Lesson 1/Learning Event 4
Open Gradation
The mix contains a range of sizes of coarse aggregate, fine aggregate, and mineral filler. "Open"
describes the blend. It has voids or unfilled spaces in it, and a good representation of all particle
sizes, down to the #80 sieve. Below the #80 sieve, there are gaps in the particle sizes. It is used
only for road mixes (mix in place).
FIGURE 2. OPEN GRADATION
Uniform Gradation
Uniform gradation consists of aggregate particles which are all approximately the same size.
The particle size is less than one inch. Uniformly graded materials are used extensively as cover
aggregates for surface treatments, seal coats, etc.
FIGURE 3. UNIFORM GRADATION
Macadam Gradation
A macadam graded aggregate consists of coarse, uniformly graded aggregate particles (all about
the same size- to 3 inches).
FIGURE 4. MACADAM GRADATION
Aggregates are angular in shape and rough in surface texture. Aggregates very seldom occur in
nature as angular, so it necessary in most cases to crush the aggregate to obtain the desired
angular particles.
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