Page:America's Highways 1776–1976.djvu/334

 Cement Reference Laboratory (CRL) at the National Bureau of Standards. It was an ASTM sponsored activity actively supported by Public Roads from its inception. The CRL’s duty was to determine whether the laboratories’ equipment was in order and to observe whether the proper techniques were being used in making the tests.

The simplification, standardization, and uniform application of aggregate gradations has been a major effort since 1936. This work led to the early adoption of a simplified practice of specifying sizes of coarse aggregate for concrete. In 1962 Public Roads encouraged the States and other agencies to adopt simplified procedures for aggregates used in bituminous construction. The recommendations included the development and adoption of standard aggregate sizes, standard sieves, and a standard method of reporting gradations. Public Roads also developed a new gradation chart that showed desired combinations of aggregate sizes in graphical form. Since fewer blends were required, all customers could be supplied from only a few stockpiles and producer costs are minimized. This chart is now in wide use for evaluating aggregates in bituminous paving mixtures.

In 1928 studies were made of concrete containing rounded gravel coarse aggregate versus the angular material produced by crushing ledge stone or large-size waterworn gravel. This research determined that crushed stone is generally preferred for paving work because of the superior strength of the resulting concrete.

Concrete slabs are subjected to daily applications of deicing agents, such as calcium chloride, to determine the durability of the concrete or the effectiveness of various protective treatments.

Research on concrete freezing and thawing was also being conducted at this time. Public Roads research led to the development of new concrete specifications requiring denser and more durable types of coarse aggregate. Other research in this area included the development of air-entrainment techniques and the establishment of a list of acceptable air-entrainment admixtures. Air entrainment is a process that puts air bubbles in the cement to relieve the stresses caused by freezing water. Later, Public Roads assisted in the development of ASTM and AASHO specifications and guidelines for air-entraining agents.

Beginning in the 1920’s, Public Roads became concerned with the need for improved field performance of such common highway coating materials as paints and galvanizing for metals for guardrails, more durable materials for culverts, and more lasting and visible paint for lane markings and directional highway signs. A special chemical unit was established to conduct research in this area.

A significant result of this effort was the development in the late 1940’s of a modified anticorrosion paint primer for the bridge steel being shipped to the Philippines for rebuilding its war-damaged highway network. The standard red lead-linseed oil primer then in use was found to be badly scratched and significantly stripped from the steel after its arrival in the Philippines. To compound the problem, the exposed steel also corroded rapidly when stored under the humid Philippine conditions. Studies showed that a pigment combination of red lead and iron oxide, as well as a combined base of linseed oil and alkyd resin, would provide adequate corrosion protection and would be tough enough so that shipment damage and deterioration in storage was minimal. The specification developed has since become an AASHO standard used by a number of State highway departments.

Another development in coating materials was an abrasion-resistant paint system for highway structures. Exceptionally high wind velocities combined with wind-borne ice and soil particles in the Alaskan Copper River Delta produced almost immediate and extensive abrasive damage to the standard bridge paint system in use. Laboratory and field research by Public Roads and the Alaska Department of Highways were completed in 1965 and demonstrated that rubber-based coating systems offered superior abrasive resistance to these destructive forces.

Because traffic paints do not last long in heavy traffic, there has been a continuing interest in developing better and more economical lane marking material. This has led to three distinctly new and rather revolutionary types of lane markers. In general, the new materials have been developed by industry with evaluations performed by State highway departments and technical assistance and funding help from Public Roads.

The new materials are:
 * Prefabricated plastic striping which is supplied either as short rectangular segments or in rolls like paper towels and applied to the road surface with permanent cement. 328