Recycled aggregate crushing value testing measures the resistance of aggregates derived from construction and demolition waste to crushing under a standardized compressive load, and it is the single most important mechanical quality indicator for recycled concrete aggregate. This guide explains the applicable GB/T, BS, EN and ASTM standards, sample preparation requirements, step-by-step test procedures, calculation formulas, and classification limits that determine whether a recycled aggregate can be used in structural concrete, non-structural concrete, or road construction applications.
Technical Overview
Recycled aggregates are produced by crushing and processing construction and demolition (C&D) waste such as discarded concrete, bricks, tiles, and mortar. Because recycled concrete aggregate (RCA) particles are coated with adhered cement mortar and may contain weaker contaminants, they are inherently more crushable than natural crushed stone. The crushing value test, sometimes called the crushing index test, quantifies this weakness by subjecting a specified particle fraction to a standardized compressive load and measuring the proportion of fines generated.
The result is expressed as a percentage: a lower crushing value indicates stronger, more wear-resistant particles suitable for higher-grade applications, while a higher value restricts the material to lower-strength or unbound uses. Accredited third-party laboratories routinely perform this test for recycled aggregate producers, ready-mix concrete suppliers, contractors, and engineering supervision authorities, because the crushing value directly governs the quality class assigned to the material and therefore its permissible end uses.
Applicable Standards and References
- GB/T 25177 – Recycled coarse aggregate for concrete, which defines Class I/II/III classification limits
- GB/T 14685 and GB/T 14684 – Test methods for the crushing index of coarse and fine aggregates
- JGJ 52 – Technical requirements and test methods for sand and crushed stone for ordinary concrete
- JTG E42 (T 0316) – Crushing value test method for aggregates in highway engineering
- BS 812-110 – Methods for determination of aggregate crushing value (ACV)
- EN 1097-2 – Determination of resistance to fragmentation by the Los Angeles method
- ASTM C131 and ASTM C535 – Resistance to degradation of small-size and large-size coarse aggregate
- ASTM C1747 – Determining the resistance of recycled aggregates to fragmentation in a rotating steel drum
- JGJ/T 240 – Technical specification for the application of recycled aggregate concrete
Testing Samples
Recycled Coarse Aggregate from Waste Concrete
The most common sample type is coarse RCA produced by crushing waste structural concrete. Typical test fractions are 9.5 mm to 19.0 mm for the GB/T method or 10.0 mm to 14.0 mm for the BS 812-110 method. Approximately 3 kg to 5 kg of dried, quartered material is required per determination, and testing is normally performed on three parallel specimens with the average reported.
Mixed Recycled Coarse Aggregate
Aggregates processed from mixed demolition streams may contain brick, tile, glass, wood, plastics, or bituminous fragments. Because these impurities significantly increase the crushing value, the contaminant content should be determined and reported together with the crushing result so that the data can be interpreted correctly against the classification limits.
Recycled Fine Aggregate
Recycled fine aggregate (typically smaller than 4.75 mm) is evaluated with a modified crushing index method using a smaller fraction, as described in GB/T 14684. The result is used mainly to qualify material for use in mortar, masonry units, and non-structural concrete.
Recycled Aggregate for Road Applications
For unbound base, subbase, and cement-stabilized layers, aggregate suppliers and highway contractors test the 9.5 mm to 13.2 mm fraction in accordance with JTG E42 (T 0316) to demonstrate compliance with pavement material specifications, which generally permit higher crushing values than structural concrete standards.
Testing Items
Crushing Value (Primary Test Item)
The crushing value is defined as the mass percentage of the test sample that passes the 2.36 mm sieve after the sample has been compacted and compressed under the specified load. It directly reflects the particle strength, the amount of adhered mortar, and the durability of the recycled aggregate under production, handling, and service stresses.
Complementary Tests Usually Performed Together
- Particle size distribution (gradation) analysis
- Water absorption and apparent and bulk density
- Content of attached cement mortar and foreign impurities
- Los Angeles abrasion loss or rotating drum fragmentation resistance
- Soundness against sulfate attack and freeze-thaw cycling
- Crushed and broken particle content and flakiness index
- Chloride and sulfate chemical contamination
Testing Methods
Apparatus
- Rigid steel cylinder with an internal diameter of approximately 150 mm, fitted with a base plate
- Hardened steel plunger that enters the cylinder with a small clearance
- Compression testing machine with calibrated load measurement and controlled loading rate
- Metal tamping rod with a rounded end for compacting the sample
- Test sieves including 19.0 mm, 13.2 mm, 9.5 mm, 10.0 mm, 14.0 mm, and 2.36 mm sizes
- Balances accurate to 1 g and a ventilated drying oven controlled at 105 ± 5 °C
Sample Preparation
The laboratory sample is first reduced by splitting or quartering to obtain the required test portion. The designated particle fraction is obtained by dry sieving, washed if necessary to remove dust, and dried to constant mass in the oven. The specimen is then allowed to cool to room temperature before testing so that moisture does not affect the compaction and crushing behavior.
