WATER-REDUCING AND RETARDING CHEMICAL ADMIXTURES General.-As far as classes of material are concerned, there are no new chemical admixtures for concrete but the situation with respect to one class (set-retarding and water-reducing admixtures) has changed materially within the last 5 years as a result of expiration of a patent by which the manufacture of the lignin base material was controlled. As a result there has been a resurgence of interest in this class of materials and there have appeared on the market possibly 40 or more new trade name materials in this class most of which are believed to be lignin base materials. There has also been a resurgence of interest in purchase specifications and methods of evaluation of performance of these materials. Although no standard purchase specification for this class has ever been adopted by either ASTM or the Federal Government, ASTM has now undertaken to develop purchase specifications for chemical admixtures which will cover this class and accelerating admixtures. A proposed specification is currently under consideration for adoption. It is understood that the proposed specifications will cover five types of chemical admixtures as follows: Type A, water-reducing admixtures. Type C, accelerating admixtures. Type D, water-reducing and retarding admixtures. Type E, water-reducing and accelerating admixtures. This general class has been further classified into four chemical classes as follows: (1) Lignosulfonic acids and their salts. (2) Modifications and derivatives of lignosulfonic acids and their salts. (3) Hydroxylated carboxylic acids and their salts. (4) Modifications and derivatives of hydroxylated carboxylic acids and their salts. Investigations and use problems.-The corps and others have carried on investigations of this class of materials during the last 4 or 5 years. The aims of the corps investigations have been to develop information on the characteristics and performance of this class of materials to determine whether or not their use would be beneficial in corps work and if so to provide a basis for preparation of suitable purchase specifications and criteria for use of these materials. The corps has contributed to the work of ASTM on development of the purchase specification for chemical admixtures referred to previously through participation in Subcommittee III-h of ASTM Committee Č-9 which has developed the proposed specification. These investigations have shown that behavior of these materials is variable and unpredictable. Differences in composition of cement seems to be the primary factor which influences the variable performance of these materials. At their best, the water-reducing agents have been demonstrated to reduce water requirements by 15 to 20 percent. At their worst some of the agents with some cements give no reduction in water required. In addition to the problem of variable performance there are two other problems with these materials for which no satisfactory solution has yet been developed. One of these is the "slump loss" problem. Some of these materials cause concrete to tend to lose slump (become stiffer in consistency) more rapidly than similar concrete without the agent. This tendency complicates the practical problems of transporting and placing the concrete. The other problem is that of abnormal hardening. Some of the lignin materials have been known to delay hardening of concrete to such a degree that no appreciable gain in strength occurs up to as much as 4 days after placing. In a tunnel lining project in California the concrete in the crown came down with the forms when they were removed about 10 hours after the concrete was placed. (See Journal of the American Concrete Institute for March 1961.) Removal of forms at such an early time is common practice in lining tunnels with concrete. Following removal of the forms the concrete in this case remained soft enough to mold by hand for a period of 4 days. The admixture used was a lignin base material. It is understood that occurrences of this type have been frequent with lignin base admixtures. (See Journal of the American Concrete Institute for September 1961.) The case cited is one of the very few that have been publicized. The cause of the abnormal hardening in this case is believed to have been due to the fact that the sulfur trioxide content of the portland cement used was lower than required for normal hardening with the agent used. To date the corps has made limited use of retarders and some but even less use of water-reducing agents. When used, contract specifications have been adaptations of the proposed ASTM speci fications. Use of this class of materials will be possible in corps work when satisfactory purchase specifications have been developed and the problems discussed have been solved. Also it will be necessary to develop a basis by which economic benefit will be assured and protected. This is one of the difficult problems because the corps uses entrained air in essentially all concrete placed and air-entrainment results in a dependable reduction in water requirement of from 10 to 15 percent from that required for comparable concrete made without entrained air. On the matter of retardation there will evidently be hot weather placing situations where it will be necessary to delay and control the rate of stiffening (set) of the concrete in order to properly execute the construction and in these instances use of a retarder will be especially advantageous. OTHER CHEMICAL ADMIXTURES Air detraining admixture. This is a new admixture for use in concrete where the combination of materials being used entrains too much air. This agent reduces the amount of air entrained to the desired amount. Under the corps practice of thorough preconstruction investigation of concreting materials and addition of the air entraining admixture at the mixer this problem is not confronted. Thus the corps finds essentially no use for this material. Integral hardeners.