University of Colorado at Boulder students started the fall semester this week with three new buildings under construction and the completion of a $3.3 million campus improvement project. Since last October, work crews have refurbished 43 entryways to campus buildings, installed new carpet in 93 classrooms and Norlin Library study areas, applied new asphalt on many campus streets and replaced sidewalks, university officials said. A number of classrooms also were upgraded with new projectors, chalkboards, chairs, tables, ceiling fans, fixed seating and wall finishings.