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Beyond the Pavement Patch

Beyond the Pavement Patch. Applications of Maturity Testing for Bridges, Structures and Pre-Cast Concrete. July 19, 2006. Presented by John P. Gnaedinger, Pres. Con-Cure Corporation, St. Louis, MO. Willow Island Cooling Tower Collapse.

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Beyond the Pavement Patch

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  1. Beyond the Pavement Patch Applications of Maturity Testing for Bridges, Structures and Pre-Cast Concrete July 19, 2006 Presented by John P. Gnaedinger, Pres. Con-Cure Corporation, St. Louis, MO

  2. Willow Island Cooling Tower Collapse 51 Workers were killed when a cooling tower collapsed. It was shown that the primary cause was “green” concrete. In-place strength was lower than test cylinder strength, leading to interest in better in-place strength determinations.

  3. Pavement Patches And Maturity Testing • DOTs and paving contractors have benefited from Maturity Testing for years. • Allows pavement patches to be opened to traffic quickly without the need to cast, cure, transport and test concrete test samples • Mainline paving operations are also benefiting from this testing by learning the soonest joints can be saw-cut. • Rapid acceptance because risks are minimal BUT… Beyond the Pavement Patch, there are many more applications that benefit from Maturity Testing!

  4. Estimating In-Situ Strength Development • Need in-place strength for… • Form removal • Application of Post-tensioning • Shore and reshore removal • Rapid Scheduling and Safety ESPECIALLY IN COLD WEATHER

  5. Early form removal … • Speeds up construction • Requires less form/shoring inventory • Allows other trades early access • Sooner completion date • Increases profits

  6. 200% Effect of Curing Temperature on the rate of strength gain 100% Relative Strength (to 3d@70F) 50% 52F 70F 96F Curing Temperature

  7. ACI 318 & 301 Allow the Following Test Methods • Field Cured Cylinders(ASTM C31 & C 39) • Cast-in-place Cylinders (ASTM C 873) • Penetration Resistance* (ASTM C 803) • Pullout Strength* (ASTM C 900) • Break-off* (by ACI 301) (ASTM C 1150) • Maturity Testing*(ASTM C 1074) * require correlation

  8. Contractors need a … • Simple • Economical • Reliable method to determine in-place strength.

  9. Field-cured Cylinders • “Cured same as structure” • Variable temperature differences • Conservative strength estimate • Commonly used - simple & economical Typically, Underestimate In-place Strength

  10. Comparison: Field-Cures vs. Reality Structure =Larger mass =warmer temps & better hydration Test Cylinders= smaller mass = cooler temps “The Bathtub Test”

  11. Proper quality control is essential... • Fact: Test samples do not reflect the influence of temperature extremes, weather conditions, critical curing conditions, concrete thickness and any number of other actual job site conditions. • See Photo, next slide.

  12. Concrete Cylinders at jobsite. • Date: March 17 2001, 7:30 a.m. • Ambient Temperature at the time the photo was taken: 38º F • Curing conditions of deck: Heated & Covered, with full jacketing. The deck is hot The cylinders are not 

  13. From: Plante, et. al., “Influence of Curing Conditions on Concrete Specimens at Construction Site,” ACI Materials Journal V. 97, No. 2, March-April 2000, pp. 120-126. Referencing: Richardson, D. N., “Review of Variables that Influence Measured Concrete Compressive Strength,” N.A.A. Circular No. 132, 1991, p. 112.

  14. Maturity Testing: A New Paradigm. Today: But New Techniques Exist: The construction industry relies on field-cured cylinder testing to determine strength of curing concrete. Using an established ASTM Standard, in-place strength can be determined accurately and instantly.

  15. Principle of Maturity Testing The temperature at which concrete is cured determines the strength of the concrete at any given point in time.

  16. Principle of Maturity Testing The relationship between the temperature history of a concrete and its strength can be empirically determined, and is called its maturity index.

  17. Principle of Maturity Testing Concrete of a given mix at the same maturity has approx. the same strength, regardless of the temperature and time history that made up that maturity.

