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SPECIAL CEMENTS AND THEIR USES A catalog of special-purpose cements and the specific needs they meet

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number of special cements are now available to the concrete construction industry. Each type serves a specific function in terms of application, performance and d u ra b i l i t y. Although each may be used by itself to answer a special construction need, some may be used with other standard or special types to achieve special esthetic or functional objectives. The following descriptions of various special cements deal only with the basic characteristics of the cements and their applications. ASTM specifications cover most types of cement used in construction. Notable current exceptions are masonry, regulated-set, calcium aluminate, shrinkage-compensating, self-stressing, and oil well cements. In all cases, the first rule in using any special cement is to follow the manufacturer’s recommendations as closely as possible. Properly used, special cements can serve a va ri e t y of specialized re q u i re m e n t s. Improper application is always costly. Many of the special portland cements with which we are concerned here are for the most part simply variations of the well-known portland cement types 1, II and III. Some mention should be made of portland cement Types IV and V also. Type IV (ASTM C 150) is a minimal heat generating cement for use principally in those situations where heat generation must be minimized with respect to both rate and amount. Typical applications include massive concrete structures such as large gravity dams where temperature rise due to heat of hydration during hardening is a criti-

cal factor. Strength development with Type IV is slower than with Type I cement but ultimate strength is comparable. Demand for Type IV has dropped in recent years and very little is now produced. Type V (also ASTM C 150) is a sulfate-resisting cement. Whereas Type II cement is used as a precaution against moderate sulfate attack, Type V is designed for use in concrete that is to be exposed to severe sulfate attack. It is used principally where soils or ground waters show very high sulfate content. Since the amount of tricalcium aluminate in Type V cement is low, heat generation is relatively low during the first days of hardening and early strength gains are slower than with Type I cement.

Air-entraining cements The improved workability and durability of portland cements containing entrained air are well known. They are designated as Types IA, Type I IA and Type IIIA of ASTM C 150 and are produced by intergrinding with the cement clinker, during manufacture, acceptable amounts of air-entraining additions to comply with the ASTM specifications. These cements generally provide a sufficient amount of entrained air in concrete to meet most job conditions. They will not, howe ve r, infallibly produce a specified amount of air in the concrete and when this happens it may be necessary to add air-entraining admixtures at the mixer. The air content of concrete made with the agent added at the mixer is more controllable than in concrete made with air-entrained cement. Where care-

ful control is not practical, air-entraining cements are useful to insure that at least a significant portion of the required air content will be obtained.

Blended hydraulic cements The three kinds of blended hydraulic cements available are portland blast-furnace slag cement, portland pozzolan cement and slag cement; their ASTM designation is C 595. Portland blast-furnace slag cement is available as Type IS for use in general concrete construction or as Type I S-A where entrained air is desired. If moderate sulfate resistance is specified by the specification writer, this is indicated by the addition of the letters MS to the selected type designation. Where moderate heat of hydration is desired, the letters MH are added. Thus a portland blast-furnace slag cement which is air-entraining and has moderate heat of hydration and moderate sulfate resistance would be designated as Type IS-A-MH-MS. These cements are produced by blending portland cement and finely granulated blast-furnace slag or by intergrinding them. Grinding fineness is generally greater than for standard portland cement, providing the ability to reach a comparable ultimate strength. These cements have lower heat of hydration and harden more slowly than does standard portland cement. For this reason, curing time should be lengthened, particularly in cold weather. Concrete made with portland blast-furnace slag cement of Types IS-MS and IS-A-MS will successfully resist attack by sea water and sim-

ilar materials. Such cements are t h e re f o re widely used in marine construction, especially in Eu ro p e. They are suitable for use in large masses of concrete because of low heat of hydration. They are not recommended for use in pre s t re s s e d concrete. Portland pozzolan cements are specified in four types, designated Type IP, IPA, P and PA. The first two are used in general concrete construction, the latter two in concrete construction where high strengths at early ages are not required. Those with the A designations are, of course, the air-entraining counterparts of the other two. Portland pozzolan cement is a mixture of ordinary portland cement and finely ground pozzolan in which the pozzolan is 15 to 40 percent of the bag weight. A poz zo l a n is a siliceous or siliceous-aluminous material that will react chemically in the presence of moisture with calcium hydroxide (which is released during the hydration of the portland cement). Typical pozzolanic materials are some of the diatomaceous e a rt h s, opaline cherts and shales, tuffs, volcanic ashes, some fly ashes, calcined clays and shales of the montmorillonite type, and precipitated silica. Pozzolans by themselves are often used as cement replacements. This reduces the quantity of portland cement per cubic yard of concrete and subsequently the total heat of hydration, a desirable feature when large masses of concrete are placed. Maximum temperature is reduced, with a subsequent reduction in thermal stresses and cracking on cooling. The reduction in heat generation may require greater precautions when this cement is used in relatively thin sections of concrete placed in cold weather. At the sacrifice of lower early strength, portland pozzolan cement provides economical mass concrete with reduced early heat generation potential. It requires a prolonged period of moist curing for attainment of normal ultimate strength.

