332 TKSTlXc; OF I 'OKI' LAN I) K.MKNT. 



briquettes ought to l>t> thoroughly set before they are 

 taken >ut of the moulds. This is best done by using 

 moulds which open, so as to obviate the forcing out of 

 the briquette. The most convenient moulds are those 

 which are fixed in a frame, so that the ramming does not 

 force out the cement and cause the mould to lift. 



The briquettes should be kept 24 hours in air after 

 gauging, and then placed in water for a stated time, such 

 as 7, 14. :?s days or more, before testing. 



When the time for keeping the briquettes in water has 

 elapsed they are to be taken out and broken in a tension 

 machine by applying the tension load until fracture takes 

 place. Generally speaking, the tensile strength increases 

 with the time which is allowed to elapse between gauging 

 and testing, that is, if the cement is from a good sample. 

 A faulty cement may yield good results after a week, and 

 show signs of deterioration after a further lapse of time. 



Besides neat cement that is, cement alone worked up 

 with water tests of a mixture of sand and cement are 

 frequently made. In these tests the cement is mixed with 

 a definite amount of sand in gauging, the most usual 

 proportion being three parts of sand to one of cement, the 

 minimum quantity of water being found by trial as in the 

 case of neat cement. The sand used for this purpose 

 should be clean, uniform, coarse sand, thoroughly washed. 

 In the great majority of cases a standard sand from 

 Leighton Buzzard is used. This is supplied ready for use, 

 having been washed and screened so as to pass a 20 to the 

 inch sieve and to be retained by a 30 to the inch sieve. 

 The treatment is otherwise the same as in the case of neat 

 cement. 



Having regard to the fact that cement is never used 

 neat in works of construction, but always mixed with 

 some quantity of neutral matter, it is held by many 

 authorities that briquettes made of sand and cement yield 

 more reliable results than do those of neat cement. 



The machines used for tension tests of cement 

 briquettes are of very simple construction ; in fact, any 

 ordinary tension machines, such as those previously 

 described in these pages,f may be used so long as they are 



t See pages 69, 89, 259, and 260. 



