop Introduction

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Instructors

Dennis Dvorak

Jim Grove

Mike Praul

FHWA Resource Center

(708) 283-3542

dennis.dvorak@dot.gov

ATI Inc. / FHWA

Office of Infrastructure, Washington D.C. (515) 294-5988

jim.grove@dot.gov

FHWA Maine Division

(207) 512-4917

michael.praul@dot.gov

CPU 6- 3

Agenda Workshop Introduction

Module 1: Quality Assurance Concepts

Module 2: Concrete Materials

Module 3: Concrete Properties and Testing

Module 4: QC and Agency Acceptance

Module 5: Pre-Paving and Mix Production

Module 6: Paving

Module 7: Utilizing Quality Concepts

Module 8: Quality in Field Practice

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What is this Workshop about?

Common Sense Tools

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Goal: Plant Seeds

What do you do today? What are you striving to accomplish? What should the agency test and inspect? What should the contractor test and inspect? How should we accept concrete pavement? What new tools and technologies can you use

to build better pavements?

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CPU 6 Learning Objectives

By the end of this module, you will be able to • Name four key inspection items of dowel bar

placement • Identify three inspection items for aggregate

stockpiles • Describe four advantages of stringless paving • Explain the purpose of the two types of texture

provided by the burlap drag and the tining. • Name two aspects of sawing that are critical to

preventing random cracks.

Module 2 CPU 6- 7

Pre-Paving and Mix Production

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Pre-Paving Activities

Pre-Paving (Chapter 4) Subgrade/Subbase Construction Staking, Stringline and Stringless Construction Fine Grading Dowel Basket Placement Steel Placement (CRCP) Paver Preparation

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Foundation System

Stiffness Stability Uniformity

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Staking and Stringline

Paving hubs and construction stakes • Set to the proper offset and projected grade

Stringline • Securely place pins • Adjust tension with winches and tie-offs • Eyeball for smoothness

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Stringless

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Stringless Construction

Advantages • Smoother pavement • Safer construction site • Eliminates staking operation • Facilitates one-lane construction

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Fine Grading

Controls pavement thickness and smoothness • Check tolerances • Blend trimmed material with granular subbase to

avoid segregation • Fill low areas, blend, recompact and fine grade

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Dowel Basket Placement

Improper load transfer Faulting

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Dowel Basket Placement

Securing the baskets

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Group Activity

Which way is the paver moving?

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Basket Layout

Transverse spacing as specified (joint layout) Aligned correctly

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Basket Placement Stakes or clips are adequate for anchoring the

basket Adequate number of stakes/clips per basket Bond breaker

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Poor Dowel Alignment

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Basket Inspection

Specified coating and condition of coating Specified dowel diameter Correct basket height Dowel spacing Clean

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Basket Location Marking

Durable marking Pins Both sides of the pavement!

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Steel Placement (CRCP)

Affects crack spacing • Adequate chairs for support • Periodically anchored into subbase to resist

movement from the paver • Correct bar size and spacing • Staggered laps

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Paver Preparation

Extrusion process

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Slipform Paver Functions

Consolidation Shaping Surface finish Pavement smoothness

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Paver Preparation

Vibrator spacing and operation Tie bar inserter location Fix hydraulic leaks

Hydraulic fluid is not a concrete admixture!

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Paver Preparation

Shaping • Slab dimensions

o Side form dimensions

• Pan settings o Cross slope o Crown breaks o Angle of attack

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Paver Preparation

Tie bar inserter location

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Plant Site and Mixture Production (Chapter 5) Aggregate Stockpile Management Plant Set-Up and Calibration Mixture Production Transporting Concrete

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Aggregate Stockpile Management

Minimize segregation • Build long and wide-NOT high! • Build stockpiles in tiers to avoid

segregation

Fines at the top

Coarse at the bottom Picture courtesy of Martin Marietta Materials

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Group Activity

What’s wrong with this picture? Sampling

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Uniform Moisture • Stable and well drained foundation underneath

stockpiles • Place a separation layer on top of soil • Draw from areas of known moisture content

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Contamination • Mud balls

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Plant Set-up and Calibration

Calibrate scales and water meters • Each time the plant is set-up • At regular intervals

Verify that the batch control computer • The correct mix design(s) • Appropriate aggregate moisture contents

TEST BATCH!

