Page:America's Highways 1776–1976.djvu/335

 * Thermoplastic striping applied hot by either extrusion or spraying and capable of self-adhesion to the road surface. The stripe has good visibility and excellent life characteristics.
 * Plastic dots reflectorized to have high visibility in rainy weather and protected by steel or other housings or base plates, the unit being firmly cemented to the pavement surface. These devices are being designed to have a very low profile, and the cement now available holds them so firmly to the pavement surface that they are not readily torn loose by street sweepers or even by snowplows.

Each of these lane-marking developments is somewhat more expensive in the initial installation than conventional painted striping, but the initial extra cost is often offset several times over by the greatly extended life, which has proved to be as much as ten times that of painted stripes.

During the late 1940’s and early 1950’s Public Roads pioneered in the application of sophisticated instruments to help solve materials problems. Infrared spectroscopy was developed to identify the nature and understand the behavior of chemical admixtures for concrete, mineral composition of aggregates, and other highway materials. An infrared spectrophotometer was acquired in the late 1950’s and was successfully applied to analyzing, classifying, and regulating the use of certain admixtures for concrete, such as water reducers, hardening retarders, and air-entraining chemicals. These materials were of such complex chemical nature that they had defied earlier less sophisticated methods.

In 1908, Director Page reported on 13 experimental road sections on main roads connecting New York and Boston. These experiments resulted in the successful upgrading and restoration of deteriorated travel surfaces with various water-gas and coal tar products used primarily as dust palliatives. Additional reports by Page during the period 1909 through 1918 covered numerous experiments involving dust prevention and road preservation. These early treatments did much to make automobile travel faster and more pleasant and were relatively inexpensive for a single application. However, since they required frequent renewal, the total cost was appreciable, and they finally had to be abandoned.

Infrared spectrophotometry analysis can identify substances present in such materials as paints, concrete admixtures coatings, rubber, etc., by determining the frequency at which radiation is absorbed by the substance.

In the early 1930’s, a gradual transition took place from dust control treatments to surface treatments, using tars and asphalts and better mineral cover. Also, during this period and continuing into the 1950’s, many miles of penetration and waterbround macadam pavements were built. These roads served growing highway needs very successfully, and considerable mileage has survived to the present time. Concurrent with the development of more substantial surface treatments, primarily in the east and the south, many central and western States experimented with and developed effective procedures for the type of pavement known as bituminous road mix.

In this period, Public Roads research was very active in coordinating field studies of roads in service with laboratory research on materials. In the 1930’s, for example, studies in Colorado and Wyoming demonstrated the need for sealing or “surface treating” road-mixed surfacings. As a result, bituminous seal coating became a fairly regular procedure. Another example was a study of bituminous concrete roads in Ohio which demonstrated the general serviceability of this paving.

Many articles were published documenting the Bureau of Public Roads’ research on portland cement concrete pavements. Among the earliest was a study in 1919 on the behavior of concrete slabs. The measured curling and warping movements of the slab were evaluated, in addition to the effect of wheel loading, and a thickness design formula based on the corner break was developed. This was followed in 1923 by Dr. H. M. Westergaard’s theoretical analysis of slabs on an elastic medium. There followed a period of detailed studies by Bureau of Public Roads’ researchers lasting until 1936 to verify and expand his results into a comprehensive design procedure, published as The Structural Design for Concrete Pavements, which has remained the basic guide for a decade or more.

Experimental roads continued to be built to test new concepts in concrete pavement. In 1921, the Bureau of Public Roads built the first experimental continuously reinforced concrete pavement near Washington, D.C., where many of the basic principles related to that type of pavement were developed. In 1937 the Bureau, in cooperation with the Indiana State Highway Department at Stilesville, began an extended field test of continuously reinforced concrete pavement, which now comprises a significant portion of the Interstate System mileage. The BPR also worked with industry in 1957 to produce the first U.S. prestressed concrete highway pavement, and, subsequently, built a 3,200-foot experimental section of pavement at Dulles International Airport in 1971. This concept too is gaining widespread acceptance. 329