Q.: Is there a standard mix to use for exposed aggregate flatwork if you do not want to seed the top of the concrete with a special aggregate?
A.: No, there is not a standard mix; but you should design the mix or choose the mix with the desired end result in mind. This means that you will probably want to consider what maximum size of aggregate is best for the effect you want to achieve. Pea gravel (3/8-inch maximum) is a popular size for the purpose. It is often helpful to use a single size of coarse aggregate (1/4 to 3/8 inch, or 3/8 to 3/4 inch, for example) rather than a graded aggregate. This tends to give a good appearance. If you use anything other than a standard mix you should make sure it has the proper workability; if not, you may have to increase or decrease the sand content to make it suitable for placing and finishing. All of this presupposes that the mix will be designed for adequate strength (preferably 4000 psi if for outdoor use in a freezing climate), will have a slump of 2 to 4 inches and, if to be exposed to weather, will be air entrained.