Aggregate crushing value testing standards define the standardized procedures used to evaluate the resistance of construction aggregates to crushing under gradually applied compressive loads. This technical guide explains the governing standards, sample preparation, testing methods, calculation principles, and typical acceptance limits for crushing value testing. Engineers, quality controllers, and material suppliers can use this overview to select the correct procedure and interpret results accurately.
Technical Overview
The aggregate crushing value (ACV) test is a fundamental mechanical evaluation method used to measure the ability of coarse aggregate to resist crushing under a gradually applied compressive load. The result is expressed as the percentage ratio of the mass of fines produced by crushing to the total mass of the original test portion. A lower crushing value indicates stronger, more durable aggregate that will maintain particle integrity during compaction, trafficking, and long-term service.
Crushing behavior is one of the most important quality indicators for aggregates used in road construction, railway engineering, and concrete production. Aggregates with excessive crushing values will degrade during placement and compaction, generating fines that reduce bearing capacity, impair drainage, and compromise the structural performance of pavement layers and concrete elements. Crushing value testing is therefore a mandatory acceptance test in most aggregate specifications worldwide.
Primary Governing Standards
- GB/T 14685 (Pebble and crushed stone for construction) specifies the crushing index test for coarse aggregate used in concrete.
- GB/T 14684 (Sand for construction) specifies the crushing index test for fine aggregate.
- JTG E42 (Test Methods of Aggregate for Highway Engineering), procedure T 0316, specifies the coarse aggregate crushing value test for highway materials.
- BS 812-110 defines the classic aggregate crushing value (ACV) method, which remains widely referenced internationally.
- BS 812-111 covers the ten percent fines value (TFV), a related measure obtained from the same apparatus.
- EN 1097-2 specifies tests for resistance to fragmentation of aggregates, including the Los Angeles method.
- ASTM C131 and ASTM C535 specify Los Angeles abrasion tests, which are frequently used in North American practice as the complementary degradation requirement.
- IS 2386 (Part 4) and AS 1141.21 provide equivalent crushing value procedures in Indian and Australian practice respectively.
Testing Samples
Coarse Aggregate Test Portions
For the standard crushing value test, a single-size coarse aggregate fraction is required. BS 812-110 uses the 10 mm to 14 mm fraction, while the Chinese highway method JTG E42 (T 0316) uses the 9.5 mm to 13.2 mm fraction. The aggregate is first washed to remove dust and fine particles, then oven-dried to constant mass at 105 ± 5 °C, and finally separated into the required size fraction using standard test sieves. Elongated and flaky particles are excluded where the specification requires it, because particle shape significantly influences the crushing result.
Fine Aggregate Samples
Fine aggregate, such as natural sand or manufactured sand, is evaluated using a dedicated crushing index procedure defined in GB/T 14684. A smaller cylindrical pressure mold with a piston assembly is used, and the sample is subjected to a specified static load. The crushed material is then sieved through fine sieves, and the crushing index is calculated as the percentage of crushed mass relative to the total test portion.
Sampling and Preparation Requirements
- Field samples shall be obtained using recognized sampling techniques so that they are representative of the delivered material lot.
- laboratory samples are reduced by quartering or splitting to obtain the required test portions.
- At least two parallel test portions are prepared so that repeatability can be verified.
- Moisture conditioning, drying temperature, and sieving tolerances shall follow the applicable standard exactly, since deviations directly affect the measured value.
Testing Items
Crushing value testing typically forms part of a broader mechanical and physical evaluation program for aggregates. The directly related testing items include:
- Coarse aggregate crushing value (ACV): percentage of fines produced under a 400 kN static compressive load.
- Fine aggregate crushing index: equivalent measure for sand and manufactured fines.
- Ten percent fines value (TFV): the load required to produce ten percent fines, useful for stronger aggregates.
- Aggregate impact value (AIV): a complementary dynamic-load degradation measure.
- Los Angeles abrasion and resistance to fragmentation (EN 1097-2, ASTM C131/C535): related degradation tests under impact and abrasion.
- Particle size distribution, flakiness index, and soundness, which are commonly tested alongside crushing value for full specification compliance.
Testing Methods
Apparatus
- A hardened steel cylinder with an internal diameter of approximately 150 mm.
- A steel plunger and rigid base plate that fit the cylinder with close tolerances.
- A metal tamping rod of 16 mm diameter and about 600 mm length with a rounded end.
- A compression testing machine with sufficient capacity and controlled loading rate, typically able to apply 400 kN.
