CONCRETE MIX DESIGN

5. Grading and type of aggregate

• Aggregate grading influences the mix proportions for a specified workability and water-cement ratio.
• The relative proportions between coarse and fine aggregate in concrete mix influence concrete strength.
• Well graded fine and coarse aggregate produce a dense concrete because of the achievement of ultimate packing density.
• If available aggregate, which obtained from natural source, does not confirm to the specified grading, the proportioning of two or more aggregate become essential.
• Additionally, for specific workability and water to cement ratio, type of aggregate affects aggregate to cement ratio.
• Lastly, an important feature of a satisfactory aggregate is the uniformity of the grading that achieved by mixing different size fractions.

6. Quality Control at site

• The degree of control could be evaluated by the variations in test results.
• The variation in strength results from the variations in the properties of the mix ingredients, in addition to lack of control of accuracy in batching, mixing, placing, curing and testing.
• Finally, the lower the difference between the mean and minimum strengths of the mix lower will be the cement-content required. The factor controlling this difference is termed as quality control.