40 



(25) The table on page 39, from Taylor & Thompson is 

 safe for the strength of Portland cement concrete in direct 

 compression. 



(26) That Taylor & Thompson discuss the choice of 

 mixture relative to cost on pages 43, 44 and 45, and give 

 the tables on pages 41 and 42 following. 



(27) That various cements are composed of the follow- 

 ing ingredients. Table on page 43. 



(28) That fine grinding makes a cement which ia 

 stronger tested with sand; weaker neat; quicker setting; 

 produces larger volume of paste, and is less affected by 

 free lime. Tables on pages 44, 45 and 46. 



(29) That the quantity of water for cement pastes can 

 be deduced from Feret's formula: 



Plastic Mortars. 



Dry Mortars. 



Wr= percentage of water for mortar In terms of weight 

 of the mixture of dry materials. 



P = percentage of water required for neat cement of 

 normal consistency. 



fif parts of sand by weight to 1 part cement. 



(30) The setting of cements can be tested by means 

 of a wire 1-12 in. in diam. loaded to 1 A Ib. by observing 

 when the same is supported without leaving an indenta- 

 tion. (See Taylor & Thompson). 



(31) If a Portland cement passes the boiling test its 

 ultimate soundness is assured. 



DESIGN. 



In design the following working stresses can be taken 

 with safety if the conditions here specified are observed 

 when the concrete is placed. 



(1) That the cement has passed the specifications of 

 the American Society for Testing Materials. (See pai,'e 114 

 for complete specifications). 



(2) That the sand is clean and sharp and does not 

 contain loam exceeding 10% of the total volume. 



(3) That the stone is a durable crushed stone or 

 equally good gravel. 



(4) That these are mixed in the proportion of 1:2:4 

 by volume. 





