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

CONCRETE MIX DESIGN TECHNICIAN SCHOOL

M& T CONTACTS l WALTON JONES(RALEIGH) l MARIA LONG(WILLIAMSTON) l DAN ALLEN (WILMINGTON) l DARRELL LUMLEY(RALEIGH) l HENRY TRAYWICK (FAYETTEVILLE) l ROBERT FOSQUE(GREENSBORO) l SANDRA POTTS(SALISBURY) l MARK THOMAS (MATTHEWS) l TRACH CHURCH(WILKESBORO) l CHARLES BULLOCK(ASHEVILLE)

AME’s l HENRY TRAYWICK DIV 1,2,3,6 l JESSICA SMITHDIV 4,5,7 l PAM CARRIKERDIV 8,9,10 l KEN HAMBY DIV 11,12,13,14

INSTRUCTOR l WALTON JONES l

PLEASE TELEPHONES OFF OR ON VIBRATE

BATHROOMS

CLASS HOURS

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

PREREQUISITES FOR CLASS

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

QUESTIONS

REVIEW Concrete Field & Batch Technician School

Review Topics l Components Of Concrete l Moisture Calculations and Batch Weight Adjustments l Field Tests

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

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

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

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

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

TOTAL MOISTURE l Moisture on the surface and the moisture in the pours and capillaries of an aggregate. l Total Moisture is calculated by: Wet Wt. - Dry Wt X 100 Dry Wt.

Determine Total Moisture l Given the following weights, determine the total moisture: Wet Weight555.4 grams Dry Weight523.2 grams l Is this a Fine or Coarse Aggregate sample?

Answer X 100 = 6.2% This is a Fine Aggregate sample

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

ANSWER X 100 = 1.9% This is a Coarse Aggregate Sample

Determine Free Moisture l Given the following moistures, determine the Free Moisture: Fine Agg.Total Moisture6.2% Absorbed Moisture0.4% Coarse Agg.Total Moisture1.9% Absorbed Moisture0.7%

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

Batch Weight Adjustment Problem l Mix design weights are as follows: Cement555 lbs Sand1222 lbs Stone1865 lbs Water290 lbs

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

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

Water Adjustment l Total additional water from sand and stone. l 64 lbs lbs. = 131 lbs. l 290 lbs. (design water) lbs. = 159 lbs. Adjusted Water Wt. = 159 lbs.

Corrected Batch Weight l Corrected weights for ONE cubic yard: Cement555 lbs. Sand1286 lbs. Stone1932 lbs. Water159 lbs. l What are the weights for a 9 cubic yard load?

Pull Weights l For a 9 yard load - multiply batch weights for one yard load times 9. l Corrected weights for 9 cubic yard load: Cement4995 lbs. Sand11,574 lbs. Stone17,388 lbs. Water1431 lbs.

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

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

BATCHING TOLERANCES l CEMENT- ± 1% l FLY ASH - ± 1% l SAND- ± 2% l STONE- ± 2% l WATER - ± 1%

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

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

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

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