GA pilot reported a lack of published and verbal clarification of taxiway status that resulted in an incursion of a closed taxiway.

Narrative

While parked on the ramp; I received my taxi clearance from BIS Ground: 'Taxi to Runway 13 via Charlie.' No specific routing instructions were given to reach Taxiway C; which is common. As I began taxiing from the ramp under that clearance; I noticed a stop sign positioned near what appeared to be a newly surfaced taxiway (A2); along with a sign instructing ground vehicles to contact ATC before crossing.Since I had a valid taxi clearance; had not received any instructions to avoid that route; and there were no NOTAMs or advisories indicating that Taxiway A2 was closed; I believed it was acceptable to use A2 to transition to Taxiway C. The signage seemed intended for airport maintenance vehicles rather than aircraft and the pavement looked as if it was ready for use.After crossing A2; Ground Control advised that Taxiway A2 was not currently in use due to recent resurfacing. I acknowledged; apologized for the misunderstanding; and continued as instructed. Shortly after; I received takeoff clearance and departed without further issue.In hindsight; I should have contacted Ground for clarification before crossing the stop sign. I believe the primary contributing factor was a lack of mutual communication with ground control; lack of advisory's/notice's with the repavement; and lack of situational clarity on my end. Specific routing instructions; an advisory regarding A2's recent closure; or me inquiring about the area before crossing would have prevented the confusion.Going forward; I will verify any ambiguous signage or unclear taxi routes with Ground Control before proceeding. I have also scheduled additional instruction to refresh my knowledge of airport surface operations and signage interpretation.I'm writing this as both a reflection and a reminder to other pilots: when in doubt--ask. If something feels uncertain; clarification is the safest and most professional option. That's exactly what I will do next time I am faced with a similar situation.