Aggregate crushing value (ACV) testing is a fundamental quality-control test used to evaluate the resistance of coarse aggregate to crushing under gradually applied compressive loads on Class-I highway projects. This article explains the applicable standards, sample requirements, testing items, step-by-step test procedures, acceptance limits, and practical applications of crushing value detection for Class-I highway construction. Engineers, laboratory technicians, and construction supervisors can use this guide to ensure that aggregates for asphalt pavements, cement concrete pavements, and stabilized base courses meet the required strength specifications.
Technical Overview
The aggregate crushing value (ACV) is a quantitative index of the ability of coarse aggregate to resist crushing under a gradually applied compressive load. In the standard test, a specified mass of aggregate is confined in a rigid steel mold and loaded to a fixed force of 400 kN; the crushing value is calculated as the percentage by mass of fines produced, expressed relative to the original oven-dry mass of the test specimen. A lower crushing value indicates stronger, more crush-resistant aggregate.
Class-I highways are high-standard dual-carriageway arterial roads in China, typically designed for speeds of 60 to 100 km/h and carrying heavy traffic volumes. Because aggregates in asphalt surface courses, cement concrete pavements, and semi-rigid base courses on these roads are subjected to repeated high wheel loads, weak particles that break down during compaction and service can generate excess fines, reduce mixture stability, accelerate rutting and cracking, and shorten pavement service life. For this reason, crushing value is a mandatory acceptance item for coarse aggregates used on Class-I highway projects.
The test method is standardized in China as T 0316-2005, "Resistance to Crushing of Coarse Aggregate," within JTG E42-2005, the Standard Test Methods of Aggregate for Highway Engineering. Acceptance limits are specified in complementary construction standards, including:
- JTG E42-2005 — test procedure for the aggregate crushing value (T 0316-2005) and aggregate sampling (T 0301)
- JTG F40-2004 — Technical Specification for Construction of Highway Asphalt Pavements, which sets crushing value limits for coarse aggregate in asphalt mixtures
- JTG/T F20-2015 — Technical Guidelines for Construction of Highway Roadbases, which sets crushing value limits for aggregates in cement-stabilized and graded granular base and subbase courses
- JTG/T 3310-2019 — Technical Specifications for Construction of Highway Cement Concrete Pavements, which governs coarse aggregate quality for concrete pavements
Because specification editions and project-specific requirements evolve, the applicable limits should always be verified against the current edition of the governing standard and the contract documents.
Testing Samples
Coarse Aggregates for Asphalt Pavement Layers
Coarse aggregate destined for asphalt surface, intermediate, and bottom courses is sampled from quarries, stockpiles, cold-feed belts, or hot-bin discharge at the mixing plant. The crushing value is evaluated on the 9.5 mm to 13.2 mm size fraction, which is sieved out from the representative field sample. Igneous rocks such as basalt and diabase, and high-quality granite, typically yield low crushing values, while weaker sedimentary or weathered materials must be verified carefully before approval for Class-I highway surface courses.
Coarse Aggregates for Cement Concrete Pavements
For cement concrete pavement slabs, crushed stone and gravel aggregates are sampled at the aggregate production plant or the concrete batching plant. Concrete pavements on Class-I highways experience severe flexural fatigue loading, so aggregate crushing resistance is controlled alongside crushing-related durability indices. The same 9.5 mm to 13.2 mm test fraction is used for the crushing value determination.
Aggregates for Base and Subbase Courses
Aggregates for cement-stabilized macadam, cement-treated aggregate, lime-flyash stabilized material, and graded crushed stone base and subbase courses are sampled from the material source, stockpiles at the mixing station, or the paved layer. Crushing value limits for these materials are tiered according to the traffic load classification defined in JTG/T F20-2015, with stricter requirements for base courses carrying extremely heavy and extra-heavy traffic.
Sample Preparation Requirements
Proper sampling and preparation are essential for representative results:
- Samples shall be taken in accordance with T 0301 of JTG E42-2005, using random sampling and quartering or splitting to obtain representative portions
- The 9.5 mm to 13.2 mm particle fraction is extracted by dry sieving; approximately 3 kg of this fraction is required for each determination
- At least two parallel specimens are needed, and additional material should be retained for retesting; a total sample of roughly 10 kg is recommended
- The test fraction is washed to remove surface dust and oven-dried to constant mass at 105 °C ± 5 °C, then cooled to room temperature before testing
Testing Items
The core testing item is the aggregate crushing value itself, expressed as a percentage to the nearest 0.1%. The governing acceptance limits commonly applied to Class-I highway works are summarized below:
- Asphalt surface course (expressway and Class-I highway): crushing value not greater than 26%
- Asphalt intermediate and lower courses (expressway and Class-I highway): crushing value not greater than 28%
- Asphalt courses on lower-class roads: crushing value not greater than 30%
- Cement-stabilized base course, extremely heavy and extra-heavy traffic: crushing value not greater than 22%
- Cement-stabilized base course, heavy, medium, and light traffic: crushing value not greater than 26%
- Cement-stabilized subbase course: crushing value not greater than 30%
- Cement concrete pavement: stricter limits, commonly in the range of 16% to 20% depending on the layer and traffic level, as specified in the current concrete pavement construction specification
In practice, the crushing value is tested as part of a suite of coarse aggregate acceptance items, which typically also include apparent relative density, water absorption, flakiness and elongation index, Los Angeles abrasion loss, soundness, and deleterious materials content. These companion results help diagnose the cause when a crushing value result is marginal or non-conforming.
