Water-reducing admixtures of type D often delay the setting time of concrete by one to three hours (Fig. 6-5). Some water-reducing admixtures may also entice air into concrete. Admixtures based on lignin can enhance air content by 1 to 2 percentage points. This increased porosity can lead to a more permeable product that allows water to drain faster. The main advantage of using a water-reducing admixture is that it reduces the amount of water required for successful concrete casting. This reduction can be as much as 20 percent or more, which can significantly cut down on drying costs and fuel consumption during construction. The reduced need for water means that less-expensive materials can be used, resulting in lower cost projects. In addition, reducing the amount of water needed reduces the risk of unwanted moisture getting into the structure. Finally, reducing the amount of water used in concrete makes it possible to use slower-setting types of cement, which results in stronger concrete with better durability. Water-reducing admixtures work by absorbing any excess water present in the mix design. This leaves more dry material available for hydration, which leads to a stronger product. The exact mechanism behind how these additives work is still being studied by scientists. It is known that they interact with some of the reactive components in cement such as calcium hydroxide or aluminum oxide powder. These reactions prevent premature hydration and allow the cement particles to absorb more water later on when needed.