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NCDOT Concrete Certification School: Mix Design and Technician Training

The NCDOT Materials and Tests Unit offers a Concrete Certification School aimed at educating technicians on concrete mix design and ensuring compliance with industry standards. This intensive program covers crucial topics such as aggregate properties, moisture calculations, weight adjustments, and the role of various admixtures. Participants will engage in classroom instruction from experienced instructors and will be required to pass a math exam as well as a review of practical applications. This training is essential for those pursuing NCDOT Batch Technician Certification.

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NCDOT Concrete Certification School: Mix Design and Technician Training

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  1. WELCOME N.C. DEPARTMENT OF TRANSPORTATION MATERIALS AND TESTS UNIT CONCRETE CERTIFICATION SCHOOL

  2. CONCRETE MIX DESIGN TECHNICIAN SCHOOL

  3. M& T CONTACTS • WALTON JONES(RALEIGH)919-733-7091 • MARIA LONG (WILLIAMSTON) 252-792-7627 • DAN ALLEN (WILMINGTON) 910-371-6964 • DARRELL LUMLEY(RALEIGH) 919-556-7606 • HENRY TRAYWICK (FAYETTEVILLE) 910-486-1732 • ROBERT FOSQUE(GREENSBORO) 336-334-3611 • SANDRA POTTS(SALISBURY) 336-993-2300 • MARK THOMAS (MATTHEWS) 704-847-1314 • TRACH CHURCH(WILKESBORO) 336-903-9107 • CHARLES BULLOCK(ASHEVILLE) 828-298-1516

  4. AME’s • HENRY TRAYWICK DIV 1,2,3,6 • JESSICA SMITH DIV 4,5,7 • PAM CARRIKER DIV 8,9,10 • KEN HAMBY DIV 11,12,13,14

  5. INSTRUCTOR • WALTON JONES 919-733-7091

  6. PLEASETELEPHONES OFF OR ON VIBRATE

  7. BATHROOMS MENS WOMEN

  8. CLASS HOURS 8:30 - 4:30

  9. SCHEDULE • DAY 1&2 Review Schools, Agg. Gradation, Wt.-Vol. Relationships • DAY 3 Admixtures, Placing Conc., ACI Mix Design • DAY 4 Fly Ash, Mix Design Variations, Hot & Cold Weather Conc. & Curing, Exam, Review • DAY 5 Math Exam

  10. PREREQUISITES FOR CLASS

  11. NCDOT BATCH TECHNICIAN CERTIFICATION MUST BE CURRENT, OR MUST HAVE SUCESSFULLY COMPLETED BATCH SCHOOL CLASSROOM PORTION

  12. QUESTIONS

  13. REVIEWConcrete Field & Batch Technician School

  14. Review Topics • Components Of Concrete • Moisture Calculations and Batch Weight Adjustments • Field Tests

  15. Components Of Concrete • Cement - The bonding agent. • Sand - Gives workability to the mix. • Stone - Filler material, aids in strengthening the mix. • Water - Causes a chemical reaction called hydration. • Air Agent - For freeze/thaw, durability • Retarder - Slows setting time.

  16. Components Cont. • Water and Cementitious Materials - Portland cements, fly ash, slag. • Fine and Coarse Aggregates - Sands and stones (60-80% of mix). • Chemical Admixtures - Air entrainers, retarders, water reducers, super-plastizers.

  17. Components Cont. • Paste - A combination of cement, water, and entrained air. • Setting Time - The time that it takes for a cement paste to begin hardening. • Mortar - Paste and fine aggregates. • Concrete - Mortar and coarse aggregate.

  18. Aggregates • 60% to 80% of the volume of the mix is aggregates. • Sand may be natural or manufactured and it’s texture will be from fine to coarse. • Stone may be angular from a quarry, or rounded from a pit. • Standard stone sizes for structural concrete from Table 1005-1: #57, #67, and #78.

  19. Moisture Calculations & Batch Weight Adjustments • Calculate Total Moisture in fine and coarse aggregate stockpiles. • Calculate Free Moisture Total Moisture - Absorbed Moisture • Use Free Moisture to calculate batch weight adjustments. • Mix designs are based on SSD weights.

  20. TOTAL MOISTURE • Moisture on the surface and the moisture in the pours and capillaries of an aggregate. • Total Moisture is calculated by: Wet Wt. - Dry Wt. ---------------------- X100 Dry Wt.

