Did you know that concrete has air in it? Certain kinds of concrete have more than others. Interior concrete has air in it just from the natural churning and turning from the drum. Exterior concrete has air added to it by the concrete company. You only want so much though, because too much air can make the concrete weak and very hard to finish. Why do they put air in concrete? It’s a way to keep your concrete from freezing in the winter and popping or flaking off. You see concrete will absorb moisture and therefore when it gets below freezing the moisture will freeze in the concrete. That is where the air comes in. The air in the concrete has formed small bubbles throughout the concrete. When the water freezes in the concrete and expands the air bubbles give the ice a place to go. Any way I thought you might be interested. So the next time you do a concrete project ask the guy who is estimating your project if the concrete has air in it. If so, ask him why and see what he says.