Test Procedure According to GB/T 14685 / JGJ 52
- Weigh the prepared specimen and record the initial mass m0.
- Fill the steel cylinder with the 9.5 mm to 19.0 mm fraction, level the surface, and insert the plunger so that it rests squarely on the aggregate.
- Place the assembled mold on the compression machine and apply the load at a uniform rate of approximately 1 kN/s until a total force of 200 kN is reached.
- Hold the load steady for about 5 seconds, then release the load smoothly and remove the mold.
- Sieve the crushed material over the 2.36 mm sieve and weigh the mass m1 retained on the sieve.
- Repeat the determination on at least two additional specimens and report the mean value to the nearest 0.1 percent.
Test Procedure According to BS 812-110 (ACV Method)
- Use the 10.0 mm to 14.0 mm fraction and fill the measure in three layers, tamping each layer 100 times with the tamping rod.
- Position the plunger horizontally on the surface of the aggregate without imparting additional load.
- Apply the compressive force uniformly so that 400 kN is reached in 10 minutes.
- Hold the maximum load for 10 seconds, release it, remove the crushed sample, and sieve on the 2.36 mm sieve.
- Weigh the fraction passing the sieve and calculate the aggregate crushing value.
Calculation and Expression of Results
The crushing value is calculated as CV = (m0 − m1) / m0 × 100 %, where m0 is the original dry mass of the test specimen and m1 is the mass retained on the 2.36 mm sieve after loading. In the BS 812-110 expression, the mass passing the 2.36 mm sieve is divided directly by the total specimen mass. The individual results of parallel determinations should agree within the repeatability limits stated in the applicable standard; otherwise, additional specimens must be tested.
Quality Classification Limits for Recycled Coarse Aggregate (GB/T 25177)
- Class I: crushing value not greater than 12 percent, suitable for structural concrete up to the strength grades permitted by JGJ/T 240
- Class II: crushing value not greater than 20 percent, suitable for lower-grade structural members and non-structural concrete
- Class III: crushing value not greater than 30 percent, mainly suitable for cushion layers, backfill, and low-load pavement applications
Factors Affecting Test Results
- Quantity of adhered cement mortar on the recycled particles
- Strength grade of the parent concrete from which the aggregate was recovered
- Content of brick, tile, glass, and other weak contaminants
- Particle shape, angularity, and flakiness of the test fraction
- Loading rate, compaction effort, and accuracy of the 2.36 mm sieving operation
- Moisture condition of the specimen at the time of testing
Applications
Crushing value data are the gatekeeper for nearly every engineering use of recycled aggregate. Only material meeting the strictest class limits may be incorporated into reinforced and prestressed concrete elements, while intermediate classes are accepted for precast non-structural products, partition blocks, pavement concrete, and cement-stabilized road bases. Higher crushing value material remains valuable as unbound granular base, pipe bedding, general backfill, and feedstock for recycled bricks and mortars, provided complementary tests confirm environmental and dimensional suitability.
- Quality classification and certification of recycled aggregate production lines
- Mix proportion design and acceptance control for recycled aggregate concrete
- Verification of aggregate quality after screening, washing, or mortar-removal upgrading processes
- Tender submittals, supervision checks, and dispute resolution on construction projects
- Research and development of low-carbon concrete using circular construction materials
FAQ
What is the crushing value of recycled aggregate?
It is the percentage by mass of a standardized aggregate fraction that is crushed to fines finer than 2.36 mm when the sample is compressed under a specified load in a rigid steel cylinder. It measures the intrinsic particle strength of the recycled material.
Why is the crushing value of recycled aggregate usually higher than that of natural aggregate?
Recycled particles carry a porous layer of adhered cement mortar, and they often include weaker brick and tile fragments. These constituents crack and comminute more readily under compression, so a higher proportion of fines is generated during the test.
What limits must recycled coarse aggregate meet for use in concrete?
Under GB/T 25177, Class I requires a crushing value of 12 percent or less, Class II of 20 percent or less, and Class III of 30 percent or less. Highway specifications under JTG E42 define separate, typically more tolerant limits for pavement layers.
Which particle size fraction is used for the test?
The GB/T method uses the 9.5 mm to 19.0 mm fraction compressed to 200 kN, while the BS 812-110 method uses the 10.0 mm to 14.0 mm fraction compressed to 400 kN. The fraction must always match the standard being applied.
How many specimens are tested and how is the result reported?
A minimum of three parallel determinations is customary, and the arithmetic mean is reported to the nearest 0.1 percent after verifying that the spread between results falls within the repeatability allowance of the standard.
Can a recycled aggregate that fails the crushing value limit still be used?
Yes, provided it is directed to a lower-grade application consistent with its actual class, or it is upgraded by removing brick and tile contaminants, reducing adhered mortar through further crushing and screening, or blending with higher-quality natural aggregate before retesting.
How long does a typical crushing value determination take?
Excluding oven drying, a single determination takes about 20 to 30 minutes including loading, sieving, and weighing; with sample preparation, a complete three-specimen test report from an accredited third-party laboratory is normally issued within three to five working days.