Solution: The original plan is to repair 0.48km every day, and the total engineering quantity can be calculated after 30 days: 0.48×30= 14.4 (km). If 0.02km is repaired every day, the current daily workload can be calculated as: 0.48+0.02=0.5 (km), and then time = workload ÷ work efficiency. It takes 28.8 days to complete the repair.

Engineering problem is the focus of mathematics application problem teaching in primary schools, the extension and supplement of fractional application problem, and an important tool to cultivate students' abstract logical thinking ability. It is a powerful penetration of the idea of one-to-one correspondence of functions in application problems. The engineering problem is also the difficulty of the textbook. The engineering problem is an application problem that regards the total workload as the unit "1", which is abstract and difficult for students to identify. By comparison, the concept is established. Give full play to students' dominant position in teaching and solve cooperation problems by using students' existing knowledge.

Basic quantitative relationship: workload ÷ work efficiency = working hours.