EVALUATION OF SMA USED IN MICHIGAN (1991). NCAT REPORT

Stone Matrix Asphalt (SMA) is a new technology that has recently been imported from Europe to the United States. SMA typically consists of a high concentration of coarse aggregate along with high filler content, high asphalt content and some additive such as cellulose or mineral fiber to prevent drainage of the asphalt cement. SMA has been used in Europe for a number of years and has proven to be a cost effective mixture for high traffic volumes. It was initially used to resist abrasion from studded tires but has been used in the last few years to provide greater rutting resistance. SMA does cost more initially but the additional cost is offset by improved performance. It is too early to estimate the cost of SMA in the U.S., but the price should reduce as more and more SMA is placed and as contractors become familiar with handling this new mixture. In the Summer of 1991, five states placed SMA sections. These five states were Michigan, Wisconsin, Missouri, Georgia, and Indiana. Since there has been very little testing of SMA mixtures in the U.S., it was difficult to select the optimum asphalt content for the SMA mixture for the projects in these states and it was also difficult to estimate performance. The objective of this study was to evaluate the sensitivity of SMA mixture properties to changes in proportions of various mixture components. This study was performed using the same materials and job mix formula as that used in the Michigan project. The mixture components that were varied to evaluate sensitivity included amount of cellulose (Arbocel), asphalt content, percent passing the No. 4 Sieve, and percent passing the No. 200 Sieve. The properties used to evaluate the effect of these changes included tensile strength, Marshall stability, flow, Gyratory Properties (GSI, GEPI, and shear stress to produce 1 degree angle), resilient modulus, creep, and physical properties including voids, voids in mineral aggregate, and voids filled. This was a limited study using one aggregate, one asphalt cement, and one additive. The results of this study are useful in identifying trends, problem areas, and for providing preliminary guidance. Care must be taken in using the results to make general statements about SMA. Briefly, conclusions and recommendations are as follows: (1) the HMA performed better than the SMA in most laboratory tests; (2) the addition of fiber had little effect on the VMA (voids in mineral aggregate) and the optimum asphalt content; (3) the best way to increase the optimum asphalt content is to lower the percent passing the No. 4 Sieve; (4) the performance of SMA mixtures in the laboratory is significantly affected by the aggregate gradation which indicates that very close control of the aggregate gradation during construction is required; (5) the SMA mixtures had much lower tensile strength values (indirect tensile strength and resilient modulus) than the HMA mixture; and (6) the gyratory shear stress to produce one degree angle is the one test that the SMA mixture generally performed better than the HMA mixture.

Language

  • English

Media Info

  • Features: Figures; References; Tables;
  • Pagination: 41 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00666279
  • Record Type: Publication
  • Report/Paper Numbers: NCAT Report No. 93-3
  • Files: NTL, TRIS
  • Created Date: Sep 27 1994 12:00AM