Aggregate Testing

Testing for roadbase construction

While the below tests are not technically aggregate tests, roadbase material is a well graded material consisting of course and fine aggregates and therefore the below are required in conjunction with aggregate testing.

CBR Value

The California Bearing Ratio test (CBR test) is a penetration test that assesses the strength of subgrade soil and other paved areas, including roads, pathways, and airstrips. Developed by Caltrans, the CBR test is crucial in designing flexible pavements and has been adopted globally since its introduction in the 1930s, including in Australia.

For laboratory testing, remoulded samples compacted at the suitable moisture content are used. This allows simulation of the expected subgrade moisture content and disturbance levels during and after construction. Alternatively, when conducting the CBR test in-situ, the impact of seasonal changes in moisture content must be taken into account. Read more about CBR testing here (link to CBR blog)

Grading or Particle Size Distribution (PSD)

A particle size distribution (PSD) test for road base material is a laboratory test that measures the distribution of particle sizes in a sample of material used in road construction. The PSD test is typically performed on soil, gravel, or crushed rock aggregates that are intended for use as base materials in road construction.

During the test, the material sample is passed through a series of standardized sieves with different mesh sizes, and the weight of material retained on each sieve is measured. The results are then plotted on a graph to produce a particle size distribution curve that shows the proportion of material in each size range.

The PSD test provides valuable information about the grading and uniformity of the material, which are important factors in determining its suitability for use as a road base. The test results can be used to determine the maximum and minimum particle sizes, the percentage of fines, and the grading of the material, which are essential parameters for designing a stable and durable road base.

Atterberg

The Atterberg test is a group of laboratory tests that measure the consistency and plasticity of soil, including those used as road base materials. The tests are named after their developer, the Swedish soil scientist Albert Atterberg.
The Atterberg tests consist of three main tests; the liquid limit, plastic limit, and shrinkage limit tests. These tests are used to determine the water content at which the soil transitions between different states, such as from a plastic to a liquid state or from a plastic to a solid state.

In the context of road base material, the Atterberg tests can be used to assess the suitability of a soil material for use as a road base or subgrade. The tests provide information about the soil’s plasticity, which is important in determining its ability to withstand deformation and support the weight of the overlying pavement layers. The results of the Atterberg tests can also be used to classify soils according to their plasticity index and determine their optimal moisture content for compaction. Overall, the Atterberg tests play an important role in the design and construction of stable and durable road base materials.

What are the quality tests of aggregate?

Wet/Dry Variation

The ratio of the load required to produce a 10% increase in fines for the oven-dry (OD) to the saturated surface dry (SSD) condition.

Aggregate Crush Value (ACV)

Aggregate Crush Value (ACV) is a test that measures the resistance of aggregate to crushing under a gradually applied compressive load. During the ACV test, a standard amount of aggregate is subjected to a compressive load and the crushing strength of the aggregate is determined. The ACV is calculated by dividing the mass of the crushed aggregate by the initial mass of the test sample and multiplying it by 100. The test results provide a measure of the aggregate’s resistance to crushing and its ability to withstand a given load or stress.
The ACV test is important in determining the quality and durability of aggregates used in construction applications such as road construction and concrete production. The results of the test are used to determine whether the aggregate meets the required standards and specifications for its intended use. In general, the higher the ACV value, the stronger and more durable the aggregate is likely to be.

Degradation Factor

Refers to the measurement of how much an aggregate material deteriorates over time due to weathering, abrasion, or other factors.
Sodium Sulphate Soundness: A method of testing the weathering resistance, particularly to frost action of aggregate material. A sample is soaked in saturated sodium-sulphate solution, drained, and dried. This is repeated and the sample examined for cracks.

Point Load Testing

The Point Load strength test is based on the indirect tensile strength test or rock core by fracturing a specimen of rock using a machine equipped with conical platens and a load measuring system.

Los Angeles Abrasion

The Los Angeles abrasion test (LA abrasion) is a determination of the loss, on abrasion, of aggregate particles by means of the Los Angeles abrasion testing machine. The test is applied to aggregate particles from crushed rock, gravel or crushed slag, or to crushing derived from rock spalls or drill cores.