Lightweight Concrete for Accelerated Bridge … Lightweight Concrete for Accelerated Bridge...
Transcript of Lightweight Concrete for Accelerated Bridge … Lightweight Concrete for Accelerated Bridge...
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Lightweight Concrete forAccelerated Bridge Construction
ABC Center at Florida International University (FIU) Webinar
Thursday, July 14, 2011 – 1:00 to 2:00 pm EST
Reid W. Castrodale, PhD, PEDirector of Engineering
Carolina Stalite Company, Salisbury, NC
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• Lightweight Aggregate (LWA)– Geotechnical use of LWA
• Lightweight Concrete (LWC)• Design of Structures with LWC• Benefits of Using LWC• Cost of LWC• Projects Using LWC
Outline
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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
LWA is just a lighter rock!
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Geotechnical Use of LWA
• LWA can be used as structural fill– Compacted in‐place bulk density
• LWA: 40‐65 pcf; NW soils: 100‐130 pcf – Bulk Loose density (dry)
• LWA: 30‐50 pcf; NW soils: 89‐105 pcf– Angle of internal friction
• LWA: 35°‐45°+; NW sand & gravel: 30°‐38°– Abrasion resistance
• LWA: 20‐40% loss; NWA: 10‐45% loss– LWA is free draining
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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– Allowed 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
• See ESCSI website or local LWA supplier for more info on properties of LWA and LWC
LWA is just a lighter rock!
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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
SDC SDC
Density ranges shown are approximateConsult local concrete suppliers for available densities
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• “Equilibrium density” is defined in ASTM C 567– Density after moisture loss has occurred with 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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• Carries tracks for automated people mover (APM) between terminal and new rental car facility (CONRAC)
• Design used long span pretensioned tub girders– Very heavy girders with maximum spans of 143 ft– 5 ft deep precast pretensioned box girder– 12 ‐ 16 ft wide slab cast on tub before detensioning
• Girders were erected in 2007
CONRAC APM, Atlanta, GA
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• Girder designs exceeded 255 kip capacity for pair of straddle lift cranes in plant– With actual concrete density & quantity of steel, largest girder would weigh 291 kips
• Fabricator computed concrete density (SDC)required to stay below 255 kip limit– Using 125 pcf and 139 pcf concrete for groups of girders, all would weigh less than 255 kips
CONRAC APM, Atlanta, GA
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Design using LWC
• US bridge design specifications address LWC– Modifiers for tensile strength, shear, etc.– Special shear resistance factor, – Reduced modulus of elasticity
• Increases elastic shortening loss & cambers• Can be beneficial for substructures & decks
– Time dependent effects: CR, SH & Losses• For HS LWC these quantities are very similar to NWC
• US design specifications do not address SDC
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• Reduced weight of precast elements– Affects 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 LWC
Opposite of what many expect!
Focus of this webinar
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Enhanced Durability
– Bond between aggregate and paste– Elastic compatibility– Internal curing– Reduced cracking tendency– Resistance to chloride intrusion– Fire resistance– Resistance to freezing and thawing– Wear and skid resistance– Alkali‐silica reactivity (ASR) resistance
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• Absorbed moisture within LWA is released over time into the concrete
• Provides enhanced curing– Increased hydration of cement & SCMs– Especially helpful for HPC with low w/cm such as may be used for rapid construction or repairs• HPC impermeable to externally applied curing water• Shown to reduce shrinkage and permeability
– Improves tolerance of concrete to improper or inadequate curing, often an issue with ABC
Internal Curing
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Internal Curing
• Unrestrained mortar shrinkage to 7 days• From research at Purdue University for ESCSI
No LWA
Increasing % of LWA sand
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Internal Curing
No LWAIncreasing % of LWA sand
• Restrained mortar shrinkage ‐ time to cracking• From research at Purdue University for ESCSI
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Concrete Cracking Tendency Tests
• Research at Auburn Univ. for ESCSI• Testing uses cracking tendency frames
– Restrained shrinkage tests– Concrete temperature is controlled– 3 types of LWA; 3 LWC mixes + NWC control
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• Sand LWC & All LWC did not crack during test, but were forced to crack at end of test
• Results for one type of LWA shown
• Complete results in report
NWC IC
SLWCALWC
ICNWC
Spring - 73 deg.
Summer - 95 deg.