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Verify Mixture Quality in the Field

Mixture verification stage • Compares field concrete to the mixture design

Is this the same concrete? Trial Batch

SAME ?

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Mixture Production

Segregation resistance Air void system Uniformity Workability Strength Durability Shrinkage

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Recommended Practices

Use aggregates from areas of known moisture content

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Adjust moisture compensation as needed

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Adequate mixing time • Uniformity • Air entrainment • Strength • Workability

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Quality Control

Monitor mixture quality during production and react to changes • Aggregate moisture and gradation • Concrete temperature • Slump • Unit weight • Air content • Microwave water content • Heat Signature

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Transporting Concrete

Traffic considerations Anticipate the unexpected

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Maintain haul route

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Wash out trucks as necessary

Module 2 CPU 6- 53

Paving

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Pre-Paving Activities Placement, Finishing, Texturing, Curing and Sawing (Chapter 6) Spreading Concrete Slipforming Insertion of Dowels and/or Tie Bars Hand Finishing Texturing Curing Sawing Weather Adjustments

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Spreading Concrete

Place concrete in front of the paver Distribute concrete evenly Avoid segregation => effects

• Permeability • Strength • Shrinkage

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Spreading Concrete

Continuous supply of concrete to the paver Consistent head => smoothness Communication

• Spreader operator • Paver operator

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QC Checklist Items

Spreader width – narrower than paver Steering alignment with respect to paver Concrete depth behind the spreader– account

for width and consolidation

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QC Measurements Real Time / On-the-grade-tests All measure change

• Unit weight • Air content / system • Concrete temperature • Slump

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Slipform Paver Functions

Consolidation Shaping Surface finish Pavement smoothness

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Consolidation

Match vibrator frequency to workability and paver speed

Electronic vibrator monitor

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Over-Vibration

Vibrator Trails Segregation

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Shaping Extrusion pan – trueness and cross-slope/crown Adjust overbuild to form neat edges Curb dimensions

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Shaping

Paver attitude and extrusion pressure • Bug holes • Tears

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Smoothness

Don’t stop the paver

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Smoothness

Pad line profile influences slab profile • Therefore pad line design and construction

impacts smoothness

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QC Measurements

Vibrator monitor Smoothness Thickness

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Key Inspection Items

One contractor example • Tape QC Inspection list on the paver • Offset alignment – every 50’ • Stringline – constant • Edge slump – every 50’ • Slab width – every 50’

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Visually inspect the pavement edge and surface for proper consolidation

Some voids are preferable to having too much water on pavement surface

Slurry from excess water

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Appropriate Actions

Adjust vibrator frequency Adjust speed Refine mixture proportions Stop paving if the edge keeps falling

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Dowel Bar Inserters Insert dowels at planned locations Insure bond breaker is applied Mark the location of the dowels Check consolidation around the bars

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Mark dowel insertion locations for verification and sawing (BOTH SIDES!)

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Check Dowel Location

Real-time Non Destructive Testing (NDT) Core verification after first day

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Real Time

Verify dowel bar location behind the paver

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NDT Inspection Options

Periodically verify steel location behind the paver • Cover meter (pachometer) • GPR after hardened • MIT-SCAN-2

Ground Penetrating Radar

Pachometer

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MIT-SCAN-2

One limitation • Cut the tie wires

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Typical Practices

Insert tie bars at planned locations

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Fill surface voids Avoid over-finishing

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Recommended Practices Identify bumps and dips

• Overlap straightedge by 1/2

Correct bumps and dips

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Effect of Hand Finishing

492+20 492+40 492+60 492+80 493+00 493+20

Distance (ft)

Roughness Profile (in/mi)

at the pan

behind hand finishers

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Burlap drag is clean • May need to clean or replace during the day

Check hand tools for trueness

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Typical Practices

Wetting of the burlap • Uniform • Light application • Consistent

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Not Recommended Practices

“Blessing” the slab Adding water to the surface

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Water/Cementitious Ratio

How close are the duckies in your hot tub?

