The Long Term Pavement Performance (LTPP) SPS-2 experiment for Rigid Pavements is the largest and most comprehensive concrete pavement research program undertaken in the world.

The pooled fund project will be concluding in October of this year, and in recognition of the value of this research, Larry Scofield provides a look back at the research and its major results.

Fourteen states constructed SPS-2 experiments, which consisted of 12 core test sections, along with optional additional sections of interest to the respective state, at each location. The SPS-2 projects were constructed between 1992 and 2000 and 64 % of the original 207 test sections are still in service.

The experiment evaluated the effects of five design variables on plain jointed dowelled concrete pavement:  Specifically, thickness, flexural strength, lane width, base type, and drainage. In addition, climatic region and subgrade soil were also evaluated.  Comprehensive materials testing and rigorous performance monitoring occurred from cradle to grave.

In 2013 seven states (AZ, CA, CO, GA, KS, NC, WA) formed a pooled study to investigate creating a SPS-2 preservation experiment to extend the life of the original experiment. The Washington DOT was the lead state for the pooled fund.  As the experiment evolved, it was realized that it would be useful to compare the predicted performance to the actual performance of each test section. With the advent of AASHTO’s PMED software, it is now possible to compare the predicted performance assumed by the design, to actual in-service performance. Table 1 indicates the many investigations that have occurred during this study.

The pooled fund contracted with NCE in 2015 to conduct the SPS-2 research. As part of the pooled fund effort, NCE participated in all the SPS-2 Tech Days held at many of the sites. ACPA will be adding highlights of the research program to our website soon.