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CHAPTER 4
Simple Performance Test Specimen
Fabrication System
4.1 Recommended Standard device was developed to simplify and automate test specimen
Practice for Performance Test fabrication for the SPT. Based on a thorough specimen size
Specimen Fabrication and geometry study conducted during NCHRP Project 9-19,
the required test specimen for the SPT is a 100 mm (4 in.) di-
A recommendation made by several reviewers of AASHTO ameter by 150 mm (6 in.) tall cylindrical specimen that is cut
TP62 was that the test specimen fabrication procedures should and cored from a larger 150 mm (6 in.) diameter by 175 mm
be removed from AASHTO TP62 and moved to a separate (6.9 in.) gyratory specimen prepared in a Superpave Gyratory
standard practice so that additional guidance on specimen Compactor (4). The specimen size, 100 mm (4 in.) in diam-
fabrication could be provided. Since NCHRP Project 9-29 was eter with a height to diameter ratio of 1.5, is needed to ensure
developing equipment for specimen fabrication, it was logical that fundamental material properties are measured in the
that a recommended standard practice of performance test SPT. The test specimen is sawed and cored from a larger
specimen fabrication be developed by the project team. The gyratory compacted specimen to minimize air void gradients
resulting practice is contained in Appendix A. Major items in the specimen, and to provide smooth sides for attaching
addressed in this practice include: instrumentation and flat, parallel ends to minimize end
effects during testing. Specimens prepared in the Superpave
· HMA mixture preparation; gyratory compactor have higher air void contents near the
· Over-sized gyratory specimen preparation; ends and circumference of the specimen.
· SPT test specimen preparation; Test specimen preparation for the SPT is a multi-step
· SPT test specimen air void content; and process. Appendix A presents a draft standard practice for
· SPT test specimen storage. preparing SPT test specimens. First, tall gyratory specimens
must be prepared to an air void content that is 1 to 2 percent
The recommended practice also includes two important higher than the desired air void content of the test specimen.
appendices that provide additional guidance for preparing SPT During this step, it is critical that the mold be loaded in a
specimens. The first is a procedure for obtaining the target air manner that minimizes segregation in the specimen. Next,
void content for specimens from mixtures that the technician the 100 mm (4 in.) diameter test specimen must be cored
is not familiar with. This procedure was developed at Arizona from the larger gyratory specimen. Finally, the test specimen
State University during NCHRP Project 9-19. The second is cut to the appropriate length by sawing approximately 12.5
appendix provides a method for evaluating the uniformity of mm (1/2 in.) from each end of the specimen. During the cor-
air void contents within SPT test specimens. The appendix is ing and sawing operations, it is critical the test specimen be
intended help identify the gyratory specimen height that yields properly clamped and the cutting be performed at the proper
the most uniform air voids for a given laboratory. rate to ensure a smooth specimen with flat parallel ends is
prepared.
In evaluating the specimen preparation process, it was
4.2 Automated Specimen
determined that an automated system for coring and sawing
Fabrication Equipment
the specimens would be beneficial to the future implementa-
The remainder of this chapter documents the development tion of the SPT. Such a system would reduce the amount of
of the automated coring and sawing device for the SPT. This skilled labor needed to prepare test specimens. It also would
