LIGHTWEIGHT CONCRETE BENEFITS FOR PBES DEPLOYMENT

Reid W. Castrodale, PhD, PEDirector of Engineering

Carolina Stalite Company, Salisbury, NC

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After completing this Module, you will be able to:• describe how lightweight aggregate is

manufactured• identify the classifications of lightweight concrete• identify several advantages of using lightweight

concrete for PBES bridges• recall several PBES projects where lightweight

concrete was or could have been used

Learning Outcomes

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• In early 1900s, Stephen Hayde discovered method to manufacture lightweight aggregates (LWA) from shale, clay and slate– Some bricks bloated during burning– Development of rotary kiln process began in 1908 – Patent for expanding LWA using a rotary kiln

process was granted in 1918• The first use of lightweight

concrete (LWC) was for ships in World War I

Development of LWC

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• Early use of LWC in a bridge project– San Francisco-Oakland Bay Bridge– Upper deck of suspension spans

was constructed using LWC in 1936– Lower deck was rebuilt with LWC

for highway traffic in 1958– Both decks are still in service

Development of LWC

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Structural LWA

• LWA is manufactured– Raw material is shale, clay or slate– Expands in kiln at 1900 – 2200 deg. F

– Gas bubbles formed in softened material are trapped when cooled

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• Rotary kiln expanded LWA– Range from 1.3 to 1.6

• Normal weight aggregate– Range from 2.6 to 3.0

• Twice the volume for same mass

• Half the mass for the same volume

SoilGravel

ESCS Agg.

Limesto

neSand

1 lb. of each aggregate

Relative Density

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• LWA is lighter than NWA • But LWA still satisfies typical specifications

required of NWA for use in most construction applications– Different gradations – AASHTO M 195

• A non-concrete application for LWA– Geotechnical fill– Can be used on ABC projects

LWA is just a lighter rock!

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Geotechnical Use of LWA

• LWA can be used as structural fill

– LWA is free draining

Property LWA NWA or Soils

Compacted in-place bulk density 40-65 pcf 100-130 pcf

Bulk Loose density (dry) 30-50 pcf 89-105 pcf

Angle of internal friction 35°-45°+ 30°-38°

Abrasion resistance (Loss) 20-40% 10-45%

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Pentagon Secured Entrance

LWA fill was used between MSE walls– Reduced anticipated settlement from 15” to 6”– Reduced settlement time from 180 days to 60 days– Enabled contractor to meet tight project schedule

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• When LWA is used to make LWC– Same batch plants and mixing procedures– Same admixtures– Can use same mix design procedures– “Roll-o-meter” for measuring air content

• LWA has higher absorption than NWA– Needs to be prewetted, especially for pumping

• Visit ESCSI website or contact LWA supplier for more info on properties of LWA and LWC

LWA is just a lighter rock!

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• LWA is used to reduce density of concrete

• “All lightweight” – all aggregates, both fine and coarse, are lightweight

• “Sand lightweight” – lightweight coarse aggregate and normal weight sand

• “Specified density” – blend of NW and LW aggregate to achieve target density (SDC)

• Density of LWC is checked during placement for QC

Lightweight Concrete

Most common

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• AASHTO LRFD Specs (Section 5.2)– Lightweight concrete: "Concrete containing

lightweight aggregate and having an air-dry unit weight not exceeding 0.120 kcf …"

– Normal weight concrete: “Concrete having a weight between 0.135 and 0.155 kcf”

• Concrete that falls between these definitions is often called specified density concrete (SDC)

Definitions

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Spectrum of Concrete Density

All LWC Sand LWC NWC

90 - 105 pcf 110 - 125 pcf 135 - 155 pcf

LW Fine NW Fine NW Fine

LW Coarse LW Coarse NW Coarse

Specified Density Concrete (SDC)

Density ranges shown are approximateMust add allowance for reinforcement (typ. 5 pcf)

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• “Equilibrium density” is defined in ASTM C 567– Density after moisture loss has occurred over time– Often used for dead load calculations

• “Fresh density” used for QC tests during casting– Designer or supplier must specify– Must use for precast member weight at early age– May use for final design loads for large elements

• Add reinforcement allowance to concrete density when computing dead loads (typ. 5 pcf)

Specifying Density of LWC

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Sand LWC for Bridge Decks• TennDOT includes in Standard Specifications• NCDOT, UDOT, etc. have std special provisions• Other states have project special provisionsAll LWC • Has not been used in recent years• Special provisions have been developed for

NCDOT

DOT Specifications for LWC

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Semi-LWC for Girders• INDOT allows in design manual (120-130 pcf)

– Recurring special provisions being developed

Sand LWC for Girders• GDOT has special provisions (10 ksi at 120 pcf)• VDOT has special provisions (8 ksi at 125 pcf)Approved aggregate lists• A number of states have approved LWA sources

DOT Specifications for LWC

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GDOT Special Provisions

• Special provisions for 10 ksi sand LW HPC girders– Maximum air-dry density is 120 pcf– Size of LW coarse aggregate = ½ in.– Minimum cement factor = 650 lbs/cy– Maximum water-cement ratio = 0.330– Slump acceptance limits = 4½ ± 2½ in.– Entrained air acceptance limit = 5 ± 1½ %– Max. chloride permeability = 3,000 coulombs

• Same as for NW HPC, except density & aggr. size

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• Reduced weight of precast elements– Improves handling, shipping and erection– Can also improve structural efficiency

• Enhanced durability– Reduced cracking tendency– Reduced permeability– Tighter quality control with a specified density

• LWC can be used to achieve both accelerated construction and longer-life structures

Benefits of Using LWC

Opposite of what many expect!