Well-made concrete produced from this special cement has increased resistance to mild chemical attack. In those localities where alkali-aggregate reaction occurs in concrete, portland pozzolan cement may serve, with proper mix design, to p re vent deterioration. Slag cements are designated Types S and SA of ASTM C 595. Slag cement, available in both plain and air-entraining types, is an intimate blend of at least 60 percent waterquenched blast-furnace slag and the balance hydrated lime. They are used as a blend with portland cement in making concrete and with h yd rated lime in making masonry mortar. They also have some refractory applications.

Natural cement Designated in ASTM C 10 as Type N or, with entrained air as Type NA, natural cement is produced by finely grinding calcined argillaceous limestone. The temperature of calcination is only as high as necessary to drive off carbon dioxide and water but not to sinter. Natural cement is lower in calcium oxide than are standard portland cements. It is now used primarily in making masonry mortars because these require high water retention capacity to compensate for suction from dry masonry units that would otherwise inhibit curing and detract from bond strength. The cement has a very high Blaine fineness. It requires an extremely long period for full strength development and for this reason its use in construction is limited; in many areas it has disappeared from the market.

Masonry cements These are available in either gray or white and vary considerably in chemical composition. They are not covered by ASTM specifications. Most are mixtures of portland cement, air-entraining additives and finely ground supplemental materials. Over and above the basic setting and strength requirements, they are formulated primarily for their abili-

ty to impart to masonry mortars w o rk a b i l i t y, water retention and plasticity. When combined with sand and water, masonry cement produces a highly workable mortar. Proportions will vary according to need from a low of about I to 2 1/2 to a high of about I to 5 by volume. (A p ro p o rtion of I to 3 is common.) These mortars have high plasticity, good water retention, minimum volume change, and no delayed expansion. When mixed with washed concrete sand they are suitable for external rendering and internal plastering. If a setting accelerator is used in cold weather, the quantity required is usually about half that which would be used with ordinary portland cement and no more than this amount should ever be used. Most masonry cements contain adequate a i r- e n t raining agents and, unless mixing is inefficient, no additional agent should ordinarily be required. Plasticizers, likewise, should seldom be added; if they are used it should be determined beforehand that they do not detract from strength.

White portland cements Types 1, IA, 111 and IIIA meet the requirements of ASTM C 150. White cement has found broad acceptance throughout the modern concrete construction industry. Its inherent beauty, especially when used to create special architectural effects, usually offsets its cost, which is nearly twice as much as natural or standard cements. It is currently being used rather widely in construction of white or colored walls, exposed aggregate surfaces and similar special concrete applications . Manufactured of materials of low iron and manganese content, white cement also has an extremely low water-soluble alkali content. In other respects, its basic chemical composition is the same as that of gray portland cement. It is ground more finely and has a lower range of specific gravity.

The types of white cement meet all the requirements of standard portland cements of the same type and can be used for exactly the same purposes as ASTM C 150 cements. Their strength is generally a little less than that of ordinary portland cement. To compensate for slightly lower rate of strength gain, the cement content of white cement mixes is usually increased by 10 to 15 percent. White cement is usually chosen for use in mixes for colored concrete walls and other tinted surfaces because it enhances color brightness. Colored cements are available that are made from white cement and pigments. These have good nonstaining and uniform color properties. They are offered in dry-batched form with specially selected aggregates. Their use is in cement paints, precast stone, terra z zo - c o n c re t e floors, internal and external renderings, and for setting and pointing work. The use of white cements requires careful attention to cleanliness on the job site. Mixing and placing equipment, form materials and trowels must be absolutely clean and free from rust, dirt and other contaminants. Sand aggregate must be extremely fine and uniform in color. To produce uniformity over the entire surface, mix proportions, mixing time, and placing and finishing procedures have to be identical for the entire job. Special care must be exercised in form construction to assure tight forms that will avoid sand streaking. Form oils should be of a type that will eliminate the possibility of discoloration . Surface burns are avoided by troweling while the surface is moist. Curing media used should be carefully selected to avoid discoloration. Clean nonstaining membrane-curing compounds or sheets of plastic should be used or the concrete cured by ponding. Any subsequent surface finishing procedures for special effects, such as sandblasting, should be carefully timed with a

consistent delay period between time of placing and time of special finishing.