-This is not a new class but new products in the class have come on the market in the last few years. Investigations conducted over the years by the corps and others have universally revealed that well-designed, well-controlled, and properly placed concrete is adequate for any service condition to which corps concrete is subjected in civil works. The corps has no apparent need for this class of material in civil works. Surface hardeners.-This is not a new class but new products periodically appear on the market. These materials are intended primarily for alleviation dusting which results from wear and which is characteristic of poor quality concrete floors. The corps does not normally have a requirement for this material in civil works. Accelerating agents.-This is not a new class but new materials do occasionally come on the market. The material used most frequently is calcium chloride. There is considerable evidence available that calcium chloride is not suitable for use in prestressed concrete, since it apparently contributes to corrosion causing so-called "stress corrosion" failure. A need exists for materials which will accelerate hardening (strength gain) but will not cause corrosion of prestressing steel. Expanding agents.-This is not a new class but new materials do occasionally become available. These materials perform the function of counteracting the shrinkage (setting shrinkage) which occurs during the early stages of stiffening. They find usefulness primarily in mortars and concrete for setting machinery bases and in certain special types of concrete such as preplaced aggregate concrete. Small quantities of aluminum powder are useful for this purpose and some of the products on the market sold for this purpose are basically aluminum powder. Others use other metallic forms including finely divided iron. The behavior of these materials particularly those including iron is difficult to predict and control. Composition of the portland cement used with these materials substantially affects their behavior and performance. The corps is currently engaged in an investigation aimed at developing improved purchase specifications and practices for use of these materials. When perfected these will eliminate the need to refer to these materials in contract specifications by trade name "or equal" and will provide for improved performance of these materials in corps work. Waterproofing agents. This is not a new class but new products in the class occasionally become available. There are two types in the class, namely, integral (included in the mix) and surface treatment. These materials are not generally used in corps civil works construction since good quality materials and proper manufacturing will normally provide the desired degree of water tightness. Inhibitors of corrosion of reinforcing steel.-A process for use of sodium benzoate as an inhibitor of corrosion of reinforcing steel has been patented in England. As far as is known the process has not been used in the United States. The corps has had no major corrosion problems with reinforcing steel since most of the corps structures are in nonsaline surroundings. JOINT CLEANUP Construction joints (stoppages) in monolithic (bonded) concrete are usually cleaned by washing with high velocity water or air and water before the concrete has hardened or by wet sandblasting after the concrete has hardened. To be effective, the first of these procedures must be carefully timed and timing varies with weather conditions, particularly ambient temperature. The only new development in this connection is a chemical (in liquid form) put on the market about 5 or 6 years ago. It is a retarder which is applied to the surface to be cleaned immediately after the concrete is placed and compacted. It delays the setting of the mortar to a depth of about 1⁄4 to % of an inch thus allowing a longer period of time for completion of the cleanup operation when performed by washing with water or air and water. The one product so far available for this purpose was tested by the corps for the primary purpose of determining whether or not its use would be harmful. Test revaled that it was not harmful and could be used without fear of detriment to the quality of the work. The product has not been very widely accepted because of its cost and because there is a lack of information on behavior and effectiveness in varying weather under field conditions. As far as is known only one product is currently being promoted for this purpose. It seems logical to assume that any retarder in such form as to be readily and uniformly applied to a construction joint surface would be equally as effective for this purpose as the one material now being promoted for this purpose. Estimated cost of