PORTLAND CEMENT TESTING. 185 



CONCLUSIONS. 



1. We believe that the composition of Portland cement best adapted 

 for use in tropical climate should be within the following limits : 



Per cent. 



Silica 22 -24 



Alumina 5-7 



Lime 62 -65 



Magnesia 0.0- 4 



Sulphur trioxide 1.0- 2 



Water and carbonic acid 0.5- 3 



2. "Soundness" in accelerated tests deserve special attention here, 

 because of the prevailing high temperature. Perfect soundness is espe- 

 cially important for concrete works which are exposed to the intense 

 heat of a tropical sun. 



3. "Underburning" is fatal to the eflBciency of Portland cement to be 

 used in the Tropics, as the unstable compounds so formed are most easily 

 attacked and decomposed by the energetic atmospheric influences. 



4. All "sound" cements should be protected from additional aeration 

 as much as is practicable, as othenvise quick setting or low tensile 

 strength is liable to be developed. 



5. Sound and well-burned cements, high in silica and low in alumina, 

 will withstand climatic influences best both before and after gauging. 



6. High alumina cements give fairly satisfactory results if they are 

 used before they develop quick setting. Quick setting is sure to develop 

 in such cements if they are exposed to the air for any considerable length 

 of time. 



7. Samples sent to the testing laboratory should be preserved in pack- 

 ages which thoroughly protect the cement from the atmosphere. 'No 

 accurate results consistent with the quality of the cement as it exists in 

 the barrel at the time of sampling will otherwise be possible. Setting 

 tests made at the laboratory before and after exposure should be insisted 

 upon, and if quick setting develops by this additional seasoning the 

 cement should be rejected. 



This work will be continued and our effort will be to secure samples of 

 as many grades of cement as is possible, in order more thoroughly to test 

 the soundness of these conclusions. 



