CC2 Test Items- Test Plan

Test Background

The CC2 main test items were constructed in 2004 and tested during the period April – December 2004. The CC-2 test items replaced the CC-1 test items in the medium strength subgrade area of the NAPTF. The new items consisted of three rigid pavement types: portland cement concrete (PCC) on conventional base (MRC); PCC on grade (MRG); and PCC on the existing Econocrete stabilized base (MRS). Three existing transitions between test items were also rebuilt, and two of these were relocated. A fourth transition was built up to final grade with a thin concrete overlay. The work covered a length of 325 ft. and a width of 66 ft. Limits of the test areas were as follows: Transition 4, station 300 to 325; MRC, station 325 to 400; Transition 5, station 400 to 425; MRG, station 425 to 500; Transition 6, station 500 to 525; MRS, station 525 to 600; and Transition 7, station 600 to 625 (station numbers are in feet, measured from the origin at the west end of the NAPTF). Test item construction was completed on April 30, 2004.

Geometric Design 

Each of the three new test items was 75 ft. long by 60 ft. wide and separated by 25 ft. long rigid transitions.  The slab size was 15 by 15 ft.  There was a total of 20 slabs per test item.  The selection of the slab size was based on the results of a previous experiment conducted at the NAPTF.  The results demonstrated the reduction of corner cracking due to curling when using a smaller size slab.

Pavement Design 

The materials were selected according to FAA construction standards.  The test item built on 10 in. of conventional subbase (P-154 Uncrushed Aggregate) was called MRC, on grade MRG and on 6 in. of stabilized base (P-306 Econocrete), built during the original rigid pavement construction, MRS. All the test items were placed on a medium strength clay subgrade.  The upper 4 ft. of the subgrade were rebuilt to a target CBR of 7 under MRG and MRC.  The slab thickness of 12 in was selected as optimum to support heavy loads and fail within a reasonable time.  The design layout of the test items is presented in Figure 1. 

 

Material Properties

The target values for the material properties for the new rigid test items were as follows:

      P-501 (PCC Slab) E=4,000,000 psi

      P-306 E=700,000 psi

      P-154  E= (Variable)

      Subgrade (Clay CH) E= 10,500 psi (CBR=7)

 

The k values obtained from plate load testing for the North Wheel Track (NWT) and South Wheel Track (SWT) are presented in Table 1:

Table 1. Plate Load Test Results

 

The concrete mix laboratory flexural and compressive strengths at 28 days for the three test items are presented in Table 2.  The mix, designed for 750-psi flexural strength, contained 50% flyash class “C” in the cementitious mix.  The flyash was used to reduce the concrete strength and control curling of the slabs by allowing thicker slabs for a given pavement life.  The properties of mixes with various replacement proportions of the flash were studied previously at the NAPFT.

 

Table 2.  Test Items Concrete Mix Laboratory Strength

 

Predicted Life

The current FAA design procedures, Layered Elastic Design FAA (LEDFAA 1.3) based on layered elastic theory and the Finite Element Design FAA (FEDFAA 1.3) beta testing procedure were used to predict the number of passes to failure for the three test items under 4- and 6-wheel gear loads.  Table 3 shows the calculated life by FEDFAA and LEDFAA for the new rigid test items with Subgrade CBR 7 and 9, and the average flexural strengths shown in Table 2.

 

Table 3. Life Calculated by FEDFAA and LEDFAA

Number of Passes to Failure by FEDFAA (as configured at the time the predictions were made)


                                                                                                       Number of Passes to Failure by LEDFAA


Test Parameters

 In order to support the above objectives, the following parameters were established for CC2 testing:

 1.      Test Items

a.       General. Three new test items will be constructed on medium-strength subgrade (target CBR 7).

i.                   Test Item MRS (PCC on existing P-306 econocrete).

ii.                  Test Item MRC (PCC on P-154 aggregate subbase).

iii.                 Test Item MRG (PCC on natural subgrade).

b.      Dimensions.

i.                    All test items 4 slabs @ 15 ft. = 60 ft. wide.

ii.                   All test items 5 slabs @ 15 ft. = 75 ft. long.

iii.                  Test items separated by 25 ft. transitions.

c.       PCC Slabs

i.                   Slab nominal dimensions 15 x 15 ft.

ii.                  Target slab thickness = 11 in.

iii.                 All joints doweled (longitudinal and transverse joints).

iv.                 PCC mix: minimum 50% Cl. C fly ash replacement to reduce strength (increase design thickness). Target 28-day beam break strength = 750 psi.

v.                  28 day wet burlap cure.

d.      Traffic Load

i.                   6-wheel gear configuration on North Carriage, 54-in dual spacing and 57-in tandem spacing.

ii.                  4-wheel gear configuration on South Carriage, same spacing as six-wheel.

iii.                 Start at 55,000# per wheel.

iv.                 Run 66-position wander pattern (same as CC1). Wander pattern to be centered on longitudinal edge load position on both sides.

e.       Instrumentation. An instrumentation plan was prepared but is subject to change. The following sensor types are to be installed in each test item (typical). The test objectives that each type of instrumentation supports are indicated in parentheses:

i.                   Horizontal embedded strain gages (H-bar) (4,5)

ii.                   Surface-mounted strain gages (4,5)

iii.                  Vertical displacement transducers (6)

iv.                  Horizontal displacement transducers (4,6)

v.                   Instrumented dowel bars (4)

vi.                 Temperature sensors (thermistors) (6)

vii.                Relative humidity sensors (6)

viii.               Soil moisture sensors (6)

ix.                 Maturity meters (7)

f.       Construct a fourth test item on the high-strength subgrade if funding permits.

Monitoring

 1.      Repetitions to failure. Traffic test monitoring will be based on three observations:

 a.       Visual survey. The pavement surface will be periodically inspected for evidence of cracks, spalls and other structural distresses. Cracks will be mapped and crack maps updated regularly. Distress data will be used to compute an equivalent SCI, which then can be plotted versus coverages.

b.      HWD tests. These can be used to track deterioration in support conditions and/or loss of joint LTE.

c.       Embedded sensors. Loss of sensors or unusual readings provide evidence of structural failure.

 2.      Failure conditions. Technically, structural failure of test items is defined in terms of the crack density. Testing will proceed until a “shattered” slab condition (slabs broken into 6 or more pieces) is observed.

 3.      Curling. Slabs will also be monitored for evidence of upward curling:

a.       Vertical displacement transducer (VDT) readings at slab corners and interiors give evidence of slab-base separation.

b.      Visual observation of slab displacement or rocking under wheel load.

c.       HWD testing.

Please refer to the document links below for additional Test Plan information and documentation

Thickness Design for CC-2 12 Inch Slab

CC2 Proposed Cont Traffic

Design Cross Section (Test Area Diagrams)

MCR Revised Plan