Chapter 4 Aggregates Aggregate Sources Recycled concrete and

Chapter 4: Aggregates

Aggregate Sources ● Recycled concrete and asphalt ● Crushed rock ● Sand gravel deposits ● Experimental recycling of other materials

Types of Rock ● Igneous - rock formed by cooling of molten material ● Sedimentary - rock formed by the settlement in ancient seas ● Metamorphic - igneous or sedimentary rock changed by heat/pressure

Aggregate Types ● Fine Aggregate - passing through #4 and retained on the #200 screen ● Coarse Aggregate - material larger than #4 ● Pit Run - straight from pit with no processing ● Crushed Gravel - gravel crushed to produce fractured faces and desired size

More Aggregate Types ● Crushed Rock - bedrock crushed for use ● Screening - material separated by different screen size ● Concrete Sand - sand with the fines washed out ● Fines - material passing the #200 screen

Aggregate Properties of aggregates used to determine use include: ● Gradation ● Specific Gravity and Absorption ● Hardness ● Durability

More Aggregate Properties ● Shape and Surface ● Deleterious Substances ● Crushing Strength ● Soft and Lightweight Materials

Sampling ● Sampling is the most critical step in testing aggregate ● If possible the sample should be taken from the finished product ● Sampling from stockpiles should be avoided Large stockpiles segregate making it hard to obtain a representative sample

Sampling, cont. ● Stopping the conveyor belt and taking a cross section of the material ● Take three or more samples and combine ● ASTM C 136 provides minimum sample size ● Sample is reduced in size for testing using a splitter box

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