Aggregates - Properties, Sampling & Testing

Aggregates

$Learning Objectives$

Classify aggregates by size, source, density, particle shape, and intended use.
Perform and interpret representative sampling, sample reduction, sieve analysis, fineness modulus, and gradation calculations.
Distinguish oven-dry, air-dry, saturated surface-dry, and wet aggregate states.
Calculate absorption, free moisture, and concrete batch-water corrections.
Explain specific-gravity, bulk-density, abrasion, soundness, cleanliness, shape, and reactivity tests.
Translate aggregate results into concrete, asphalt, base-course, and quality-control decisions.

$Why aggregate quality controls mixture performance$

Aggregates typically occupy most of the volume of concrete and asphalt. Gradation, stiffness, strength, shape, texture, absorption, cleanliness, durability, and chemical stability influence workability, binder demand, dimensional stability, permeability, pavement response, and cost. Reliable testing begins with a representative sample rather than with the laboratory apparatus.

$Aggregate classifications$

Fine aggregate: material predominantly passing the 4.75 mm (No. 4) sieve within the grading limits of the governing specification.
Coarse aggregate: material predominantly retained on the 4.75 mm (No. 4) sieve.
Natural aggregate: sand, gravel, or crushed rock obtained from natural deposits or quarries.
Manufactured aggregate: processed aggregate such as manufactured sand or lightweight aggregate produced through controlled industrial processes.
Recycled aggregate: processed material recovered from suitable existing construction materials; performance depends strongly on source control and processing.
Lightweight, normal-weight, and heavyweight aggregate: categories based on material characteristics and intended concrete use rather than one universal stockpile-density cutoff.

$Nominal Maximum Aggregate Size$

Specification-dependent size descriptor related to the smallest sieve through which most of the aggregate is permitted to pass. It must not be confused with maximum aggregate size; use the definition in the governing standard or mixture-design procedure.

$Representative sampling is part of the test$

A precisely executed laboratory test can still be misleading if the sample does not represent the stockpile, moving stream, truck, or lot. Sampling location, increment count, sample size, segregation, contamination, moisture change, and sample reduction must be controlled and documented.

$Representative sampling workflow$

STEP-BY-STEP

Define the lot or production quantity represented by the sample.
Obtain increments from locations or times that minimize selection bias and account for segregation.
Combine increments when the governing practice requires a composite field sample.
Protect the sample from contamination, moisture change, and loss of fines.
Record source, date/time, location, material designation, nominal size, and sampler.
Reduce the field sample to the required test size using an approved splitter or controlled quartering process without selectively removing particle sizes.

$Common stockpile sampling bias$

A convenient scoop from an exposed stockpile surface may overrepresent a particular size or moisture condition. The sample should represent the material actually being accepted or incorporated into the work.

$Gradation$

Distribution of aggregate particle sizes, normally reported as percentages retained or passing a specified sieve series.

$Sieve-analysis workflow$

STEP-BY-STEP

Obtain a representative reduced sample and condition/dry it as required.
Determine original test mass.
Arrange clean sieves from largest opening to smallest with a pan below.
Shake for the method-defined duration without excessive sieve loading.
Determine mass retained on each sieve.
Check recovered-mass closure against the original mass within the method tolerance.
Calculate percent retained, cumulative percent retained, and percent passing.
Compare the complete grading with the specified envelope and plot the gradation curve when useful.

Percent Retained

Mass retained on a sieve divided by total test mass.

\%R_i=\frac{m_i}{m_T}\times100

Variables

Symbol	Description	Unit
$\%R_i$	Percent retained on sieve i	%
$m_i$	Mass retained on sieve i	g or kg
$m_T$	Total dry test mass	g or kg

Percent Passing

Percentage of the sample finer than a specified sieve.

\%P_i=100-\%R_{cum,i}

Variables

Symbol	Description	Unit
$\%P_i$	Percent passing sieve i	%
$\%R_{cum,i}$	Cumulative percent retained through sieve i	%

$Fineness Modulus (FM)$

Empirical index representing relative coarseness of an aggregate grading. It is not a particle size and does not by itself establish compliance with a grading specification.

Fineness Modulus

Sum of cumulative percentages retained on the specified standard sieve series divided by 100.

FM=\frac{\sum_j \%R_{cum,j}}{100}

Variables

Symbol	Description	Unit
$FM$	Fineness modulus	-
$\%R_{cum,j}$	Cumulative percent retained on each specified sieve j	%

$Interactive gradation simulations$

Use the simulations to explore sieve distributions and the effect of grading on aggregate behavior. Use the companion worked examples for complete calculations and specification interpretation.

