When mixing concrete on the jobsite, it's quite hard to achieve the compressive strength specified on its mix design, especially when you need around 4,000 up to 7,000 psi of compressive strength. This is where admixtures for concrete come in. Ingredients added to concrete, other than Portland cement, aggregates, or water, are referred to as concrete admixtures. While not required, they are sometimes used selectively to improve the concrete mix. Admixtures are used in concrete to alter its properties in various ways. Some common uses include improving workability, increasing or decreasing cure time, and increasing concrete strength. Admixtures can also be used for aesthetic reasons, such as to change the color of the cement. Whenever possible, concrete workability, water tightness, and strength should be achieved by selecting suitable types of aggregate, Portland cement, and maintaining a good water-cement ratio. In this episode, we're going to solve this problem using concrete admixtures, particularly the type of admixture that most small to medium projects need. - Water-Reducing Admixtures Water-reducing admixtures reduce the amount of water needed to produce concrete of a given consistency. They can also be used to improve the slump of concrete without requiring additional water, resulting in a lower water-cement ratio. By lowering the water-cement ratio, water-reducing admixtures can provide greater concrete strength while retaining the same workability. Lignin sulfonic acids and metallic salts are commonly used as water-reducing admixtures. - Superplasticizers Superplasticizers are organic compounds that transform a stiff concrete mix into one that flows more freely. They work by coating cement particles, causing them to break away from the lumps that typically result from mixing cement and water. Superplasticizers give each cement particle a negative charge, which causes them to repel each other providing a more thorough distribution. They are used either to facilitate placement of concrete or to reduce the water content of a concrete mix in order to increase its strength. - Accelerating Admixtures Accelerating admixtures, or accelerators for short, make concrete cure more quickly. In addition, they accelerate the strength development of concrete. Strength development can be further accelerated by using Type III high-early-strength Portland cement. By curing concrete at higher temperatures or lowering the water-cement ratio, additional acceleration can be achieved. Accelerators are typically used in cold weather to develop strength faster in order to offset potential freeze damage. With that, let's find out how admixtures can save cement cost while allowing you to achieve sufficient strength based on the function of the concrete.