Infrastructural is the adjective for the basic systems a country, city, or big organisation needs in order to work: roads, rail, ports, power, water, hospitals, banks, the internet backbone. So infrastructural spending is money for those systems, not for one pretty building. Infrastructural problems are when those systems are weak, old, or missing. The noun you already know is infrastructure; this form just lets you put the idea in front of another noun. Though actually, news writers sometimes pile it on because it sounds serious — ‘infrastructural challenges’ when they mean ‘the roads are bad.’ It is a heavy, official-sounding word. Learners can use it, but naming the roads and power lines is often clearer, and that is fine.