Concrete Ideas, pt. Just Say No to Abuse Declaring War on Terrorism. It may be something as simple as a sidewalk or as complicated as footings for a foundation wall. The majority of concrete is the aggregate.
Aggregate is a mixture of clean sand and gravel.
The final ingredient is water. The water combines with the cement in a chemical process called hydration. What this means is that the cement begins to form crystals between the pieces of aggregate, resulting in a strong, solid rock-like material. The key to good quality concrete is the right amount of water. Too much water will result in weak concrete.