SLWCALWC
Cracking Tendency Test Results
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• Silver Creek Overpass, UT• Constructed in 1968• Chloride content after 23½ years in service
Resistance to Chloride Intrusion
Depth Sand LWC Deck NWC Appr. Slab
0" to ½" 36.7 lbs / CY 20.5 lbs / CY
½" to 1" 18.0 lbs / CY 18.0 lbs / CY
1" to 1½" 7.7 lbs / CY 15.7 lbs / CY
1½" to 2" 0.5 lbs / CY N/A
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Permeability at 28 days (coulombs)
Specification requirement 2,500
Average value 989
Max./ min. range 1,467 / 593
Standard deviation 245
Resistance to Chloride Intrusion
• Test results for sand LWC used in VA Route 33 bridge deck completed in 2007– Results are for 17 samples over a 6 month period
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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 on cost of bridge
– Cost / SF assumes 9 in. thick deck (average)– Premium depends on cost of LWA, cost of NWA being replaced, and aggregate shipping cost
Sand LWC Premium / CY Cost / SF
$20 / CY $0.56 / SF
$30 / CY $0.83 / SF
$40 / CY $1.11 / SF
Cost Premium for LWC Decks
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• Cost premium for sand LWC in Mod BT‐74 girder– Assume $30 / CY premium = $6.83 / LF– Cost for sand LWC for 150 ft girder = $1,024
• Cost reduction from using sand LWC– Shipping from plant to site (~290 mi) = $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 from using sand LWC $177
Cost Premium for LWC Girders
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• But using sand LWC for girder & all LWC for deck eliminates a girder line from each dual– Premium for all‐LWC deck = $400,000– From bid tabs, assume girder cost of $180 / LF– Total cost for dropped girder line = $1,080,000 – Total savings (girder + deck) = $1,129,560– Net savings for bridge superstructure = $729,560
• Girder wt reduction = 23.1 kips (17%)• Interior bent reaction reduction = 773 kips (25%)
Cost Premium for LWC Bridge
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• Comparisons often neglect other sources of savings– Reduced handling and transportation costs– Reduced erection and rental costs– Reduced cost & time for substructure & foundations– Reduced structural modifications for rehab projects
• Check with local concrete suppliers to obtain an estimate of cost for LWC– Lack of familiarity in some areas may increase the cost of LWC for initial projects
Cost Comparisons for LWC
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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 ksi5 pcf allowance is added to account 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 Bridge, 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 LWC for box beam would make beam pick nearly equal to NWC substructure elements
Ext. Box Beam Weight Chng. % 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
ght p
er F
oot (
lbs)
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– To limit weight of NWC beam, 12 ft width not used– 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
ght p
er F
oot (
lbs)
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 Chng. % 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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Coleman Bridge, Yorktown, VA
• Bridge replaced in 1996– 26 ft wide with 2 lanes to 74 ft wide with 4 lanes and shoulders
– Spans floated into place– Total closure only 9 days
• Sand LWC deck was used based on cost savings and good experience in VA
• Sand LWC helped reduce structure weight– Piers were reused & caps only had to be widened– Reduced the steel required in new trusses
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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– In service for 73 years
17'-1"
3'-0"(TYP.)
5'-6"(TYP.)
2" 9"¢ STRINGER
0.02'/FT.7"0.02'/FT.
1¼" M
MC
OVE
RLA
Y ¢ STRINGER17'-1"
3'-0"(TYP.)
5'-6"(TYP.)
2" 9"¢ STRINGER
0.02'/FT.7"0.02'/FT.
1¼" M
MC
OVE
RLA
Y ¢ STRINGER
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
• 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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Questions?
For more information on LWA and LWC• Contact Reid Castrodale: [email protected]• Visit the Expanded Shale, Clay and Slate Institute website: www.escsi.org
• Contact local LWA suppliers− listed on ESCSI website
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Additional Slides
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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 LWA & 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 all LWC in 1936
– Lower deck was rebuilt with LWCfor highway traffic in 1958
– Both decks are still in service
Development of LWA & 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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18 plants in the USSee www.escsi.org for locations
ESCS Manufacturing Plants in US
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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 1 lb. of each aggregate
Relative Density
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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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• NCHRP Report 380 "Transverse Cracking in Newly Constructed Bridge Decks" (1996)– "Using low‐elasticity aggregates should therefore reduce thermal and shrinkage stresses, and the risk or severity of transverse cracking."
– Recommends using concretes with a low cracking tendency - Low early modulus of elasticity- Low early strength concrete
• LWC has lower modulus but retains strength
Reduced Modulus of Elasticity