STRENGTH OF CONCRETE. XXXI. 



Tensile strength of concrete. — The same concrete described in the 

 foregoing tests was tested in tension: large size briquettes were 

 prepared in which the proportions were the same as in the 

 standard English and American briquettes used in cement testing, 

 but the smallest section was 10 inches by 10 inches =100 square 

 inches. The accurate preparation of such large specimens by 

 ordinary workmen in timber moulds, and the subsequent testing 

 in the machine, was by no means an easy matter, and although 

 they were tested carefully the results cannot be looked upon as 

 representing the true tensile strength of the concrete in the work, 

 as the nature of the process used in making the specimens must 

 have rendered the results lower than would have been obtained 

 on specimens prepared in the laboratory; they are recorded in 

 Table Series VII. 



Conclusions on the compressive strength of concrete. — Fig. 1 

 Series I., shows the compressive strength of bluestone concrete of 

 three proportions with three kinds of sand, from which it is clear 

 that bluestone dust is superior to either Nepean River sand or 

 Sydney white sand, also the Sydney white sand comes out a little 

 better than the river sand in this concrete, it will be observed 

 that there is a fall in strength from 30 to 80 days, which would 

 probably rise again at a later period, but the tests were not 

 carried beyond the ages shown. 



Fig. 2, Series I., shows the compressive strength of Nepean 

 River gravel concrete of the same three proportions and the same 

 three kinds of sand ; here the Sydney white sand is best for the 

 6 to 1 and 8 to 1 concrete, but the bluestone dust is best in the 

 10 to 1 concrete, and in every case the Sydney white sand is 

 better than the Nepean River sand. 



Fig. 3, Series I., shows the compressive strength of sandstone 

 concrete of the same three proportions, mixed with the same three 

 sands, from which it will be seen that the effect of the sand is less 

 than in Figs. 1 and 2, being about equal in the 6 to 1, and differ- 

 ing slightly in the others. 



