Menu Close

The ZORN AT is currently the world’s most modern instrument for the evaluation of the quality of the compaction of asphalt and for determining the suitability for traffic of asphalt layers.

With the “Hinweispapier frühere Verkehrsfreigabe” (information paper on early opening to traffic of asphalt road surfaces) published in 2019 by the Forschungsgesellschaft für Strassen- und Verkehrswesen e.V. (FGSV), an initial technical standard for the usage of the ZORN AT is available. The revolutionary measuring device enables the user to determine in a binding manner the suitability for traffic of asphalt layers. The paper supplements the information on waiting periods for laying binder and wearing courses stipulated in the German code for laying asphalt. The desire for shorter construction times can therefore be better addressed while safeguarding the quality of the asphalt at the same time. The inclusion in the contract of tests using the ZORN AT also helps to prevent legal problems between the contractor and client.

As a tool for the determination of the quality of the asphalt compaction on the spot, the ZORN AT is also a valuable addition to the obligatory material tests in the laboratory.

The test with the ZORN AT is based on the principle of operation of the lightweight deflectometer for soil. Like the ZORN ZFG, it is remarkably easy to use. The latest sensor technology in the ZORN AT safeguards the highest precision and repeatability of the tests, even on hardened asphalt layers.

ZORN AT design study – ZORN AT-3000 GPS


Modified lightweight deflectometer for determining the AVF value of freshly laid asphalt (binder and wearing courses) corresponding to H FVA (Hinweise zur Früheren Verkehrsfreigabe von Verkehrsflächen aus Asphalt – information paper on early opening to traffic of asphalt road surfaces).

Principle of operation:

The ZORN AT-3000 GPS is a modified Lightweight Deflectometer ZFG in the context of the information paper H FVA. The device is exactly matched to the requirements for early opening to traffic. A 10 kg falling weight generates an impact force of 6.28 kN and in this way presses a ram with a diameter of 50 mm vertically against the road surface. In this way the tester simulates the passing traffic and makes it possible to assess the resistance to deformation of asphalt layers from a surface temperature of 60 °C. The deformation of the asphalt is determined via the movement of the ram. An acceleration sensor provides precise data on the deformation and velocity of the ram. The related values flow into the calculation of a characteristic (Avf) in percent. The ZORN AT-3000 GPS makes this calculation automatically for each test point.

Characteristic related to opening for traffic:

The surface deformation initially includes elastic and irreversible plastic elements. Given sufficient cooling and hardening of the asphalt, these reach a minimum value of 0.2 mm and are exclusively elastic. An asphalt surface is considered safe for traffic if all stipulated test points have reached Avf= 100%. The test method is suitable for binding and wearing courses. Experience with Stone Mastic Asphalt (SMA) and other asphalt types is available for the ZORN AT-3000 GPS.


During the re-surfacing of heavily used asphalt roads, there is an increasing requirement for reduced cooling times and the possibility of opening the road to traffic earlier. Although the applicable standard in this situation, ZTV Asphalt-StB, permits in principle a reduction in the standard time limits (24/36 hours), a reduction can involve contractual uncertainties. A working group of the Forschungsgesellschaft für Straßen- und Verkehrswesen (FGSV) prepared the “Hinweise zur Früheren Verkehrsfreigabe von Verkehrsflächen aus Asphalt” (information paper on early opening to traffic of asphalt road surfaces) (H FVA) about this issue. The document helps clients and contractors alike to set the boundary conditions for construction measures such that legally water-tight early opening to traffic is possible. There is no contradiction between reduced construction time and high quality here. The basis for this reduction is the testing of the asphalt laid and compacted using the ZORN AT-3000.

Technical features:

  • Round test ram Ø50 mm with high-performance acceleration sensor
  • Modified loading device with 10 kg falling weight
  • Calibrated impact force 6.28 kN
  • Robust electronics box with integrated printer and GPS
  • Rechargeable battery for the mobile supply of power (including 12 V charging cable)
  • Software ZORN FGVF
  • Two lightweight cases for safe transport and storage of components
  • Temperature sensor


–    Device in use for testing (without packaging)

o Weight:  42.0 kg

o Height:       120.0 cm

–    Carrying Case (without measuring device):

o Weight: 12.6 kg

o Height:      100 cm L x 31 cm W x 31 cm H


–    Duration of the testing per testing position (approx.): 1 minute
–    Automatic data acquisition and calculation of the characteristic
–    Indication of individual deformation per test impact
–    Automatic calculation of the characteristic for opening to traffic AVF
–    Automatic storage and transfer of the test results via SD card.
–    Wireless data transfer to a PC (WiFi) optional
–    User interface languages: German/English