Automation of aggregate size-gradation analysis

A main component in a pavement structure is mineral aggregate. In the surface layer of an asphalt pavement, aggregate represents more than 90 percent (by weight) of the compacted asphalt concrete hot mix. Therefore, optimum aggregate properties must be sought to ensure optimum properties for the hot mix, and the consequently constructed pavement. One of the most important properties of an aggregate blend is its size gradation, which defines the percentages of different particle sizes included in the blend. For each pavement type, aggregate must satisfy, among other requirements, a size gradation envelope which defines, for each particle size, the maximum and the minimum allowable percentages of aggregate from that size in the blend. An asphalt-concrete aggregate blend may contain particles ranging in size from 30 mm down to less than 75 ;Aggregate size gradation is determined by the well-known and widely-used "sieve analysis" method. One major drawback of this procedure is the consumption of time and effort. The time factor is a major barrier to implementing the sieve analysis procedure as an aggregate gradation control measure in asphalt plants where production rates are high and interruptions to the production process are very undesirable. However, the variations of aggregate gradations in asphalt concrete mix production suggest the need for an on-line monitoring of mixed-aggregate size distributions. The result is a need for a rapid process for determining aggregate size gradation.;This thesis reviews potential technologies/methodologies to develop the required process. It also reviews the systems developed to automate the size-gradation analysis of aggregates, and assesses their applicability for testing asphalt-concrete aggregate blends.;The thesis then reports on a new, simple, and low cost system to automate aggregate size-gradation analysis of the fine portion of a sample from an aggregate blend. It is based on the differential settling of aggregate particles in a fluid medium, due to the differences in net driving forces of gravitation and drag when particles are settling due to their own weights. A prototype system, using a fractionating column (filled with water) and photocells to detect differential settling, has been fabricated and used to analyze fine aggregate blends (comprised of particles passing the 2.38 mm or ;The thesis concludes with recommendations to enhance the described system and overcome its deficiencies, and to develop a comprehensive automated system that could be used in an asphalt plant.