270 Journal of Agricultural Research voi. x, no. 5 



TOUGHNESS TESTS 



Toughness tests were made on 2- by 2-inch cylinders, using the Page 

 impact machine for testing rock. The procedure was similar to that 

 employed in the standard rock test, except that a 2-inch instead of a 

 I -inch cylinder and a }4 instead of a 2 kgm. hammer were used. The 

 test consisted of a i-cm. fall of the hammer for the first blow, followed 

 by a 2-cm. fall, etc., until the cylinder was fractured. The height of 

 blow at failure in centimeters was used as an indication of the relative 

 toughness of the mortar. The results of tests are plotted in figure 4, 

 using the Feret triangle. Each result plotted is the average of three 

 tests. An inspection of the diagram shows at once that considerable 

 variation in toughness may be obtained, owing to differences in sand 



grading, but that, in 

 general, toughness in- 

 creases with the per- 

 centage of coarse sand 

 in the mix. The con- 

 tour lines, which bound 

 areas of equal tough- 



^___^ ness, show in a general 



/\ /\ /\ /\ /\ /\ y^ way the relative resist- 



/ 7 \--Jv,./\ X X ) v~A ''^ ^"^^ ^^ impact devel- 



' / \/\A\/ V \A\/ \^ ° *'^ oped by the use of dif- 



A/VM/VAAAAa ferent mixtures. The 



' "' A A /A^A' A A- A ^""^^ ""^ maximum 



(/ \y Vy \./ \/ \/ \./ \ <. toughness is seen at the 



^/\,/\A /\ A/^"A A A A top of the triangle and 

 ^ i; % — "> "„ — \ if "„ ^ - ^ — ^ — % — ^ includes sand having 



lATCBIAl- iADta NO. 50 3tE.vC. 



from 60 to 90 per cent 



Fig. 4. — Graph of toughness tests of artificially graded sand mortar. q£ coarSe f rom O tO 20 

 Proportions i to sj^ by weight. 



per cent of medmm, 

 and from 5 to 35 per cent of fine material. The area of minimum toughness, 

 as would be expected, lies toward the lower left-hand corner and includes 

 the very line sands. It may be noted also that, with a given percentage 

 of coarse sand, say 50, the highest results were obtained when the pro- 

 portions of medium and fine sand were about equally divided. On the 

 other hand, for a given percentage of either medium or fine sand, the 

 toughness appears to increase as the proportion of coarse sand increases. 

 In general, it would seem that the toughness of a cement mortar increases 

 with the amount of coarse sand present in the aggregate up to the limit 

 of maximum toughness, which, for this mix appears to be obtained with 

 a sand having about 80 per cent of coarse, 10 per cent of medium, and 10 

 per cent of fine material. The general effect of coarse sand on toughness 

 is shown clearly in figure 5, which is replotted from the results shown 



