Lightweight Concrete for PBES ElementsReid W. Castrodale, PhD, PE

Director of EngineeringCarolina Stalite Company, Salisbury, NC

Representing the Expanded Shale, Clay and Slate Institute

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• LWA is a manufactured product• LWA is not a new product• LWA is a lighter rock• LWA meets aggregate specifications• LWA has higher absorption• LWA is durable• LWA typically costs more than NWA• LWA can be used for internal curing• LWA can be used as geotechnical fill

Lightweight Aggregate (LWA)

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• LWC is not a new product• LWC is made using same process and equipment• LWC weighs less than NWC• LWC has enhanced durability• LWC typically costs more than NWC• DOT specifications for LWC• PBES applications for LWC

Lightweight Concrete (LWC)

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• LWA is a manufactured product• LWA is not a new product• LWA is a lighter rock• LWA meets aggregate specifications• LWA has higher absorption• LWA is durable• LWA typically costs more than NWA• LWA can be used as geotechnical fill for ABC

projects

Lightweight Aggregate (LWA)

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

• Gas bubbles form in softened material • Gas bubbles remain after cooling• Clinker is crushed and screened

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Stephen Hayde discovered that LWA could be manufactured from shale, clay and slate• Observed that some bricks bloated during burning• Began developing rotary kiln process in 1908 • Patent for rotary kiln process was granted in 1918

First use of LWA was for LWC to build ships in World War I• Launching of the

USS Selma in June 1919

LWA is not a new product

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Rotary kiln expanded LWA• Specific gravity: 1.3 to 1.6

Normal weight aggregate• Specific gravity: 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

LWA is a lighter rock

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LWA satisfies typical specifications required of NWA for structural concreteLWA conforms to AASHTO M 195 gradations and other properties• Coarse gradations are shown• Several gradations of fine

aggregate are available

LWA meets aggregate specs

¾" ½" 3/8"

5/16" Fines

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Pores in LWA particles reduce density• Result - increased absorption• But pores are not all connected- Does not act like a sponge

• Absorption range for LWA in US: 6% to 40%

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LWA has higher absorption

An expanded slate LWA particle soaked in water with fluorescent yellow dye for 180 days, then split open.

Absorption at the time of testing was 8% by mass.

0.73"

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LWA is durable

LWA is a vitrified ceramic material• Hardness equivalent to quartz

LWA meets requirements for• LA abrasion test• Freeze-thaw test for aggregate• Soundness tests

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LWA typically costs more

Reasons for increased cost of LWA• High-temperature processing

• Shipping from the manufacturing plant

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LWA is a high-performance low-density geotechnical fill• In-place density: 45 to 60 pcf• Angle of internal friction: ≥ 40• Free draining

Benefits for ABC projects• Reduces settlement• Reduces load on walls• Fast installation - like 57 stone

LWA as geotechnical fill

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• LWC is not a new product• LWC is made using same process and equipment• LWC weighs less than NWC• LWC has enhanced durability• LWC typically costs more than NWC• DOT specifications for LWC• PBES applications for LWC

Lightweight Concrete (LWC)

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

built using 95 pcf all LWC in 1936• Lower deck was reconfigured for

highway traffic using LWC in 1958• Both decks are still in service

LWC is not a new product

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When LWA is used to make LWC• Can use same mix design procedures• Same batch plants and mixing procedures• Same admixtures• Same placing and finishing methods• Higher absorption of LWA requires prewetting,

especially for pumping• “Roll-o-meter” for measuring air content• Can make self consolidating LWC, i.e., SCC

LWC uses same processes

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LWC weighs less than NWC

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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Reduced weight of precast elements• Affects handling, shipping and erection

- Reduces costs- Improves safety

• Improves structural efficiency• Reduces seismic loads• Reduces foundation loads• May get more concrete in a truck• May get more pieces on a truck

