Concrete: What is it, What do you do with it, and How do you fix it?

1. Concrete: What is it,What do you do with it, and How do you fix it? Jim Grove Federal Highway Administration/Global Consulting Inc. 2012 Alaska Concrete Summit December 5, 2012

2. Outline • How does the hydration process work? • How does it affect what we do in the field? • What are some highway uses for concrete? • New construction • Overlays • What do we do with it later?

3. How does the hydration process work? • What’s going on • NOT going to talk CHEMISTRY! • How does it relate to what I do • How does it affect what I do

4. INTEGRATED MATERIALS AND CONSTRUCTION PRACTICES: A State-of-the-Practice Manual IMCP MANUAL http://www.cptechcenter.org/publications/imcp/index.cfm

5. Cement Chemistry Shorthand

6. Five Stages of Hydration

7. What’s in the Bag? • Ground clinker • Gypsum (sulfate) Gypsum < < Clinker

8. Cement Particles

9. Jim’s Axiom Cement chemistry is as simple AS‘S

10. Four Main Compounds in Cement Hydration B Belite Aluminate Family A Silicate Family C Alite C3A s Gypsum (Sulfate) C-3PO

11. Only 6 Basic Thing You Need to Know • There are 2 Families of Reactions • Aluminates • Silicates • There are 4 Compounds that Count • Alites • Belites • C3A • Sulfates AS ‘S

12. ASA,B,C’s Aluminates Silicates

13. Aluminates

14. Aluminates • C3A and sulfate dissolves into solution (silicates begin to dissolve also) • Within the solution, C-A-S-H forms and coats the cement grain / C3A • Coating slows the reaction • Amount of sulfate in the solution is key • If this goes nuts, you are in deep doodoo! (Peter Taylor)

15. Aluminates Why should I care? Affects the Dormancy Stage!

16. Aluminates Why should I care? Where false set and flash set happens! Can be mixed through? Heat given off? Too much gypsum False set YES NO Flash set Too little gypsum Can be mixed through? Heat given off? NO-Permanent YES

17. Aluminate Family • First reaction • You won’t see it! • All over before the truck gets to the paver • Contributes to the coating of the C3A • Affects the dormancy period • Two critical aspects of the gypsum • Amount of sulfate in the solution • Form of the sulfates

18. Silicates

19. Silicates Why should I care? • Strength happens here! • Determines when you can saw • Cracking happens here • How soon you can drive on it • Permeability happens here!

20. B A Silicates • Strength comes from • Alites (C3S) • Early reaction • Belites (C2S) • Later reaction • They create: Calcium Silicate Hydrate Causes Stuff to Harden Contact Stringy Hairs C-S-H through

21. What Can Atomic Fireballs Tell Us About Cement Hydration? • Reaction happens when water is present • The reaction gives off heat- exothermic • The reaction happens on the surface

22. Silicate Reactions Causes Stuff to Harden Calcium Silicate Hydrate Calcium Hydroxide Calcium Silicates + + Water C-S-H CH Water Paste Cement Calcium Carbonate

23. Silicate Reactions • Silicates start dissolving when the water hits the clinker-but slowly • Contributes calcium ions to the solution • When the solution becomes super-saturated, C-S-H forms

24. Super-Saturated: Calcium Ions Wow!! Some None

25. Silicate Family • Alites- early reaction • Belites- later/long term reaction • Start when water hits them-but slowly • Continues during the dormant stage • C-S-H forms when solution becomes super saturated with calcium ions-beginning of the hardening stage • Give concrete it’s strength • Contributes to lower permeability

26. Goal: Long Life Pavements Old US 20 Woodbury Co - 1921 Old US 20 Woodbury Co - 2000 Photo courtesy Iowa DOT Library

27. How do we get back to the future? Supplementary Cementitious Materials (SCM’s)!!

28. How about SCM’S? • Most concrete has more than cement • What is the effect of SCM’S? • Fly Ash • Slag (GGBFS) • Natural pozzolans

