PROPORTIONS AND MIXTURES 127 



Better results can be obtained with the batch mixer, because a 

 definite quantity of materials is added and thoroly mixed be- 

 fore any concrete is discharged from the mixer. By allowing the 

 materials to remain in the mixer for a definite period of time, 

 they are more completely mixed, and all parts are of uniform 

 proportion. In the continuous mixer, the dry materials are 

 fed automatically from a hopper into a mixing trough where 

 water is added and where the entire mass is mixed and carried 

 along by blades to the discharge end, where the concrete is 

 discharged continuously. 



FIG. 140-a. Another batch mixer. 



121. Consistency of Mixtures. The amount of water 

 used in making concrete will depend on the use for which the 

 concrete is intended. There are three consistencies ordi- 

 narily referred to in discussing concrete. They are generally 

 called the "dry," "quaky" and "wet" mixtures. The dry 

 mixture is of about the consistency of damp earth and is used 

 where the concrete is tamped into place. The quaky mixture 

 is so named because it is wet enough to quake when it is 

 tamped. It is used in molded products requiring reinforcing, 

 such as fence posts, beams, columns, etc. It is also used in 

 sidewalks, floors and foundations. The wet mixture contains 



