Fine Aggregate Angularity: Uncompacted Void Content

A fine aggregate angularity report uses loose uncompacted void content as an indirect indicator of particle shape and surface texture. Reproducing the percentage requires the calibrated measure volume, net dry aggregate mass, bulk-dry specific gravity, test method, and report precision.

Method A, Method B, and Method C prepare and interpret the aggregate differently. Keep the method name with the result before comparing samples or applying a project specification.

How is fine aggregate angularity calculated?

Subtract the aggregate's calculated solid volume from the calibrated measure volume. Divide the remaining volume by the measure volume and multiply by 100.

• U is uncompacted void content, in percent.
• V is the calibrated cylindrical-measure volume, in millilitres.
• F is the net dry mass of fine aggregate in the measure, in grams.
• G_sb is the bulk dry specific gravity of the fine aggregate.

Net mass means the filled-measure mass minus the empty-measure mass. Use the unrounded V, F, and G_sb values in the equation. The governing method controls the calculation precision, number of determinations, averaging, and final report rounding.

What does uncompacted void content measure?

ASTM C1252-23 covers loose uncompacted void content of fine aggregate. Under a known grading, the result indicates particle angularity, sphericity, and surface texture relative to fine aggregates tested at the same grading.

ASTM associates higher Method A or B void content with greater angularity, lower sphericity, rougher surface texture, or a combination of those properties. Lower values are associated with rounder, smoother, or more spherical particles under the same test basis.

The test is indirect. It does not count fractured faces or measure compacted-mixture air voids. ASTM lists possible relationships with concrete water demand, grout or mortar flow, asphalt-mixture stability and voids in mineral aggregate, and fine-aggregate stability in base material. Mixture proportions, binder, grading, compaction, and other aggregate properties still affect those outcomes.

How do Methods A, B, and C differ?

ASTM C1252 has 3 procedures. Method A uses a standard graded sample, Method B tests 3 individual size fractions separately, and Method C tests the material finer than the 4.75 mm (No. 4) sieve in its as-received grading.

Single-size fractions usually leave more void space than a well-graded sample because smaller particles are unavailable to occupy spaces between larger particles. ASTM therefore says the Method A result is not directly comparable with the average of Method B's individual fractions.

Method C can support mixture-proportion work because it retains the as-received grading effect. It cannot isolate shape and texture when gradation changes between samples. Use the sand sieve-analysis guide to check whether 2 Method C samples have the same particle-size distribution.

Which mass and specific gravity belong in the formula?

Use the net dry aggregate mass held by the calibrated measure and the bulk dry specific gravity required by the method. Keep the tare, filled mass, and net mass visible so a reviewer can reproduce F.

Bulk dry, saturated-surface-dry, and apparent specific gravity use different particle-volume states. Substituting SSD or apparent specific gravity changes F/G_sb and therefore changes U. The sand specific gravity and absorption guide explains those states and their report labels.

Worked example: can you reproduce the WSDOT result?

The January 2026 WSDOT FOP for AASHTO T 304 gives V = 99.8 mL, F = 146.2 g, and G_sb = 2.636.

First calculate the aggregate volume term: 146.2 ÷ 2.636 = 55.4628. The unoccupied part of the measure is 99.8 − 55.4628 = 44.3372. Dividing by 99.8 and multiplying by 100 gives 44.426%.

A reverse check returns the recorded mass:

This check confirms the arithmetic. The sample, apparatus, preparation, material flow, strike-off, balance, and G_sb records still need their method and quality checks.

How are 2 determinations averaged and reported?

Calculate each determination first, then average the results in the order and precision required by the governing method. Consider a 100.0 mL measure, G_sb of 2.650, and 2 net masses.

The WAQTC FOP inside WSDOT's January 2026 manual calculates each determination and the average to 0.1%. The WSDOT errata on page 1 replaces the report instruction and requires the final uncompacted-void average to the nearest 1% for WSDOT reporting. This example would be reported as 46% under that errata.

Read the adopted agency document as a complete package. Another agency, contract, or ASTM-controlled report can use a different precision. Do not apply WSDOT's errata to an unrelated project.

How much can specific gravity change the result?

A small G_sb change can move U enough to affect a result near a specification threshold. WSDOT states that a 0.05 specific-gravity difference changes calculated void content by about 1 percentage point.

