BDCS Notes - Soundness of Aggregates

Aggregate Properties: Soundness and Durability

Soundness: The ability of aggregate to withstand weathering. Also called durability.

Soundness is desired in severe climatic conditions. Water freezing in the voids of aggregates generates stresses that can fracture the stones.

ASTM C88 – Simulates weathering by soaking the aggregates in either a sodium sulfate or magnesium sulfate solution. Sulfates cause crystals to grow in the aggregates, simulating the effects of freezing.

A sample is subjected to cycles of sulfate-soaking for 16 hours. Drying follows the soaking process. After five cycles, the aggregates are washed and dried, weighed, and the average percentage loss the entire sample is computed. The result is compared with allowable limits to determine whether the aggregate is acceptable.

BDCS Notes - Evaluation of Aggregate Sources

Evaluation of Aggregate Sources

Civil engineers select aggregates for how they meet specific project requirements, rather than their geologic history. The physical and chemical properties of rocks determine acceptability of an aggregate. Cost and availability are also key to consider when selecting an aggregate. Often, the wisest decision is finding out how to use locally available material in the most cost-effective manner.

Potential aggregate sources are evaluated for:

1. The quality of their larger pieces

2. The nature and amount of fine material

3. The gradation of aggregate

Drilling Cores / Trial Blasts – Investigate the extent and quality of rock in the quarry.

Cores and trial blasts also evaluate:

1. Grading

2. Particle Shape

3. Soundness

4. Durability

5. Amount of Fine Material

Cores are examined petrographically for:

1. General Quality

2. Suitability for Various Uses

3. Amount of Deleterious Materials

Sand and gravel pits are evaluated by:

1. Collecting Samples

2. Performing a Sieve Analysis

In an aggregate:

A high amount of large gravel and cobble sizes = NEED FOR CRUSHING

A high amount of fine material = NEED FOR WASHING

How aggregate can be used in a structure:

1. Used as a Base Material

2. Asphalt Concrete

3. Portland Cement Concrete