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LIGHTWEIGHT CONCRETE BENEFITS FOR PBES DEPLOYMENT Reid W. Castrodale, PhD, PE Director of Engineering Carolina Stalite Company, Salisbury, NC.

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Presentation on theme: "LIGHTWEIGHT CONCRETE BENEFITS FOR PBES DEPLOYMENT Reid W. Castrodale, PhD, PE Director of Engineering Carolina Stalite Company, Salisbury, NC."— Presentation transcript:

1 LIGHTWEIGHT CONCRETE BENEFITS FOR PBES DEPLOYMENT Reid W. Castrodale, PhD, PE Director of Engineering Carolina Stalite Company, Salisbury, NC

2 2 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

3 3 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

4 4 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

5 5 5 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

6 6 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 Soil Gravel ESCS Agg. Limestone Sand 1 lb. of each aggregate Relative Density

7 77 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!

8 88 Geotechnical Use of LWA LWA can be used as structural fill – LWA is free draining PropertyLWANWA or Soils Compacted in-place bulk density40-65 pcf pcf Bulk Loose density (dry)30-50 pcf pcf Angle of internal friction35°-45°+30°-38° Abrasion resistance (Loss)20-40%10-45%

9 9 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

10 10 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!

11 11 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

12 12 AASHTO LRFD Specs (Section 5.2) – Lightweight concrete: "Concrete containing lightweight aggregate and having an air-dry unit weight not exceeding kcf …" – Normal weight concrete: Concrete having a weight between and kcf Concrete that falls between these definitions is often called specified density concrete (SDC) Definitions

13 13 Spectrum of Concrete Density All LWCSand LWCNWC pcf pcf pcf LW FineNW Fine LW Coarse NW Coarse Specified Density Concrete (SDC) Density ranges shown are approximate Must add allowance for reinforcement (typ. 5 pcf)

14 14 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

15 15 Sand LWC for Bridge Decks TennDOT includes in Standard Specifications NCDOT, UDOT, etc. have std special provisions Other states have project special provisions All LWC Has not been used in recent years Special provisions have been developed for NCDOT DOT Specifications for LWC

16 16 Semi-LWC for Girders INDOT allows in design manual ( 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

17 17 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 = – 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

18 18 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

19 19 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

20 20 Cost of LWC Increased cost of LWA – Additional processing – Shipping from the manufacturing plant

21 21 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 / CYCost Prem. / SF $20 / CY$0.56 / SF $35 / CY$0.97 / SF $50 / CY$1.39 / SF

22 22 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 TypeCost Prem. / LFCost 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

23 23 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 / $0.65 / LF ea. = $390 – Total cost reduction = $1,201 Net savings by using sand LWC girder$177 Sample Girder Cost Analysis

24 24 PBES Applications for LWC All LWCSand LWCSDCNWC 105 pcf120 pcf135 pcf145 pcf These are fresh densities for concrete up to about 6 ksi Add 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

25 25 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

26 26 Mill Street Bridge, NH % Chng. Weight as Des. Chng. Weight as Built Chng. 150 pcf039 t025 t0 125 pcf17%32 t7 t20 t5 t 110 pcf27%28 t11 t18 t7 t Precast foundation elements – Project did not use LWC Comparison for abutment footings – Abutment walls have similar weights

27 27 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 CapWeightChange% Chng. 150 pcf16 t pcf13 t3 t17% 110pcf12 t4 t27%

28 28 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 CapWeightChange% Chng. 150 pcf29 t pcf24 t5 t17% 110 pcf21 t8 t27%

29 29 Project did not use LWC Precast columns – Max wt = pcf – Max wt = pcf – Using 128 pcf SDC could have eliminated pedestal for tall columns Precast caps – Max wt = pcf – Max wt = pcf Edison Bridges, FL

30 30 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

31 31 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 spanWeightChange% Chng. 150 pcf16.0 t pcf13 t3 t17% 125 pcf - Solid16.4 t0.4 t+3%

32 32 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 BarrierWeightChange% Chng. 150 pcf13.7 t pcf11.4 t2.3 t17% 110 pcf10.1 t3.6 t27%

33 33 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 BeamWeightChange% Chng. 150 pcf69 t pcf57 t12 t17%

34 34 NEXT F Beams Compare section weights for NEXT 36 F – 155 pcf; Sand 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 8 ft10 ft12 ft8 ft10 ft12 ft 16%

35 35 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 8 ft10 ft12 ft8 ft10 ft12 ft NEXT D Beams 16%

36 36 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 & DeckWeightChange% Chng. 158 pcf45 t pcf37 t8 t18% NWC density was obtained from girder fabricator Specified concrete compressive strength = 10,000 psi

37 37 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 DeckWeightChange% Chng. 145 pcf132 t pcf116 t16 t12% 105 pcf106 t26 t20%

38 38 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 Lewis & Clark Bridge, OR/WA

39 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 – million lbs – Sam White Lane over I-15 – million lbs – I-15 Southbound over Provo Center Street – 2 moves of 1.5 and 1.4 million lbs Bridges set with SPMTs, UT

40 40 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 … GirderDeckWeightChange% Chng. 152 pcf150 pcf1,282 t pcf120 pcf1,049 t233 t18% 127 pcf105 pcf996 t286 t22% Comparison with all LWC deck is not in Manual

41 41 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

42 42 Questions? For more information on LWA and LWC Contact Reid Castrodale: Visit the Expanded Shale, Clay and Slate Institute website: Contact local LWA suppliers: listed on ESCSI website


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