Aggregate Crushing Value Test Steps: Complete Procedure, Apparatus, and Standards

The aggregate crushing value test measures the resistance of coarse aggregates to crushing under a gradually applied compressive load, making it a key quality indicator for concrete, asphalt, and road construction materials. This article provides a complete, step-by-step guide to the crushing value test procedure, covering apparatus, sample preparation, loading, sieving, calculation, and reporting in accordance with recognized standards such as BS 812-110, GB/T 14685, and JTG E42. Engineers, laboratory technicians, and quality control specialists can use this reference to perform the test consistently and interpret the results correctly.

Technical Overview

The aggregate crushing value (ACV) test is a widely used laboratory method for evaluating the mechanical strength of coarse aggregates. The result expresses, as a percentage, the mass of fine material produced when a prepared single-sized aggregate specimen is subjected to a specified compressive load. A lower crushing value indicates stronger, more crush-resistant aggregate, while a higher value signals a greater tendency to degrade under compaction and service loads. Because weak aggregates can break down during handling, paving, and long-term traffic loading, the crushing value is a routine acceptance and quality control parameter in concrete production, asphalt paving, and unbound pavement layer construction, and the test is regularly performed by accredited third-party laboratories.

Test Principle

A single-sized fraction of coarse aggregate is compacted in a rigid steel cylinder using a tamping rod. A plunger is seated on the aggregate surface, and a compression testing machine applies an axial load at a controlled, uniform rate. After the target load is reached and briefly held, the crushed specimen is removed and sieved. The ratio of the mass passing the 2.36 mm sieve to the original specimen mass, multiplied by 100, gives the crushing value.

Governing Standards

• BS 812-110 defines the classic aggregate crushing value method, in which a total load of 400 kN is applied within approximately 10 minutes.
• GB/T 14685 specifies the crushing index for pebbles and crushed stone used in construction, applying a total load of 200 kN.
• JTG E42 (test method T 0316) governs the crushing value of coarse aggregates for highway engineering, using a 400 kN load.

Where a project specification references a particular standard, the apparatus dimensions, test fraction, load, and calculation defined in that document must always take precedence over general descriptions.

Testing Samples

Crushed Stone and Gravel for Concrete

For concrete aggregates tested under GB/T 14685, the crushing index is determined on the 9.5 mm to 19 mm size fraction. Under BS 812-110, the standard specimen consists of aggregate passing the 14 mm (or 12.5 mm) test sieve and retained on the 10 mm sieve. Only sound, representative particles of the specified fraction should be included, with undersize and oversize material removed by screening.

Coarse Aggregates for Asphalt Mixtures

For bituminous mixtures and surface treatments tested under JTG E42 (T 0316), the 9.5 mm to 13.2 mm fraction is typically used. Because asphalt mixtures transmit concentrated stresses through the stone skeleton, a low crushing value is especially important for surface course and high-traffic applications.

Sampling and Conditioning

• Obtain a representative field sample following recognized sampling practice and reduce it by quartering or riffle splitting.
• Wash the test fraction to remove adhering dust and fines that could artificially inflate the result.
• Dry to constant mass at 105 ± 5 °C, or air-dry where permitted by the governing standard, and cool to room temperature before testing.
• Verify the size fraction by screening immediately before specimen preparation.

Testing Items

• Aggregate crushing value (ACV): the percentage of fines generated under the specified compressive load.
• Ten percent fines value (TFV): a complementary determination of the load required to produce 10 percent fines, often requested when aggregates are too weak for a meaningful ACV result.
• Auxiliary checks: verification of test fraction gradation, moisture condition, and specimen mass, which are prerequisites for a valid crushing value determination.

The crushing value is frequently performed alongside related mechanical tests, such as Los Angeles abrasion (ASTM C131 and ASTM C535), aggregate impact value, and soundness testing, to build a complete picture of aggregate durability.

Testing Methods

Required Apparatus

• An open-ended steel cylinder with an internal diameter of approximately 150 mm (152 mm in some national standards), supplied with a base plate and a removable plunger.
• A compression testing machine with capacity of at least 400 kN and a verified, controllable loading rate.
• A metal tamping rod approximately 16 mm in diameter and 600 mm long, with one end rounded.
• A balance readable to 1 g or better.
• Test sieves, including the 2.36 mm sieve and the sieves defining the test fraction.
• A ventilated drying oven capable of maintaining 105 ± 5 °C, plus trays, brushes, and sample splitting equipment.

Specimen Preparation Steps

• Clean the interior surfaces of the cylinder, base plate, and plunger, and seat the cylinder securely on the base plate.
• Fill the cylinder with the prepared aggregate in three layers of approximately equal depth, following the layer count stated in the governing standard.
• Compact each layer with 25 evenly distributed strokes of the tamping rod, allowing the rod to fall freely from roughly 50 mm above the aggregate surface.
• Heap the final layer slightly above the rim before tamping, then level the surface flush with the top of the cylinder using the rod as a straightedge.
• Weigh the aggregate to the nearest 1 g and record this as the initial specimen mass, m0.

