Aggregates, including for example crushed stone, sand and gravel, are one of the most fundamental components used in construction.
Approximately fifty percent of aggregates are shipped for highway construction, either as road base or a primary component of asphalt and concrete. Aggregates are also used in commercial and residential construction as base for foundations, concrete and parking lots. Other uses for aggregates, some of which require a high-quality, chemical-grade limestone, include: riprap for erosion control; railroad ballast; flux stone; filter stone; agricultural limestone; production of cement and lime; desulfurization; acid neutralization; animal feed supplements; and plastic and paint fillers. Regardless of the use, the production requirements of stone aggregates are complex because the material must be crushed to multiple sizes, often washed to remove fines and impurities, and sometimes processed further in order to meet the specification for its intended use. Without the physical and chemical properties provided by aggregates, modem construction materials and methods, as well as a multitude of industrial products, would not be possible.
Product requirements often dictate the percentages of flat particles, elongated particles or flat and elongated particles in coarse aggregates. For example, flat or elongated particles of aggregates for some construction uses may interfere with consolidation and result in harsh, difficult to place materials. Flat particles are defined as those particles that exceed a specified ratio of width to thickness. For example, if the ratio is 3:1, the width cannot exceed three times the thickness. (A specification will give a percentage and then the ratio, such as 20% 3:1, meaning a sample fails the specification if more than 20% of the particles (individual pieces or by mass of the total sample) tested have ratios that exceed 3:1.) Elongated particles are defined as those particles that exceed a specified ratio of length to width. Flat or elongated particles are defined as those particles of aggregate having a ratio of width to thickness or length to width greater than a specified value. Flat and elongated particles of aggregate are defined to be those particles having a ratio of length to thickness (maximum to minimum) greater than a specified value.
Sieve size is the size of an opening that a particle can pass through. The specification may require that the amount of particles passing through the opening be determined (xe2x80x9cpercent passingxe2x80x9d). Alternatively, the specification may require that the percent of the sample that does not pass through a specified opening be determined (xe2x80x9cpercent retainedxe2x80x9d).
Crushers are conventionally used to crush large aggregate particles (e.g., rocks) into smaller particles. One particular type of crusher is known as a cone crusher. A typical cone crusher includes a frame supporting a crusher head and a mantle secured to the head. A bowl and bowl liner are supported by the frame so that an annular space is formed between the bowl liner and the mantle. In operation, large particles are fed into the annular space between the bowl liner and the mantle. The head, and the mantle mounted on the head, rotate eccentrically about an axis, causing the annular space to vary. As the distance between the mantle and the bowl liner varies, the large particles are impacted and compressed between the mantle and the bowl liner. The particles are crushed and reduced to the desired product size, and then drop down from between the mantle and bowl liner.
Aggregate is a description of the product based on how much of the product passes (or could be given as how much is xe2x80x9cretained onxe2x80x9d) a specified number of sieve sizes, or openings. For example, an ASTM (American Society of Testing and Materials) #57, a typical product used in concrete and asphalt construction, is described by using sieve sizes as follows (sieve sizes are square openings):
Prior apparatus and methods for measuring individual particles of aggregate of specific sieve size to determine the ratio of width to thickness, length to width, or length to thickness include that disclosed in Standard Test Method for Flat Particles, Elongated Particles or Flat and Elongated Particles, in Coarse Aggregate, ASTM Designation D 4791-95, the entire contents of which is incorporated herein by reference. This test method uses a proportional caliper device that consists of a base plate with two fixed posts and a swinging arm mounted between them so that the openings between the swinging arm and the two fixed posts maintain a constant ratio. The axis position can be adjusted to provide the desired ratio of opening dimensions. The axis position must be moved to change the ratio being measured. A complete re-measuring of the particle under test each time a new ratio is selected is thus required. This device is therefore capable of measuring only one ratio at a time and is therefore capable of only determining whether a particle is larger or smaller than a single ratio.
Additionally, ASTM D 4791 details how to measure flat and elongated particles using a proportional caliper device that determines pass/fail for one ratio at a time. Specifications are based around using the proportional caliper device and specify the ratio and the maximum percent of the sample that can exceed the given ratio. In the xe2x80x9cSuperpavexe2x80x9d asphalt pavement mix design specification, for example, 10% on a 5:1 ratio means that no more than 10% of the aggregate sample can have a maximum dimension greater than five times the minimum dimension. Most aggregate specifications currently (and historically) use 10% on a 5:1 ratio, which is adequate for controlling excessive flat and elongated particles.
However, describing the flat and elongated particles present in a sample using the percent found at one ratio doesn""t give a true picture of the various ratios found within a sample as described later in this paper. A good analogy would be to describe the gradation of an ASTM #57 stone by giving only the percent passing the xc2xd-inch sieve. Without the information on the 1 inch, xc2xe inch, xe2x85x9c inch and #4 sieve, a complete picture of the gradation of the sample cannot be determined.
Without a complete picture of the various particle shapes in a sample, it is difficult to accurately evaluate performance results as determined by the current research efforts concerning particle shape. Several Departments of Transportation (DOT""s) and universities are developing automated procedures that determine aggregate particle shapes (Button, 2000), however the equipment costs involved (up to $30,000) make these devices far too expensive to be used in the typical aggregate laboratory. In addition, measurements with the automated devices are still aimed at determining the percent found at one specified ratio rather than gathering Multiple Ratio Analysis data.
Accordingly, there is still a need for an inexpensive and readily usable arrangement for determining aggregate particle shapes.
The present invention is directed to a method and apparatus for compiling data permitting evaluation of aggregate particle shapes.
In one aspect, the invention includes a method for performing multiple ratio analysis of aggregate particles. This method includes the steps of measuring a first maximum dimension of a particle, measuring a second maximum dimension of a particle in a direction substantially perpendicular to the first maximum dimension, and inputting the first maximum dimension and second maximum dimension into a computer having a processor. Using the computer, a particle ratio of the first maximum dimension to the second maximum dimension for the measured particle is computed and the particle ratio is classified into one of a predetermined plurality of different ratio ranges, each of these plurality of different ratios representative of a different range of particle shapes.
Another aspect of the invention includes an apparatus for multiple ratio analysis. This apparatus includes a measurement device configured to measure a dimension of an aggregate particle along at least one axis at a time, a computer, and a computer-readable medium bearing an instruction set executable by the computer. The instruction set permits the computer to calculate an aggregate particle ratio for an aggregate particle by determining a ratio of a first maximum dimension and a second maximum dimension of the aggregate particle. The instruction set also permits the computer to classify the aggregate particle ratio into one of a predetermined plurality of different aggregate particle ratio ranges, each of the plurality of different aggregate particle ratios representative of a different range of aggregate particle shapes.
Still other objects and advantages of the present invention will become readily apparent from the following detailed description, simply by way of illustration of the best modes contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.