Consider using a ready-made mix. There are several companies that manufacture easy-to-mix varieties for making statues. Fiber-reinforced, sand-mixed and surface-bonding concretes, which can be successfully molded into specific forms, come in bags and only need to be mixed with water before pouring into molds.
Investigate glass-fiber reinforced concrete. This type of concrete is slightly more complicated, since the glass fibers need to be mixed into the emulsion base before it can be used for molding the statue. After the concrete is dry, it must be sprayed with a special finishing spray before being placed outside. Glass-fiber concrete, which comes in a kit, is the most environmentally friendly because it uses less water than other varieties.
Make your own mix. This is a bit trickier because you need to know the exact amount of each ingredient or else your mix will be too wet or too dry. A basic recipe is 2 qts. of Portland cement, 3 qts. of sand, 3 qts. of vermiculite and 1 qt. of water. Pour each of the dry ingredients into a 5-gallon contractor's bucket and slowly add water, stirring until the mix is fully blended.