Ncat Completes Two National Studies on Sma and Superpave

The National Center f’or Asphalt Trchnolofiy (NCAT) has just complctd two Nation;ll Coopwrrive HicThw:tv Rr<e:lrch Pq!ram (NtHR6) Projects: NCHRP 9-X. “Designing Stone Matrix Asphalt (SMA) Mixtures.” and NCHRP 9-9. “Reilnement of Superpave Gyratory Compaction Procedure.” Dr. Ray Brown. NCAT director. was the p r i n c i p a l invcsti:etor on both pmjects. The fint project on SMA represented ;I XI million. Ihwyeclr research effort. SMA i?, detined ;1s 3 gap-graded hot mix asphalt (HMA) that maximizes the a\phalt cement content and coarse qprepte frz&on. This provides il \tahlc htonc-on-ctonc skclctal StwcttIw held together hy il rich mixture of asphalt cement. filler. and stabili/inf asent. SMA has hssn used in Europe for murc than 25 years to providr :I tlur;~hlr ;~nd rllr-resistant pwcment. Within the l!nited States. SMA hns been tlszd succ~~slully since 1991 OII numerous p a v e m e n t s \uhJ”tcd to high tl-afflc VOlUlllr. heavy whrzl load?. and high tire pressures. Some \tatec routinely use S M A even though a n~ltionrllly ;lccepted mixnIrc design proced~~re has not been abailable until now. Generally recipe type !,pKzifica1iona are used for SMA in Europe. If a food mixture design procedure is dweloped and adopted. it should he possible to improve the perfotmance of SMA. The primary ohjcctivc of this project w,s todevelop;r straightforward. sr;~nd;~rd mix design procedure for lconrirlurd 011 ,Mg’ 2) In This Issue