Few of us realize how many years of experimentation and pioneering have gone into the concrete which is so much a part of today's construction scene. We know, of course, that it didn't reach its highly developed state overnight, that it took many men working over many years to bring us the tools and techniques that we accept so casually today. The Portland Cement Association has compiled some of the more interesting landmarks of progress made during concrete's formative years and we are passing along just a few of these. 1868 ... The first shipment of portland cement arrives in the United States from Europe. A patent is obtained on "artificial stone" made from concrete. It is used to build a house in Chicago. A method of reinforcing concrete grain elevator walls with iron straps in patented. 1876 ... Thaddeus Hyatt experiments with reinforced concrete beams and pioneers a design theory. Although he is preceded by Joseph Monier who was issued the patent in France, his success leads to the widespread development of reinforced concrete in the United States. A reinforced concrete house is built in New York. 1916 ... Portland Cement Association founded with headquarter in Chicago. Stephan Stepanian apples for patent on first workable, self-discharging motorized transit mixer. Patent application refused. 1930 ... Concrete arch of 612 feet is completed on a bridge in France. This dramatizes the possibility of hollow-section ribs both for arches and girders. Low heat cement is used in Hoover Dam, where, for temperature reduction, a refrigeration plant chills water for circulation through a pipe grid embedded in each 5 foot lift. 1943 ... A design surface imparted to the spillway of the Shasta Dam by using vacuum mats, which, through atmospheric pressure and suction, take off excess water from concrete. 1950 ... Hyperbolic parabolid shells begin appearing in the US.