Page:America's Highways 1776–1976.djvu/468

 training is needed. Furthermore, such a system provides the manager with the information needed to insure that equipment is being used efficiently and effectively, and to aid him in selecting the best unit for the work to be done.

Grading operations on Interstate 94 in North Dakota. After a water distribution truck moistens the soil, sheeps foot and ballastable rollers compact it.

Since 1971 the Federal Highway Administration, when requested, has assisted State organizations interested in discussing the basic components of a maintenance management program. State highway maintenance organizations that have implemented a maintenance management system are presently reviewing management practices in equipment management and capital outlay programs and are establishing district and area boundaries for related maintenance programs.

Construction industry associations were instrumental, as in previous periods, in the development of new equipment in such areas as tamping and vibrating rollers to speed up compaction of embankments and base courses. The use of nuclear devices for testing compaction on soil and base courses became more widespread as these devices made this type of testing much faster. Large screw augers were being used more frequently for structure foundation excavation. New equipment developed for subsurface investigation made it possible for more precise bidding on excavation work, because the contractor could depend on more accurate subsurface information.

The laser beam has become a very useful tool for engineers in establishing line and grade for pipe laying, eliminating the need for off-set lines and batter boards. New methods of making pipe and specialized equipment for cleaning pipe have also come into use during this period.

New methods for handling concrete, such as concrete pumps and new deck finishing equipment, have made bridge work more productive and enabled contractors to produce safer, smoother riding bridge roadways. Stay-in-place steel forms for concrete bridge decks were developed and thereby eliminated the need for the removal of the forms, an often hazardous and difficult operation.

Precast concrete units such as culverts and barricades came to be widely used, also.

Spreading and finishing equipment for pavements were developed into quite sophisticated machines that eliminated much of the hand work. New types of equipment for texturing and grooving concrete pavement surfaces came into use to help provide more skid resistance.

Large automatically controlled, central-mix plants were quite extensively used in concrete pavement work in this period from 1964 to 1974. Some States permitted asphalt plants to operate without screens, using variable speed belts and multiple cold feed bins for gradation control. Also, some asphalt plants were equipped with surge storage, which allowed them to produce asphaltic concrete continuously without having to stop the plant to wait for haul trucks. The development of practical electronic systems for automatic grade controls, which used sensing devices to follow a string-line or guide-wire, was very important.

Significant advances in equipment in nearly every field of use were seen during this period in an effort by the industry, as a whole, to obtain faster, more efficient production with less “down time.”

Many advances have been made in developing new materials and techniques for highway construction. A new technique of presplitting faces of road back slopes before blasting for excavation gave a much more even back slope in rock cuts. Various treatments, such as lime and water-proof membranes, were put into use to help overcome the problems of swelling soils. Even though they had been in use for many years, synthetic aggregates were seeing more use in highway work during this period. New types of coatings for structural steel and culvert pipe, as well as pipe jointing materials, were being produced. 462