Dependence on Aggregates as Building Blocks of Our Infrastructure

Dependence on Aggregates as Building Blocks of Our Infrastructure.

Highways, bridges, airport runways, dams, and railway beds are all integral components of a country’s infrastructure. Their quality and long term endurance are dependent on the quality and strength of the crushed stone aggregates and natural and manufactured sand that get combined in the particle blends used to produce cement and asphalt concretes for their construction. Coarse Aggregate is crushed stone, usually granite, limestone, gravel and slag, between 90 and 4.75 millimeters in sieve sizes. Fine Aggregate is natural, manufactured, or combination sand, between 9.5 millimeters and 75 microns in sieve sizes.

End users of these construction materials are generally regulatory agencies like departments of transportation, airport and railway authorities. These groups issue specifications to their suppliers based very closely on the various standard tests which have been written for large regions globally, many ASTM and AASHTO standards for the US, British standards for Europe, Indian standards for India, etc.

These test standards vary from one to another, but are very similar. They include various types of tests, but one of the major groups of tests are for measuring the geometric (or morphological) parameters of the particles in the aggregate blends. These various geometric parameters correlate to physical properties of the end construction, like load-bearing strength, degree of internal frictional strength, wear rate,  and bonding/binding strength with the cement or asphalt matrix. Until just recently, the only ways to make these measurements were manually, by screening samples of aggregate products into different size classes to calculate their size distributions, and then running

a myriad of manual tests on samples of the different size fractions using: hand-held gauges to measure various sizes of individual particles like length, width and thickness, a series of rod screens; measuring water-filled void spaces in large containers; abrading samples and measuring the % of the abraded fines; and more. These are very manpower intensive and can take up to days to complete, which leads some suppliers to make them only once a week on a collected sample. There is now, however, an automated 3-Dimensional Dynamic Image Analyzer which can make all these measurements on a large representative sample of particles in one sample run. Achieving all these results in under an hour, without operator subjectivity, rather than up to a day, and with concern about operator error, is a huge savings in time and expense. And this much time savings contributes greatly to improved productivity, fewer unscheduled plant shut-downs and less time to reach process equilibrium upon start-up.

Meanwhile, additional research is underway to make other either improved or additional measurements, like particle surface area, particle surface roughness or texture, angularity, and three-dimensional volumes. All these parameters too can be measured on the 3-D image analyzer.

Particle Length, Width and Thickness (all three major axis size dimensions) need to be measured to then calculate some of the important geometric parameters for aggregate as ASTM requires, the 3 Flat, Elongated, and Flat & Elongated particles parameters. The 3-D mode is also required for measuring the British Standard’s Flakiness Index results. Results of both these standard tests give numbers which correlate with the load-bearing strength of the final road bed. The 3-D mode is patented by, and available only in Microtrac’s line of PartAn3D Dynamic Image Analysis Instruments; in both on-line process and in lab bench top Models for R&D and QC labs. Microtrac has more than 40 on-line PartAn line instruments installed and operating globally, and many more lab models.

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