In early 1900s, Stephen Hayde discovered method to manufacture lightweight aggregates (LWA) from shale, clay and slate S

1. LIGHTWEIGHT CONCRETE BENEFITS FOR PREFABRICATED BRIDGE ELEMENTS & SYSTEMS (PBES) DEPLOYMENTReid W. Castrodale, PhD, PEDirector of EngineeringCarolina Stalite Company, Salisbury, NC

2. Development of LWC • 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

3. Development of LWC • 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

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

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. Most common Lightweight Concrete 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

8. Definitions • 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)

9. Spectrum of Concrete Density SDC SDC Density ranges shown are approximate Must add allowance for reinforcement (typ. 5 pcf)

10. Specifying Density of LWC • “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)

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. Cost Premium for LWC • 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

17. Sample Girder Cost Analysis • 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

18. PBES Applications for LWC • 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 These are fresh densities for concrete up to about 6 ksi Add 5 pcf allowance for reinforcement

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 • 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

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

23. Edison Bridges, FL • 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

24. Woodrow Wilson Br, VA/DC/MD • 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

25. Okracoke Island, NC • Precast cored slabs • Project did not use LWC • 21” deep by 3 ft wide • 30 and 50 ft spans

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

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

28. NEXT F Beams 16% 8 ft 10 ft 12 ft 8 ft 10 ft 12 ft • 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

29. NEXT D Beams 16% 8 ft 10 ft 12 ft 8 ft 10 ft 12 ft • Compare section weights for NEXT 36 D • 12 ft width not used to limit weight of NWC section • Max. span charts are provided for sandLWC • 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 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

32. Lewis & Clark Bridge, OR/WA • 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

33. Bridges set with SPMTs, UT • 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

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 …” Comparison with ALWC deck is not in Manual

35. 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