PHASE II REPORT - Caltrans

3.6.2 The European Mixing Test
Based on the test evaluation criteria presented in Section 3.2 of the report (Technical
Approach), ISSA TB-113 was proposed for use as a basis to determine the mixing time. The
test can be used as a very good indicator of compatibility of the mix components as well as to
estimate the available mixing time for the slurry system. However, the test is highly variable,
largely because:
• stirring (mixing) is carried out by hand and will vary to one operator to another
• the assessment of the viscosity of the mix is also subjective and will be different from
one test operator to another
As an alternative, a more rational, automated test procedure was needed. The project team
considered the European mixing test, which was later called the Automated Mixing Test or AMT.
In this test, the slurry system components are mixed in a cup similar to the one used in TB-113.
However, mixing is carried out with an automated motor. The device measures changes in
viscosity (torque) with time, during the mixing process, and is shown in Figure 3.2. In Figure
3.3, a schematic of the device and its components are shown.
The test can be used to determine a mixability parameter (cohesion limit where coating occurs
to >95 percent) and a workability parameter (a cohesion value where the mix will still flow).
These can be defined by observing the consistency and be quantified by the cohesion value
and shape of the mixing curve. An example of this curve is provided in Figure 3.4. These
parameters could be measured over a range of shear values, temperatures, and other
parameters.
The mixing test uses a torque transducer to measure stiffness of a mix and it is similar to TB-
106. However, the test method is computerized and standardized and has been under
development in Europe for a decade.
18