The aggregate crushing value (ACV) test is a fundamental mechanical assessment that measures the resistance of coarse aggregates to crushing under a gradually applied compressive load, expressed as the percentage of fines generated. This article provides a comprehensive guide to crushing value determination standards, covering internationally recognized specifications such as ISO 20290-3, BS 812-110, GB/T 14685, and JTG E42, along with apparatus requirements, sample preparation, step-by-step procedures, calculation methods, acceptance criteria, and typical applications in concrete and asphalt construction.
Technical Overview
The crushing value (also called the aggregate crushing value, ACV, or crushing index) quantifies the ability of a coarse aggregate to resist fragmentation when subjected to a steadily increasing compressive load. In the test, a prepared mass of aggregate is confined in a rigid steel cylinder and loaded through a plunger; the crushing value is calculated as the percentage of the original mass that passes a 2.36 mm sieve after loading. A lower crushing value indicates stronger, more crush-resistant aggregate, which is essential for the long-term performance of concrete structures, asphalt pavements, and unbound base courses.
Crushing value determination is governed by several national and international standards, which are broadly similar in principle but differ in specimen gradation, maximum load, and reporting conventions:
- ISO 20290-3 – Determination of aggregate crushing value (ACV) for aggregates for concrete, harmonized with the traditional British method.
- BS 812-110 – Testing aggregates, method for determination of the aggregate crushing value; the companion BS 812-111 covers the ten percent fines value (TFV).
- GB/T 14685 – Chinese standard for pebble and crushed stone for concrete, specifying the crushing index test for building aggregates.
- JTG E42-2005 (Test Method T0316) – Chinese highway engineering aggregate test methods, widely used for asphalt pavement and road base materials, with acceptance limits given in JTG F40.
- BS EN 1097-2 and ASTM C131/C535 – related methods that evaluate resistance to fragmentation by the Los Angeles abrasion approach, often specified as an alternative or complementary index.
Because the results of these methods are not directly interchangeable, the applicable standard must be stated whenever a crushing value is reported, and testing should be performed by competent, accredited third-party laboratories or qualified in-house facilities using calibrated equipment.
Testing Samples
Crushed Stone and Gravel for Concrete
Coarse aggregate intended for structural concrete is the most common sample type. Under GB/T 14685, the crushing index of crushed stone and natural gravel is evaluated for classification into Grade I, Grade II, and Grade III categories, which in turn determine suitability for exposure classes and strength grades of concrete. Under BS 812-110 and ISO 20290-3, the standard test fraction is aggregate passing a 14 mm sieve and retained on a 10 mm sieve.
Coarse Aggregate for Asphalt Pavement and Road Bases
Aggregates used in hot-mix asphalt surface courses, binder courses, and cement- or bitumen-stabilized base materials are tested in accordance with JTG E42-2005 Test Method T0316. The standard specimen is the 9.5 mm to 13.2 mm fraction, and crushing value limits are specified by the pavement design specifications for different road classes.
Manufactured Sand and Fine Aggregates
Crushed manufactured sand produced from parent rock is evaluated for its crushing index under the corresponding fine aggregate standards, such as GB/T 14684. Because fine aggregate has a much larger specific surface, this test uses a reduced specimen configuration and reflects the integrity of crushed particles in mortar-rich mixtures.
Specialty Aggregates
Railway ballast, riprap, filter stone, and lightweight aggregates may also be assessed for crushing resistance using the appropriate sector specifications. In these cases, the fraction tested and the loading regime are adapted to the particle size and service condition defined by the governing standard.
Testing Items
A typical crushing value determination program includes the following measurable items:
- Aggregate crushing value (ACV) – the percentage by mass of fines passing the 2.36 mm sieve after application of the specified compressive load.
- Crushing index of concrete aggregate – the equivalent parameter defined by GB/T 14685 for construction aggregates.
- Ten percent fines value (TFV) – the load in kilonewtons required to produce 10 percent fines, determined under BS 812-111, often used when the ACV exceeds the specification limit or when a more sensitive strength measure is needed.
- Pre-test verification items – sieve gradation of the test fraction, particle shape check, wash loss, and moisture condition of the specimen.
- Post-test verification – accuracy of the mass of fines and confirmation that the plunger remained essentially horizontal during loading.
Testing Methods
Apparatus and Calibration
The core apparatus comprises a rigid open-ended steel cylinder with an internal diameter of approximately 150–154 mm depending on the standard, a removable base plate, and a hardened steel plunger that fits inside the cylinder with a small annular clearance. Auxiliary equipment includes a round-ended metal tamping rod (typically 16 mm in diameter), a compression testing machine of adequate capacity with verified load indication, test sieves of 14 mm, 13.2 mm, 10 mm, 9.5 mm, and 2.36 mm aperture, and a balance readable to 1 g. The load cell and dial of the compression machine must be calibrated at regular intervals against traceable reference standards.
