PART VII. PUZZOLAN CEMENTS. 



CHAPTER XLI. 

 PUZZOLANIC MATERIALS IN GENERAL. 



PUZZOLANIC materials include all those natural or artificial materials 

 which are capable of forming hydraulic cements on being simply mixed 

 with lime, without the use of heat. Many materials possess this property, 

 but relatively few have ever attained to sufficient commercial impor- 

 tance to be discussed here. In composition the puzzolanic materials 

 are largely made up of silica and alumina, usually with more or less 

 iron oxide; some, as the slags used in cement-manufacture, carry also 

 notable percentages of lime. As might be inferred from this compo- 

 sition, most of the puzzolanic materials possess hydraulicity to a greater 

 or less degree of themselves, but the addition of lime usually greatly 

 increases their hydraulic power. 



The term puzzolan, here adopted for this group of cementing mate- 

 rials, is a corruption of the adjective form of the name pozzuolana. 

 It has no particular etymological excuse for existence, but will be 

 accepted in this volume for the sake of uniformity, as it seems to have 

 been adopted by various authorities in the United States. 



Natural Puzzolanic Materials. 



Natural puzzolanic materials are quite widely distributed, though 

 they have never attained much commercial importance, save in Europe. 

 As regards their origin, they are of two classes: In the first class may 

 be included all those which are the direct products of volcanic action, 

 the material being a fine volcanic ash or dust deposited either on the 

 slopes of the volcano or carried by the wind to lakes or streams in 

 which the ash is deposited. This group includes the more active puzzo- 

 lanic materials, its chief representatives being pozzuolana proper, san- 



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