Aggregate crushing value test results quantify the resistance of coarse aggregates to gradual crushing under an applied compressive load, serving as a key indicator of mechanical quality for road, railway, and concrete applications. This article explains how crushing value experiments are conducted under standards such as BS 812-110, GB/T 14685, and JTG E42, how the results are calculated and interpreted, and which acceptance limits apply to different engineering uses.
Technical Overview
The aggregate crushing value (ACV) is a fundamental mechanical property test used to evaluate the strength and durability of coarse aggregates. The test measures the percentage of fine material produced when a prepared aggregate specimen is subjected to a standardized compressive load in a steel mold. A lower crushing value indicates stronger aggregate that is better able to resist degradation under traffic loading, compaction, and long-term service stresses.
Crushing value experiments are widely referenced in international and national standards, including BS 812-110, GB/T 14685 for construction aggregates used in concrete, and JTG E42 (Test Method T0316) for highway engineering aggregates in China. Related procedures such as the ten percent fines value (TFV) test provide complementary strength data. Because the test is simple, repeatable, and directly reflects field performance, crushing value results are routinely required in material acceptance specifications, quarry quality control, and verification testing performed by accredited third-party laboratories.
Testing Samples
Crushed Rock Aggregates
Crushed igneous, sedimentary, and metamorphic rocks such as granite, basalt, and limestone are the most common materials tested. Samples are collected from stockpiles or production belts using recognized sampling procedures, then reduced by quartering or splitting to obtain representative test portions. The material is washed, dried to constant mass, and sieved into the specified size fraction, typically 10.0 mm to 14.0 mm for the BS 812-110 method or 9.5 mm to 13.2 mm for the highway engineering method.
Natural Gravel and Pebbles
Natural gravels and pebbles used as concrete aggregates are tested to determine their crushing index, because water-worn particles often exhibit lower crushing resistance than freshly crushed rock. GB/T 14685 assigns separate classification limits for crushed stone and pebbles, so the sample source and particle type must be clearly identified before testing.
Recycled and Artificial Aggregates
Recycled concrete aggregate, steel slag, and manufactured lightweight aggregates are increasingly evaluated by crushing value testing to confirm their suitability for structural and pavement applications. These materials typically show higher variability, so larger and more frequent samples are recommended to obtain statistically reliable results.
Testing Items
A complete crushing value experiment report generally includes the following determined parameters:
- Aggregate crushing value (ACV), expressed as the percentage by mass of fines passing the 2.36 mm sieve after loading
- Crushing index for crushed stone or pebble, as specified in GB/T 14685 for concrete aggregates
- Ten percent fines value (TFV), the load required to produce 10 percent fines, often reported alongside ACV
- Original specimen mass, mass retained on the 2.36 mm sieve, and mass passing the sieve
- Maximum applied load, loading duration, and observed specimen behavior during the test
Testing Methods
Apparatus
The standard test setup consists of an open-ended steel cylinder with an internal diameter of 150 mm, a fitted plunger and base plate, a hardened steel tamping rod, a compression testing machine with adequate capacity and calibrated load indication, a balance readable to 0.1 g, and calibrated test sieves including the 2.36 mm fines sieve. All equipment must be verified and maintained under the laboratory's quality management system.
Specimen Preparation
The aggregate is sieved to isolate the required single size fraction, and sufficient material is prepared to allow at least two parallel determinations. Depending on the governing standard, the specimen is placed in the cylinder in layers, each compacted with a specified number of tamping strokes, and the surface is leveled off without disturbing the particles.
Test Procedure
In the widely used BS 812-110 and JTG E42 T0316 procedure, the filled cylinder with plunger is positioned in the compression machine, and the load is applied at a uniform rate so that a total force of 400 kN is reached in approximately 10 minutes. The load is then released, the crushed specimen is removed, and the material is sieved over the 2.36 mm sieve. In the GB/T 14685 concrete aggregate method, a 9.5 mm to 19.0 mm specimen is loaded to 200 kN, held briefly, and then sieved in the same manner. Each determination is performed in duplicate.
Calculation and Result Expression
The crushing value is calculated from the measured masses. For the ACV method, the result is the mass of material passing the 2.36 mm sieve divided by the original specimen mass, multiplied by 100. For the GB/T 14685 crushing index, the result is the difference between the original mass and the mass retained on the 2.36 mm sieve, divided by the original mass, multiplied by 100. Results are reported to one decimal place as the mean of two determinations; if the difference between duplicates exceeds the repeatability limit of the standard, the entire test is repeated.
Interpretation and Acceptance Criteria
Lower results indicate stronger aggregate. Typical specification limits vary by application and aggregate class. Under GB/T 14685, Class I crushed stone is generally limited to a crushing index of 10 percent or less and Class I pebble to 12 percent or less, while Class II and Class III materials are permitted progressively higher values up to 30 percent. Highway asphalt specifications commonly require crushing values of approximately 26 percent or less for surface course aggregates, with somewhat relaxed limits for lower pavement layers. The applicable project specification should always be consulted for the governing acceptance threshold.
Applications
Crushing value experiment results are used throughout the construction materials industry for material selection, quality control, and compliance verification:
- Acceptance of coarse aggregates for asphalt pavement surface, binder, and base courses
- Quality classification of crushed stone and pebble for structural concrete production
- Assessment of unbound base and subbase materials for highway and airfield construction
- Screening of railway ballast and trackbed aggregates for crushing resistance
- Quarry production control and optimization of crushing plant settings
- Independent verification and material certification by accredited third-party laboratories
- Evaluation of recycled and alternative aggregates for sustainable construction projects
FAQ
What is considered a good crushing value result?
Generally, a lower value is better. Aggregates with a crushing value below 10 percent are regarded as very strong and suitable for high-grade concrete, while values up to about 25 to 30 percent may be acceptable for lower-grade applications such as road base, depending on the governing specification.
How is the crushing value calculated?
The result equals the mass of fine material passing the 2.36 mm sieve divided by the original specimen mass, multiplied by 100. In the GB/T 14685 crushing index method, the formula uses the loss in mass after sieving relative to the original mass.
What is the difference between ACV and the ten percent fines value?
The ACV measures the percentage of fines generated under a fixed standard load, whereas the TFV determines the load required to produce exactly 10 percent fines. The two tests are related, and the TFV generally provides better discrimination between stronger aggregates.
Which standards govern crushing value experiments?
Commonly referenced standards include BS 812-110, GB/T 14685, and JTG E42 for highway engineering aggregates. Related mechanical property tests are covered by EN 1097 and ASTM standards, depending on the region and specification.
What factors can affect the accuracy of results?
Poor sampling representativeness, incorrect particle size fraction, non-uniform loading rate, inadequate compaction of the specimen, sieve wear, and uncontrolled moisture content are the most frequent sources of error. Strict adherence to the standard procedure and duplicate testing minimize variability and ensure reliable, comparable results.