Focus of webinar

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Enhanced Durability

• Improved bond between aggregate & paste• Elastic compatibility• Internal curing• Reduced cracking tendency• Improved resistance to chloride intrusion• Increased fire resistance• Enhanced resistance to freezing & thawing• Good wear and skid resistance• Alkali-silica reactivity (ASR) resistance

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Cost of LWC

• Increased cost of LWA– Additional processing

– Shipping from the manufacturing plant

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• Effect of sand LWC deck on cost of bridge

– Cost / SF assumes 9 in. thick deck (average)– Premium depends on cost of LWA, cost of NWA

being replaced, and shipping cost

Cost Premium for LWC

Sand LWC Premium / CY Cost Prem. / SF

$20 / CY $0.56 / SF

$35 / CY $0.97 / SF

$50 / CY $1.39 / SF

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• Effect of sand LWC girders on cost of bridge– Assume $30 / CY cost premium for sand LWC– Girder spacing assumed to be 10 ft

Girder Type Cost Prem. / LF Cost Prem. / SF

PCBT-29 $4.97 / LF $0.50 / SF

PCBT-61 $6.63 / LF $0.66 / SF

PCBT-93 $8.35 / LF $0.84 / SF

Cost Premium for LWC

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• Cost premium for sand LWC in Mod BT-74 girder– Assume $30 / CY = $6.83 / LF– Cost premium for LWC for 150 ft girder =

$1,024• Cost reduction by using sand LWC girder

– Shipping from plant to site =

$811• NWC girder = 69 t; LWC girder = 58 t, or 11 t less

– Drop 4 strands / girder @ $0.65 / LF ea. =

$390– Total cost reduction =

$1,201

• Net savings by using sand LWC girder $177

Sample Girder Cost Analysis

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PBES Applications for LWC

All LWC Sand LWC SDC NWC

105 pcf 120 pcf 135 pcf 145 pcf

These are fresh densities for concrete up to about 6 ksiAdd 5 pcf allowance for reinforcement

• Sand LWC & Specified Density Concrete– Use for any precast or prestressed conc. elements

• All LWC – Can be used for any precast concrete element– Data not yet available for prestressed elements

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• Consider sample projects – Precast foundation elements– Precast pile & pier caps– Precast columns– Precast full-depth deck slabs– Cored slabs & Box beams– NEXT beams & Deck girders– Full-span bridge replacement units with precast deck– Bridges installed with SPMTs

Impact of LWC on PBES

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Mill Street Bridge, NH

% Chng.

Weight as Des. Chng. Weight

as Built Chng.

150 pcf 0 39 t 0 25 t 0

125 pcf 17% 32 t 7 t 20 t 5 t

110 pcf 27% 28 t 11 t 18 t 7 t

• Precast foundation elements– Project did not use LWC

• Comparison for abutment footings– Abutment walls have similar weights

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Okracoke Island, NC

• Precast pile caps– Project did not use LWC

• End bent pile cap – 2 pieces– Size: 21 ft long x 3.67 ft x 3 ft– 3 pile pockets per piece

Pile Cap Weight Change % Chng.

150 pcf 16 t 0 0

125 pcf 13 t 3 t 17%

110pcf 12 t 4 t 27%

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Lake Ray Hubbard, TX

• Precast pier caps– Project did not use LWC

• Typical pier cap on 3 columns– Size: 37.5 ft long x 3.25 ft x 3.25 ft

Pier Cap Weight Change % Chng.

150 pcf 29 t 0 0

125 pcf 24 t 5 t 17%

110 pcf 21 t 8 t 27%

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• Project did not use LWC• Precast columns

– Max wt = 45 tons @ 150 pcf– Max wt = 37 tons @ 125 pcf– Using 128 pcf SDC could have

eliminated pedestal for tall columns

• Precast caps– Max wt = 78 tons @ 150 pcf– Max wt = 65 tons @ 125 pcf

Edison Bridges, FL

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• Deck replacement with full-depth precast deck panels in 1983

• Sand LWC was used for panels– Allowed thicker deck– Allowed widened roadway with no

super- or substructure strengthening– Reduced shipping costs and erection loads

• Sand LWC deck performed well until bridge was recently replaced to improve traffic capacity

Woodrow Wilson Br, VA/DC/MD

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Okracoke Island, NC

• Precast cored slabs– Project did not use LWC

• 21” deep by 3 ft wide– 30 and 50 ft spans

Ext. 50 ft span Weight Change % Chng.

