In asphalt paving, especially for structural maintenance measures, reducing the length of these cooling periods makes sense both from a traffic point of view and economically.
To do this, the placed asphalt layer must have sufficient resistance to deformation to allow it to be reopened to traffic.
To determine the required and sufficiently long cooling time, it is not sufficient to simply measure the surface temperature of the poured asphalt layer.
The surface temperature often deviates significantly from the internal temperature of the asphalt layer due to weather related problems.
The earlier determination of the reopening time to traffic depends on the improvement of the resistance of the poured asphalt layer to deformation during the cooling stage.
This requires measuring the deformation behavior of the asphalt layer continuously during the cooling phase.
According to the publication titled “Notes on reopening asphalt pavements to traffic” (2022) published by the Road and Transportation Research Association of Germany (FGSV), depending on the deformation behavior of the laid asphalt base layer determined by the Light Weight Deflectometer (LWD), a section of the road is blocked to traffic. A method has been identified in which an earlier time to reopen can be derived and the use of LWD instead of known fixed cooling times is more effective.
For this purpose, Zorn Instruments completed the production of the modified LWD AT 2.0 Asphalt Tester, the prototype of which has been developed since 2010, this year. The revolutionary ZORN Asphalt Tester can be used alternately for the following test procedures:
- "Additional notes on the opening of asphalt pavements to traffic" (H VVA), FGSV Germany, 2022
- Determination of elastic surface deformation and determination of deformation modulus Evd Asphalt (non-standardised)
The purpose of this test is to help determine the appropriate cooling time of asphalt pavements before they are opened to traffic, based on the deformation behavior of a new roller compacted asphalt surface. The test can be used in place of or in addition to known fixed cooling times.
For the evaluation of deformation behavior, a modified LWD device is used according to the principles of axial-dynamic indentation testing. Immediately after compaction, 5 consecutive load pulses are applied to the asphalt surface. Depending on the deviation and deviation differences that occur, the deformation behavior of the fresh asphalt surface is evaluated accordingly.
Working with the principle of falling weight deflectometer, the device provides compression control of the bituminous asphalt concrete between the asphalt roller.
It is suitable for wear layer, bitumen layer and surface layer testing.
It effectively complements existing control methods such as dynamic bending and tensile tests or a nuclear density and moisture meter.
The device, which can be used with a single user, is fast, secure and low cost.
During the road paving process, it reduces the waiting time.
The device makes 5 drops on a 20, 30 or 50 mm diameter plate with a weight of 10 kg.
The crash of each drop is recorded on the SD card; It can also be printed on the thermal printer on the device.
All data on the SD card can be examined with the software of the device.
Measurements can be evaluated with a linear (linear) or exponential (exponential) approach.
The modulus of deformation can be obtained in MPa or MN/m2 at a standard temperature of 20°C / 68°F.
The firmness of the asphalt layer increases as the difference in slump between one fall and the next fall decreases.
The temperature of the asphalt is a very important parameter in the calculations, so it is measured by the sensor on the device near the test point.
Drop weight: 10 kg
Drop height: 54 cm
Force: 6.28 kN
Pulse duration: 17 ms
Plate diameter: 20 mm / 30 mm / 50 mm
Temperature: °C / F
Measuring range: 500 MPa / 1000 MPa / 1500 MPa