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Quality in the Concrete Paving Process
Module 2 CPU 6- 1
Quality in the Concrete Paving Process
Workshop Introduction
Quality in the Concrete Paving Process
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Instructors
Dennis Dvorak
Jim Grove
Mike Praul
FHWA Resource Center
(708) 283-3542
ATI Inc. / FHWA
Office of Infrastructure, Washington D.C. (515) 294-5988
FHWA Maine Division
(207) 512-4917
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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.
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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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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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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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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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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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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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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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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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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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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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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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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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Pre-Paving Activities
Plant Site and Mixture Production (Chapter 5) Aggregate Stockpile Management Plant Set-Up and Calibration Mixture Production Transporting Concrete
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Pre-Paving Activities
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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Aggregate Stockpile Management
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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Aggregate Stockpile Management
Contamination • Mud balls
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Pre-Paving Activities
Plant Site and Mixture Production (Chapter 5) Aggregate Stockpile Management Plant Set-Up and Calibration Mixture Production Transporting Concrete
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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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Pre-Paving Activities
Plant Site and Mixture Production (Chapter 5) Aggregate Stockpile Management Plant Set-Up and Calibration Mixture Production Transporting Concrete
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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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Recommended Practices
Adjust moisture compensation as needed
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Recommended Practices
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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Pre-Paving Activities
Plant Site and Mixture Production (Chapter 5) Aggregate Stockpile Management Plant Set-Up and Calibration Mixture Production Transporting Concrete
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Transporting Concrete
Traffic considerations Anticipate the unexpected
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Transporting Concrete
Maintain haul route
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Transporting Concrete
Wash out trucks as necessary
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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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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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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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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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Key Inspection Items
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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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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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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Recommended Practices
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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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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Recommended Practices
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)
20
40
60
80
100
120
140
160
Roughness Profile (in/mi)
at the pan
behind hand finishers
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Recommended Practices
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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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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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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Recommended Practices
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
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0.00
0.05
0.10
0.15
0.20
0.25
0.30
96 98 100 102 104 106 108 110
A-weighted Overall OBSI Level, 60 mph, SRTT (dB ref 1 pW/m²)
Pro
bab
ilit
y D
en
sit
yDiamond Grinding
Drag
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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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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Key Inspection Items
Cure as soon as practical Even and complete coverage Consistent operating speed
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Key Inspection Items
Edge covered also Even and complete coverage
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Key Inspection Items
Curing compound meets specification Emulsion
• Agitate • Prevent freezing
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Recommended Practice Apply cure before surface drying occurs
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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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Recommended Practices
Adequate number of saws on the project
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Recommended Practices
Joints marked accurately
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Recommended Practices
• Saw in the window
• Timing is critical
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Key Inspection Items
Specified sawing depth and width Record and log sawing depth Ample saw blades on-hand
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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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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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Recommended Practices
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
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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
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Thank you for your attention.