Water - Cement Ratio

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Water - Cement Ratio
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Water/Cement Ratio

• The number of pounds of water per pound of
  cement.
• A low ratio means higher strengths, a high ratio
  means lower strengths.
• For NCDOT, the ratio depends on the class of
  concrete, whether an air agent is used or not,
  and the shape of the stone - rounded or angular.

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W/C Ratio Cont.

• Example
• W/C 0.500, and Water 250 pounds
• How much cement is needed?
• 250 / 0.500 500 pounds of
  cement

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W/C Ratio Cont.

• Example
• W/C 0.500, and Cement 600 pounds
• How much water is needed?
• 0.500 X 600 300 pounds of water
• 300 pounds / 8.33 36.0 gallons

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Water/Cementitious Problem

• Cement Used in Mix 436 pounds
• Fly Ash in Mix 131 pounds
• Maximum Water 36.0 gallons
• Total Water 33.5 gallons
• Metered Water 27.5 gallons
• Free Water in aggregates 50 pounds
• Determine the design w/c ratio and the batched
  w/c ratio

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SOLUTION Design W/C

• Add Cement And Fly Ash
• 436 131 567 pounds
• Convert Design Water Into Pounds
• 33.5 X 8.33 279 pounds
• Plug Into Formula W/C Ratio
• 279 / 567 0.492
• (carry answer to three places after decimal)

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Batched W/C Ratio

• Add Cement And Fly Ash
• 436 131 567 pounds
• Convert Metered Water Into Pounds
• 27.5 X 8.33 229 pounds
• Add free water 229 50 279 Lbs
• 279 / 567 0.492

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W/C Ratio with Ice

• Determine the W/C ratio if 68 pounds of ice is
  used to lower the temperature of the concrete.
• The W/C ratio remains the same because the
  quantity of total water does not change.

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QUESTIONS
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Solids And Voids

• In determining mix designs, you must use an
  aggregate dry rodded unit weight.
• This weight is determined at the lab.
• In the procedure for determining this weight,
  only the coarse aggregate is used.
• Therefore, there is a of solids and a of
  voids in the container.

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Formula Solids Voids

• Solids
• Dry Rodded Unit Weight
• (Spec. Gravity) X (62.4)
• The Answer Is Then Multiplied Times 100
• To get Voids
• Subtract Solids from 100

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Example

• Dry Rodded Unit Weight 96.6 pcf
• Specific Gravity Of Agg. 2.80
• Solids 96.6 0.553
  (2.80 X 62.4)
• 0.533 X 100 55
• Voids 100 - 55 45

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Terms I Should Know.

• Abrasion Resistance of an Aggregate
• Durability
• Hydration
• Ph
• Saturated Surface Dry
• Set Retarder
• Unit Weight
• Water / Cement Ratio
• THAT IS ENOUGH FOR A MONDAY!!

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Pass Out Day 1 Mix Design Problems
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PROBLEM SOLUTION

• 1.Water 209 15 224 gals
• 224 X 8.33 1866 pounds
• Add all material
• 40607733 13,586 1866 27,245
• Divide by unit weight
• 27,245 7.1 cu. yd.
• (142.10 X 27)

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PROBLEM SOLUTION

• 2. Water / Cement Ratio
• 1866 / 4060 0.460
• 3. (A) Solid
• 88.6 0.508 X 100 51
• (2.79 X 62.4)
• (B) Void 100 51 49

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PROBLEM SOLUTION

• 4. Wet Sand
• 5.9 - 0.5 5.4 5.4 / 100 0.054
• 0.054 X 1102 59.5 pounds
• 1102 60 1162 pounds (batch weight)
• Dry Sand
• 0.5 / 100 0.005
• 0.005 X 1102 5.5 pounds
• 1102 - 6.0 1096 pounds

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PROBLEM SOLUTION

• 5. SSD sand weight ?
• 1720 / 1.062 1620 pounds SSD sand

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PROBLEM SOLUTION

• Gallons of Water from Wet Sand
• 1720 1620 100 pounds / 8.33 12.0 gallons

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HOMEWORK PROBLEM
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QUESTIONS