Illustrative Gradation Shapes

Compare curve shapes only. These are synthetic teaching data—not a Fuller design curve, soil classification, or specification envelope.

Loading chart...

Engineering interpretation: gradation must be compared with the full governing specification and intended function. A smooth curve is not automatically “best,” and a narrow distribution does not by itself establish density, permeability, or suitability.

Sieve Analysis, Mass Closure & Fineness Modulus

Record the original dry test mass and the mass retained on each sieve. The recovered-mass check is evaluated before interpreting the grading results.

Laboratory/test simulatorModels recorded sieve masses and mass closure; grading acceptance still requires the specified envelope and method tolerances.

Relevant standards map

ASTM C136/C136M· MethodASTM C117· MethodASTM C33/C33M· SpecificationASTM C702/C702M· PracticeASTM C127· MethodASTM C128· MethodASTM C566· Method

Practice controls sampling/specimen preparation where applicable → test method defines measurement → specification/code defines required performance → project documents define the controlling acceptance basis. Do not infer acceptance from a standard designation alone.

Laboratory evidence chain

1. Sample / lot represented
2. Specimen identity and condition
3. Apparatus and verification status
4. Procedure and method-critical controls
5. Raw readings / observations
6. Checked calculation
7. Validity and deviation review
8. Engineering interpretation
9. Specification / code comparison
10. Traceable report and disposition

Original dry test mass1000 g3/8 in · 9.5 mm0 gNo. 4 · 4.75 mm20 gNo. 8 · 2.36 mm75 gNo. 16 · 1.18 mm145 gNo. 30 · 0.600 mm220 gNo. 50 · 0.300 mm250 gNo. 100 · 0.150 mm190 gPan · <0.150 mm100 g

Recovered mass

1000 g

Mass recovery

100.00%

Mass-closure gate: compare the recovery with the tolerance in the governing method before reporting the analysis. This tool deliberately does not invent a universal allowable loss.

Sieve	Retained	Cum. retained	Passing
3/8 in	0.0%	0.0%	100.0%
No. 4	2.0%	2.0%	98.0%
No. 8	7.5%	9.5%	90.5%
No. 16	14.5%	24.0%	76.0%
No. 30	22.0%	46.0%	54.0%
No. 50	25.0%	71.0%	29.0%
No. 100	19.0%	90.0%	10.0%
Pan	10.0%	100.0%	0.0%

Fine-aggregate fineness modulus index

2.42

FM=\frac{\sum(\text{cumulative percent retained on the specified FM sieve series})}{100}

FM is an index, not an acceptance grade. Evaluate the complete grading against the governing specification.

No. 200 boundary: dry sieving alone is not the complete method for accurate material finer than 75 µm. Where required, pair the sieve analysis with the specified washing method and report the correct basis.

$Aggregate moisture states$

Oven Dry (OD): permeable pores are considered dry after the prescribed drying procedure.
Air Dry (AD): particle surfaces are dry while internal permeable pores contain less water than SSD.
Saturated Surface-Dry (SSD): permeable pores are filled to the method-defined reference condition with no free surface water.
Wet: aggregate contains water above the SSD state; the excess contributes free water to a concrete or asphalt process.

$Absorption$

Increase in aggregate mass from OD to SSD, expressed as a percentage of OD mass.

Aggregate Absorption

Water absorbed from OD to SSD relative to OD mass.

A=\frac{W_{SSD}-W_{OD}}{W_{OD}}\times100\%

Variables

Symbol	Description	Unit
$A$	Absorption	%
$W_{SSD}$	SSD mass	kg
$W_{OD}$	Oven-dry mass	kg

$Total Moisture Content$

Water present in a field aggregate relative to the reference dry mass used by the test method.

Free Moisture Above SSD

Approximate free-moisture percentage when total moisture and absorption use the same OD-mass basis.

M_{free}\approx M_{total}-A

Variables

Symbol	Description	Unit
$M_{free}$	Free moisture above SSD	%
$M_{total}$	Measured total moisture	%
$A$	Absorption	%

$Batch corrections require a consistent mass basis$

For rigorous concrete moisture correction, convert the SSD design mass to its OD-equivalent mass, then convert the OD mass to the measured wet mass. This prevents the common error of mixing SSD-based quantities with moisture percentages defined on an OD basis.

$Interactive aggregate-moisture simulation$

Use the simulation to compare OD, SSD, and wet aggregate states and their effect on batch water. Confirm final production adjustments using measured stockpile moisture and the approved mixture procedure.

