It’ll be another hot day in the parts of Iowa where it’s not storming and that could lead to a “blowup.” Tuesday’s 90-degree temps crumbled the concrete on part of Des Moines’ freeway, causing traffic troubles, but Claude Frazier in the D-O-T’s maintenance force says such “blowups” are not that unusual. It’s caused by the heat, as he explains winter cold shrinks the concrete and sumemr’s sun makes it expand, but without any place to move it expands and buckles at its weakest point. A hot day is no guarantee there will be blowups, but the road-maintenance veteran says if it happens, it’s likely to be late in the day. They usually don’t “blow” till late evening when temperatures are hottest, often during afternoon rush hour when both the weather and traffic are heating up the pavement. Frazier says blowups only happen in concrete pavement, but could appear on any city street or rural highway when the weather’s hot.