Concrete is a material that quite literally holds our cities together. This ubiquitous gray material’s importance to modern urban life is undeniable, from homes and apartment buildings to bridges, viaducts, and sidewalks.
Concrete is the most widely used building material globally because of its beauty, strength, durability, and thermal mass. Its extreme versatility makes it a very useful building material for any human settlement, from ancient Rome to modern-day New York City. It’s also a major component of concrete masonry, which was invented by Joseph Aspdin in England in 1824 and patented in 1825.
It’s typically made by mixing sand (aggregate), Portland cement (a fine powder made from limestone and clay), water, and rocks or gravel into a paste. The paste hardens and bonds together the aggregates into a solid mass over varying lengths of time.
Concrete has extremely high compressive strength (it doesn’t crack underweight) but significantly lower tensile strength (it cracks when being pulled). Steel rods called rebar are often added to concrete structures before the concrete sets to compensate for this imbalance in concrete’s behavior under tension and compression. The rebar adds tensile strength to the structure.