Weathering concrete sleeper track

[nhdesigns]

As the title suggests I was wondering if anyone can help me out with weathering track that has concrete sleepers. I know how to weather wooden sleeper style track and points but don’t know how to go about the same with concrete sleepers. 
 

Most of the track is PECO code 100 concrete sleeper style track used on my layout. My layout is set in the BR sector era of the West Midlands area of the west coast mainline with overhead catenary. 
 

I know how to weather the rails and where to add buildups of oil and dirt from trains that would be stationary close to the signals but don’t know what to use for the concrete sleepers. 
 

I do intend to use an airbrush on weathering the track but just wanted to know what colours would be suitable for giving the track sleepers a worn in look and heavy use.

 

Thanks for any help and advice on this.