Major improvements

RUBBER PRODUCTS

The tire and rubber manufacturing industry has provided four major tire improvements for wheel-type construction machinery which has given impetus to its phenomenal development in a short span of years:

(1) The development of nylon cords has greatly increased durability and heat resistance.

(2) Wide base treads afford better traction and flotation and permit higher operating speeds.

(3) The new tubeless tires for earthmovers and graders have eliminated flap and tube troubles, facilitated field mounting and repairs, and thereby greatly reduced downtime.

(4) High pressure compactor tires for pneumatic rollers which are capable of exerting contact pressures of 80-95 pounds per square inch.

In addition, the industry is now producing conveyor belts which provide eight times greater performance than those previously used and wire-braided hose that can withstand up to 1,000 pounds per square inch. Greater efficiency from these improvements in tires and other rubber products are reflected in thousands of units of construction machinery.

Duplex truck tires

Duplex tires which were developed recently for military purposes as a replacement for dual tires have also been successfully operated on commercial transport trucks and on several types of highway construction machinery on an experimental basis. In addition to providing easier riding, less vehicle maintenance, better traction and mobility, they also exert less contact pressure on highway pavements and therefore their widespread adoption would tend to reduce pavement damage and maintenance costs.

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Calcium chloride

CHLORIDE SALTS

Calcium chloride is produced from natural brine wells and as a byproduct of the ammonia soda process of producing soda ash.

Annual production at the present time is estimated at about 600,000 tons, of which slightly more than half is devoted to highway purposes. It is used as a dust palliative for soil-aggregate roads, for snow and ice control purposes, and as an accelerator for portland cement concrete poured in cold weather.

Field tests have revealed that calcium chloride materially assists in compacting soil mixtures by reducing the compactive effort required for certain soils. The effects of calcium chloride seem to be most pronounced on base course mixtures which contain an appreciably amount of minus 200 mesh material. Conversely, the calcium chloride permits the use of less binder material than would otherwise be required.

In addition to facilitating compaction, it has been demonstrated that resistance to the penetration of moisture into the compacted soil and to subsequent damage by frost action is increased.

For high-type pavements where calcium chloride is used to aid compaction, the materials are normally mixed at a modern central plant in order to achieve close control on the amounts of flakes and water added. As previously mentioned, a modern plant is capable of producing in excess of 500 tons of mix per hour.

In winter maintenance, calcium chloride is used in flake or pellet form by itself and in combination with sodium chloride. It is also used as an agent to keep sand and other abrasives in condition to apply with mechanical spreading equipment. When mixed with sodium chloride, the ratio is usually one part to three parts of the sodium salt. The decision as to whether calcium chloride will be applied with or without sodium chloride depends on existing and anticipated temperatures and pavement conditions. The mixture of chloride salts is usually more effective at a temperature range of 30° F. to 25° F. The chemical mixture combined with sand is quite effective for temperatures under 25° F. and to a point where plowing operations will provide a clear pavement.

Sodium chloride

Coarse sodium chloride salt which is largely produced from mining operations is used principally as a snow and ice control chemical. It has also been used to a limited extent for mixing with base and surface courses of secondary roads. It is estimated that 5 million tons were used for highway purposes in 1961.

Sodium chloride is particularly effective for melting snow and ice when the temperature is about 30° F. and above. As previously indicated, its effectiveness at temperature under 30° F. is enhanced by the addition of one part calcium chloride to three parts sodium chloride.

When used in proper amounts and with reasonably controlled moisture conditions, compaction is facilitated through the use of sodium chloride.

EPOXY AND POLYESTER RESINS

The epoxy and polyester resins are newcomers to highway usage. Most of the plastics have greater strength per unit of weight than metals; they also offer a wide range of chemical resistance properties. Epoxy resins

During the past 5 years, an increasing number of State highway departments have used epoxy or thermosetting resins for seal coatingprimarily on portland cement concrete bridge decks. These epoxy cements are applied as a thin layer, in quick-setting liquid form, to a clean roadway surface for sealing and waterproofing. Fine crushed aggregate of hard, sharp, and angular character is then added, before the resin hardens, to provide a skid resistant sandpaperlike finished product. This type of seal coat construction has been used in California, Connecticut, Kansas, Minnesota, New Jersey, New York, Ohio, and Wisconsin. The material has also been used in maintenance work for spot patching of pavements and for repairing disintegrated concrete in bridges.

Although this type of construction is relatively new, an estimated 1 million pounds of epoxy resin have been used in the past 5 years for highway construction and maintenance. The material has the following qualities: resistance to chemicals and other solvents; light weight; good adhesion; quick cure; toughness; resistance to cracking and freezing; and antiskid qualities in combination with abrasives. Polyester resins

Another possible adaptation of plastics to the highway field is for guardrail beams. During 1959, car impact tests on beams made of polyester resin reinforced with glass fibers were conducted in Rhode Island. These beams were cast in the same form as conventional metal guardrail. The results of the test did not seem sufficiently conclusive either to warrant use of this new type of guardrail as standard or as a fully competitive alternate to conventional types. Additional experimentation by industry with this material for guardrail, culvert, underdrains, and other highway uses is desirable.

Polyethylene films. At least 23 State highway departments have published specifications on the use of polyethylene film as a curing blanket or vapor barrier for portland cement concrete pavement. One of the principal advantages of this new adaptation of existing materials to the highway field is the flexibility of the film in providing good contact with the pavement. It aids in keeping the surface uniformly moist throughout the curing period. These plastic films also do not gain weight after rainfall and do not crack or mildew when wet. They can be reused by the contractor from 6 to 20 times without replacement.

Polyethylene film is also used in tape form to cover sawed joints in concrete paving during the curing period.

EXPLOSIVES

The constant increase in crawler tractor size and the more recent development of rear-end-mounted rippers have made it possible to excavate shale, weathered rocks, and other tight materials without the aid of explosives. These trends have been more than offset by the increased volumes of excavation required for a modern highway and by a 50-percent increase in aggregate requirements since the initiation of the expanded highway construction program. As a result, highway construction and maintenance during 1962 are expected to require about 140 million pounds of explosives.

Ammonium nitrate

Ammonium nitrate, which is also a fertilizer, is one of the newer types of explosives which are becoming more popular in quarrying operations and in the excavation of rock cuts. The relatively recent adaptation of diesel fuel as the hydrocarbon additive once the powder has been "prilled" or formed into small globes appears to have produced an extremely low-priced and effective explosive. A special surface treatment applied to the prills instead of a clay coating imparts anticaking characteristics and increases the blast sensitivity of the ammonium nitrate-fuel oil mixture.

This new method of using ammonium nitrate was due in part to the development of suitable rotary drills which are capable of producing dry blast holes, thus eliminating the need for water-resistant explosives. Several explosives manufacturers now furnish prilled ammonium nitrate in weatherproof plastic bags to facilitate handling and storage.

Other new developments

Ammonium nitrate is also used to replace a part of the nitroglycerin in extra grade dynamite to help impart lower velocity characteristics. Other new developments in explosive materials include

(1) Cast primers to prime explosive columns, particularly those using ammonium nitrate with diesel fuel. These primers do not contain nitroglycerin, are highly waterproof, and provide a very high detonation pressure.

(2) Electric detonators with precise delay interval that will assure no overlapping of discharges.

(3) Improved nonelectric detonators for use in areas where electrical interference presents a hazard. These are especially adaptable to bottom primes and produce less noise than ordinary prime cord.

(4) A nonnitroglycerin gelatin explosive which has more explosive punch per pound and is particularly adaptable to bottom loads in hard massive rock.

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