The first seconds in a building's life.

• Position: Construction

No matter if it is a giant complex, a high-rise, or an underground project, modern architecture cannot get along without concrete. The component in concrete that holds the other components together is cement. In order to control the properties of concrete, it is important to know what occurs as it hardens. Scientists now have successfully watched the first few seconds in the "life" of cement by means of X-ray diffraction. In the journal Angewandte Chemie, they explain the role of the superplasticizers in this process.

Concrete is made from sand, gravel, additives, water, and cement. Portland cement is a complex mixture of finely ground limestone, clay, sand, and iron ore--mainly calcium silicate with fractions of aluminum and iron compounds and sulfates. Once mixed with water, chemical reactions occur among the components of cement, and it solidifies and hardens. When the process is finished, it remains solid and stable, even underwater.

The enormous stability of concrete comes from crystalline needles that form during this process and are interlocked firmly with each other. Various additives are used to optimize the properties of concrete, including a class of superplasticizers based on polycarboxylate (PCE). These improve the flow of concrete, making it easier to pour. The water content can be reduced to improve the concrete's compressive strength.

"Detailed insight into the different stages of the hydration process is essential for a more complete understanding of how these processes can be...