LWC weighs less than NWC

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

Results in more durable concrete

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Additional cost of LWC depends on• Cost of LWA• Cost of NWA being replaced• Shipping cost for both aggregates• Familiarity of contractor and concrete supplier

with LWC- LWC is commonly used for building construction in most

major metropolitan areas

LWC typically costs more

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Range of cost for sand LWC bridge deck

• Cost / SF assumes 9 in. thick deck (average)

FHWA reports that average bridge unit cost in 2010 ranged from about $55 to over $500 / SF

Sand LWC Premium / CY Cost Prem. / SF

$20 / CY $ 0.56 / SF

$40 / CY $1.11 / SF

$60 / CY $1.67 / SF

LWC typically costs more

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Range of cost for sand LWC bridge girders• Assume $60 / CY cost premium for sand LWC• Girder spacing assumed to be 10 ft

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

PCBT-29 $9.93 / LF $0.99 / SF

PCBT-61 $13.25 / LF $1.33 / SF

PCBT-93 $16.71 / LF $1.67 / SF

LWC typically costs more

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Increased cost is offset by potential savings• Increased piece size- Fewer pieces = faster erection

• Reduced piece weight- Shipping and erection

• Reduced foundation loads• Fewer truck loads in congested areas

LWC can reduce the overall project cost

LWC typically costs more

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Example for NCDOT Mod BT-74 bridge girders• Cost premium for sand LWC in 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

LWC typically costs more

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Sand LWC for Bridge Decks• TennDOT includes in Standard Specifications• NCDOT, UDOT, etc. have standard special provisions• Other states have project special provisions

All LWC • Special provisions have been developed for NCDOT

Sand LWC for Girders• GDOT has special provisions (10 ksi at 120 pcf)• VDOT has special provisions (8 ksi at 125 pcf)• INDOT allows in design manual (120-130 pcf)

DOT Specifications for LWC

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GDOT special provisions - 10 ksi sand LWC 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

DOT Specifications for LWC

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Prewetted LWA delivers curing moisture in NWC• Replace a fraction of the NW sand with the same

volume of prewetted fine LWA

Water absorbed in the prewetted fine LWA • Released over time into the concrete• Does not enter into the mix water immediately• Does not affect the w/cm

Basic benefits of internal curing• Increases cement hydration• Allows more complete reaction of SCMs

Internal Curing with LWA

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More efficient use of cementitious materialsImproves durability of NWC mixtures• Reduces cracking tendency - Reduces shrinkage- Reduces curling and warping of slabs

• Improves robustness of concrete construction- More tolerant of inadequate external curing- More resistant to rapid temperature changes

• Reduces chloride penetration - Delays onset of corrosion

Internal Curing with LWA

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Internal Curing with LWA

Denver Water Company – Lonetree Basin Tank #2• 10 mg Concrete Water Storage Tank

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Internal Curing with LWA

Internal Curing vs. No Internal Curing – 1 day after placement• Highlands Ranch, CO – 92F ambient, 20% RH• No conventional curing

With internal

curing

Without internal curing

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Internal Curing with LWA

Indiana DOT Test in 2010• Internally cured slab had no visible cracks after 1 year• Slab without IC was cracked after a few months

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Internal Curing with LWA

Indiana DOT Test in 2010Preliminary observations after 1 year in service• No difference in finishing was reported• Compressive strength of IC concrete

- 10% less at 1 day- About equal at 10 days- 20% stronger at 3 months

• Rapid chloride permeability tests for IC concrete- 10% lower charge passed at 28 days- Nearly 40% lower charge passed at 3 months

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Actual and potential applications • 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

PBES applications for LWC

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Project did not use LWCPrecast 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- Lower shipping cost & erection loads

• Allowed roadway widening with no super- or substructure strengthening- Reduced project cost and duration

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 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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I-95 in Richmond, VA

Prefabricated full-span units • First project completed in 2002• Steel girders and sand LWC deck

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

3 bridges 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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LWC can be used to achieve both accelerated construction

and longer-life structuresFor more information on LWA and LWC• Contact Reid Castrodale: rcastrodale@stalite.com• Visit: www.escsi.org