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Texturing

Micro texture • Drag texture with adequate contact area • Dry pavement friction

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Texturing

Macro Texture • Wet weather skid resistance • Reduce hydroplaning

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Steering and elevation controlled automatically

Consistent operating speed Goal is:

• Uniform/true grooves

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Recommended Practices Adjust tine angle and length

• Texture depth • Tine spacing

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Minimize Positive Texture

Results in more noise • Clean drags • Clean tines • Straight tines

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100 dBA

106 dBA

Longitudinal

Tining

Module 2 CPU 6- 95

96 98 100 102 104 106 108 110

A-weighted Overall OBSI Level, 60 mph, SRTT (dB ref 1 pW/m²)

yDiamond Grinding

Longitudinal Tining

Transverse Tining

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Appropriate Actions

Do not delay texturing at the expense of curing Don’t let the tine rake stop in the down position

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Cure as soon as practical Even and complete coverage Consistent operating speed

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Edge covered also Even and complete coverage

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Curing compound meets specification Emulsion

• Agitate • Prevent freezing

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Recommended Practice Apply cure before surface drying occurs

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Adequate number of saws on the project

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Joints marked accurately

Module 2 CPU 6- 105

• Saw in the window

• Timing is critical

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Specified sawing depth and width Record and log sawing depth Ample saw blades on-hand

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Prepare for Weather Changes

Cold front sudden drop in temperature • Be prepared to cover

o Plastic o Burlap o Blankets

• Avoid thermal shock

Use HIPERPAV to predict impact

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Use HIPERPAV to assess risk of cracking Refer to page 93 of the “Testing Guide”

Tensile

Strength

Critical Tensile

Stresses - Top

Critical Tensile

Stresses - Bottom

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@ 9:00 P.M.

HIPERPAV Software tool for assessing cracking risk

@ 1:00 A.M. @ 5:00 A.M. Placement on the

night of 5/21/12

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HIPERPAV Software tool for assessing cracking risk

@ 8:00 P.M. @ 12:00 A.M. @ 4:00 A.M. Placement on the

night of 5/22/12

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Wet Weather Considerations (Rain) Be prepared to cover Schedule hand pours, shoulders, etc. Do not finish-in rain water Grind/groove texture to remove damaged

surface

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Hot Weather Considerations Reduce mix temperature Sprinkle subbase Night placement Morning placements are most at risk

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Cold Weather Considerations

Increase mix temperature Reduce SCM content in the concrete mixture Do not place on frozen subgrade/subbase Cover slab to protect from freezing for 48 hours Replace cover after sawing to avoid thermal shock Monitor concrete temperature with recording

devices

Module 2 CPU 6- 115

Concrete Properties and Testing

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Air Void System New Testing Devices

Super Air Meter (SAM) • Modification of existing air test • Measures air system quality

o Has its own scale to measure results

• Test o Test three times at different pressures o Repeat

• Small bubbles implode • Field friendly

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Microwave Water Content

Developed in SHRP I

Sample from the truck

Indicator for: • Strength • Permeability • Uniformity • Shrinkage

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Permeability (Surrogate Tests for Durability)

Rapid Chloride Penetrability Test (Indirectly)

Became standard in 1977 Most common test Indicator of vulnerability to

water and chloride ingress Generally 24 hours to

condition and 6 hours for testing

ASTM C1202

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Permeability (Surrogate Tests for Durability)

Wenner Probe/Surface Resistivity Test (Indirectly)

Provisional AASHTO Standard TP 95-11 State specification Louisiana: DOTD TR 233 28-day age is being used Instant results on hardened concrete Easily measures the right property

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Heat Signature (Calorimetry) Measures the heat of hydration

• Similar to maturity Measures temperature of in-place, field concrete

• Measure temperature under controlled conditions

About a day and half Equipment is relatively inexpensive Procedure is simple: 1. Cast a standard cylinder 2. Place it in the calorimeter 3. Push the ON button

Module 2 CPU 6- 121

Thank you for your attention.

Quality in the Concrete Paving · PDF fileQuality in the Concrete Paving Process CPU 6- 6 ......

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