"While they may dig up minerals for international distribution, are they actually building railways, bridges, roads etc?..."

No, they simply supply construction aggregates to the construction industry. They are not a construction company.

One unusual thing about Polaris is that they own a tugboat. They use it to manoeuver ships at their loading facility. At first it struck me as odd that a construction aggregate supplier would use ocean going vessels for delivery, but then I realized that the cheapest way to move materials, is by boat, not rail. Of course, after arrival at a destination harbour, further shipping is usually done by rail.

"...I'll do some comparisons..."

If you are comparing construction aggregate companies, an interesting one would be Athabasca Minerals (ABM on TSX-V). They are smack dab in the middle of tar sands country supplying aggregates for construction projects in the tar sands. I've never owned it, so don't know much about it, but I would suspect that with the current economic downturn in the Fort McMurray area, the prospects are not that exciting in the short term.