✓ Pass/Fail medium temperature original binder test (T315-11)
✓ Pass/Fail high temperature RTFO binder (T315-11)
✓ Pass/Fail high temperature PAV binder (T315-11)
✓ Linearity test (T315-12)
✓ Grade determination test (R29-02)
✓ Optional research grade software
Multi-Stress Creep and Recovery Test (MSCR)
Is a relatively new method for testing asphalt binders which is performed on the Dynamic Shear Rheometer CRT-DSRII. The test applies to both modified & neat (unmodified) asphalt binders, with results relating to both rutting characteristics and the effectiveness of elastomeric modification. This method is detailed in AASHTO TP 70-09
Maximized Sample Throughput
For QC testing, sample throughput is of paramount importance. Therefore, every feature of the Dynamic Shear Rheometer CRT-DSRII design has been implemented with the goal of minimizing the time required to make each measurement. This includes loading the sample through to reaching thermal equilibrium, collecting the data and finally cleaning the unit. For example, the CRT-DSRII has been designed with measuring systems and gap setting which eliminates much of the operator time required when using conventional or modified general purpose rheometer units. Additionally, CRT-DSRII’s temperature control system offers rapid thermal equilibrium as well as extremely stable control. In practice, for the overall test sequence, the CRT-DSRII achieves up to three times the throughput of a conventional rheometer.
Temperature Control – patented design
Bituminous materials are extremely temperature sensitive with large variations in their material properties over just a fraction of a degree centigrade. It is typical to see a 20% change in modulus for only a 1ºC change in temperature. Without accurate temperature control in a rheometer’s design, this can lead to erroneous passing or failing of AASHTO PG graded materials with potentially disastrous commercial consequences. For this reason, AASHTO specification T315-02 (6.1.2) states that temperature control may be by means of a liquid or a gas (as the heat transfer medium). By implication, this simply excludes systems which use heated enclosures to radiate heat onto the sample, where it is almost impossible to ensure the absence of temperature gradients. To fully optimize temperature control, the Dynamic Shear Rheometer CRT-DSRlI incorporates a clean and easy to use system which completely immerses the sample in a temperature controlled liquid (patented). For testing bituminous materials, the design out-performs all other types of temperature control including forced gas convection ovens and radiatively heated plates. This is because the relatively high thermal conductivity of the liquid, which is in direct contact with the sample, allows for a much better heat transfer into the test specimen – up to 25 times faster than other systems. Temperature gradients within the sample are completely eliminated and in order to achieve the required 0.1ºC specified by AASHTO, the Dynamic Shear Rheometer CRT-DSR controls the sample temperature to 0.03ºC or better. Because of the rapid heat transfer into the sample, thermal equilibrium (the time that the sample takes to react to the liquid temperature) is near instantaneous due to the intimate contact of the sample and the circulating liquid. This is important in optimizing throughput, as the long thermal equilibrium times of non-liquid based systems can mean that they take up to half an hour to properly equilibrate. This problem more than outweighs the often – and falsely – perceived benefit of the rapid set-point changes achievable with other types of control.
Gap Setting – Simple and thermally stable
The Dynamic Shear Rheometer CRT-DSRII gap can easily be changed to any desired value. For simplicity, both of the specification testing positions are clearly marked and can be easily selected. With most rheometer systems, the gap must be constantly reset during a day’s testing and must be readjusted every time the temperature or the measuring systems are changed. The DSRII addresses both of these issues, eliminating continual resetting of the gap to help optimize sample throughput and operator error. The Dynamic Shear Rheometer CRT-DSRII measuring systems are designed to be easily interchangeable. The unique coupling arrangement of the lower system together with quick fit upper systems ensure that the gap need not be reset whenever the upper or lower plates are removed or replaced. If necessary, samples can be loaded remotely onto the lower plate for convenience. On a general purpose rheometer, changes in temperature may affect the gap zero point due to thermal expansion of the measuring systems, which requires either rezeroing or the pre-programming of a motorised mechanical adjustment. To remove the need for any gap adjustments, the CRT-DSRII features automatic expansion compensation (AEC) to keep the gap constant as the temperature changes.
A Choice of Mechanical or Air Bearing
The Dynamic Shear Rheometer CRT-DSRII is offered in two forms having either a mechanical or an air Bearing. The Mechanical Bearing system offers a cost effective solution for Superpave testing and is especially suitable for applications where compressed air is not available. It exceeds all current AASHTO testing protocols. Mechanical Bearing units can also be upgraded to Air Bearing units if testing requirements change. The Air Bearing version incorporates an air bearing to the same robust design as found on research grade rheometer units. It requires a supply of compressed air and is warranted to withstand even the most adverse industrial laboratory environments. It is ideally suited to specification testing, as well as having excellent research capabilities and longevity.
The Air Bearing system used is impervious to dirt and other contaminants, as well as being extremely strong and robust.