Construction Cycle 2 (CC-2) Test Strip (PCC)
Prior to full construction of the CC2 test items, a PCC test strip was constructed to study the effects of slab size and mix design on pavement curling during early age of the concrete. This study was motivated by the observation that most of the concrete slabs constructed in Construction Cycle 1 (CC1) had exhibited significant curling and premature corner breaks under traffic. Factors such as concrete mix, slab size, and curing procedure were examined for their potential in mitigating curling. Experience gained was to be applied to the placement and curing of the new concrete test items over the medium strength subgrade.
This test strip replaced part of the existing CC-1 portland cement concrete (PCC) test item over the low-strength subgrade. The existing test item had consisted of three lanes of 20 ft. by 20 ft. concrete slabs. The slabs in the south and center lanes were removed and replaced with the new slabs. The underlying econocrete (P-306) subbase was retained during their construction. Four new 15 ft. by 15 ft. slabs and two new 20 ft. by 20 ft. slabs were installed in a continuous placement in each of the south and center lanes. A three-aggregate concrete mix was placed in the south lane. A two-aggregate mix, similar to the one used in the original CC-1, was placed in the center lane. A formed longitudinal joint, reinforced with steel dowels, provided the boundary between the north and south lanes. Saw-cut grooves provided the transverse boundaries between slabs. As temperatures dropped during the winter months, the grooves induced cracking, forming joints at the slab boundaries. The slabs were covered with burlap and wet-cured for 28 days. The concrete was placed in November, 2001.
Following the curling study, landing gear load tests were conducted under static, slow roll, and traffic conditions. Traffic tests started March 18, 2002, and were completed on April 11, 2002.
More than 200 sensors were embedded in the test slabs for data collection. The sensors were of two types, static and dynamic. Static sensors were used to monitor temperature and moisture. Moisture sensors existed in the subgrade from CC-1 and were re-used. Experimental vibrating wire strain gauges and resistance crack indicators were also part of the static system. Dynamic sensors measured concrete strains and pavement deflections. Test vehicle operations triggered data retrieval from the dynamic sensors at an increased sampling rate. Sensor data collected during both traffic and non-traffic time periods were processed and stored in a computer database maintained on-site. The database is searchable online using the tools below.
Summary of Daily Traffic Repetitions
The traffic data for flexible and rigid pavement test items are available. Daily and monthly traffic repetitions, as well as current traffic totals, are given for each test item. It is strongly recommended that users consult this table to become familiar with the trafficking history before searching the static and dynamic data.
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