In this video, at the 6:25 mark, you can see a truck drive in front of the crawler, spraying water on the gravel ahead of the treads. Why did they do this?
According to https://www.popularmechanics.com/space/rockets/a15777930/launching-to-space-at-a-crawl/
it is to reduce dust created as the crawler crushes some of the "Alabama River Rock".
Photo showing the crushed rock behind the crawler. (Source - Organic Marble)
According to the documentary 'When We Were Apollo', the gravel was not part of the original design, but added as a sacrificial bearing surface to stop damage that was occurring to the internal bearings. (Which raises the question: is it raked after use, and periodically replaced?)
I can tell you why as I’ve been involved in the project for years. When the crawler rolls over that river rock it crushes it and the resulting crushing motion releases silica dust in every form (total, inhaleable, and most importantly, respirable). When the crawler rolls out, a team of crawler technicians are escorting it both on the ground and on the crawler. Studies have shown that these workers past and present have suffered respiratory issues as a result of this silica. As a result, the watering of the river rocks prior to the crawler crushing them, is an attempt to reduce this silica dust release.