Sample Preparation
The sample is reduced by riffle splitting or quartering to obtain a representative quantity, then washed over the fine sieve to remove dust and dried to constant mass at 105 ± 5 °C. After cooling to room temperature, the single-size test fraction is extracted by sieving: 10 mm to 14 mm for BS 812-110 and ISO 20290-3, 9.5 mm to 13.2 mm for JTG E42 T0316, and approximately 9.5 mm to 19.0 mm for GB/T 14685. The aggregate is placed in the cylinder in three approximately equal layers, each compacted with 25 strokes of the tamping rod distributed uniformly over the surface, and the surface is leveled without additional compaction.
Step-by-Step Procedure
- Position the filled cylinder with base plate on the lower platen of the compression machine and seat the plunger on the leveled aggregate surface, ensuring the plunger axis is vertical.
- Apply the compressive load at the uniform rate prescribed by the standard: BS 812-110 and ISO 20290-3 require the full 400 kN to be reached in approximately 10 minutes; JTG E42 T0316 specifies a rate of 1 kN/s up to 400 kN, held for 5 seconds; GB/T 14685 specifies a total load of 200 kN for the crushing index of concrete aggregate.
- Release the load completely, remove the cylinder, and extract the crushed specimen.
- Sieve the entire specimen over the 2.36 mm sieve, taking care to avoid artificial degradation during handling, and weigh the fraction passing the sieve to the nearest gram.
Calculation and Reporting
The crushing value is calculated as the ratio of the mass of fines passing the 2.36 mm sieve to the original mass of the test specimen, multiplied by 100, and is reported to the nearest 0.1 percent. The report must identify the standard applied, the particle size fraction tested, the maximum load and loading rate, the individual and mean results, and any deviations from the standard procedure. When a ten percent fines value is required, the applied load is adjusted in follow-up trials and the force corresponding to exactly 10 percent fines is derived by interpolation in accordance with BS 812-111.
Precision and Quality Control
Duplicate determinations on separate specimens should be conducted, and the difference between results must fall within the repeatability limits stated in the governing standard; otherwise, further tests are required and the mean of acceptable values is reported. Key quality controls include verifying machine calibration, confirming the single-size gradation of the specimen, ensuring consistent tamping effort, and preventing loss or contamination of fines during extraction and sieving.
Acceptance Criteria and Specification Limits
Typical specification limits vary by application and road or concrete class. Under GB/T 14685, crushed stone for concrete is commonly classified with crushing index limits of 10 percent for Grade I, 20 percent for Grade II, and 30 percent for Grade III. Under Chinese asphalt pavement specifications such as JTG F40, coarse aggregate for expressway and first-class highway surface courses is generally limited to a crushing value of 26 percent, with slightly relaxed limits for lower road classes and base layers. Project specifications must always be consulted, as contract documents may impose stricter values for heavy-duty pavements, airfields, or high-strength concrete.
Applications
Crushing value data are used throughout the construction materials supply chain:
- Quarry and crushing plant quality control, where the index confirms that processing changes have not degraded particle strength.
- Concrete mix design and pre-qualification, ensuring that coarse aggregate strength is compatible with the specified concrete strength grade and exposure conditions.
- Asphalt pavement design, where low crushing values help maintain skid resistance, resist rutting, and preserve the interlocking skeleton of stone mastic and dense-graded mixtures.
- Unbound base and subbase acceptance, verifying that aggregates will survive compaction and traffic loading without excessive breakdown.
- Railway ballast and hydraulic engineering stone evaluation, where crushing resistance under concentrated loads is a primary durability indicator.
- Independent acceptance testing by accredited third-party laboratories for contractors, owners, and supervision engineers, and comparative benchmarking of alternative material sources.
FAQ
What is the difference between crushing value and Los Angeles abrasion value?
The crushing value measures resistance to slow, statically applied compression and reflects particle strength, whereas the Los Angeles test (BS EN 1097-2, ASTM C131) measures resistance to impact and abrasion in a rotating drum with steel balls. Both assess mechanical durability, but they simulate different degradation mechanisms, and most specifications treat them as complementary rather than interchangeable.
Which particle size fraction should be tested?
The fraction depends on the standard: 10 mm to 14 mm for BS 812-110 and ISO 20290-3, 9.5 mm to 13.2 mm for JTG E42 T0316, and approximately 9.5 mm to 19.0 mm for GB/T 14685. Results from different fractions or standards must not be compared directly against limits written for another method.
What should be done if the source lacks sufficient particles in the specified fraction?
When the standard fraction cannot be obtained, the test may be performed on the nearest available single-size fraction and clearly reported as a non-standard determination, or the ten percent fines value may be determined instead as a more adaptable strength measure. In all cases, the deviation must be documented.
Why must the specimen be washed and dried before testing?
Surface dust and moisture can alter the interparticle contact conditions, cushion or lubricate particles during loading, and contaminate the mass of fines passing the 2.36 mm sieve, producing biased results. Washing and oven drying to constant mass at 105 ± 5 °C standardize the initial condition of every specimen.
How does crushing value relate to concrete and pavement performance?
Aggregates with high crushing values break down during mixing, compaction, and service, increasing fines content, reducing interlock and stiffness, and lowering the achievable strength and durability of the composite. Specifications therefore cap the crushing value to safeguard long-term structural performance, particularly for heavy-traffic pavements and high-strength concrete.