Laboratory Batching Procedure Corrected for Fines and Moisture

Abstract

A key step in mix design is the selection of an appropriate aggregate structure since this affects mix performance and the amount of asphalt in the mix. This paper explores the effects that fines adhered to larger particles have on the batch gradation and the resulting optimum binder content and dust proportion. It shows that conventional batching procedures can produce gradations with a substantially larger percent passing the sieve No. 200 relative to the target gradation. A batching procedure that corrects for fines adhered to larger particles and trapped moisture is proposed and shown to replicate the target gradation. Asphalt content was determined using the superpave method for both a gradation batched conventionally and a gradation batched with the corrected procedure. It is shown that the asphalt content and volumetrics obtained in both cases are substantially different. To obtain more-representative batch gradations, the corrected procedure is recommended for routine batching of specimens. Further research is recommended to assess potential changes in mix design criteria and effects on performance tests.