concrete for bonded floors did not show any advantage over conventional methods. Nevertheless, they do show promise for use in repair of damaged concrete and for protection of concrete against erosion or cavitation when subjected to high velocity flow of water. In making repairs on essentially vertical surfaces where it is not practical to use sand-cement or neat cement grout, epoxies seem to offer an opportunity to secure better bond than is obtained by placing fresh concrete against hardened concrete without grout. Epoxies also seem to be useful as the binder to make epoxy grout or concrete for patching. They also appear to have possibilities as protective coatings on concrete which will be subjected to high velocity flow of water. Research is underway by the corps and possibly by others to determine whether or not epoxies can be successfully used for the purposes described and if so to determine how they should be used to get maximum benefits. We plan to accelerate our investigations into the uses of epoxies.

Epoxy resins are readily available from many sources. One of the problems in investigating epoxies is the large number of epoxy resins on the market and the lack of information regarding the chemical composition of these materials. In spite of this problem it may be possible to develop a performance-type specification which will permit purchase of epoxy resins without regard to chemical composition.

Epoxy resins are quite expensive. Prices range from $14 to $16 per gallon f.o.b., place of manufacture.

Polyvinyl acetate.-This material which is a synthetic organic chemical compound was reported to be useful in combination with portland cement for bonding fresh concrete to hardened concrete for bonded floor topping and similar work. It was also reported to be useful as an admixture in concrete. A review of the experience of others with this material indicated that it performed as claimed in a dry atmosphere but did not perform well in water or in high humidity atmosphere. Since most corps concrete is subject to one or both of these conditions in service polyvinyl acetate has limited application to our work.

CONSTRUCTION MATERIALS FOR FOUNDATION TREAT

MENT, AND EARTH AND ROCKFILL DAMS

FOUNDATION TREATMENT

Frequently, soil and rock foundations of large structures such as dams require consolidation over and above that provided by nature. Natural fractures, faults, or subsurface water courses which might endanger the integrity of structures or result in excessive seepage, must be sealed to obtain sound foundation conditions. This objective is achieved by several methods and materials, of which two in particular are constantly changing with new demands and construction experiences. The two methods referred to are foundation grouting and rock bolting. The first involves injection of liquid cementitious compounds into the subsurface materials, at controlled pressures. The second, rock bolting, employs high-strength steel bolts with expanding anchor ends to literally pin or bolt rock masses together.

Chemical grout.-Grout is generally considered to be any combination of liquid and/or solid cementitious materials which, when injected into subsurface materials, will result in their consolidation. Grouts composed of portland cement and water are used most frequently to accomplish this objective in the case of fractured rocks. However, to consolidate soils such as sand and gravel, chemical solutions which after injection and combination underground will react to produce gels or precipitates, generally afford the only satisfactory grouting medium. While several chemical solutions have been tested and used with varying degrees of success in the past, rather recently a product known as AM-9 has received considerable attention from both engineers and the construction industry. This product is manufactured by the American Cyanamid Co., and consists of a water-soluble mixture of two organic chemicals, acrylamide and N.N'-methylenebisacrylamide, in proportions that can be made to combine chemically to produce stiff gels. Two catalysts, ammonium persulfate and B-dimethylaminopro-pionitrile, are used to initiate and control the gelling process as the chemicals are injected underground. The manufacturer claims that AM solutions will gel in concentrations as low as 3 percent by weight and as high as 50 percent, the solubility limit.

AM-9 chemical grout and the two catalysts may be mixed together as batches and injected underground with conventional grout pumps, or the chemical solutions may be injected separately by a metering process, which permits closer control of the gel time by separate injection of the ammonium persulfate. The corps proposes to conduct tests of this material, along with those including other chemical solutions, in connection with the 1963 fiscal year research program.

Rock bolts. While bolting of rock masses to preserve their integrity has been used in mining and tunneling for roof support for almost 100 years, scientific modification of bolts to meet requirements of large engineering structures is a relatively recent development. The

common mine roof bolts which have been adapted to rock bolting are of two basic designs, the slot-and-wedge and the expansion-shell types. Anchorage of the slot-and-wedge type of bolt is obtained by driving the slotted bolt over the wedge at the bottom of the hole, causing the slotted end of the bolt to expand against the side of the hole. Tensioning of the bolt is obtained by tightening a nut against a steel bearing plate. The expansion-shell type bolt is anchored to the rock in the hole by expansion of a shell similar to that of the conventional Molly bolt, while the bolt is being tensioned against the bearing plate on the rock face.

Two more recent developments of rock bolting are the perforatedsleeve bolt and the modified rock anchor bolt. The perforated-sleeve bolt was first designed for use for rock support where it was necessary to have a greater degree of permanence than obtained by unprotected steel bolts. In this method perforated steel pipes are cut in two longitudinally, and filled with plastic mortar. Both half-round parts are then wired together and inserted in the hole, after which the bolt is driven through the mortar, resulting in essentially complete filling of the hole by the extruded mortar, tube, and bolt. This grouted type of bolt anchorage is superior in low-strength rocks which are not adapted to the more conventional rock bolt.

