134 



CEMENTS, LIMES, AND PLASTERS 



The amount of slaked lime used in making lime-sand brick will 

 amount to 5 to 10 per cent of the whole mass, averaging about 8 per 

 cent. If all of this 8 per cent of lime be combined with silica in the 

 richest possible silicate (CaO.SiO 2 ), it will take up only 7 per cent of 

 sand. So that on the most hopeful possible basis only 15 per cent 

 of the brick would have any binding properties, the remainder being 

 merely uncombined and inert sand. 



General processes of lime-sand brick manufacture. The general 

 processes involved in the manufacture of lime-sand brick are, in order, 

 as follows: 



a. Slaking the lime. 



6. Mixing the lime and sand. 



c. Pressing the mixture into molds. 



d. Hardening the brick. 



Necessary properties of the sand. All the sand should pass a 20-mesh 

 screen, and it is desirable that part of it (say 10 per cent) should be 

 fine enough to pass a 150-mesh screen. Clayey material in the sand is 

 detrimental to the strength of the brick made from it. The compo- 

 sition of the sand grains themselves probably has little influence on the 

 strength of the resulting brick; but in order to secure a light and uni- 

 form color it is desirable that the sand should consist almost entirely 

 of grains of quartz and that the dark silicate minerals (hornblende, 

 garnet, mica, etc.) should be present in no great quantity. 



In testing the influence of size of sand, Peppel * used mixtures in 

 various proportions of two sands. These gave the following results 

 on sieving: 



The coarse sand was a very pure sharp glass sand; the fine sand 

 was crushed quartz. Made up into bricks with 5 per cent of lime the 

 results shown in the following table were obtained. 



* Trans. Amer. Ceramic Soc., vol. 5. Page 4 of pamphlet edition. 



