clinker, as it is ground. In general, air-entrainment may be controlled to a much greater extent by the use of admixtures  with  normal  cements  during  mixing.  This combination  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 the fresh concrete. These bubbles reduce the capillary and water channel structure within hardened concrete and restrict the passage of water. That prevents the buildup of  damaging  water  pressure  in  the  pores  when  concrete is  frozen;  therefore,  air-entrained  concrete  has  greatly increased durability in outdoor locations exposed to freezing weather. types I, II, III, IS, and IP cements are available as air entrained. The letter A is added after the type 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 are white  cement,  waterproofed  cement,  and  oil  well cement. White cement is made from selected materials to  prevent  coloring,  staining,  or  darkening  of  finished concrete.  Waterproofed  cement  has  water-repellent materials added. The finished and set concrete has a water-repellent  action.  Oil  well  cement  is  specially made  to  harden  properly  when  used  under  high temperature  in  deep  oil  wells. Identification of Cement The EA assigned to a construction battalion may be asked to identify unknown material received by the supply department. Every effort should be made to identify  the  material  directly  by  obtaining  and,  if necessary,   translating,   all   labels,   tags,   shipping documents,  manufacturing  sheets,  and  all  other  papers that may contain applicable information. When this does not produce satisfactory results, the simple procedures outlined in the following paragraphs generally will supply enough information to permit a tentative, if not conclusive,  identification.  The  positive  identification  of cement,  because  of  the  wide  variety  of  related-  or similar-appearing   materials,   requires   a   complete chemical  analysis  and  physical  tests. Make the following tests to determine whether the material is a cement, and then attempt an identification of its type. HARDENING.—   Select a small sample of the material and mix it with enough water to make a plastic paste of a consistency similar to that generally used in cement mortars. Then mold it into a pat about 3 inches in diameter and 3/4 inch thick. Observe the paste several times an hour to determine whether or not the paste is setting (hardening). The cement has attained a final set when the surface is hard enough to be unmarked when a pencil point or a fingernail is pressed against it with moderate force. If it sets within 1 to 10 hours, the material is probably a cement. COLOR.— If it has been fairly well established that the material in question is a cement, color may serve as a means of further classification. If the material is gray, it is likely to be a portland cement; if brownish gray, it may be a natural cement; if black, an aluminous cement; and  if  white,  it  probably  is  hydraulic  lime,  plaster,  or possibly  white  Portland  cement, AIR-ENTRAINED  CEMENT.—  In the test to determine whether or not a given material contains an air-entraining agent, place a sample of the material in a glass cylinder to a depth of about 1 inch. Add water to a depth of about 6 inches and shake the cylinder and its contents vigorously. If a considerable volume of stable, persistent  foam  forms  on  the  surface,  the  cement probably contains an air-entraining agent. HIGH-EARLY-STRENGTH  CEMENT.—  A way to recognize high-early-strength cement (Type III) is  to  make  a  batch  of  concrete  using  the  unknown material and at the same time a similar batch using a known  cement.  Concrete  that  contains  high-early- strength cement will usually harden in less time than concrete containing regular portland cement. High- early-strength   concrete,   if   molded   into   standard concrete beams and tested after 3 days for flexural strength, should have a modulus of rupture more than 150  pounds  per  square  inch  higher  than  similar specimens containing regular portland cement concrete. A discussion of flexural strength testing will follow later in this chapter. Water Water plays an important part in the concrete mix. Its principal uses are to make the mix workable and to start hydration. Any material in the water that retards or changes  the  hydration  process  is  detrimental.  A  good rule of thumb is “if it’s good enough to drink, it may be used  for  concrete.” ORDINARY  WATER.—  The  materials  found  in some types of water include organic compounds, oil, alkali, or acid. Each has its effect on the hydration process.  Organic  material  and  oil  tend  to  coat  the aggregate and cement particles and to prevent the full chemical  reaction  and  adherence.  The  organic  material may also react with the chemicals in the cement and create a weakened cementing action, thus contributing 13-20