ACI METHOD OF MIX DESIGN – Absolute volume method
In 1991,the American Concrete Institute(ACI) published guidaelines for normal, heavyweight and mass concrete mix design. The absolute volume method of mix design as described by ACI committee 211 is presented.
It has the advantages of simplicity that it:
- Applies equally well with more or less identical procedure to rounded or angular aggregate.
- To regular or light weight aggregates.
- To air entrained or non-air-entrained concretes.
A Properly Proportioned Concrete Mix Should Posses These Qualities.
- Acceptable Workability of Freshly Mixed Concrete
- Durability, Strength and Uniform Appearance of the Hardened Concrete
- Class of concrete to be designed.
- Fine aggregate:
- Specific gravity
- Fineness modulus
- Coarse aggregate:
- Maximum size aggregate
- Specific Gravity
- Unit Weight (dry rodded unit weight)
- From Code Specifications:
- Cement factor (minimum cement content).
- W/C ratio (maximum W/C ratio)
- Air content (mean air content).
- Nominal Maximum size of aggregate.
The standard ACI mix design procedure can be divided into 9 basic steps:
- Compressive strength.
- Water cement ratio.
- Air content selection.
- Choice of slump
- Water content selection.
- Cement content
- Coarse aggregate content.
- Fine aggregate content.
- Adjustments for aggregate moisture
Dry Weights vs. Actual Weights
- Batch weights calculated from volumes assume dry CA and dry FA.
- Actual weight of CA and FA are NOT dry
- Adjustment based on moisture contents for both CA and FA.
- Correction for the water content is must.
The mix proportions for the actual materials to be used must be checked and adjusted by means of laboratory trials consisting of small batches.Fresh concrete should be tested for slump, workability, unit weight and air content; specimens of hardened concrete cured under standard conditions should be tested for strength at the specified age.