Aggregate Specifications and Acceptance Criteria
Reading a specification
Acceptance criteria define whether an aggregate is suitable for its intended use. A candidate must be able to read a gradation band (a table of percent-passing ranges by sieve), a deleterious-material limit, a soundness limit, and an abrasion loss limit, and then compare a test result against them. Know the difference between a target value and a limit, and between acceptance (does it meet spec?) and quality control (is the process stable?).
Traps in acceptance questions
Common traps: (1) a result that falls exactly on a limit - specifications usually define whether the limit is inclusive; (2) applying a coarse-aggregate band to a fine aggregate; (3) ignoring that a single failing sieve may be permitted within a tolerance while multiple failures are not; (4) confusing percent passing with percent retained when comparing to a band; (5) forgetting that some specifications are end-result (test the product) while others are method (follow the process).
Worked example
A specification requires 90–100% passing the 9.5 mm sieve. A test gives 89.5% passing. This is a failing result because it is below the lower limit of 90%, even though it is close. If the specification allows a tolerance of ±2% on a single sieve, the result could be accepted under that provision - but only if the tolerance clause applies.
Rule of thumb
Always state the comparison explicitly: result versus limit, and whether the limit is a maximum, minimum, or range. A number without its limit and direction is not an acceptance decision.