Testing Methods
Apparatus
The test is performed with the following equipment:
- Aggregate crushing value apparatus, comprising a rigid open-ended steel cylinder mold with an internal diameter of approximately 150 mm, a matching cylindrical steel plunger, and a steel base plate
- A compression testing machine with a capacity of at least 500 kN, capable of applying load at a controlled uniform rate
- A metal tamping rod with a rounded end for compacting the aggregate layers
- Test sieves with apertures of 13.2 mm, 9.5 mm, and 2.36 mm
- A balance readable to 1 g
- A ventilated drying oven capable of maintaining 105 °C ± 5 °C
Specimen Preparation
The oven-dried 9.5 mm to 13.2 mm aggregate fraction is thoroughly mixed and divided by quartering to obtain the required test portions. Each portion of approximately 3 kg is weighed and recorded as the specimen mass before it is introduced into the mold. Care is taken to ensure the specimen contains no adhering dust or moisture, as fines and moisture can bias the results.
Test Procedure
The test is carried out in the following sequence:
- Seat the steel mold firmly on the base plate and verify that the assembly is level and stable on the compression machine platform
- Fill the mold with the aggregate in three approximately equal layers, distributing 25 uniform tamping strokes over the surface of each layer with the tamping rod
- After compacting the final layer, add or remove individual particles by hand so that the surface of the aggregate lies essentially flush with the top of the mold
- Place the plunger horizontally on the leveled aggregate surface, ensuring it is aligned and does not tilt or jam against the mold wall
- Apply the load smoothly and uniformly so that the total force of 400 kN is reached in approximately 10 minutes, corresponding to an average loading rate of about 40 kN per minute
- Once 400 kN is reached, release the load, remove the plunger, and empty the entire crushed specimen from the mold
- Sieve the complete crushed mass on the 2.36 mm sieve and weigh the material passing, taking care to avoid sieving losses
- Repeat the full procedure on the second parallel specimen
Calculation and Precision
The aggregate crushing value is calculated as: Q'a = (m1 / m0) × 100, where m0 is the oven-dry mass of the test specimen in grams and m1 is the mass in grams of crushed material passing the 2.36 mm sieve. Two valid parallel determinations are required; if the difference between them exceeds 2 percentage points, an additional test shall be performed and the results reviewed before reporting. The reported crushing value is the mean of the valid determinations, expressed to the nearest 0.1%. All apparatus, sieves, and the balance must be within calibration, and the complete test record should identify the material source, sampling location, specimen masses, and calculated result.
Applications
Aggregate crushing value testing serves multiple functions across the lifecycle of a Class-I highway project:
- Source qualification: evaluating new quarries, gravel pits, and recycled material sources before they are approved for supply
- Batch acceptance: verifying each production lot of coarse aggregate delivered to asphalt mixing plants, concrete batching plants, and base-course mixing stations, commonly at intervals such as every 500 tonnes or per shipment as defined in the project quality plan
- Mix design verification: confirming that aggregate strength supports the performance targets of the asphalt or concrete mix design before trial sections are constructed
- Construction quality control: detecting degradation or contamination during stockpiling, handling, and compaction operations
- Supervision and acceptance: providing documented evidence for owner representatives, supervision engineers, and government quality-inspection authorities during intermediate and final acceptance
- Failure investigation and research: diagnosing the causes of premature rutting, raveling, or crushing-related pavement distress and supporting performance studies of alternative materials
FAQ
Which particle size fraction is used for the crushing value test?
The test is performed on the 9.5 mm to 13.2 mm particle fraction, which is sieved from the representative field sample, washed, and oven-dried to constant mass at 105 °C ± 5 °C. Approximately 3 kg of this fraction is required for each determination, with at least two parallel determinations per sample.
What crushing value limits apply to Class-I highways?
For asphalt pavements on expressways and Class-I highways, the typical limits are a crushing value of no more than 26% for the surface course and no more than 28% for intermediate and lower courses. For cement-stabilized base courses, the limits are generally 22% under extremely heavy and extra-heavy traffic and 26% under heavy, medium, and light traffic, with 30% commonly allowed for subbases. Cement concrete pavements are governed by stricter limits, commonly in the 16% to 20% range. The exact values must be confirmed against the current editions of JTG F40, JTG/T F20, and JTG/T 3310, together with the project specifications.
Why is a load of 400 kN applied over about 10 minutes?
The standardized load of 400 kN and the controlled loading rate of approximately 40 kN per minute reproduce a consistent, gradually applied compressive stress state within the mold. Fixing both the force and the rate ensures that results from different laboratories are directly comparable and reflect the intrinsic crush resistance of the aggregate rather than testing technique.
How does the crushing value differ from the Los Angeles abrasion test?
The crushing value test applies static, gradually increasing compression and measures the breakdown of particles under compaction-type loading, making it a direct indicator of aggregate performance during pavement construction and under traffic. The Los Angeles abrasion test, by contrast, subjects aggregate to impact and abrasion in a rotating drum with steel balls and measures resistance to wear and attrition. Both tests are normally required, as they capture different failure mechanisms.
What should be done if a crushing value result fails the specification?
The sample should first be checked for procedural errors, including excessive fines or moisture in the specimen, incorrect loading rate, incomplete leveling, or sieving losses. A retest should then be performed on additional material taken from the same lot with doubled sampling. If the non-conformity is confirmed, the affected batch should be rejected or restricted to lower-specification uses, the aggregate source should be re-evaluated, and the mix design should be reviewed before supply resumes.
What factors most commonly affect the accuracy of results?
Common sources of error include dusty or wet specimens, non-uniform or excessively fast loading, excessive flaky and elongated particles that orient and crush preferentially, uneven tamping, a plunger that tilts under load, material lost during sieving or transfer, and uncalibrated balances or sieves. Consistent technique, qualified personnel, and regular equipment calibration are essential for reliable, reproducible crushing value results on Class-I highway projects.