An area with a definite shortage of mastic adjacent to the fat spot (visibly porous) is a clear sign that this is a case of an SMA segregation—namely, separating the coarse aggregates from the mastic. If the quantities of all the ingredients have been properly selected, the high accumulation of one component in one location will result in a reduced quantity of that component in another. When an excess of mastic (fat spot) appears somewhere, the coarse aggregate content rises elsewhere, so the total sum of the components remains constant. Figure 11.2 presents a classic fat spot in a segregated SMA mixture. Figure 11.3 shows the difference between fat spot and adjacent porous section and a close-up of the mastic-rich area.
It is worth emphasizing that such segregation may happen for one or more of the following reasons:
• Substandard production of an SMA mixture
• Lack of a stabilizer, its improper metering, or its poor quality
• Excessive production temperature
• Too short a time of mixing components
• Too long a storage time of a mixture in an asphalt plant storage silo
• Improper laydown of SMA (with an improper setup of a paver)
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figure 11.2 SMA mixture segregation—separation of mastic from coarse aggregates. (Photo courtesy of Krzysztof Blazejowski.) |