Step-by-Step Loading and Sieving Procedure

• Step 1: Insert the plunger carefully so that it rests flat and level on the aggregate surface without tilting, and confirm that no particles are trapped between the plunger and cylinder wall.
• Step 2: Place the complete assembly centrally between the platens of the compression testing machine.
• Step 3: Apply the load at a uniform, continuous rate so that the specified maximum load, typically 400 kN reached within about 10 minutes for BS 812-110 and JTG E42, or 200 kN for GB/T 14685, is achieved smoothly.
• Step 4: Hold the maximum load for the dwell time specified in the standard, commonly 5 seconds, and then release the load gradually.
• Step 5: Remove the plunger and transfer the entire crushed specimen, including any particles adhering to the plunger and cylinder walls, onto the 2.36 mm test sieve.
• Step 6: Sieve the crushed material, mechanically or by careful hand agitation, until no further significant amount passes, which is commonly judged as no visible discharge within about one minute.
• Step 7: Weigh the fraction passing the 2.36 mm sieve and record it as m1; optionally weigh the retained fraction as a check that the two masses balance the original mass within acceptable tolerance.
• Step 8: Repeat the complete procedure on a second, freshly prepared specimen, and on a third specimen where the governing standard requires it.

Calculation and Reporting

The aggregate crushing value is calculated as follows: crushing value (%) = (m1 / m0) × 100, where m0 is the initial mass of the test specimen and m1 is the mass of material passing the 2.36 mm sieve after crushing. Report the mean of the valid determinations to one decimal place, or to the nearest whole percent where the standard requires. The report should identify the governing standard, the test fraction, the applied load, the individual results, and any deviations from the standard method.

Precision and Verification

If duplicate determinations differ by more than the repeatability limit stated in the governing standard, the results should be treated as suspect and the test repeated with fresh specimens. When consistent results remain unusually high, indicating weak aggregate, a ten percent fines value determination is often recommended to characterize the material more precisely.

Factors That Affect Accuracy

• Inconsistent tamping effort or non-uniform distribution of strokes, which changes the degree of compaction and particle packing.
• Contamination of the specimen with fines or use of the wrong size fraction, which inflates the crushing value.
• Deviations in loading rate or inaccurate machine calibration, which alter the crushing energy delivered.
• Insufficient or excessive sieving of the crushed material on the 2.36 mm sieve.
• Plunger misalignment or trapped particles between the plunger face and the cylinder wall during loading.

Applications

Crushing value data support decisions across the construction materials supply chain, from quarry process control to end-product acceptance testing.

• Concrete production: verifying that coarse aggregates meet crushing index or ACV limits before approval for structural and general-purpose concrete.
• Asphalt pavements: confirming that stone skeletons in surface courses and heavy-duty wearing courses can resist crushing under traffic-induced stresses.
• Unbound pavement layers: qualifying granular base and subbase materials that must retain strength during compaction and service.
• Railway construction: evaluating the degradation resistance of ballast and track bed aggregates.
• Quarry and crusher control: monitoring how changes in rock source, feed gradation, or crushing equipment affect product quality.
• Research and mix design: comparing candidate aggregate sources during materials selection and optimization studies.

FAQ

What crushing value is considered acceptable?

Acceptance limits depend on the application and the governing specification. As general guidance, premium concrete aggregates are commonly limited to roughly 10 percent or less, general construction aggregates to around 20 percent, and lower-grade uses to approximately 30 percent, while road and asphalt specifications frequently require values below about 25 to 30 percent. Always confirm the limiting value in the applicable project specification or standard.

Why is the 2.36 mm sieve used in the calculation?

The 2.36 mm sieve defines the standardized boundary between crushed fines and intact coarse particles. Expressing the passing mass as a percentage of the original mass provides a reproducible, quantitative measure of crushing susceptibility that can be compared between laboratories and against specification limits.

How does the crushing value differ from the impact value and Los Angeles abrasion?

The crushing value applies a slow, static compressive load, the aggregate impact value applies rapid shock loading, and the Los Angeles abrasion test (ASTM C131 and ASTM C535) subjects aggregate to tumbling impact and abrasion with steel balls. The three tests stress aggregates differently and are often specified together to characterize overall mechanical durability.

How many specimens are required for one result?

Most standards require at least two parallel determinations on identical, independently prepared specimens, and some require three. The reported value is the arithmetic mean of the valid determinations, provided the spread between them falls within the precision limits of the method.

Can the crushing value test be applied to fine aggregate?

No. The cylinder, plunger, and tamping procedure are designed for coarse aggregate fractions. Fine aggregate quality is assessed with other methods, such as sand equivalent testing, deleterious content limits, or mortar strength evaluation, depending on the governing specification.