The cement itself is a powder formed when you roast and crush limestone or chalk along with clay, sand and, occasionally, some other additives such as iron oxide. When you add water, the calcium and silicon in the cement react with it to form a gloopy grey gel, inside of which are millions of microscopic stony tendrils. These tendrils, crystals of calcium silicate hydrate, grow and mesh and spread their fingers throughout the gel, locking in the water and forming a kind of skeletal stone-like structure. Add some gravel and sand to the initial mix and, rather than just bonding to themselves,
...more
