Page:America's Highways 1776–1976.djvu/333

 Bituminous mixtures being prepared in the Public Roads Administration research lab for immersion-compression tests to ascertain durability of materials for highway construction in 1948.

The name “portland cement” comes from an “artificial” cement patented by Joseph Aspdin in England in 1824. Aspdin kept his process a secret, although many others tried to duplicate this product. In 1845, I. C. Johnson developed a product based on high temperature calcination that was essentially “portland cement” as we know it today. Portland cement was first manufactured in the United States in 1871.

Concrete technology was in its early development at the beginning of the 20th century. Today’s refined knowledge of concrete design and utilization is the product of a number of organizations, such as Lewis Institute, American Concrete Institute, American Society for Testing and Materials, Portland Cement Association, State highway departments, and the Bureau of Public Roads. In particular, BPE played an important role in developing knowledge of the relationship of concrete’s various components to concrete strengths and other characteristics and in developing better tests and specifications for the product. In addition, BPR performed studies which established the quantitative relation between some aggregates and the alkali content of cements and determined the value of fly ash in concrete to control the damaging alkali aggregate reactions as well as serve as a replacement for part of the cement. Other research assessed the sulfate resistance of various concretes and the relation of such resistance to cement composition. Air entraining agents to prevent freeze-thaw damage were also evaluated.

As the science of manufacturing portland cement developed and more knowledge of the effect of special compositions was gained, specialty cements such as “high-early-strength portland cement” or “sulfate resistant” cements began to appear on the market. This led to the adoption by ASTM and AASHO around 1940 of five types of standard cements.

Research engineer scans slice of concrete with microscope to determine size and distribution of air voids, important in the durability of concrete, especially under the action of freezing temperatures.

The development of standard cement tests was an important part of Public Roads’ research in the late 1920’s and early 1930’s. Difficulties arose when discrepancies were found in the results of tests run by different testing laboratories around the country whose function was to verify that highway construction materials met their required specifications and also to test samples of completed highways. This problem led to the establishment, in 1929, of the 327