STRENGTH OF CONCRETE. 



XXVII. 



Fig. 3. 



1:". <* _ 











:i-H^;:- ~pr ai 









10 20 30 40 50 60 70 SO days 



Abscissae = Age in days. Ordinates = Crushing- force in 100 His. per square 

 inch. (Mean of two tests.) 



Sandstone with bluestone dust 



Nepean River sand 



Sydney white sand 



necessary for accurate results could not be obtained, the results 

 are probably less than the actual strength of the concrete in the 

 sewerage works at the age tested ; they are recorded in the Table 

 Series II., but the results have not been plotted as they were only 

 tested at two ages. 



A third series of tests were made on similar concrete prepared 

 in a similar manner but filled into accurately made metal moulds 

 forming cubes 6 inch by 6 inch by 6 inch, the results of these 

 tests may be taken as representing fairly accurately the strength 

 of concrete in the sewerage works, they are recorded in Table 

 Series III., and plotted in figs. 4 to 8 inclusive, but they are in 

 no sense laboratory tests as the concrete was made by ordinary 

 workmen. Compression tests were also made on concrete prisms 

 3 feet high by 12 inch by 12 inch made as in Series II., the results 

 of which are recorded in Table Series IV. 



