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Clamping Pressure 200Kpa<br />
Interface of foot with sample—this is<br />
rubber. Part of the process will use<br />
different surface types on the foot to<br />
improve grip and reproducibility.<br />
Motorized gear shifts shaft through 90º. Allows precise<br />
application of twisting torque to measure resistance to shear<br />
force.<br />
Torque measurement taken at base close to interface. This<br />
will prevent bending in the shaft to influence results.<br />
Electronic torque (strain gauge) measurement will transmit<br />
to PC for display.<br />
22<br />
PC will display spread sheet to include torque<br />
time graph and calculation of peak torque.<br />
PC<br />
Figure 3.6: Schematic of the Initial Automatic Cohesion Test Method<br />
The Hilt test was also considered for measuring cohesion, but was rejected for the mix design<br />
due to reported repeatability issues.<br />
3.6.4 The Cohesion-Abrasion Test (CAT)<br />
Another test that was investigated in more detail by the team is a modified version of the Wet<br />
Track Abrasion Test (WTAT), ISSA TB-100. Although not listed in Table 3.5, the modified<br />
WTAT can be used on test samples similar to those for the wet cohesion test to evaluate the<br />
increase in strength of a slurry system in the period after placement and before opening to<br />
traffic. The CAT test is the modification to the WTAT. They are two separate tests and we are<br />
recommending the CAT. He named it CAT since it is significantly different from the WTAT.<br />
As shown in Figure 3.7, the modification consists in the use of a set of wheels instead of the<br />
standard abrasion head. Abrasion loss and short-term stone retention may be measured in this<br />
test. The test may be performed under different cure conditions to determine the effect of early<br />
water intrusion due to rain. Development of this test method is described in detail in Chapter 4.<br />
Results from this test can be used to establish a limit for stone retention with respect to cure at<br />
time and conditions. Samples should be cured under the following three laboratory conditions:<br />
• Laboratory “standard” conditions 77°F (25°C), 50 percent relative humidity).<br />
• Oven at 140°F (60°C).
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