From sidewalks to buildings around us, concrete is one of the most common materials used in construction. Indeed, it is impossible to walk down a street without spotting a structure or two fashioned out of concrete. One of the most frequently asked questions about the concrete is that why concrete does not get wet?
Unlike sponges or other materials used in daily routine, cement does not reabsorb water to become wet. The secret behind this unique behaviour is the underlying chemical properties of the concrete.
How is Concrete Made?
Concrete is a mixture of water and cement. Aggregates used to form a slurry, like sand and gravel, bring its consistency to that of the batter of cake. Portland cement is the most widely used variety in the production of the concrete. Portland cement was made from the natural ingredients (like limestone and clay) in the Britain in the mid-eighteenth century. Other compounds present in the mix include
“tricalcium silicate, dicalcium silicate, tricalcium aluminate, tetracalcium alumino- ferrite and gypsum.”
On addition of water, various chemical reaction result in the formation of a hard structure, binding all the elements together. This phenomenon may more appropriately be referred to as the curing of concrete rather than its drying out!
How Does Concrete Dry Out and Remain So?
The addition of water hydrates each of the elements in the concrete mix. Hydration transforms the structure of the element and imparts strength to the edifice. In the first week, tricalcium silicate strengthens the mix. Later, dicalcium silicate adds strength to the concrete mixture. The entire structure is cemented together by the calcium silicate hydrate that forms crystalline filaments binding the materials.
Thus, the concrete does not dry out because water becomes a part of the structure itself and imparts strength to it. As the time passes, concrete continues to cure, and its strength is reinforced.
Watch the visual description of what goes on when a concrete structure is erected in this video: