Concrete Technology

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Concrete Technology
2
Mix design

• Process
• Lab analysis of the aggregate
• Obtain the concrete specifications
• Determine the target strength
• Determine the w/c ratio
• Estimate the water content
• Determine the stone content
• Calculate the sand content

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Mix design

• Aggregate analysis

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Mix design
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Mix design

• Sand analysis
• Relative density (SG)
• Uncompacted bulk density
• Compacted bulk density

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Mix design

• Coarse aggregate analysis
• Relative density
• Uncompacted bulk density
• Compacted bulk density

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Mix design

• Concrete specifications
• Compressive strength 25 MPa
• Consistence (slump) 75 mm
• Max w/c ratio not specified
• Min cement content not specified
• Type of cement Type GP
• Max aggregate size 19.0 mm
• Method of placement pump

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Mix design

• Material properties
• Cement Type GP
• RD 3.14
• Sand RD 2.60
• FM 2.3
• Quality good
• Stone size 19.0 mm
• RD 2.65
• CBD 1540 kg/m3

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Mix design

• Determine the target strength
• Minimum compressive strength 25 MPa
• Target strength Min (1.64 x Std Dev)
• 25 (1.64x 3.0) 25 4.9 30
• Notes
• 1.64 is from statistics that allows for 5
  failures
• Standard deviation based on plant history

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Mix design

• Determine the w/c ratio
• Based on history of the materials used in the
  plant

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Mix design

• Estimate the water content
• Use figures from previous history with the same
  materials
• Using figures from table below
• Correction for stone size

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Mix design

• Calculate cement content
• w/c 0.6
• Cement 195 / 0.6 325 kg/m3

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Mix design

• Determine the stone content
• S CBD( k 0.1FM)
• where
• S stone content in kg/m3
• CBD compacted bulk density
• k factor for stone size workability
• FM fineness modulus of sand
• S 1540x (0.94 0.1x 2.3) 1093 kg/m3

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Mix design

• Calculate the sand content
• 1 cubic meter 1000 litres
• Sand required 1000 710.95 289.05
• Sand in kg 289.05 x 2.60 751.53

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Mix design

• Adjustment at trial stage
• Slump if lower or higher than expected
• Harshness (too much stone)
• Strength adjustment 0.05 5 MPa
• Moisture content of sand
• Increase sand mass
• Decrease water to be added
• Pumping adjustments
• Increase sand content
• Decrease stone content
• Increase water