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POZMIX A CEMENT 1 1980 Definition combines with the calcium hvdroxide, contributing both "Pozzolans include any siliceous materials, either to strength and water-tighmess. natural or artificial, processed or unprocessed, which in While silica is the principal constituent of all ' the presence of lime and water will develop cementitious pozzolans,most materials contain substantial quantities of qualities. They can be divided into two groups of natural alumina and iron oxide.Although the principal product of and artificial pozzolans, respectively. The natural reaction between pozzolans and calcium hydroxide is pozzolans are for the most part materials of volcanic considered to be a calcium silicate, it seems certain that ' origin. The artificial pozzolans are mainly products there are formed other more complex compounds in obtained by the heat treatment of natural materials such as which the constituents of pozzolan other than silica are clays, shales and certain siliceous rocks. Certain involved.* combustion by-products (Pozmix A)of natural materials 'Though there is much that is unknown concerning have also been found to be pozzolanic in character."* the chemistry of pozzolanic reaction, it is certain that the rate of reaction with calcium hvdroxide is dependent on ' *"The Use of Portland-PozzolanCemenrByTheBureauOf both the mineral composition and the fineness of the Reclamation" by Robert F. Blanks, Chief, Research and pozzolan.* Geology Division, Bureau of Reclamation, Denver, Colorado. The pozzolan,by combining with the free lime in the ' portland cement, renders it more sound and less ANCIENT AND MODERN USES OF susceptible to the action of corrosive sulphate and acid POZZOLANIC MATERIALS waters. As the pozzolan itself is stable in the presence of ' these waters,the mixture of pozzolan-portland cement is The use of pozzolanic cementing materials dates back more resistant to sulphate and acid brines than neat to the times of the ancient Greeks and Romans.One of the portland cement. earliest pozzolans known was a volcanic ash or ruff found near Pozzuoli, Italy, from which locality these materials Pozmix A has a specific gravity of 2.3 to 2.6, obtain their name. Such ancient structures as the depending upon the source, as compared to 3.1 to 3.2 for Parthenon, the Colosseum, the Appian Way,built by the portland cements. This difference in specific gravity Greeks and Romans some 2000 years ago are still standing results in a lighter weight slurry for the pozzolan cement as ' today attesting to the lasting quality of pozzolanic compared to a slurry of similar consistency with portland cements. This same type of cement has been in rather cerpent.All pozzolan do not have the same characteristics general use in Europe for centuries, particularly for or at least not to the same degree. For this reason, such ' marine construction.This is the same type of cementitious materials require laboratory evaluation before use. material used in the construction of ancient Aztec buildings which may presently be found in Mexico and TYPES OF POZZOLANS USED IN OIL WELL Central America. CEMENTING ' Pozzolans have a respectable history in the United Various types of natural and artificial pozzolans have States. Cement for the Los Angeles Aqueduct (1910-12) been evaluated for oil well cementing.The best pozzolanic ' was interground with a slightly active volcanic ash; and materials have been selected after investigating their pumacite was employed in an experimental way in two chemical and physical properties and further con- dams of the Los Angeles Flood Control District in the sideration was given to availability, processing costs, twenties. But the real beginning of pozzolans in America location, etc. Most outstanding is an artificial pozzolan dates from Bonneville Dam. Since that time the which is designated as Pozmix A.The data acquired in our knowledge of these useful materials has greatly increased. laboratory show only slight differences in the performance Pozzolans as a fourth ingredient of portland cement of various fly ash materials when used in oil well ' concrete have an important place in modem construction cementing slurries. Pozzolans inherently produce de- as witnessed by their use on many large construction sirable characteristics which are improvements over neat projects. cement slurries. ' CHEMICAL AND PHYSICAL PROPERTIES OF POZZOLAN CEMENTS t When portland cement hydrates, calcium hvdroxide is liberated. This chemical in itself contributes nothing to *"What You Should Know About Pozzolans", hvRaymond strength or water-tightness and can be removed by E. Davis, Director, Engineering Materials Laboratory of ' leaching. When a pozzolan is present, however, it California, Engineering News Record—April 5, 1951. 1