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Presentation on theme: "LIGHTWEIGHT CONCRETE BENEFITS FOR PREFABRICATED BRIDGE ELEMENTS & SYSTEMS (PBES) DEPLOYMENT Reid W. Castrodale, PhD, PE Director of Engineering Carolina."— Presentation transcript:


2 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

3 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

4 4 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

5 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

6 LWA should satisfy NWA specifications – Except different gradations – AASHTO M 195 LWA has higher absorption than NWA – Needs to be prewet, especially for pumping For LWC – Same batch plants and mixing procedures – Same admixtures – Can use same mix design procedures – “Roll-o-meter” for measuring air content LWA is just a lighter rock!

7 LWA is used to reduce the 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 specified, so it must be measured during placement for QC Lightweight Concrete Most common

8 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

9 Spectrum of Concrete Density All LWCSand LWCNWC 90 - 105 pcf110 - 125 pcf135 - 155 pcf LW FineNW Fine LW Coarse NW Coarse SDC Density ranges shown are approximate Must add allowance for reinforcement (typ. 5 pcf)

10 “Equilibrium density” is defined in ASTM C 567 – Density after moisture loss has occurred – Often used for dead load calculations “Fresh density” used for QC tests during casting – Use for handling loads at early age – Suggest using for final design loads in large elements Add reinforcement allowance to concrete density when computing dead loads (typ. 5 pcf) Specifying Density of LWC

11 Sand LWC for Bridge Decks TennDOT includes in Standard Specifications NCDOT, UDOT, etc. have std special provisions VDOT & other states have proj. special provisions All LWC Has not been used in recent years Special provisions are being developed for NCDOT DOT Specifications for LWC

12 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

13 GDOT Special Provisions Special provisions for 10 ksi 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

14 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 Focus for this presentation – Reduced weight for PBES deployment Benefits of LWC Opposite of what many expect!

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

16 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 shipping cost LWC Premium / CYCost / SF $20 / CY$0.56 / SF $30 / CY$0.83 / SF $40 / CY$1.11 / SF Cost Premium for LWC

17 Cost premium for LWC for Mod BT-74 girder – Assume $30 / CY = $6.83 / LF – Cost premium for LWC for 150 ft girder = $1,024 Cost reduction by using LWC – 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 LWC $177 Sample Girder Cost Analysis

18 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

19 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

20 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

21 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 CapWeightChng.% Chng. 150 pcf16 t00 125 pcf13 t3 t17% 110pcf12 t4 t27%

22 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 CapWeightChng.% Chng. 150 pcf29 t00 125 pcf24 t5 t17% 110 pcf21 t8 t27%

23 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

24 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 LWC deck performed well until bridge was recently replaced to improve traffic capacity Woodrow Wilson Br, VA/DC/MD

25 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 spanWeightChng.% Chng. 150 pcf16.0 t00 125 pcf13 t3 t17% 125 pcf - Solid16.4 t0.4 t+3%

26 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 BarrierWeightChng.% Chng. 150 pcf13.7 t00 125 pcf11.4 t2.3 t17% 110 pcf10.1 t3.6 t27%

27 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 BeamWeightChng.% Chng. 150 pcf69 t00 125 pcf57 t12 t17%

28 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 8 ft10 ft12 ft8 ft10 ft12 ft 16%

29 8 ft10 ft12 ft8 ft10 ft12 ft NEXT D Beams 16% 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

30 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 & DeckWeightChng.% Chng. 158 pcf45 t00 130 pcf37 t8 t18% NWC density was obtained from girder fabricator Specified concrete compressive strength = 10,000 psi

31 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 DeckWeightChng.% Chng. 145 pcf132 t00 120 pcf116 t16 t12% 105 pcf106 t26 t20%

32 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 – LWC saved about 14 t Existing deck was LWC – Was in service 73 years Lewis & Clark Bridge, OR/WA

33 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

34 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 …” GirderDeckWeightChng.% Chng. 152 pcf150 pcf1,282 t00 127 pcf120 pcf1,049 t233 t18% 127 pcf105 pcf996 t286 t22% Comparison with ALWC deck is not in Manual

35 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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