In theory, there exists a particular gradation that, for a given maximum aggregate size, will produce a maximum density gradation and minimize the void space between particles. This means the gradation of the particles is arranged in such a way that successively smaller sized particles will be packed within the spaces between larger particles. When it comes to practical application however, maximum density is not desirable because there is a certain volume of void space required for the asphalt binder.
What is a Gradation Test?
Gradation testing, also called sieve analysis, is a fairly basic yet essential test that measures the gradation (or distribution of aggregate particles, by size, within a given sample) to determine whether it’s compliant with design, production control requirements, and verification specifications.
They’re often used to calculate relationships between various aggregates or aggregate blends, to check compliance with such blends, and to predict trends during production by plotting gradation curves. When used in conjunction with other tests, the sieve analysis is a useful quality control and quality acceptance tool.
How a Gradation Test Works
While the test can be run on either dry or washed aggregate, a washed sieve analysis is more accurate—even though it may take longer than a dry one. A dry sieve analysis is usually performed when fast results are needed. A washed procedure will take anywhere from one to three days from the sampling phase to completion depending on the moisture content of the aggregate when it’s sampled. A dry procedure will generally take only an hour or two from sampling the aggregate to completion.
The Basic Procedure
- An adequately sized sample of aggregate is obtained from the field. Usually from a stockpile, bin, dump truck, conveyor belt or roadway.2. The sample is mixed and reduced to a size suitable for testing. This process is often referred to as “splitting” the sample.
3. The sample is dried to a constant mass and the dry mass is determined.
4. If the washed procedure is being used, the dry sample is placed in a container and covered with water. Then it’s agitated to separate all particles finer than the No. 200 sieve from the coarser aggregate.
When the fine material is suspended in the water, the wash water containing the suspended solids will be decanted into the nested sieves (consisting of a No. 200 sieve and an upper sieve ranging from No. 8 to No. 16. This step is repeated until the wash water is clear.
5. If the washed procedure is being used, the material retained on the nested sieves will be returned to the washed sample, which will be dried to a constant mass and allowed to cool. Once dry, the mass of the sample (after washing) will be determined.
6. Depending on the design of the pavement, the appropriate sieves will be assembled in order of decreasing size with the largest openings at the top and placed over a pan. The entire sample will be poured into the top sieve in the nest and sieved in a mechanical shaker.
7. The mass of the material retained on each sieve will be determined individually. The cumulative mass of each size sieve and the mass retained on all larger sized sieves will also be recorded. Gradation may be reported either as a percentage retained or percentage passing each sieve.
Arlyn Scales for Aggregate Gradation
Choosing the appropriate scale to weigh aggregates depends on the amount of aggregate you use in a sample size and the sizes of the aggregate particles you must weigh. Arlyn Scales manufactures a wide variety of scales suitable for this purpose, but let’s explore just a few of your options here.
Small scale and on-site testing would be best served by our industrial bench scales, which range in capacity and resolutions from a small 4 lb. capacity and 0.0002 lb. resolution to a larger 100 lb. capacity and 0.01 lb. resolution.
Larger aggregate gradation operations, such as those at a quarry site, would be better served by our floor scales, which range from 2,500 lb. capacity and 0.5 lb. resolution to 20,000 lb. capacity and 5 lb. resolution or higher.
Benefits of Choosing Arlyn Scales
Yet whichever size scale you choose, you can feel confident that results of your tests will be accurate. All of our industrial scales feature best of class components including stainless steel load cells for better durability, accuracy and abuse resistance; advanced digital algorithms that compensate for rough industrial conditions and provide enhanced precision; and welded construction for additional stability and durability.
Steel models come with a zinc-rich triple epoxy coating that adds corrosion and abrasion resistance for wash sieve analysis. Our stainless steel models provide additional corrosion and abrasion resistance on their own, but can be purchased with an additional corrosion resistant triple epoxy infused with garnet particles for even better resistance and years of trouble free use.
Ultra Precision Scales for Fine Aggregates
If you’re weighing fine aggregates (small than the 0.075 / No. 200 sieve), you’ll want an industrial scale that can provide precise, high-resolution measurements. Our Ultra Precision Scales feature a special weighing technology that improves scale readability to 1 part in 100,000—20 times better than the 1 part in 5,000 of our standard industrial scale models—and accuracy to 1/100 of 1%, which is 10 times better than the 1/10 of 1% offered by our standard industrial scale models.
This means a 500 lb. capacity ultra precision scale will give you a resolution of 0.005 lb. compared to a standard scale that would give you a 0.1 lb. resolution.
Weighing Components for OEM Systems
Arlyn Scales is a direct manufacturer of industrial scales and weighing components. So if you have (or want) an automated system to test gradation, we can work with you to design and develop the necessary weighing components for your conveyor system. We can also help you collect and store weight data through a variety of communication options including Wi-Fi, USB, Ethernet and Cloud.
If you’d like to learn more about our industrial or ultra precision scales and how they can help you achieve the perfect aggregate ratios, contact us today! We’ll answer any questions you may have and help you select the scale that best meets your needs.