Admixtures accomplish a variety of goals. This can be as simple as adding a pigment to color the concrete. Other admixtures are used for faster curing times in cold weather, creating extremely high-strength concrete, or for increasing the flowable nature of concrete without compromising the strength. Unfortunately, admixtures can generate unwanted results such as poor adhesion of finish-flooring. For this reason, many structural engineers and architects are hesitant to use admixtutres. We have an article that covers a number of different admixtures.