- Test sieves sized 13.2 mm, 9.5 mm, and 2.36 mm (or 14 mm, 10 mm, and 2.36 mm depending on the standard).
- A balance accurate to the resolution required by the method, and a ventilated drying oven.
Standard Test Procedure
- Sieve the dried aggregate to isolate the required single-size fraction and allow it to cool to room temperature.
- Fill the measure with the aggregate in three approximately equal layers, tamping each layer 25 times with the rounded end of the rod, and distribute the strokes uniformly over the surface.
- Level the surface gently, remove surplus particles, and determine the mass of aggregate placed in the cylinder; this is the initial mass.
- Insert the plunger, ensure it rests squarely on the aggregate surface without tilting, and position the complete assembly in the compression machine.
- Apply the compressive load at a uniform controlled rate so that the total load of 400 kN is reached in approximately ten minutes.
- Hold the maximum load for the time stated in the standard, commonly about five seconds, then release the load and remove the assembly.
- Sieve the crushed material over the 2.36 mm sieve and weigh the fraction that passes; this is the crushed mass.
- Repeat the determination on a second test portion and check that the two results agree within the repeatability limits of the standard.
Calculation and Reporting
The aggregate crushing value is calculated by dividing the mass of material passing the 2.36 mm sieve by the original mass of the test portion and multiplying by 100 to express the result as a percentage. The reported value is the mean of the valid determinations, rounded to the precision specified by the governing standard. If the difference between duplicate results exceeds the permitted repeatability limit, the test shall be repeated. Test reports shall identify the standard applied, the aggregate fraction tested, the source and description of the sample, and the individual and mean results.
Applications
Crushing value testing supports material acceptance and quality control across the construction industry. Typical applications include:
- Highway pavement engineering: acceptance of coarse aggregate for asphalt surface courses, binder courses, and unbound or cement-treated base and subbase layers, where heavy trafficking demands high crushing resistance.
- Cement concrete production: classification of crushed stone and gravel for structural concrete, where GB/T 14685 assigns crushing index limits of 10 percent, 20 percent, and 30 percent for Class I, Class II, and Class III aggregates respectively.
- Railway engineering: qualification of ballast and subballast materials that must resist particle breakage under repeated train axle loads.
- Hydraulic and airport engineering: evaluation of rockfill, filter, and drainage aggregates for dams, airfield pavements, and other heavy-duty infrastructure.
- Quarry and recycling quality control: routine verification of crushed stone, gravel, and recycled concrete aggregate production, and classification of secondary materials for structural reuse.
As a general engineering rule, heavy-duty applications such as expressway surface courses commonly specify maximum crushing values in the region of 26 percent, while lower pavement layers and general-purpose concrete may permit values up to approximately 30 percent. The exact limit always depends on the project specification and the governing standard.
FAQ
What is a good aggregate crushing value?
A lower value is always better because it indicates greater resistance to crushing. Strong igneous rocks such as basalt and granite typically produce values well below 20 percent, while weaker limestone or recycled materials may approach the specification limits. Acceptance limits vary by application; typical specification ceilings range from about 10 percent for premium concrete aggregate to 30 percent for lower-grade uses.
How does the crushing value test differ from the Los Angeles abrasion test?
The crushing value test applies a static compressive load and measures degradation by particle fracture, whereas the Los Angeles test measures degradation under combined impact and abrasion using a rotating drum with steel balls. Both evaluate mechanical durability, but they stress the aggregate differently, and many specifications require both tests for full compliance.
Which aggregate fraction is used for the standard test?
The classic BS 812-110 method uses the 10 mm to 14 mm fraction, while the Chinese highway method JTG E42 uses the 9.5 mm to 13.2 mm fraction. Using a single-size fraction ensures that particle packing effects are consistent and that results from different laboratories are comparable.
Why must two parallel determinations be performed?
Crushing value results are sensitive to small variations in particle shape, packing, and loading. Performing duplicate determinations and checking agreement against the repeatability limits of the standard verifies the precision of the result and protects against misleading single measurements.
What does the ten percent fines value measure?
The ten percent fines value (TFV), defined in BS 812-111, determines the load in kilonewtons required to produce ten percent fines from the same apparatus and fraction. It provides better discrimination for strong aggregates, where the standard 400 kN crushing test produces only a small proportion of fines.
Where can crushing value testing be performed?
Testing can be carried out in manufacturer laboratories, contractor site laboratories, or accredited third-party laboratories. For certification and dispute resolution purposes, it is recommended to use laboratories accredited to ISO/IEC 17025, which demonstrates technical competence, traceable calibration, and validated test procedures for the relevant national and international standards.