29. How SCM’s Work Calcium Silicate Hydrate Cement Calcium Hydroxide Calcium Silicates CSH + CH + Water Secondary Reaction Begins after the cement reaction Fly Ash / Slag Supplemental Cementitious Material CSH + Water + CH

30. Composition Pozzolanic Cementitious Glasser, et. al., 1987

31. Less Horsepower Secondary Reaction

32. What are some highway uses for concrete? • New construction • Full depth new pavement/runways • Predominant use in the Upper Midwest • Long life pavement • First cost competitive • Often win in alternate bidding • Overlays • Bonded overlay (formerly know as Whitetopping)

33. Iowa Climate • Very seasonal • Very changeable

34. What Is an Overlay? Rehabilitation Placing a layer of concrete over distressed existing pavement

35. Why Consider Concrete Overlays? • Consistently provide cost-effective solutions • Utilizes existing pavement structure • Eliminate removal operation • Shortens construction time • Few pre-overlay repairs are necessary • Placed using normal concrete pavement construction practices • Can be opened to traffic quickly using standard mixes

36. 2 to 6 in. thick => 15 to 25 years > 6 in. thick => >20 years Expected Service Life • Overlay service life is dependent upon : • Sound structural design • Good construction practices • Iowa 21 Whitetopping Research • 2” thick with fibers • 18 years old (1994) • Still performing well today

37. Concrete Overlay Guide second edition Contents Overview of Overlay Families Overlay types and uses Evaluations & Selections Six Overlay Summaries (11”x17” sheets) Design Section Miscellaneous Design Details Overlay Materials Section Work Zones under Traffic Key Points for Overlay Construction Accelerated Construction Specification Considerations Repairs of Overlays Second Edition September 2008 http://www.cptechcenter.org/publications/overlays/index.htm

38. Concrete Overlays • Bonded Overlay System • Thinner • Bond is integral to design • Unbonded Overlay System • Thicker • Old Pavement is base System of Concrete Overlays Over Concrete Pavements Over Concrete Pavements Concrete Over Asphalt Pavements Over Asphalt Pavements Asphalt Over Composite Pavements Over Composite Pavements Composite

39. Evaluations of Existing Pavements for Overlays • When combined with an overlay, can the existing pavement help carry anticipated traffic as: • An integrated part of the pavement (Bonded) • Or serve as a base or subbase (Unbonbded) • Determine: • Required repairs where needed • Establish the concrete overlay design thickness

40. What's the Process? Evaluate the pavement in place Choose the type of overlay If needed – repair damage Prepare interface Pave Cut joints Cure

41. Feasibility • HMA pavements with some structural integrity • Limited structural (fatigue) cracking • No stripping/raveling in HMA layers • HMA thickness after milling > 3 in to 4 in. • Rutting in HMA layers ok • Non-load associated cracking ok

42. Bonded Concrete Overlay of Asphalt Pavements • Spots of distress that aren’t visible can be determined through evaluation • Localized areas of weakness can be strengthen through patching. Milling can remove a number of asphalt surface distresses.

43. Unbonded Concrete Resurfacing of Asphalt or Composite Pavements • Use to restore structural capacity of the existing pavement • Used to increase pavement life equivalent to full-depth pavement. • Eliminates rutting and shoving problems and results in improved surface friction, noise, and rideability Normally 4” - 11” thickness

44. Surface Cleaning Power Sweeping Air Blasting Water Blasting

45. Be careful of milling too much! Construction traffic needs adequate support

46. Longer Lasting Alternative Concrete overlays resist rutting

47. Concrete Placement & Finishing Same as conventional concrete paving Slipform Fixed form Concrete placed directly on AC or on milled or leveled AC surface Conventional curing and sawing

48. New Technology – Stringless Pavingfor Overlays

49. US 18 Single Lane Paving With Through Traffic

50. Pilot Car Typically 10% loss of traffic after pilot car starts