High Precision Scales used for Aggregate Testing

large-ultra-precision-scale-1A number of related fields require understanding the particle composition of aggregate materials. These include asphalt production, the manufacturing of concrete, cement and cement products, soil testing, construction testing and particle sizing, among others.

Asphalt is commonly known as the common black material that is used to pave roads. It is also know as tarmac, blacktop, or macadam. But it actually has a number of different components. Generally, the largest single ingredient is crushed stone. Depending on the expected use of the asphalt, the standard size of the individual stone pieces are specified. A number of other complementary materials are also used, such as gravel and sand. These components can make up as much as 90 or 95 percent of the total asphalt material. But it obtains its material properties and color from the black liquid binder material that holds it together, the asphalt cement. It is a very sticky black liquid that is a petroleum by-product. Similarly, concrete is a mixture of a number of individual ingredients. Once again, the primary ingredient is crushed stone and gravel. By itself, these make up more than 40% of concrete material. Sand composes another 25% of the total. Water and Portland Cement includes most of the remainder of the non-cured material. As with asphalt, the properties of cement are highly dependent on the particle properties of the materials used. Of course, materials such as gravel, crushed stone and sand are far from being uniform. Any sample will consist of individual pieces of varying sizes. In order to determine the percentage of each range of sizes, it is necessary to take a sample of the material, and then separate out each various size. The procedure used to do this is known as sieve analysis. This can be thought of as using a number of different screens or strainers. Each one has a wire mesh screen with different screen openings. First the material is poured into a screen with the largest openings. Only the largest particles will be captured at this first stage. The remainder of the particles will pass through. This remainder is then poured through the second largest screen. As previous, only the second largest set of particles will be captured. This process is repeated with the desired number of different sized screens, resulting in a collection of particles that match the screens used. Now each of the particle collections may be weighed. The percentage of the total composed of each particle size can be calculated, and then compared to the required material specifications. The electronic scales used for this purpose must meet some very difficult requirements. They must have a very significant capacity. Samples of aggregate materials may easily weigh 100 pounds. They must be very rugged, as large amounts of aggregate materials will be dumped onto the platform. And most importantly, they must be very precise so that the percentages calculated will be exactly accurate. Standard load cell based industrial scales will generally not be accurate enough. The most common solution is to use a type of digital scale known as a force motor balance. For these high capacities, these scales will be extremely expensive. They are also not particularly rugged. A new technology, introduced by Arlyn Scales, uses Surface Acoustic Wave, or SAW transducers. These Ultra Precision Scales combine all of the required features of high capacity, extreme ruggedness, and exquisite accuracy. For example, the 100 pound capacity industrial scale has a readability of one thousandth of a pound, an accuracy of greater than one hundredth of one percent, and an overload capacity of five hundred percent. As an added advantage, they may be equipped with an optional battery pack, making them ideal for use at construction or paving sites. It is often necessary to record the particle size percentages. These Ultra Precision Scales may be equipped with a USB connection that accepts standard USB flash memory drive. Thousands of readings may be stored on the drive. This data can then be downloaded into any computer system. When used with a database program, or entered into a spreadsheet, the data can easily be compared with the required aggregate specification. Alternatively, the digital scale can be directly connected into a computer system using a serial RS-232 communication connection, or with a wired or wireless Ethernet port.