High Performance Concrete--

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High Performance Concrete--Get the Mindset
Michael F. Praul, P.E. Engineering Team
Leader FHWAMaine Division
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LPC
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HP Concrete Constituents

• Cement
• Water
• Aggregate
• Mineral Admixtures
• Fly Ash
• Silica Fume
• GGBFS
• Chemical Admixtures

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Hydration
Cement Water CSH (glue) CaOH (lime) heat
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Cement Content

• High CementHigh Water
• High CementHigh Heat
• High CementHigh Modulus

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8
7.5
7 DAY
14 DAY
3 DAY
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Modulus of Elasticity, million psi
6.5
57000
f c
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5.5
11000 psi
13000 psi
9000 psi
5
100
105
110
115
120
95
90
f c , psi
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Water Cement Ratio
0.4
0.5
0.6
High Shrinkage Zone
0.7
Low Shrinkage Zone
from Hover
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Water Addition to 6 Sacks per C.Y.
W/C 0.42
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Water Addition from W/C 0.42
1
W/C 0.43
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Water Addition from W/C 0.42
2
W/C 0.45
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Water Addition from W/C 0.42
3
W/C 0.46
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Water Addition from W/C 0.42
4
W/C 0.48
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Water Addition from W/C 0.42
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W/C 0.49
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Hydration in water-filled space
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Continued Hydration
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Continued Hydrationin water-filled space
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Water Reducers/HRWR

• Increase slump and workability of concrete
  without an increase in water-cementitious
  material ratio.
• Rapid slump loss
• High admixture cost
• Modification of concrete air entrainment and
  freeze/thaw durability characteristics

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How Water Reducers Work
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Floc Busting Action ofWater Reducers
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Flocculated w/c 0.5
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Deflocculated w/c 0.5 (HRWR)
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Pozzolans The Material Key to HPC

• Fly Ash
• Silica Fume
• GGBFS

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Pozzolan

• POZZOLAN (definition) a siliceous and
  aluminous material which, in itself, is not
  cementitous. It will, in the presence of
  moisture, combine with Calcium Hydroxide to form
  cementitous compounds.

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Pozzolanic Reaction
Cement H2O CSH CaOH
Free Lime
CaOH Pozzolan CSH
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Pozzolanic Reaction
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Fly Ash

• Class F (low calcium) - from burning anthracite
  or bituminous coal, is pozzolanic
• Class C - from burning sub-bituminous or lignite
  coal, is somewhat cementitious

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What is fly ash?

• Fly ash (definition) By-product of electricity
  generation in modern coal-fired power plants

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Fly Ash Facts

• Cement replacement, generally 10-30
• Improves workability and pumpability
• Reduces heat of hydration
• Increases ultimate strength

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Fly Ash
Portland cement
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Fly Ash Cautions

• Slower strength gain
• Temperature affects this significantly
• Carbon/AEA interaction

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Silica Fume
Dry, Compacted
Slurry
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Silica Fume Facts

• A By-Product From The Production Of Silicon Metal
  Or Ferrosilicon Alloys.
• Consists Primarily of Silicon Dioxide (SiO2).
• 100 Times Smaller Than Cement (0.1um).
• Micro-filler
• Builds high strength, early strength
• Increases water demand -- requires
  superplasticizer

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Silica Fume Production
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Silica Fume
Cement
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Silica Fume Cautions

• More difficult to handle, sticky to finish
• More expensive than fly ash or GGBFS
• Mix well to avoid balling
• Little or no bleed water
• CURE!!!!!!

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Microsilica balling
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High Strength Concrete Potential
25,000
CF 658 lb w/c 0.41
Optimized mix design
20,000
15,000
10,000
5,000
0
0
5
10
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Strength Potential
Silica Fume
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Rapid Chloride Permeability TestAASHTO T-277
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How can we use it?

• From T-277-89, 3.2 The method is suitable for
  specification acceptance, design purposes,
  service evaluation, and research and
  development.
• Mix design approval
• Project-level acceptance
• Evaluation of in-service concrete

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Project-level Acceptance

• Careful selection of acceptance parameters
• Incentive/Disincentive
• Tied to rebar cover

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Precision

• AASHTO statement is SCARY!
• Two operators in separate labs51 variation

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Rapid Chloride Permeability
32 samples
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23 State Round Robin

• Samples from MaineGGBFS HPC-type mix
• Average 730 coulombs, SD 108 coulombs
• Demonstrates appropriate use of acceptance

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GGBFS Facts

• Formed when molten iron blast furnace slag is
  rapidly chilled (quenched) by immersion in H2O
• Grades 80, 100, 120
• Has significant self-cementing properties gt Can
  be used at higher replacement levels (50 or
  more)

• Lowers heat of hydration
• May look stained initially but whitens upon
  oxidizing

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GGBFS Cautions

• Increases initial set time
• Lower early strength
• May be prone to scaling at
• higher dosages
• FHWA Materials guidance

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PERMEABILITY(VA Testing)
Ref. Mix
7 SF
20 FA
50 GGBFS
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Pozzolan Summary

• Each material contributes pozzolanically
• Differences in time
• Each has different side effects/benefits

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A Few Words About Construction
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Scaling
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Plastic Shrinkage Cracking

• PSC Control
• Erect Wind Breaks.
• Light Fog Spray.
• Evaporation Retardant.
• Curing Compound.
• Cure Immediately After Finishing.
• Have Adequate Crew On Hand.

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CuringTimely and Appropriate

• Place wet cure within 15 minutes of finishing
• Use compound if desired but do not delay wet cure
• Wet cure for as long as possible

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Curing

• Be prepared
• Burlap applied within 15 minutes of concrete
  placement.
• Consider 14 day wet cure for all decks.

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Summary

• HPC has many similarities to ordinary concrete
• There are key material differences that affect
  construction practices
• Increased attention to detail
• If it can be done here

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