To convey the significance of the Reflective Cracking Rig, it is necessary to explain the scale and parameters of its function. A helpful starting point is with the Texas Overlay Tester.
The Texas Overlay (TO) Tester is a small-scale laboratory instrument – approximately 5 inches (12.7 centimeters) wide by 7.4 inches (18.8 centimeters) long - that mimics the movement of a crack at the bottom of a hot mix asphalt layer, allowing researchers to evaluate the performance of asphalt mixtures.
The TO apparatus tests asphalt specimens that are 3 inches (7.6 centimeters) wide by 6 inches (15.2 centimeters) long. Specimens are glued to a set of base plates with half the length of the sample resting on each plate, as shown in Figure 1. One of the base plates remains fixed and one moves horizontally to simulate the opening and closing of a crack or joint.
Figure 1. Texas Overlay with test specimen
[Testing in the scale of inches]
The Reflective Cracking Rig in the NAPTF essentially translates the testing capabilities of the Texas Overlay from the scale of inches to feet! ATR’s indoor test rig emulates the Texas Overlay test at a full-scale and simulates reflective cracking due to temperature changes to the pavement. This testing machine consists of two 15 feet by 15 feet concrete base slabs set in metal trays, one fixed and the other able to move horizontally, to simulate the opening and closing of a crack or joint. The enhanced scale of the rig allows researchers to move, test and assess the performance of asphalt overlays on a real-world scale; as opposed to the inches long fabricated specimens tested on the Texas Overlay Tester. The Reflective Cracking Rig is also temperature controlled through a network of hundreds of feet of tubing embedded in the concrete slabs. The tubes connect to an exterior cooling unit that keep the asphalt – concrete interface at 32 degrees (0 degree Celsius) and makes the asphalt more brittle.
Figure 2. Reflective Cracking Rig
[Full scale testing]
Figure 3. System of cooling tubes installed under the concrete slabs