WELCOME

N.C. DEPARTMENT OF TRANSPORTATION

MATERIALS AND TESTS UNITCONCRETE CERTIFICATION SCHOOL

CONCRETE MIX DESIGN

TECHNICIAN SCHOOL

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

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

INSTRUCTOR

WALTON JONES 919-733-7091

PLEASETELEPHONES OFF OR ON VIBRATE

BATHROOMS

CLASS HOURS

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

PREREQUISITES FOR CLASS

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

QUESTIONS

REVIEWConcrete Field & Batch

Technician School

Review TopicsComponents Of Concrete

Moisture Calculations and Batch Weight Adjustments

Field Tests

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.

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.

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.

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.

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.

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.

---------------------- X 100

Dry Wt.

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?

Answer555.4 - 523.2

------------------ X 100 = 6.2%

523.2

This is a Fine Aggregate sample

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?

ANSWER1534.2 - 1505.0

---------------------- X 100 = 1.9%

1505.0

This is a Coarse Aggregate Sample

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%

ANSWERFine Aggregate:

6.2% - 0.4% = 5.8% FREE MOISTURE

Coarse Aggregate:

1.9% - 0.7% = 1.2% FREE MOISTURE

Batch Weight Adjustment Problem

Mix design weights are as follows:

Cement 555 lbs

Sand 1222 lbs

Stone 1865 lbs

Water 290 lbs

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

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

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.

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?

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.

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

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.

BATCHING TOLERANCES

CEMENT- ± 1% FLY ASH - ± 1% SAND- ± 2% STONE- ± 2% WATER - ± 1%

FIELD TEST

Sampling Freshly Mixed Concrete:AASHTO T-141 ASTM C-172

Slump Test:AASHTO T-119 ASTM C-143

Unit Weight:AASHTO T-121 ASTM C-138

Air Content with Pressure Air Meter:AASHTO T-152 ASTM C-231

Air Content by Volumetric Method:AASHTO T-196 ASTM C-173

Air Content by Chace Indicator:AASHTO T-199

Making and Curing Test Specimens:AASHTO T-23 ASTM C-31

Temperature of Freshly Mixed Concrete:ASTM C-1064

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.

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.

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.

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