Buff-colored cements Cements that impart a buff or tan hue to the finished concrete are commercially available. Most of these cements depend upon the use of certain raw materials for the color of the cement. Recent innovations in the manufacturing process have made possible the production of buff cements that do not require selected raw materials, a development that contributes to the consistency of the buff color in the finished product. There are no ASTM specifications for these cements .

Regulated-set cement Regulated-set cement is a hydraulic cement related to portland cement but containing an additional rapid-setting, rapid-strength-producing ingredient. There is as yet no ASTM specification. Various formulations provide controllable setting or handling times that range from one or two minutes to approximately 45 minutes. The correspondingly rapid strength development levels are also adjustable, depending upon the needs of the contemplated application. The Portland Cement Association has been granted patent protection on this type of cement and currently it is available from five manufacturers. Except for the regulated-set and early strength properties which are of significance during the first few hours in particular, tests show the physical characteristics of concrete made with regulated-set cement to be similar to comparable mixes made with standard portland cement. Handling time is influenced by mix temperatures along with control by basic formulation. Low mix t e m p e ra t u res lengthen and high t e m p e ra t u res shorten handling times. Ambient temperature to which a mix is exposed has little influence. Curing procedures are the same as those for standard portland cement concretes. Handling, plac-

ing, consolidating and finishing of freshly mixed mortars or concretes must be completed within the handling time available; revibration or rework after initial hardening is not feasible. Also to be considered is the significantly greater heat of hydration, which may or may not be advantageous, depending on the circumstances. Suggested applications include the manufacture of products such as block, pipe, and prestressed, precast or extruded elements; paving for airports and median barriers; patching and resurfacing of highways and bridge decks; vertical slip-forming; and f i re p roofing columns and beams. Specialized uses include lightweight insulating concrete, pelletizing iron ore, foundry molds, shotcrete, winter concreting, and underwater patching.

Calcium aluminate cement There is no ASTM specification for this type of cement, which is sometimes also called aluminous cement. Concrete made with calcium aluminate cement hardens very rapidly and gains its maximum strength in 24 hours. It contains calcium aluminates rather than the calcium silicates that make up the major portion of portland cements; its special manufacturing process makes it costly. The rapid hardening properties of this special cement make it an excellent choice for specialized concrete applications. In combination with insulating or refractory types of aggregates, it can be used for temp e ra t u re applications up to 3,000 degrees F. Its high 24-hour strength makes possible the application of full working loads within one day after placing. The use of selected corrosion-resistant aggregates provides resistance to weak acids and other similar corrosive materials. Calcium aluminate cement has a high water demand, combining with water in a quantity equal to about 55 percent of its weight. Other cements and lime are not recommended for use with this cement.

Retarding admixtures may be used, but their use will depend strictly on temperature conditions at placing. The cement is dark in color. It tends to produce a rather harsh concrete; this can usually be offset by increasing sand content. Delayed curing will be harmful, and normal curing procedures may not be applicable because curing must be achieved during the first 24 hours after placement. At normal temperatures curing can be initiated at the time of setting, 8 to 10 hours after mixing. The concrete may be sprayed or sprinkled intermittently for 24 hours after placing but must not be allowed to begin to dry during this period. Caution must be exercised in the storage of calcium aluminate cement. If stored or mixed at temperatures above 85° F., it may lose considerable strength and durability. A recommended procedure is to make low-slump mixes using ice water, keeping concrete temperatures below 74°F., and compacting and placing when ambient temperatures are below 85° F.

Expansive cements No ASTM specifications have been adopted for expansive cements, but a test to evaluate expansion will perhaps become a standard in a year or so. The cements are h yd raulic cements that expand during the early hardening period. The expansive component is anhydrous calcium sulfoaluminate or refixtures of tricalcium aluminate and gypsum in the right proportions. Three types have been designated by the American Concrete Institute, not on the basis of physical properties but on the basis of the major components used to make them. Type K is made up of anhydrous tricalcium aluminate, portland cement clinker, calcium sulfate and lime. Type M contains portland cement clinker, calcium aluminate cement and calcium sulfate. Type S contains portland cement that has a high tricalcium aluminate content and more than the usual amount of calcium

