clinker, as it is ground. In general, air-entrainment maybe controlled to a much greater extent by the use ofadmixtures with normal cements during mixing. Thiscombination results in a concrete with tiny, distributed,and separated air bubbles (up to millions per cubic foot).The entrained air bubbles improve the workability of thefresh concrete. These bubbles reduce the capillary andwater channel structure within hardened concrete andrestrict the passage of water. That prevents the buildupof damaging water pressure in the pores when concreteis frozen; therefore, air-entrained concrete has greatlyincreased durability in outdoor locations exposed tofreezing weather. types I, II, III, IS, and IP cements areavailable as air entrained. The letter A is added after thetype to signify that it is air entrained; for example,air-entrained pozzolan cement is known as Type IP-A.In addition to the types described above, there arewhite cement, waterproofed cement, and oil wellcement. White cement is made from selected materialsto prevent coloring, staining, or darkening of finishedconcrete. Waterproofed cement has water-repellentmaterials added. The finished and set concrete has awater-repellent action. Oil well cement is speciallymade to harden properly when used under hightemperature in deep oil wells.Identification of CementThe EA assigned to a construction battalion may beasked to identify unknown material received by thesupply department. Every effort should be made toidentify the material directly by obtaining and, ifnecessary, translating, all labels, tags, shippingdocuments, manufacturing sheets, and all other papersthat may contain applicable information. When this doesnot produce satisfactory results, the simple proceduresoutlined in the following paragraphs generally willsupply enough information to permit a tentative, if notconclusive, identification. The positive identification ofcement, because of the wide variety of related- orsimilar-appearing materials, requires a completechemical analysis and physical tests.Make the following tests to determine whether thematerial is a cement, and then attempt an identificationof its type.HARDENING.— Select a small sample of thematerial and mix it with enough water to make a plasticpaste of a consistency similar to that generally used incement mortars. Then mold it into a pat about 3 inchesin diameter and 3/4 inch thick. Observe the paste severaltimes an hour to determine whether or not the paste issetting (hardening). The cement has attained a final setwhen the surface is hard enough to be unmarked whena pencil point or a fingernail is pressed against it withmoderate force. If it sets within 1 to 10 hours, thematerial is probably a cement.COLOR.— If it has been fairly well established thatthe material in question is a cement, color may serve asa means of further classification. If the material is gray,it is likely to be a portland cement; if brownish gray, itmay be a natural cement; if black, an aluminous cement;and if white, it probably is hydraulic lime, plaster, orpossibly white Portland cement,AIR-ENTRAINED CEMENT.— In the test todetermine whether or not a given material contains anair-entraining agent, place a sample of the material in aglass cylinder to a depth of about 1 inch. Add water toa depth of about 6 inches and shake the cylinder and itscontents vigorously. If a considerable volume of stable,persistent foam forms on the surface, the cementprobably contains an air-entraining agent.HIGH-EARLY-STRENGTH CEMENT.— Away to recognize high-early-strength cement (Type III)is to make a batch of concrete using the unknownmaterial and at the same time a similar batch using aknown cement. Concrete that contains high-early-strength cement will usually harden in less time thanconcrete containing regular portland cement. High-early-strength concrete, if molded into standardconcrete beams and tested after 3 days for flexuralstrength, should have a modulus of rupture more than150 pounds per square inch higher than similarspecimens containing regular portland cement concrete.A discussion of flexural strength testing will follow laterin this chapter.WaterWater plays an important part in the concrete mix.Its principal uses are to make the mix workable and tostart hydration. Any material in the water that retards orchanges the hydration process is detrimental. A goodrule of thumb is “if it’s good enough to drink, it may beused for concrete.”ORDINARY WATER.— The materials found insome types of water include organic compounds, oil,alkali, or acid. Each has its effect on the hydrationprocess. Organic material and oil tend to coat theaggregate and cement particles and to prevent the fullchemical reaction and adherence. The organic materialmay also react with the chemicals in the cement andcreate a weakened cementing action, thus contributing13-20
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