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75 that passes the 4.75-mm (No. 4) sieve and is retained on appears to be no relationship between LA abrasion and the 2.36-mm (No. 8 sieve). It does not appear that any long-term abrasion or wear of the pavement surface. of the current consensus property tests can be used to LA abrasion is specified by 96% of responding agencies. address this size fraction. A maximum LA abrasion loss of 40% is the most com- Uncompacted voids in fine aggregate, AASHTO T304, mon specification level. appears to be a reasonable screening test for fine aggre- gate blends. Numerous other tests have been investi- gated, but to date none consistently show a better rela- 6.2.2 Sulfate Soundness tionship with performance. Of agencies that specify AASHTO T304 or an equiva- The research revealed the following about sulfate soundness: lent, 51% have adopted the specification criteria recom- mended for the Superpave mix design system; 21% of Of the responding agencies, 66% specify sodium sul- state agencies specify more stringent criteria. fate soundness and 31% specify magnesium sulfate There are materials with uncompacted voids contents in soundness. the range of 43% to 45% that test as false negatives. A maximum sodium sulfate soundness loss of 12% is These materials have a demonstrated history of field specified by the majority of the agencies using that performance under high traffic even though they do not procedure. meet the uncompacted voids content specifications for Magnesium sulfate soundness loss and micro-deval abra- high traffic. sion loss are highly correlated. The micro-deval test is Research should be conducted to relate the CAR test to also related to abrasion of particles in the pavement. the rutting performance of HMA. Borderline aggregates The micro-deval test is more precise than the sulfate that fail the current fine aggregate uncompacted void soundness tests. content specifications for high traffic but that provide The micro-deval test should replace sulfate soundness good performance should be investigated in-depth as test for measuring aggregates' resistance to abrasion, wet- part of this study. ting and drying, and slaking. Research may need to be Of state agencies, 46% continue to limit natural sand conducted to identify specifications for specific aggre- content by specifications. Limits between 10% and 15% gate types, similar to those used by Ontario. are most common. States prone to freeze-thaw cycles should consider a freeze-thaw test, such as AASHTO T103, in addition to the micro-deval abrasion loss 6.1.4 Sand Equivalent No recent research has been able to corroborate the rela- 6.3 GRADATION tionship between clay-like particles, identified by the sand equivalent test, and moisture damage in the laboratory. How- The restricted zone--included in the original Superpave ever, the phenomenon that produces this type of failure may mix design system--was demonstrated to be unnecessary. It be difficult to duplicate in the laboratory. has been removed from most current Superpave specifications. The methylene blue value appears to be a better indicator Accelerated testing at the 2000 NCAT Test Track indicates of harmful clays in fine aggregate than is the sand equivalent no difference in the rutting performance of coarse-graded ver- test. There is concern by some agencies that the test is not sus fine-graded Superpave mixtures. suitable for routine specifications. 6.4 AGGREGATE PRODUCTION 6.2 SOURCE PROPERTIES Following are the conclusions reached regarding source Following are the conclusions reached regarding source properties: properties. In addition to crusher type, aggregate particle shape can be improved by 6.2.1 LA Abrasion Running the crusher with a full or choked feed cavity to promote interparticle crushing. The research revealed the following about LA abrasion: Operating crushers in closed circuits where a recircu- lating feed can be used to fill the crusher cavity. LA abrasion is related to aggregate breakdown during Reducing the reduction ratio, reducing the feed size, handling, mixing, placement, and compaction. There or increasing the circulating load.