  18. Concrete of a given mix at the same maturity has the same strength, regardless of the temperature and time history that made up that maturity. CONCRETE Cold Hot Concrete Temperature Concrete Temperature M2 Concrete Strength M1 Time Time M Maturity (EA or TTF) M1=M2=M

  19. Recognized, recommended and referenced Test Methods: • ASTM C1074, “Standard Practice for Estimating Concrete Strength by the Maturity Method.” • ACI 306 (Chapter 6), 228 and many other references • SHRP C376 • AASHTO • OSHA Sec. 1926:171:B(c)

  20. 4 Steps of Maturity Testing • Establish Maturity Curve for mix • Embed sensors & launch maturity meters • Read meters • Interpret data

  21. 4 Steps of Maturity Testing • Establish Maturity Curve for mix • Embed sensors & launch maturity meters • Read meters • Interpret data

  22. 4 Steps of Maturity Testing • Establish Maturity Curve for mix • Embed sensors & launch maturity meters • Read meters • Interpret data The sensors are placed in the structure by drilling a small hole in the formwork and threading the sensor plug through the hole. The meter is attached below.

  23. 4 Steps of Maturity Testing • Establish Maturity Curve for mix • Embed sensors & launch maturity meters • Read meters • Interpret data Here, the sensor tip is protected from damage during placement operations by securing the wire and sensor to the underside of the rebar

  24. View showing sensor and meter together, with wire running through formwork. Rebar Sensor Tip Wire Maturity Meter There is no limit to the number of meters that can be deployed for a given pour.

  25. 4 Steps of Maturity Testing • Establish Maturity Curve for mix • Embed sensors & launch maturity meters • Read meters • Interpret data

  26. 4 Steps of Maturity Testing • Establish Maturity Curve for mix • Embed sensors & launch maturity meters • Read meters • Interpret data

  27. 4 Steps of Maturity Testing • Establish Maturity Curve for mix • Embed sensors & launch maturity meters • Read meters • Interpret data

  28. 4 Steps of Maturity Testing • Establish Maturity Curve for mix • Embed sensors & launch maturity meters • Read meters • Interpret data

  29. 4 Steps of Maturity Testing • Establish Maturity Curve for mix • Embed sensors & launch maturity meters • Read meters • Interpret data

  30. Why Do Maturity Testing? The Benefits:

  31. The Benefits of Maturity Testing. Pull cables and strip forms ASAP =Project Acceleration. Curing times are usually cut dramatically, esp. in the winter. Test cylinders typically lag far behind the structure. Extend the construction season.

  32. The Benefits of Maturity Testing. Save money by assessing cold weather protection to ensure sufficient temperatures for curing without wasted heating. Can also allow early termination of external heating or thermal protection.

  33. The Benefits of Maturity Testing. Open pavements to traffic sooner=get paid sooner Determine optimal saw-cut times

  34. The Benefits of Maturity Testing. Save money by reducing or eliminating reliance on field-cured test samples. • The High Cost of Waiting: • What does it cost to have a crew waiting on the job for the field-cured samples to achieve the required strength when the slab is already there?

  35. The Benefits of Maturity Testing. Improve site safety by not stripping forms or stressing cables too soon

  36. The Benefits of Maturity Testing. Improve concrete quality by learning the temperature history of the concrete. Compensate for changes in field conditions on-the-fly.

  37. The Benefits of Maturity Testing. • Reduce Costs and improve performance of concrete by optimizing mix designs • Lower cement factors, controlled heat of hydration, at lower cost • Important in the age of cement shortages

  38. The Benefits of Maturity Testing. • Monitor critical areas of a structure. • Non-destructive, inexpensive and cost-effective.

  39. When Should You Do Maturity Testing? The Applications:

  40. Applications: • Parking Garages • Bridges • High-rise concrete buildings • Post-tensioned structures • Cold & Hot Weather concreting • Mass Concrete Projects • Pre-cast and prestressed concrete

  41. Expressed another way: Any time-sensitive placement where knowing the in-place strength would be beneficial for quality, engineering or economic reasons

  42. Case Histories: Post-tensioned structures • Parking garages • Bridges • High-rise concrete buildings

  43. Parking Garage: Children’s Hospital, St. Louis 2000-01

  44. Parking Garage: Children’s Hospital, St. Louis 2000-01 • Con-Cure conducted maturity testing for 33 pours at a post-tensioned parking structure in St. Louis during November, December, January, February, March and April. • Mix: Metro Concrete 6000psi mix with Microsilica and FiberMesh. • Required strength to begin stessing operations: 3450psi.

  45. 5377 PSI 3.4 days EA

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