The modified rock anchor bolt was developed by industry from a design prepared by geologists in the Office, Chief of Engineers. It is essentially a modification of the basic rock bolt design, with an extension to the outer end of the bolt to which reinforcing steel can be attached. The initial development of this bolt was dictated by the need in many instances for a device which would not only serve to hold rock together before covering it with concrete, but which later could serve also as a foundation anchor for the concrete structure.

The use of rock bolts by the Corps of Engineers is very extensive, and will continue to increase as experience in this form of rock stabilization is acquired by the construction industry. The cost of rock bolting varies with the style and size of bolts used, as well as the specific geologic conditions in which they are used.

Earth and rockfill dams.---Studies are underway as part of the civil works investigation program to determine more reliable test methods of soil properties. This includes the stress-strain characteristics of sand and gravels, the influence of large gravel sizes on the densities and shear strength of compacted gravels, the influence of pore water pressures on the shear strengths of compacted and undisturbed clays, and the most reliable method of measuring such pressures. Studies are also in progress as to the influence of time on the strain characteristics of compacted clays. It is planned to include studies of weak broken rocks and gravels to determine the most suitable means of determining their strength-strain properties which will be useful in the design of high embankments where such materials may be available for construction. Studies are also planned for the strength-strain properties of weak stratified rocks such as shales which are often encountered in the foundations of hydraulic structures.

OTHER CONSTRUCTION MATERIALS

ACRYLIC PLASTIC FOR CONTROL ROOM CEILING

Clear acrylic plastic panels (methyl methacrylate) in the form of corrugated sheets or molded control lenses suspended below suitably arranged fluorescent lights have been used in the construction of luminous ceilings in the control rooms of hydroelectric power plants. (See fig. 14.) Luminous ceiling-type lighting systems are particularly suitable for control rooms as they provide practically uniform lighting intensity on horizontal surfaces over the entire area and also provide adequate lighting of indicating instruments on the vertical panels of switchboards without objectionable glare. Acrylic plastic material has a high and constant light transmission factor, good light diffusion characteristics, excellent color stability, and good dimensional stability. Where luminous ceilings are provided, the use of this material is evaluated along with formed glass control lenses and open aluminum or plastic egg-crate type ceiling panels on the basis of the quality of illumination provided, installed first cost, annual cost, and cost of maintenance. The material is known under trade names of Lucite and Plexiglas and can be procured under Federal specifications L-P391, October 23, 1956, and L-P-507, July 6, 1961, and under MIL Specifications P-5425B(1).

POLYVINYL CHLORIDE ELECTRICAL CONDUIT

Polyvinyl chloride (PVC) rigid plastic electrical conduit is acceptable as an alternate to other types of electrical conduit for use in duct banks and in other locations where its use can be justified on the basis of economy or corrosion control. This type of conduit is particularly suitable for use in certain locations where severe corrosive conditions exist, such as some of the high-voltage switchyards at hydroelectric projects and certain coastal installations. Plastic conduit is evaluated along with other suitable corrosion-resistant types of conduit on the basis of economy in installed first cost, reduced maintenance, and increased life. The plastic conduit material and conduits are specified to conform to the chemical and physical characteristics and tests required in OCE Guide Specification CE-303.06, June 15, 1961, which are more rigid, in certain respects, than the requirements of Interim Federal Specifications L-C-00740 (GSA-FSS), February 15, 1961, for "Conduit and Fittings, Plastic." This material is commercially available from at least three sources.

PAINTS

Vinyl resin. Spray-applied vinyl resin coatings have been used extensively in recent years for the protection of ferrous surfaces subjected to water immersion or atmospheric exposure. It has replaced the coal-tar enamel coats previously used on penstocks because of application advantages, and it provides the additional advantage of a

smaller friction loss. Present activities at the corps' Rock Island Paint Laboratory include the search for improvements in the formulations and in procedures for surface preparations.

Urethane coatings. These relatively new coatings are being investigated extensively. The problem concerns the development of a formula that will serve adequately on water-immersed steel surfaces. Some urethane paints formulated by the corps' Rock Island Paint Laboratory, and which are presently being tested, give promise of performing well. A principal advantage appears to be its good resistance to abrasion.

Epoxy resin-coal tar coatings.-Various formulations of this type of coating have recently been evaluated at the corps' Rock Island Paint Laboratory to determine their service and application properties. This program is being continued to improve the paint's properties. Problems involved which are being investigated include the slow cure time, only fair abrasion and adhesion qualities, blistering underwater and unpleasant odor.

JOINT MATERIALS

Plastic water stops.-Extruded polyvinyl chloride has been used for water stops in recent years on a limited basis. The labyrinth type has important installation advantages and is presently being used at tunnel monolith joints. For a long time, rubber was considered the best material for flexible water stops needed at joints subjected to differential movements. However, attention also is being given to polyvinyl chloride for this application because it promises to have