Test Objective

 

Phase I: CC4 Baseline Test (July - October 2006)

Construction Cycle Four (CC-4) was an initiative of The Innovative Pavement Research Foundation (IPRF). It was undertaken to improve the understanding of the influence of design parameters on unbonded concrete overlays of airfield pavements, thus enabling improvement of design methodologies. The Baseline Experiment was developed to address the following:


  1. Overly response.
  2. Effect of underlying discontinuities on overlay response.
  3. Relative deterioration of the overlay and underlying pavement after trafficking.
  4. Deteriorations in terms of distress and structural response as compared to SCI Model.

The CC-4 pavement involved the replacement of three concrete test items, three transitions and an asphalt overlay of the CC-2 pavement extending from station 300 to 600. Removals reached a clean medium strength subgrade (DuPont Clay) about 2 ft. below the designed top surface of the CC-4 concrete overlay.


The upper 10 inches of the subgrade were conditioned to an average CBR of 8.0 at an average moisture content of 29.8%. Similar values were obtained for the conditioning of a number of the subgrade lifts below during CC-2.


A P-154 granular base course was placed and compacted between stations 300 to 600. A 6 inch thickness was targeted except between stations 500 and 575 (Test Item 3) where the thickness was designed to be 5 inches. An average compaction level of 94.9% was achieved at an average moisture content of 4.6%.

The underlying concrete layer was placed on the base course at the full 60 ft. width of the pavement. Joints forming the individual slabs of the test items were established by saw cutting.


The concrete overlay was similarly placed. The joints between the overlay slabs were initiated by partial saw cuts through the layer thickness. The overlay slabs measured 12 ft.-6 ins. by 12 ft.-6 ins. with the exception of the slabs at the pavement centerline which measured 12 ft.-6 ins. by 10 ft. Steel dowels were set in place connecting the joints between slabs and between slabs and transitions. The 10 ft. transverse joints of the centerline slabs were not doweled.
An asphalt interlayer of from 1 to 2 inch thickness separated the overlay and the underlying layer. Concrete slurry from saw cutting the joints of the underlying layer was used as a parting agent between the underlying layer and the asphalt interlayer assuring an unbonded condition for the overall rigid on rigid pavement.

Many of the joints between slabs in the underlying layer were designed to be displaced and mismatched relative to the joints between slabs in the overlay. These conditions of discontinuity simulated a deteriorated underlying pavement layer.


The test pavement consisted of Transition 4, station 300 to 320; Test Item 1, 9 inch overlay above a 6 inch underlying layer, station 320 to 395; Transition 5, station 395 to 410; Test Item 2, 71/2 inch overlay above a 71/2 inch underlying layer, station 410 to 485; Transition 6, station 485 to 500; Test item 3, 6 inch overlay above a 10 inch underlying layer, station 500 to 575; and Transition 7, station 575 to 600.

A total of 270 sensors were embedded in the test pavement for data collection. The sensors were of two types, static and dynamic. There were 240 dynamic sensors and 30 static sensors. The breakdown was as follows:


Subgrade
Dynamic Static
5 Soil Pressure Cells (SP's) 3 Thermocouples (TC's)
  4 Soil Moisture Sensors (SM's)

Underlying Layer
Dynamic Static
20 Linear Position Transducers (LPT's) 3 Thermistor Trees (TH's) (3 sensors each)
40 Embedded Strain Gages (EG's) 5 Thermocouples (TC's)

Overlay
Dynamic Static
65 Linear Position Transducers LPT's) 3 Thermistor Trees (TH's) (3 sensors each)
36 Embedded Strain Gages (ESG's)  
54 Surface Strain Gages (SG's)

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 facilitated review of the data for analysis at a later time.