The Long Term Pavement Performance (LTPP) SPS-2 study, or Strategic Study of Structural Factors for Rigid Pavements, represents the most comprehensive set of concrete pavement performance data in the United States, according to a report by Larry Scofield, P.E., IGGA/ACPA.  Scofield has been studying and evaluating the SPS-2 pavements, and has prepared a brief report that shows some interesting details about the pavements that comprise the LTPP test sections.

Map show states constructing SPS-2 projects (and year of construction). The pavement design features evaluated are: concrete thickness (8” and 11”); base type; flexural strength; lane width, and drainage.

Scofield reports the SPS-2 experiment consists of 12 LTPP test sections constructed in each of 14 states ranging in age from 15 to 23 years (2015), with the first project constructed in Kansas in 1992.  The original experimental design for the SPS-2 experiment consisted of 192 test section, but only 120 (63%) were constructed.  This will hinder future statistical analysis to some degree.  

Four states constructed replicated sections of the original design, thereby producing 48 additional test sections.  Of these, three states are in the wet-freeze zone and one state is in the dry-freeze zone.  This resulted in a total of 168 SPS-2 test sections.  In addition, 40 state supplemental sections were constructed and evaluated for a total of 208 sections.

  • Of the original 144 SPS-2 core test sections constructed, 83% (119) of the test sections are still in service after 16 to 24 years of traffic.
  • Of the original 40 SPS-2 State Supplemental test sections constructed, 90% of them are still in service after 16 to 24 years of traffic.
  • Of all the SPS-2 test sections constructed (core and supplemental) 84% are still in service after carrying traffic for 16 to 24 years.
  • The SPS-2 experiment has a higher percentage of surviving sections than any other SPS project. 
  • Since 84% of the SPS-2 test sections are still in service after 16 to 24 years of traffic, the experiment has outperformed all other LTPP experiments, providing evidence of concrete pavement’s long-life characteristics and the potential to sustain heavier axle loads than currently designed for.