PHASE II REPORT - Caltrans

The shape of the traces for different configurations of mix container and stirrer did vary. In
addition, for some configurations, differences in torque were observed. Some configurations
produced poor mixing and hang up on the sides of the mixing containers. As a result, the mix
tends to break and the mixer had less material to turn. The endpoint of the mixing was
characterized by a decrease in torque (torque fall off) due to the mixer effectively turning in the
liquid left after the mixture broke. These tests were rejected and classified as poor mixing. The
best results were obtained with the combination of the small stainless steel bowl and the
standard propeller. Part of this testing was repeated with mix M4 and the results were
consistent with the previous findings and are noted in Table 4.4. An interesting observation was
that the mixes that contained the emulsion E2, continued to mix in excess of 10 minutes but
broke as soon as the mixer was turned off. This is a phenomenon often observed in the field
and is a function of the film formation process created by aggregate/emulsifier interaction. The
mechanical action appears to prevent coalescence by disrupting film formation; when the mixer
was turned off, coalescence proceeded swiftly, and the cohesion increased as a result. In CQS
type systems, the films form during agitation and cohesion build up is more gradual. As this is a
function of interaction of two materials it depends on both. As it is a function of reactivity, it is
also dependent on the conditions of temperature and as water will interfere with coalescence
and film formation, it is dependant on humidity and total water content.
The two configurations that produced best mixing results were: the standard propeller with the
small stainless steel bowl, and the large anchor stirrer with the large stainless steel bowl.
Table 4.4: Mix M4 Stirrers and Mixing Containers Combinations and Results
Stirrer Cup Type Speed rpm Mixing Result
Large Anchor Large SS Bowl 50 Adequate Mixing (AM)
Large Anchor Large SS Bowl 60 Adequate Mixing (AM)
Standard Propeller Small SS Bowl 50 Good Mixing (GM)
Standard Propeller Small SS Bowl 60 Good Mixing (GM)
The characteristic mixing trace of the large stainless steel bowl and large anchor configuration is
shown in Figure 4.8. This trace indicates that the system did not mix well, and as the material
broke, the segregation was of liquid to the center of the bowl. This trace was not indicative of
mix M4 actual behavior.
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