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Aggregates Industry Research Priorities

  1. Significance and Application of the Compacted Aggregates Resistance (CAR) Test
    The Superpave fine aggregate angularity (FAA) test rejects many 100% crushed limestone aggregates that are known to perform well. The CAR test is believed to better predict performance, properly evaluate carbonates, and permit the evaluation of blended natural and manufactured sands that would certainly have been rejected by the FAA test. The Superpave mixtures expert task group has expressed interest in the CAR test as a potential replacement for the FAA test. Research is needed to refine and calibrate the CAR test with actual performance. The adoption of the CAR test will increase use of local aggregates and reduce costs of shipping aggregates greater distances than necessary.

  2. Surface Texture of Aggregates - Measurement and Impact on Performance of Hot-Mix Asphalt (HMA)
    Technology is allowing the measurement of the surface texture of aggregates in increasing detail. Surface texture is being promoted, by some, as a significant, if not the predominant, factor in aggregate contribution to performance of HMA. However, gradation also certainly plays a key roll. The FHWA is establishing testing procedures, collecting surface texture data, and can be expected to set specification limits based on perceived benefits. The aggregates industry needs to be proactive by conducting research to assist in evaluating surface texture as one contributor to performance of HMA and to establish limits based on performance measures.

  3. Blending of Fine Aggregates for Concrete
    Current concrete aggregate specifications have served the industry well, but were developed when natural sand was the predominant source of fine aggregates. Processing techniques have changed along with increasingly restricted access to traditional sources of fine aggregates. It is now imperative that specifications be developed accounting for new types and sources of fine aggregates. Additionally, blending of different fine aggregates is economically necessary but has historically not been extensively utilized. Research is needed to establish guidelines for blending different fine aggregates to meet fresh and hardened concrete performance requirements. These guidelines will permit the use of new sources of fine aggregates and extend the service life of traditional deposits now facing extensive environmental and permitting pressures.

  4. Effect of the Volume Percentage of Aggregates on Performance of Portland Cement Concrete and Hot Mix Asphalt
    The cost of portland cement concrete (PCC) and HMA should decrease if more aggregate fills the volume of these mixtures, thereby requiring less of the expensive constituent - the cement or bituminous binder. The volume percentage of aggregate in a mixture is a function of gradation and maximum aggregate size. It influences "packing" and load transfer through the mixture, which affects performance. This research will develop guidelines for the design of PCC and HMA mixtures to increase the aggregate volume while maintaining or improving performance.

  5. Creation of a Performance-Based Specification for Aggregates in Concrete
    Many state DOTs are exploring or beginning to develop performance related specifications for concrete. The increasing use of warranties increases the need for these specifications. Since aggregates comprise 75-80% of the concrete, the performance of the concrete is highly dependent on aggregates. Other research has shown that new blends of high-fines aggregates in concrete work very well. These specifications must be properly written to allow maximum utilization and the most efficient use of locally available materials. This research will develop guide specifications to assist specifying agencies and material suppliers.

  6. Relate Performance Data from Existing Flexible Pavement Databases to Aggregates
    There are many existing databases containing data from many disparate sources, research programs and test sites. This wealth of information needs to be mined to assist in developing performance-related specifications. It has long been the ultimate objective within the pavements community to identify performance measures and then develop specifications that are based on performance. The data to statistically support this development appears to exist in the databases and need to be examined.

  7. Evaluate Mineral Filler for Use in HMA and Stone Mastic Asphalt (SMA)
    Excess fines accumulated during production are a major issue facing the aggregates industry. One possible solution is to increase the use of these fines as mineral filler in asphalt mixes. Mineral filler is known to improve performance of asphalt in many instances. Research is needed to understand how increased quantities of mineral filler affect performance of standard HMA and SMA. Mineral filler plays an especially key role in SMA mixes. There are several competitive materials used for this application. Aggregate fines need to be characterized and evaluated for use as mineral filler in this growing market.

  8. Statistically-based Quality Control Plans for Production and End Use
    Good quality control (QC) plans improve the quality and consistency of the final product. Many agencies are moving to warranty and other contracting measures as a means of rewarding or penalizing contractors. Statistically based QC plans are needed for the aggregates industry to both insure quality products and to counter false claims.

  9. Aggregates Phase and Gradation Changes in the Ignition Oven
    Aggregates obtained from a HMA sample, using the ignition oven to extract the bitumen, may have undergone physical changes due to high temperatures in the oven. Gradations run on these extracted aggregates may give results that do not reflect the actual gradations at time of construction. If these false results are used for QC or QA purposes the aggregate may be erroneously penalized. While this is a critical need, the equipment manufacturers may be close to solving this problem. If so, this issue will no longer need to be researched.

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