sulfate. For any of these, the expansive properties may be varied over a considerable range. In the United States two basic formulations for expansive cements have been developed. One, called shrinkage-compensating cement, is designed to expand and compensate for the shrinkage that occurs in conventional portland cement concrete as it hardens. The other, called self-stressing cement, is designed to generate greater expansive forces in the concrete when it hardens; if provision is made for sufficient restraint by embedding high-tensile steel in the concrete, or other suitable method, prestress will be achieved. Self-stressing concrete expands as it cures and stretches the reinforcing steel within it. The tension imparted to the reinforcement precompresses the concrete member by reaction. Self-stressing concrete applications include precast concrete pipe, precast arc h i t e c t u ra l panels, highway pavement, sidewalks and tunnel linings. Data from the Portland Cement Association indicate that the physical properties of concrete made from shrinkage-compensating cement are for the most part similar to comparable mixes made with standard portland cements. Slump loss may be greater under some circumstances, especially if extended mixing times are involved. Although strength gain may be low during the period of expansion, subsequent s t re n g t h s, modulus of elasticity, freeze-thaw resistance and abrasion resistance are comparable to those obtained with standard cements. Susceptibility to sulfate attack may be greater than with standard portland cements. The concrete may crack as a result of drying or temperature drop. To obtain the crack-reducing advantage of shrinkage-compensating c o n c re t e, restraint to expansion must be provided, either externally or internally, with the amount of restraint being dependent on the expansion characteristics of the conc re t e, design requirements of the

element and the environment to which it will be exposed. The restrained expansion induces a compressive stress in the concrete during the expanding period which helps offset the subsequently occurring shrinkage stresses . Applications will probably include slabs on ground in uncove re d floor areas of industrial buildings, highway and airport paving, parking decks, plazas and malls having areas below for parking or pedestrian use, many types of water-holding struct u re s, recreational areas, and food processing or pharmaceutical buildings and storage areas where c ra c k - f ree surfaces are functional hygienic requirements. Shrinkagecompensating concrete, of course, cannot be expected to ove rc o m e cracking caused by settlement, overloading, inadequate design or poor construction.

Oil well cements A P I Standard I OA, of the American Petroleum Institute Specification for oil well cements sets requirements for six classes. These special cements were developed for concrete used to seal oil and gas wells and are designed to set and cure at the high temperatures and pressures of oil-well grouting. They produce a low-viscosity, slow-setting slurry which reduces the amount of pressure required for pumping into place. Most of these cements include a retarder as well as a friction-reducing additive. They remain fluid for up to four hours and then harden very rapidly.

Plastic cements These are cements made and used only in California. There are no ASTM specifications written for them, but they must meet requirements set forth in California’s Uniform Building Code. According to this Code, they must meet the strength and most other provisions for ASTM Type I or Type I I portland cements. Plastic cements were designed for use in cement plaster and stucco,

but they are also used in masonry mortar applications. They contain a relatively high amount of entrained air and the Uniform Building Code allows up to 12 percent substitutive replacement for the portland cement content. The replacement materials are added to contribute plasticity. Their use is not recommended for general concrete construction.

Gun plastic cement A gun plastic cement is available that was developed specifically for application by pumps or guns. Manufactured by blending fine asbestos fibers into regular plastic cement, it is designed to overcome segregation while it is being pumped .

Waterproof cements Type I or IA cements with waterproofing agents added are used for concrete construction that is subject to hydrostatic pressure such as occurs in basement walls and storage tanks for liquids. Caution is advised in their use since cement alkalies may react with the waterproofing agent and diminish the effectiveness of these cements.

cements. There is no ASTM specification for them.

Magnesite cement This is produced by combining magnesium oxide with a solution of magnesium ox yc h l o ri d e. ASTM specifications C 275 and C 276 give the physical and chemical requirements of the magnesia and the magnesium ox yc h l o ri d e, respect i ve l y. A long series of other ASTM specifications set the requirements for mixing with water and for measuring a number of physical properties. This special cement has good strength and elastic properties. Because it can readily be polished it is used for floor toppings. It is easily damaged by water, but water resistance can be provided by including a small amount of copper in the mix design.

Hydrophobic cement This is produced the same way as o rd i n a ry portland cement but a small amount of water- re p e l l e n t material is added that forms a protective coating around each particle of cement. This coating retards hydration until the cement is mixed with water and keeps it from deteriorating when stored in humid environments. A low water/cement ratio can be used. It is used in soils stabilization and in concrete mixes to be pumped.

Strontium and barium cements These are cements in which the calcium has been either completely or partially replaced by either strontium or barium. Barium cement is extremely resistant to sea water; strontium cement can withstand higher temperatures than ordinary

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