  21. Determine Total Moisture • Given the following weights, determine the total moisture: Wet Weight 555.4 grams Dry Weight 523.2 grams • Is this a Fine or Coarse Aggregate sample?

  22. Answer 555.4 - 523.2 ------------------ X 100 = 6.2% 523.2 This is a Fine Aggregate sample

  23. Determine Total Moisture • Given the following weights, determine the total moisture: Wet Weight 1534.2 grams Dry Weight 1505.0 grams • Is this a Fine or Coarse Aggregate sample?

  24. ANSWER 1534.2 - 1505.0 ---------------------- X 100 = 1.9% 1505.0 This is a Coarse Aggregate Sample

  25. Determine Free Moisture • Given the following moistures, determine the Free Moisture: Fine Agg. Total Moisture 6.2% Absorbed Moisture 0.4% Coarse Agg. Total Moisture 1.9% Absorbed Moisture 0.7%

  26. ANSWER Fine Aggregate: 6.2% - 0.4% = 5.8% FREE MOISTURE Coarse Aggregate: 1.9% - 0.7% = 1.2% FREE MOISTURE

  27. Batch Weight Adjustment Problem • Mix design weights are as follows: Cement 555 lbs Sand 1222 lbs Stone 1865 lbs Water 290 lbs

  28. Sand Adjustment • Using the FREE MOISTURE 5.2%, adjust sand weight. • 5.2 / 100 = 0.052 • 1222 X 0.052 = 63.5 lbs. (Water) • 1222 + 64 = 1286 lbs. Adjusted Sand Weight = 1286 lbs

  29. Stone Adjustment • Using the FREE MOISTURE 3.6%, adjust the stone weight. • 3.6 / 100 = 0.036 • 1865 X 0.036 = 67.1 lbs. (Water) • 1865 + 67 = 1932 lbs. Adjusted Stone Wt. = 1932 lbs

  30. Water Adjustment • Total additional water from sand and stone. • 64 lbs. + 67 lbs. = 131 lbs. • 290 lbs. (design water) - 131 lbs. = 159 lbs. Adjusted Water Wt. = 159 lbs.

  31. Corrected Batch Weight • Corrected weights for ONE cubic yard: Cement 555 lbs. Sand 1286 lbs. Stone 1932 lbs. Water 159 lbs. • What are the weights for a 9 cubic yard load?

  32. Pull Weights • For a 9 yard load - multiply batch weights for one yard load times 9. • Corrected weights for 9 cubic yard load: Cement 4995 lbs. Sand 11,574 lbs. Stone 17,388 lbs. Water 1431 lbs.

  33. BATCH TOLERANCES • CEMENT MUST BE BATCH WITHIN ± 1% OF MIX DESIGN WEIGHT • FLY ASH MUST BE BATCHED WITHIN ± 1% OF MIX DESIGN WEIGHT • SAND MUST BE BATCHED WITHIN ± 2% OF THE MOISTURED CORRECTED MIX DESIGN WEIGHT

  34. STONE MUST BE BATCHED WITHIN ± 2% OF THE MOISTURE ADJUSTED MIX DESIGN WEIGHT. • WATER MUST BE BATCHED WITHIN ± 1% OF THE MOISTURE ADJUSTED MIX DESIGN AMOUNT.

  35. BATCHING TOLERANCES • CEMENT- ± 1% • FLY ASH - ± 1% • SAND- ± 2% • STONE- ± 2% • WATER - ± 1%

  36. NCDOT Certification • Concrete Field Technician: Qualified to perform concrete acceptance tests on NCDOT projects. Certified as a “Grade 1 Field Test Technician” by ACI. • Concrete Batch Technician: Certified to batch Ready Mixed, Precast, or Prestressed Concrete for NCDOT projects.

  37. What Does This Mean? • Anyone testing or batching concrete for a NCDOT project shall be certified. • A Field and Batch Technician should be properly trained, knowledgeable, and competent to perform their duties.

  38. Concrete Mix Design Technician • Learn how to perform Sieve Analysis, Fineness Modulus, Design Concrete Mixes using the Absolute Volume Method, and Vary Mixes using the 5% Deviation Method. • Pass this course and become certified to design and vary concrete mixes.

  39. BREAK

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