Aggregate Moisture Correction

Moisture and absorption are entered on an oven-dry mass basis. The SSD design mass is first converted to its OD equivalent, then to the actual wet batch mass.

SSD design mass800 kgAbsorption1.5 % OD basisTotal moisture4.0 % OD basis

State: Above SSD / free surface moisture

OD-equivalent mass

788.18 kg

W_{OD}=W_{SSD}/(1+A)

Wet batch mass

819.70 kg

W_{wet}=W_{OD}(1+MC)

Mixing-water correction

Subtract 19.70 kg

W_{water,vs\,SSD}=W_{wet}-W_{SSD}

This exact workflow avoids applying the difference of two OD-basis percentages directly to an SSD mass.

$Specific-gravity states and bulk density$

Bulk specific gravity, OD: uses OD mass and a bulk particle volume that includes permeable pores.
Bulk specific gravity, SSD: uses SSD mass with the same bulk-volume convention.
Apparent specific gravity: excludes permeable pore volume from the particle-volume reference.
Bulk density/unit weight of aggregate: mass occupying a calibrated container under a defined loose, rodded, or jigged procedure; it includes interparticle voids and is not particle specific gravity.

$Particle Shape and Surface Texture$

Geometry and texture of particles that influence packing, interlock, workability, binder demand, and bond. Angular rough particles often increase interlock but can require more paste or binder than smooth rounded particles.

$Material Finer than 75 μm (No. 200)$

Fine dust, clay, or other material passing the No. 200 sieve that can alter water demand, adhesion, durability, and mixture performance; allowable quantity depends on material source and specification.

$Los Angeles Abrasion$

Standardized index of aggregate resistance to abrasion, impact, and degradation in a rotating drum. Lower loss generally indicates better resistance under the test, but the acceptance limit is application-specific.

$Sulfate Soundness$

Accelerated durability index based on repeated salt crystallization and drying. It is a screening method and should not be described as a literal reproduction of field freeze-thaw exposure.

$Deleterious constituents and cleanliness$

Potentially harmful constituents include clay lumps, friable particles, excessive fines or coatings, organic impurities, soft/weak particles where restricted, lightweight contaminants, and source-specific chemical contaminants. Each is evaluated using the method and acceptance limit applicable to the intended use.

$Alkali-Silica Reaction (ASR)$

Potentially expansive reaction involving susceptible forms of silica in aggregate, alkalis in the concrete pore solution, and sufficient moisture; it can produce cracking, joint distress, movement, and loss of serviceability.

$ASR evaluation and mitigation$

Establish aggregate reactivity through the required test program, petrography, and reliable service history where applicable.
Use qualified nonreactive aggregate when feasible.
Use an appropriate cementitious system and SCM combination demonstrated to control expansion.
Reduce moisture ingress through durable concrete and effective detailing where practical.
Follow project-specific performance criteria instead of relying on a generic low-alkali label alone.

$Aggregate property-to-test matrix$

Engineering property	Typical evidence family	Main engineering use
Particle-size distribution	Sieve analysis	Concrete/asphalt grading and blending
Fines/cleanliness	Washing and deleterious-material methods	Water/binder demand and durability
Specific gravity and absorption	Fine/coarse aggregate SG methods	Absolute-volume mix design and moisture correction
Bulk density and voids	Calibrated-container method	Proportioning and production checks
Abrasion/degradation	LA abrasion	Durability screening for concrete, base, and pavement use
Soundness	Salt soundness	Durability screening
Particle shape	Flat/elongated/angularity methods	Workability, packing, and pavement interlock
Reactivity	ASR/ACR evaluation program	Durability and mitigation design

$When an aggregate result is outside specification$

Confirm sample identity, lot, and representativeness.
Check sample size, conditioning, apparatus, sieve condition, balance verification, and calculations.
Determine whether the method or specification permits repeat testing and how resampling must occur.
Evaluate whether blending, washing, reprocessing, moisture adjustment, or rejection is permitted.
Document the nonconformance and engineering disposition rather than silently averaging a failure with unrelated results.

Key Takeaways

Representative sampling is part of aggregate testing, not an administrative afterthought.
Gradation requires the complete particle-size distribution; fineness modulus is only an index.
Concrete batching must correct aggregate moisture relative to SSD using a consistent mass basis.
Abrasion, soundness, cleanliness, shape, strength, and chemical reactivity address different durability/performance mechanisms.
The defensible workflow is sample → reduce → condition → test → calculate → validate → compare with specification → document disposition.

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