If you live in a colder climate subject to frequent periods of freezing and thawing, then air entrainers are a must in you exterior concrete.These admixtures are added to the fresh concrete during mixing to form a network of tiny air bubbles. But don't worry -- these bubbles won't affect the strength of your concrete. Instead, when the moisture in the concrete freezes and causes expansion, they will relieve the internal pressure and help prevent cracking. Learn more about the benefits of air entrainment.

Although the name brings to mind the unpleasant thought of incinerated insects, fly ash is actually a byproduct from coal burning plants and a valuable additive that makes concrete stronger, more durable and easier to work with. Fly ash aids the formation of cementitious compounds to enhance the strength, impermeability and durability of concrete. Another plus: Using fly ash in concrete conserves resources because it can replace up to 30% of the cement in the mix.

Water-reducing admixtures (sometimes called "superplasticizers") reduce the amount of water needed in the concrete mix and make it easier to place and finish. By reducing the amount of water in the mix (or the water-cement ratio), they increase the strength of the concrete and make it less permeable. Learn more about the importance of water reduction.