ConcreteConcrete is a material used in building construction, consisting of a hard, chemically inert particulate substance, known as an aggregate (usually made from different types of sand and gravel), that is bonded together by cement and water.

Everyone knows that all roads lead to Rome, but lesser known is that 5300 miles of those roads were built from concrete. From 300 B.C. to 476 A.D., the Romans used pozzolana cement from Pozzuoli, Italy, to build the Appian Way, as well as the Roman baths, the Coliseum and Pantheon, and the Pont du Gard aqueduct in southern France. The mix consisted of small gravel and coarse sand mixed with hot lime and water and horsehair to reduce shrinkage. That also is when the world saw admixtures in their most primitive forms of animal fat, milk, and blood.

Ancient Chinese used cementitious materials to hold bamboo together in boats and in the Great Wall of China. The Assyrians and Babylonians used clay as the bonding substance or cement. The Egyptians used lime and gypsum cement. In 1756, British engineer, John Smeaton made the first modern concrete (hydraulic cement) by adding pebbles as a coarse aggregate and mixing powered brick into the cement. In 1824, English inventor, Joseph Aspdin invented Portland Cement, which has remained the dominant cement used in concrete production. Joseph Aspdin created the first true artificial cement by burning ground limestone and clay together. The burning process changed the chemical properties of the materials and Joseph Aspdin created a stronger cement than what using plain crushed limestone would produce.

The other major part of concrete besides the cement  is the aggregate. Aggregates include sand, crushed stone, gravel, slag, ashes, burned shale, and burned clay. Fine aggregate (fine refers to the size of aggregate) is used in making concrete slabs and smooth surfaces. Coarse aggregate is used for massive structures or sections of cement.

Concrete that includes imbedded metal (usually steel)  is called reinforced concrete or ferroconcrete. Reinforced concrete was invented (1849) by Joseph Monier, who received a patent in 1867. Joseph Monier was a Parisian gardener who made garden pots and tubs of concrete reinforced with an iron mesh. Reinforced concrete combines the tensile or bendable strength of metal and the compressional strength of concrete to withstand heavy loads. Joseph Monier exhibited his invention at the Paris Exposition of 1867. Besides his pots and tubs, Joseph Monier promoted reinforced concrete for use in railway ties, pipes, floors, arches, and bridges.

Advent of the ready-mixed truck

Machines and methods to batch and mix the materials used in concrete paving were just being developed at the turn of the 20th century. In particular, a steam-powered concrete "paver" that mixed concrete onsite and moved with the other paving machines as the work progressed gained wide acceptance as the preferred method of producing concrete for pavement.

At first, wheelbarrows were used to "batch" and load the paver's skip hoist. Five-ton dump trucks would haul the sand and stone to the worksite and dump the materials in piles along the roadside. Then the workmen would hand-shovel the materials into wheelbarrows that also served as volumetric measures to load the skip hoist for the two-bag (about 11 cubic feet) steam-powered concrete mixer (paver).

Bags of cement also were spaced along the roadside and hand-dumped into the skip hoist in proportion to the wheelbarrow loads and batch size. A water pipe usually was laid the entire length of the job with multiple outlets to provide water for the mix. It was a slow, back-breaking process, but it got the job done and produced many concrete roads of acceptable quality for the early lightweight cars and trucks.

Concrete ships throughout history

concrete shipThe oldest known concrete ship was a dingy built by Joseph Louis Lambot in Southern France in 1848 and featured in the 1855 World's Fair. In the 1890s, an engineer in Italy named Carlo Gabellini built barges and small ships out of concrete; the most famous being the Liguria. On August 2, 1917, N.K. Fougner of Norway launched the first ocean-going concrete ship - an 84-foot-long boat named Namsenfjord. In the 1917, the Violette was built and currently is used as a boating clubhouse on the Medway River in England. This makes her the oldest concrete ship still afloat.

In 1917, the United State finally entered World War I and steel became scarce while the demand for ships went up. Businessman W. Lesie Comyn formed the San Francisco Ship Building Co., Oakland, Calif., to begin constructing concrete ships. The first American concrete ship, a steamer named the S. S. Faith, was launched March 18, 1918. She cost $750,000 to build. She was used to carry cargo for trade until 1921, when she was sold and scrapped as a breakwater in Cuba.

With the advent of World War II, the U.S. government contracted McCloskey & Co., Philadelphia, Pa., to construct a fleet of 24 concrete ships. Innovations in cement mixing and composition made these ships stronger than the previous attempts. After the war, several of the ships were turned into a floating breakwater in Canada and 10 more were sunk as a breakwater in Virginia.