3. The prestressing strand is stretched across the casting bed. About 30,000 pounds of tension will be
applied to the cable before it's surrounded by concrete. Why? Hold a rubber band loosely
between two fingers. Now stretch your fingers farther apart. See how the rubber band
becomes taut and more resistant to downward pressure? The same principle holds true
for prestressing strands.
4. Cement, sand, stone, and water make up concrete.