Concrete Materials Information for Construction Academy

1. Concrete Materials Information for Construction Academy Michael (Mike) Bergin, P.E., State Structural Materials Engineer FDOT, State Materials Research Park August 20, 2014 Michael.bergin@dot.state.fl.us

2. Topics • Fundamentals of Good Concrete • A better understanding of w/c ratio • Slump of Concrete • Water added at the site • Penalties • Available water for hydration • Drilled shaft concrete and slump loss • Mass concrete • Specification changes

3. Topics • 346 changes based on 1/15 lettings • Performance Based Concrete Pavement, Section 350 • Slab Replacement Concrete, Section 353 (proposed changes) • Sampling Steel • New Ideas, Concepts and Research • Internal Curing • Roller compacted concrete (RCC) • Self consolidating concrete (SCC) • Ground Glass in Concrete • GTR in Concrete

4. Water Cementitious Materials Ratio and the Velcro Approach What is the w/c ratio ?

5. Cementitious Materials • Includes: • Cement • Type I, II, III • Particle size; ∼ 25 to 40 microns • Pozzolans, • Fly ash, Class F and C • Ground glass • Rice hull ash • Sugar Cane Ash • Highly reactive pozzolans • Particle size, ∼ 0.1 to 50 microns • Slag • GGBFS, grade 100 or 120 • Particle size, ∼ 20 to 40 microns

6. Pozzolans and ‘Particle Packing’ • Straight cement and high w/c (>0.41) • Particles separated by high water content • Shrinkage • Excessive bleed water • Straight cement and low w/c (≤0.41) • Particles closer together, tighter bond • A little more durable • Cement and pozzolans with low w/c • Particles • closer together, • size more distributed, • very tight bond • Durability has arrived

7. High w/c Ratio • Water • Increases initial volume • Collects in lens under the surface • Lens is a problem when traffic is placed on it • Lens may be under reinforcement • Increase in ‘bleed water’ • Delays finish work • Unwanted surface conditions and less durable concrete • Shrinkage • Surface cracking • Scaling

8. High w/c Ratio • Fines help reduce bleed water • Cementitious plus fine aggregate • 60% coarse/40 fines is a good ratio. • Rate of bleed water evaporating is regulated by external conditions (weather) • A need for curing

9. Low w/c Ratio • How much water is needed to hydrate cement? • Concrete maintains its volume • A little more is needed for pozzolans or slag • Reduces the pathways for bleed water • Still need some bleed water • More durable concrete • Increase in density • Less surface problems on finished concrete

10. Add Fly Ash or Slag • We have additional fine particles for packing and to provide pozzolanic activity • Particle packing helps minimize voids in the paste • Pozzolanic activity -concrete continues to hydrate (react) • continues as long as there is calcium, silica and moisture in the matrix. • Cement and fly ash both provide calcium and silica. • Moisture already available in mix and moist curing ??? • Some method of curing.

11. Add a low w/c ratio • Best particle packing • Less water between particles • Additional moisture (if needed) comes with wet curing or covering the surface to prevent moisture loss. • Wind • Heat • Dry conditions and low humidity

12. Water/Cement Ratio Cement particle Cement particle High W/C Low W/C Hydration Hydration

13. High w/c ratio equates to lots of shrinkage cracking

14. Shrinkage Cracking

15. Water Added at the Job and Slump of Concrete Sect. 346 • Target Slump and Tolerance Range • Here’s a helpful graphic to clarify the issue (346, Table 6) • Graphic illustrates target slump value

16. Slump Range TOLERANCE SLUMP RANGE (3”) REJECT REJECT 1-1/2” DRY 1-1/2” WET ACCEPT – WATER MAY BE ADDED TARGET SLUMP

17. When the Contractor adds water… • Determine the slump • If within the Target Slump Value • Perform other plastic properties; • Air • Temperature • Determine w/c ratio

18. 346-6: Control of Quality • 346-6.4 Tolerances: When slump is outside the tolerance range, • Make cylinders • Contractor rejects concrete • He notifies the concrete production facility to adjust the concrete mixture • He tests each subsequent load and the first adjusted load from the plant

19. 346-12: Penalty occurs… • If contractor places concrete when any of the plastic properties are outside the limits of the approved mix design • He not only assumes risk of placing non compliant concrete, the contractor is penalized the invoice price of concrete, unless the Engineer approves. • On-going drilled shaft placement • Large footer (don’t want a cold joint) • Disposition of defective materials (DDM) is required

20. The discussion of w/c ratios, slump, slump loss, and elapse time are a major concerns for drilled shafts.

21. Slump Loss? Elapsed Time? • Time it takes to loose slump - drops from 10” to 5” • Indicates how long the contractor has to place the concrete, set bolts, remove temporary casing. • to get slump, producer uses water reducing admixtures and water.

22. Drilled Shaft Concrete should not look like this!

23. Or this! Q: What is the minimum clear cover (in inches) over steel?

24. Some Probable Causes? • Concrete not workable? • Slump loss not accurate for this placement? Need new slump loss? • Contractor not ready for concrete? • Rebar spacing too tight? • Engineers increasing capacity • Second truck delayed? • How was the deficiency determined?

