Concrete is a combination of small aggregate (sand), large aggregate (gravel), a binding agent or matrix, and water. Historically, lime was used as a matrix, mostly for mortars that had no large aggregate. In 1774 the British engineer John Smeaton added crushed iron-slag to the usual quicklime-sand-water mix, making the first modern concrete for the foundations of the Eddystone Lighthouse off the English coast. Fifty years later, a new matrix was discovered. Portland cement, a calcium silicate cement made with a combination of calcium, silicon, aluminum, and iron, is the basis of modern concrete. In 1824, the English stonemason Joseph Aspdin made it by burning (on his kitchen stove) finely ground limestone and clay, then grinding the combined material to a fine powder. It was named for its original use in a stucco that imitated Portland stone. However, the burnt clay yielded silicon compounds that combined with water to form a much stronger bond than lime. It was to revolutionize the architectural and engineering world.
For the next thirty years or so, plain concrete, because of its tremendous compressive strength (resistance to crushing), was used for walls. Sometimes it replaced brick as fire-resistant covering for iron-framed structures. Reinforced concrete, developed first by the French, combines concretes compressive strength with the tensile strength (resistance to stretching) of metal at first, iron and later steel reinforcing bars or wire. The first person to employ such construction was the Parisian builder Fran