Properties of Good Quality Aggregate

It should be clean, solid, strong with durable particles, and does not contain absorbed damaging chemicals, coatings of clay, or other contaminants which can influence the hydration of cement as well as weaken the paste-aggregate bond. The following types of aggregates should not be used:

  • Brittle or vulnerable to being split.
  • Containing major amounts of soft and porous materials.
  • Specific types of "chert," as they contain very poor resistance to weathering and result in developing surface defects known as popouts



When the aggregate gradations are superior on the basis of aggregate availability and project requirements, an inexpensive concrete is formed with proper workability and finishing ability. The ratios among coarse and fine aggregates are altered depending on the unique characteristics of each aggregate, the placement method, and the finish required.

The partition line between fine and coarse aggregate should be the 3/8-inch sieve. The fineness modulus (FM) stands for an index of the fineness of an aggregate. To calculate FM, the cumulative percentages are included with mass retained on each of a specified series of sieves and the sum is divided by 100. The FM for fine aggregate should remain between the range of 2.3 to 3.1. The FM should not change in excess of 0.2; if not, mix adjustments are required. Too many fine materials will require greater water demand and lead to a sticky mix. Too much coarse material will form harsh mixes that can't be arranged, solidified, and finished smoothly & properly.

As soon as a gradation is chosen for a project, the gradation should be retained within tight ranges to attain superior batch-to-batch consistency. To achieve this, the aggregated should be accumulated properly and reworked to resist too much segregation.