208 TESTS ON CEMENT 



manner. When hardened, grout is weak, friable, and porous. 



Coloring of Mortars. Colors are often used in mortars to 

 effect contrasts, or to subdue the glaring tone of cement in 

 sidewalks or in similar situations. Red lead weakens 

 mortar and should not be used. The color of hardened 

 mortar is quite different in appearance from one that is 

 still wet, so that where it is important to secure the cor- 

 rect tints, preliminary trials should be made until the pro- 

 portions desired have been determined. 



The various materials employed to produce different colors 

 in mortar, together with the quantity required per barrel of 

 cement, are as follows: For gray, 2 Ib. of lampblack; for 

 black, 45 Ib. of manganese dioxide; for blue, 19 Ib. of ultra- 

 marine; for red 22 Ib. of iron oxide; for bright red, 22 Ib. of 

 Pompeian or English red; and for violet, 22 Ib. of violet oxide 

 of iron. 



TESTS ON CEMENT 



FIELD INSPECTION 



In order to determine correctly the structural value of a 

 shipment of cement, an examination in the field is very 

 necessary. A number of packages of cement should be 

 weighed at intervals, and the average weight should never 

 be permitted to fall below 94 Ib. per bag, since mortar and 

 concrete are usually proportioned on the assumption of this 

 weight. Each package should also be plainly marked with 

 the brand and name of the manufacturer; those not branded 

 should be discarded, and, if possible, a mixture of different 

 brands should be avoided. 



A possible indication of inferiority is the presence of lumps 

 throughout the bulk of the material. On standing, cement 

 gradually absorbs moisture from the air. At first this mois- 

 ture is present in merely a minute and harmless state, but 

 eventually it combines chemically with the cement; that is, 

 in the same manner as when cement and water are actually 

 mixed together in practice. In the first condition, lumps 

 usually appear, but they are so soft that they may be readily 



