In the last installment of our Abrasion Testing series, we wrote about the importance and use of the Micro-Deval Test Method. An equally important method for abrasion testing is the Los Angeles (L.A.) Abrasion test. In this blog post we’ll provide a recap of why this type of test matters, redefine abrasion testing and highlight the benefits of the L.A. Abrasion test.
Why Does Abrasion Testing Matter Again?
Abrasion testing determines the relative quality, toughness and durability of mineral aggregates subjected to impact and abrasion. Values derived from both the Micro Deval and the L.A. Abrasion tests offer information about the performance of an aggregate in use. This testing offers insight into how asphalt and concrete aggregates will stand up to wear and tear over time. It’s also a good indicator of changing properties in an aggregate source as part of a quality control or quality assurance program.
What is the L.A. Abrasion Test?
The Los Angeles (L.A.) Abrasion test is widely used as an indicator of the relative quality of aggregates. It measures the degradation of standard gradings of aggregates when subjected to abrasion and impact in a rotating steel drum with an abrasive charge of steel balls. The drum is fitted with an internal shelf that lifts and drops the charge and sample with each revolution, generating impact forces. After the machine has completed the required rpm, contents are removed and percent loss is measured.
How Does the L.A. Abrasion Test Work?
A sample is prepared by separating into individual size fractions of the required masses.
- The sample of specifically sized aggregates and the abrasive charge are placed in the L.A. Abrasion Machine and rotated at 30-33rpm.
- The sample is removed and washed over a No. 12 (1.70mm) sieve and placed in an oven to dry.
- The percent loss, or the difference between the original mass and the final mass is calculated.
- An L.A. Abrasion loss value of 40 indicates that 40% of the original sample mass passed through the sieve.
What are the Benefits?
It is important to consider the differences between the L.A. Abrasion and Micro-Deval test. The Micro-Deval test uses a form of wet grinding of smaller samples in a smooth drum, and loss is a function of wear and attrition. The L.A. Abrasion test uses larger dry samples and abrasive charges in a drum with a shelf. The shelf lifts and drops the sample and abrasive charge across the span of the drum, resulting in very high impact on the aggregate particles. Loss from this test is a result of fracturing and dry grinding of the particles. Still, both are generally judged to be predictive of aggregate toughness and durability although there are difficulties when trying to correlate their results. Suitability often comes down to the degree of acceptance in a given locality or jurisdiction. L.A. Abrasion is a test that has been around a very long time and has accumulated a wealth of data that most designers can use and understand. The equipment is larger and more expensive than Micro-Deval, but it is also simple, reliable and uncomplicated to operate. Modern equipment is now much safer, using enclosures to limit noise, dust and hazards from moving parts. Before committing to either method, you should consider which test is most likely to be called for your projects.
What Equipment do we Offer?
We recommend the Gilson HM-70A Los Angeles Abrasion Machine featuring:
- Fully-enclosed cabinet, lined with sound attenuating foam to reduce noise levels, dust and cover the rotating drum during operation
- Electronic safety interlocks for operation only when doors are secured
- Powerful 1hp motor to rotate the drum through a slip-clutch protected chain drive
- User controls mounted on the outside of the sound enclosure for a straightforward operation
- ASTM-approved wide steel shelf to catch and drop the aggregate sample
- Controller console to stop revolutions after a preset number, with overload protection
It’s important to remember that whatever method you choose, abrasion testing is a necessary procedure as part of a quality control process for gauging how materials will react to wear and tear over time.
Need help selecting aggregate testing equipment for your application? Call us at 800.444.1508 to speak to an expert!