25. High Slump Concrete • high slump concrete (≥7.5 ”) may have lumps and balls. • Use a grate with max opening size of 2.5” in either direction • Placement continues but, • Lumps and balls are removed • Contractor still responsible for strength • Engineer can make cylinders anytime • Department personnel to monitor • Notify DMO if balls and lumps are present

26. High Slump Concrete • If you see lumps and balls,… • DMO will evaluate the plant to ensure compliance with QC plan • Plan indicates how they are to batch high slump concrete • DMO can verify if the plant was producing in compliance with their plan • If problems persist, the DMO may revoke the plants QC plan

27. 346 Changes For lettings beginning Jan 2015

28. Section 346-2 Materials • 346-2.2 Type II cement replaced with Type II (MH), moderate heat • Required for mass (v/sa ≥ 1.0) concrete placements • 346-2.3 • Fly ash or slag is required for all concrete. • Not required for dri-cast precast elements. • New cement type is added, Type IP • Ternary blends allowed in all classes of concrete • Highly reactive pozzolans (HRP) are identified (SF, Metak, UFFA)

29. 346-3.1 General • Substituting higher strength for lower strength • Can be used in two applications if approved by the Engineer • 1. For Structural Concrete a Higher Strength can be used in lieu of Lower Strength • 2. Structural Concrete can be used in lieu of Non-Structural Concrete

30. 346-3.1 General • Acceptance of concrete is based on contract requirements. • Say contract requires C-II, 3400 psi • A higher strength (C-IV, 5500 psi) is substituted • Compressive strength results are 5,100 psi • Does the concrete pass or fail?

31. 346-3.1 General • 5,100 psi meets contract requirements • Concrete is accepted at FULL PAY • But wait a minute !!!!

32. 346-3.1 General • The minimum required for the C-IV was 5,500 psi - only achieved 5,100 • Notify DMO that concrete did not meet mix design target strength • DMO will investigate concrete producer • QC Program issue, not acceptance issue

33. 346-3.1 General • Section 347 governs non-structural concrete • Do not test concrete based on 346 • Acceptance based on delivery ticket, signed by batcher and QC certifying minimum 2,500 psi

34. 346-3.2 Drilled Shaft Concrete • Allows for slump loss test to be performed in the lab • Less than 30 cubic yards, or • Less than an maximum elapsed time of 5 hours • Concrete used during the summer, temp > 85F, perform slump loss test at hot weather conditions.

35. 346-3.3 Mass Concrete • Mass concrete is indicated on the plans (v / sa ≥ 1.0) • Control concrete temperature • Max 180F (> 180F, what happens?) • ΔT≤ 35F (interior to exterior) • Interior stays hot, exterior cools • If exceeded, contractor must take action • How would contractor control temp???

36. 346-3.3 Mass Concrete • New language is added; • Same size elements • One plan can be used • 2 elements could be placed at one time • 2nd needs to be started within 1 hour of the first. • Both need to be instrumented • Why would we want both instrumented???

37. 346-5: Sampling and Testing Methods • Table 5 • Added testing requirements for self consolidating concrete (SCC) • Also indicates that QC will use the same type of air meter as V.

38. 346-5: Sampling and Testing Methods • Table 5 – • If pressure meter is used, must have an aggregate correction factor on mix design • Curing facilities have capacity to hold all QC and V cylinders • V will use same air meter and cylinder size as QC • Can take entire concrete sample at one time from middle of load, ASTM C172

39. 346-7 Mixing and Delivering • Transit time, reject trucks exceeding the maximum transit time • Typically 90 minutes (agitator truck, HRWR) • Construction personnel need to notify the District Materials Office of concrete placements • To witness complicated placements • Mass concrete • Structural Drilled Shaft • To IA QC or V technicians

40. 346-7 Mixing and Delivering • 346- 7.3 Mixing at the Site: This is indicated in the Contractors QC plan. • 346-7.7 Adding Water: • Any water missing from the saddle tanks is; • Assumed to be in the batch and • is added to the jobsite water on the delivery ticket and included in the w/c ratio.

41. 346-7 Mixing and Delivering • Changes • No water added to truck after 130 revs • Truck has started to place within 90 min. • has 15 additional min to complete the placement • If 120 min haul time already approved, no additional time allowed.

43. 346-7 Mixing and Delivering • 346-7.8 Sample Location: Sample Correlation required when contractor can’t sample at the point of final placement. • Need 5 samples, one sample per load • What is a sample? • DMO will help with this process

45. Bottom Up Pumping

46. 346-8 Plastic Concrete Sampling and Testing • Truck Mixer Identification Card? • Inspector should request to see this. • If no card, truck cannot deliver for FDOT, reject concrete • Contractor is responsible to remove this if there are deficiencies with the truck that cannot be repaired immediately. • He is to forward id card to DMO • When any 5 loads within 2 days are outside the specified tolerances- notify DMO, they will suspend production from the plant!

47. 346-9: Acceptance Sampling and Testing • When a mix is used for a different application, the LOT is defined by that application. • Class II concrete is placed for use as Class I Pavement. • Lot size for this Class II concrete is defined as 2000 sy, or 1 days production, its placed as pavement

48. 346-9: Acceptance Sampling and Testing • Acceptance is typically a 50 cyd lot size • 346-9.2.1 Acceptance Tests can be reduced to 100 yd3 if there is consistency in strength tests (same mix, same plant, same contract) • Need 2 Sdev (95% of data) above the minimum required strength based on the class of concrete

49. 346-9: Acceptance Sampling and Testing • For Class IV or higher, need ten consecutive strength tests to determine reduced frequency • For Class III or lower, need five consecutive strength tests to determine reduced frequency • Data must come from an approved lab (Section 105)

50. 346-9: Acceptance Sampling and Testing • Need prior approval of the Engineer • Provide data prior to approval • CPAM has instructions on the process • Usually includes the DMO to help verify data.