336 TESTING OF PORTLAND CEMENT. 



175. Tests for Soundness. The most- common te8t 

 for soundness consists in making pats of the cement with 

 the minimum quantity of water necessary to produce a 

 satisfactory paste. s)>iv;i<ling the pats on a piece of clean 

 glass, and tapering off the edges. When set, these 

 are placed some in water and some in air and kept 

 for a week, and then inspected to see if any cracks 

 or changes in shape have developed themselves. This 

 test is held by some to be unsatisfactory, because the 

 pats may appear perfectly satisfactory at the end of a 

 week, and yet show signs of deterioration when the 

 offending lime has had time to do its work. It is, there- 

 fore, advisable to keep the pats for a longer time, and 

 inspect them at intervals. 



In what is known as the Faija test, introduced by the 

 late Mr. Henry Faija, an artificial age is imparted to the 

 pats by subjecting them when newly made to a moist 

 heat of 100 Fah. or 105 Fah. for six or seven hours, and 

 then placing them in warm water at about 115 to 120 

 for 18 hours longer. In all about 24 hours are taken 

 over the test. 



176. Setting Properties. The setting of cement may 

 be divided into two stages, namely, the "initial set ; ' and the 

 " permanent set." The former of these is that point when 

 the crystallisation has caused a uniting of the particles to 

 such an extent that the paste will no longer flow, and lias 

 changed its condition of partial fluidity for that of a solid. 

 This point may be tested for by placing a pat of the 

 newly-mixed cement paste on a sheet of glass, and noting 

 the point when no movement will take place on the plate 

 being shaken or tapped. Another test for the same 

 purpose, adopted in the French Government Specification, 

 is as follows : "A portion of the pat made shall be taken, 

 and a cylindrical metal box, l|in. in height and 3'4in. 

 diam. filled with it. The box will then be shaken lightly 

 for a few seconds, and the water which this shaking 

 brings to the top shall be left on the cement. A prismatic 

 needle weighing 10'5oz., and having a square section of 

 one 0'039in., is then suspended over the box by a string 

 passing over a pulley. The moment when the mass no 

 longer allows the needle to penetrate to the bottom when 

 lowered slowly and with caution will be considered as the 