Use V = 100.0 mL and F = 145.0 g:

• At G_sb = 2.650, U = 45.283%.
• At G_sb = 2.600, U = 44.231%.
• The difference is about 1.05 percentage points.

The January 2026 WSDOT FOP says fraction-specific G_sb may be needed when some size fractions differ by more than 0.05 from the value typical of the complete sample. ASTM also notes that the method's relationship to shape and texture depends on the size fractions having equal or nearly equal specific gravities.

Check mineral type, porosity, source blend, and fraction before reusing one G_sb across every sample. A value copied from a supplier sheet or earlier lot needs evidence that it represents the tested material and required grading.

What causes an impossible void result?

An ordinary result falls between 0% and 100%. A negative value means F/G_sb exceeds the measure volume. A value above 100% requires zero or negative mass, which also signals an invalid record.

Example: V = 100.0 mL, G_sb = 2.650, and F = 270.0 g. The maximum solid-volume mass implied by V × G_sb is 265.0 g. The equation returns −1.89%.

Preserve the observations and check:

• empty-measure tare and filled-measure mass;
• mL versus another volume unit;
• bulk dry versus SSD or apparent specific gravity;
• decimal placement and copied sample values;
• moisture state, contamination, and material from another run;
• measure identity, calibration, and balance record.

Do not change a negative result to zero. Use the laboratory quality procedure to correct a traceable clerical error or repeat invalid work.

Which handling errors change uncompacted packing?

The test depends on aggregate falling and occupying the measure without compaction before strike-off. Disturbance changes packing and therefore changes F.

• Vibration, tapping, or moving the measure before strike-off can pack more material into V and reduce calculated U.
• A partial flow, blocked funnel, particle loss, or spill can reduce F and increase calculated U.
• An uneven or repeated strike-off can change the retained mass.
• Material left on the measure exterior can increase the filled mass.
• A damp sample changes the recorded mass and particle flow.
• Cross-contamination changes the test grading and packing.
• Rounding F/G_sb before completing the equation can shift the final percentage.

The WSDOT FOP calls for a centered funnel and measure, free aggregate flow, one rapid strike-off pass, and protection from vibration or disturbance until strike-off is complete. The controlled method and laboratory safety procedure supply the complete apparatus, preparation, operation, and handling requirements.

Is uncompacted void content the same as mixture air voids?

No. U is the void percentage inside a loose fine-aggregate sample placed under the named C1252 or T 304 procedure. Compacted asphalt air voids, voids in mineral aggregate, concrete air content, bulk density, and soil void ratio use different specimens and equations.

The sand bulk-density guide covers mass per bulk volume. Do not transfer a U value into a quantity estimate as a compaction, waste, shrinkage, or density factor.

Which report details make the result auditable?

A complete report ties the percentage to a defined sample, test basis, and project decision.

1. Project and material: intended use, contract item, product, mix or layer, and governing specification.
2. Source and lot: producer, pit or quarry, stockpile or delivery, quantity represented, and sampling location.
3. Sample: identifier, sampling date, sampler, reduction method, test date, and laboratory.
4. Method: ASTM C1252, AASHTO T 304, agency adoption, revision, and Method A, B, or C.
5. Inputs: measure identity and V, tare, filled mass, net F, bulk dry G_sb, and G_sb source.
6. Runs: each determination, average, intermediate precision, and final report rounding.
7. Conditions: spill, blocked flow, vibration, damp material, uneven strike-off, or other deviation.
8. Decision: specification clause, required method, limit, exceptions, and action.

The May 2026 WSDOT HMA Mineral Aggregates form keeps V, F, G, U, sample-fraction masses, specification, and average visible. The sand sampling guide explains how the specimen connects to a stockpile, belt stream, delivery, or defined lot.

Does the fine aggregate pass or fail?

The project specification supplies the acceptance rule. Match the required method, aggregate use, source or blend, limit, rounding, and exceptions to the report.

A common value range from a textbook or competitor page cannot replace the contract clause. The same number can have different meaning under Method A and Method C because Method C retains the as-received grading effect.

After the material is approved for its intended use, use the Sand Calculator to estimate volume and mass from a documented supplier density. Return to the Sand material planning hub for quantity tools, test guides, and reference charts.