150 pcf 16.0 t 0 0

125 pcf 13 t 3 t 17%

125 pcf - Solid 16.4 t 0.4 t +3%

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Okracoke Island, NC

• Precast barriers– Project was not designed with LWC

• Contractor proposed casting barriers on cored slabs in precast plant– Sand LWC was used for the barrier

Barrier Weight Change % Chng.

150 pcf 13.7 t 0 0

125 pcf 11.4 t 2.3 t 17%

110 pcf 10.1 t 3.6 t 27%

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Mill Street Bridge, NH

• Precast box beams– Project did not use LWC

• NWC box beam weight governed crane size with 2 crane pick

– Using sand LWC for box beam would make beam pick nearly equal to NWC substructure elements

Ext. Box Beam Weight Change % Chng.

150 pcf 69 t 0 0

125 pcf 57 t 12 t 17%

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NEXT F Beams

• Compare section weights for NEXT 36 F– NWC @ 155 pcf; Sand LWC @ 130 pcf– No max. span

charts for sand LWC

– 16% reduction in weight for same width sections

– 12 ft wide LWC is lighter than 8 ft wide NWC

1385

1162

1489

1249

1592

1335

1000

1100

1200

1300

1400

1500

1600

1700

NWC LWC

Wei

gh

t p

er F

oo

t (l

bs)

NEXT 36 F

8 ft 10 ft 12 ft 8 ft 10 ft 12 ft

16%

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• Compare section weights for NEXT 36 D– 12 ft width not used to limit weight of NWC section– Max. span charts

are provided for sand LWC

– 16% reduction in weight for same width sections

– 12 ft LWC is lighter than 10 ft NWC

1793

1504

2000

1677

1851

1400

1500

1600

1700

1800

1900

2000

2100

2200

NWC LWC

Wei

gh

t p

er F

oo

t (l

bs)

NEXT 36 F

8 ft 10 ft 12 ft 8 ft 10 ft 12 ft

NEXT D Beams

16%

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Deck Girders, NY

• Precast deck girder – Project did not use LWC

• 41” deep deck girders with 5 ft top flange– 87.4 ft long girders

Girder & Deck Weight Change % Chng.

158 pcf 45 t 0 0

130 pcf 37 t 8 t 18%

NWC density was obtained from girder fabricatorSpecified concrete compressive strength = 10,000 psi

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I-95 in Richmond, VA

• Prefabricated full-span units – Steel girders and sand LWC deck

• Maximum precast unit weight for current project

Deck densities do not include reinforcement allowance

Deck Weight Change % Chng.

145 pcf 132 t 0 0

120 pcf 116 t 16 t 12%

105 pcf 106 t 26 t 20%

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• Deck replacement on existing truss– Sand LWC precast deck units with steel floor beams– Sand LWC density = 119 pcf– Max. deck unit weight = 92 t– Sand LWC saved about 14 t

• Existing deck was LWC– Was in service 73 years

17'-1"

3'-0"(TYP.)

5'-6"(TYP.)

2" 9"¢ STRINGER

0.02'/FT.7"

0.02'/FT.

1¼"

MM

CO

VE

RL

AY ¢ STRINGER

**Note – New panel weighs about 5% less than original**

17'-1"

3'-0"(TYP.)

5'-6"(TYP.)

2" 9"¢ STRINGER

0.02'/FT.7"

0.02'/FT.

1¼"

MM

CO

VE

RL

AY ¢ STRINGER

**Note – New panel weighs about 5% less than original**

Lewis & Clark Bridge, OR/WA

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• 3300 South over I-215 – Built in 2008– Sand LWC used for deck– Less deck cracking than bridges with NWC decks

• 3 bridges to be moved in 2011– Steel girder bridges with sand LWC decks– 200 South over I-15 – 2 spans @ 3.1 million lbs– Sam White Lane over I-15 – 2 spans @ 3.8 million lbs– I-15 Southbound over Provo Center Street

–2 moves of 1.5 and 1.4 million lbs

Bridges set with SPMTs, UT

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Graves Ave. over I-4, FL

• Complete span replaced using SPMTs– Project did not use LWC

• Comparison of weight for NWC and sand LWC– Appendix C in FHWA “Manual on Use of SPMTs …”

Girder Deck Weight Change % Chng.

152 pcf 150 pcf 1,282 t 0 0

127 pcf 120 pcf 1,049 t 233 t 18%

127 pcf 105 pcf 996 t 286 t 22%

Comparison with all LWC deck is not in Manual

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You should now be able to:• describe how lightweight aggregate is

manufactured• identify the classifications of lightweight concrete• identify several advantages of using lightweight

concrete for PBES bridges• recall several PBES projects where lightweight

concrete was or could have been used

Conclusions

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Questions?

For more information on LWA and LWC• Contact Reid Castrodale: rcastrodale@stalite.com• Visit the Expanded Shale, Clay and Slate Institute

website: www.escsi.org• Contact local LWA suppliers: listed on ESCSI website