When mixing concrete, you can make it either very dense or not that dense at all, depending on what the concrete is being used for.
For projects such as bridges, roofs, and flooring, a very dense, and consequently strongly compressed, mix of concrete is used. This compressed concrete is the strongest there is.
On the other hand, concrete with air introduced is more lightweight and is ideal for roads and airport runways, thanks to their ability to withstand the harsh weather.
As you can see, there is a lot more that goes into a good concrete mix, besides the raw materials used to form the mixture. It is important you employ a concrete expert that can evaluate your project needs and mix the perfect batch so that your concrete lasts forever while still looking good.