the material is about $0.05 per square foot of surface cleaned. The use of this material thus potentially increases the cost of cleanup by about this amount. In order to be attractive to a contractor, this material must thus provide some benefit which will offset or balance the cost of the material on the concrete. Thi might be in the form of reduced overtime costs resulting from the extended period for cleanup which would permit all cleanup to b performed during regular shift hours. This possibility seems rathe remote on the large mass concrete job where cleanup is usually con ducted around the clock. This product has had limited use on corp projects. CURING AND PROTECTION General. Essentially all permanently exposed surfaces of corp concrete structures and all surfaces to which other concrete is to b bonded (construction joints) are moist cured. The method of apply ing the necessary water is optional with the contractor. Surfac which are not to be permanently exposed such as bulkhead faces dams, and surfaces to be covered by backfill, and surfaces such as galleries of dams which are protected when in service may be cure with membrane forming compounds or moist cured at the option the contractor. Membrane forming curing compounds. This is not a new class materials but is of interest because of the manner in which it specified. For corps work any material which will form a continuo membrane and which when tested under controlled conditions w meet the moisture retention requirements of the corps specification and which does not interfere with hardening of the concrete may used. Thus any new material which meets these conditions and economically attractive will be of interest to both contractors and corps. In corps work the contractor is required to furnish the curi compound and thus the primary interest in new materials is larg shared by the producers and contractors. Most of the compounds available are so-called wax (or paraff base compounds. Resinous materials make excellent compounds are somewhat more expensive than wax base materials on the mark -te Curing compounds cost about $0.005 per square foot of surface for covered for material. There are many sources of supply and competition is very keen. Moist curing.-Contractors are using devices made from some of tes the new plastics. Some are using the so-called "soakers" which are plastic hose with perforations which open under pressure of water thus providing dispersed water sprays. Contractors will probably also make use of lightweight rigid pipe made from plastics for distributing curing water because they offer the advantage of being noncorrosive and thus protect the water from pickup of staining contaminents. Cost will have a substantial bearing on the degree to which rigid plastic pipe is used. Here again the primary interest is largely shared by producers and contractors. Insulating materials. These find two uses in construction of concrete dams. One is in providing protection against freezing of fresh concrete and the other is in protecting exposed surfaces during extremely cold weather against temperature cracking. New materials for this purpose consist mainly of the cellular plastics such as polyurethanevinylcopolymer foam, expanded polystryene and others. Corps specifications for both applications are performance specifications thus selection of materials is up to the contractor. The corps is interested in the ability of these new materials to resist change in insulating properties when exposed to weather for a period of several months. Thus some research on this is planned and will be undertaken as soon as funds become available. Plastic sheets.-Polyethelene and other plastics are made into sheets which are useful in "housing in" work areas in winter for protection of the work against freezing. These materials are of interest primarily to contractors. BONDING MATERIALS General.-In most of the concrete construction by the corps fresh concrete is bonded to hardened concrete by thoroughly cleaning the surface of the hardened concrete and by application of a layer of sand-cement grout to the surface of the hardened concrete immediately prior to placing of the fresh concrete. In two-course (bonded) floors the same procedure is followed except that a neat cement mortar is applied to the hard concrete to which floor topping is to be bonded. In repairing concrete the practice in the past has been essentially the same as described above with choice of sand-cement grout or neat cement depending on thickness of repair or in cases where repairs are to generally vertical surfaces no grout is used. Proprietary bonding materials. During recent years a substantial number of bonding agents have been put on the market. These materials are claimed to provide better bond between fresh concrete and hardened concrete than can be obtained by the conventional methods described above. They are recommended for bonded floors and for patching damaged concrete. Tests by others indicate that when an old surface is properly cleaned none of the proprietary materials produce better bond than that obtained by using portland cement grout. In view of these tests the corps has continued to use portland cement grout as the bonding agent. Epoxy resins for repair and protection of concrete. In the tests. referred to above epoxies for bonding fresh concrete to hardened |