Effects of temperature and stress on the short- and long-term compressive behavior of expanded polystyrene

The short-and the long-term compressive behavior of an expanded polystyrene (EPS) geofoam were both evaluated to assess the effects of temperature and stress. The short-term compressive strength decreased bi-linearly as temperature increased with a transition point at the temperature of 43 degrees C. For the long-term compressive creep behavior, three accelerated creep test methods were used in the evaluation: stepped isothermal method (SIM), time-temperature superposition (TTS), and time-temperature-stress superposition (TTSS). The results from these three tests were compared with that of the conventional creep test at room temperature. Due to the 43 degrees C transition in the short-term compressive strength, the predicted creep strains from SIM and TTS, employing a higher temperatures than 43 degrees C, were found to be much higher than those from the conventional test. Furthermore, the activation energies were significantly different at temperatures above and below 43 degrees C. On the other hand, the creep strains predicted from the TTSS tests were similar to those from the conventional method. The TTSS tests employed test temperatures below 44 degrees C. Instead of using elevated temperatures, higher stress levels were used to accelerate the creep. A modified four-parameter Weibull model was developed to predict the linear and non-linear creep behavior, and a good agreement was found with test data from TTSS and the conventional method.