Early Age Behavior

The service life of PCC pavements is highly dependent upon their early-age behavior. Rigid pavements are significantly affected by temperature and moisture changes during the first 72 hours following placement. Stresses in the PCC build up primarily due to the combined effects of curling and warping and restraint to axial movements at the slab-subbase interface. These stresses may be of sufficient magnitude to cause cracking because PCC strength is relatively low during this early-age period (see Figures 1 and 2). Pavement stresses during this time are extremely important to long term pavement performance.

The FHWA and the Transtec Group, Inc. have produced a software package, termed HIgh PERformance PAVing (HIPERPAV), that is capable of assessing the influence of mix design, structural design, construction methods and environmental conditions on the early-age behavior of rigid pavements. HIPERPAV was originally produced for an FHWA study of fast-track rigid pavements. The goal of this project was to develop high early strength rigid pavements that could be rapidly opened to traffic upon construction completion. What this project discovered was that rapid-setting high early strength PCC created a new set of concerns including: uncontrolled slab cracking, spalling and excessive plastic shrinkage. HIPERPAV addresses these issues and others by modeling early-age PCC pavement performance (Figure 1).

Figure 1. PCC early age crack in Palmdale, CA.

Figure 2. Close-up of early age crack.

Figure 3. One output of HIPERPAV showing early age tensile strength vs. time (screen shot courtesy of Transtec Group, Inc.)