Pavement Construction/Cross Section

Pavement Construction/Cross Section

This CC2 test strip replaced part of the existing CC1 Portland Cement Concrete (PCC) test item over the low-strength subgrade. The CC1 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.

The plan called for careful removal of the existing cracked concrete slabs and placement of new 28 cm (11-inch) thick PCC slabs on the existing econocrete subbase. Both the 6 x 6 meters (20 x 20 feet), the size of the original slabs, and the 4.5 x 4.5 meters (15 x 15 feet) test slabs were constructed to evaluate the effect of different slab sizes in controlling curling. The test strip south lane (slabs S) was placed on November 27, 2001, using the new optimized mix design (3-part mix). The 2-part mix, same as in the original construction, was placed in the test strip north lane (slabs C) on November 30, 2001. The layout of the test strip is shown in the Figure below.


  

 

A three-aggregate concrete mix was placed in the south lane.  A two-aggregate mix, similar to the one used in the original CC1, 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 27-30, 2001.

 

Test Strip Curing

Poor curing procedures were suspected for the early corner cracks in the original construction cycle due to the NAPTF being an enclosed facility. Special curing procedures were included in the test plan to prevent any possible curling due to lack of proper curing. The slabs in both lanes were covered with burlap for a 28-day wet cure period to fully hydrate the cement in a moist environment. Additionally, insulating blankets were placed on two 4.5 x 4.5 meters (15 x 15 feet) slabs (C1 and S1). The blankets were left in place to achieve and maintain no more than a 5 - 8 ºC (10 – 15 ºF) temperature differential between top and bottom of the slabs for the first three days. The blankets were placed to establish a favorable thermal gradient to induce the slabs to assume a “curl down” shape, thereby promoting full support at the slab corners. A layer of plastic was also placed over slabs C1 and S1 to reduce moisture loss. At the completion of the 28-day wet cure, a liquid sealing membrane was applied to slabs C1 and S1.

 

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 CC1 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 link below.


Search CC-2 Test Strip Database