jan. 34,1916 Effect of Variables on Asphalt Penetration Test 
815 
With regard to penetration tests at relatively high temperatures, it is 
of interest to note the accentuated effect of slight variations in tempera¬ 
ture for any given material. This is due to the fact that all of the 
materials are much softer at this temperature. Thus, for a 50-gm. load 
applied for 5 seconds a difference of 24 points' penetration for i° C. (be¬ 
tween 45 0 and 46° C.) is noted for sample 8995, while for a 100-gm. 
load applied for 5 seconds at 25 0 C. a maximum difference of 9 points' 
penetration for 1 0 (between 25 0 and 26° C.) is shown for the same material. 
THE EFFECT OF VARIATIONS IN LOAD 
The penetration of asphalt cements is most frequently determined 
under a load of 100 gm. Penetration machines are, however, designed 
so that the combined weight of needle and plunger is 50 gm. The 100-gm. 
load is then obtained by placing an additional 50-gm. weight upon the 
plunger. A 100-gm. weight may also be used with the machine, so 
that loads of 50, 100, 150, and 200 gm. are possible. All of these loads 
are occasionally used in making the penetration test. It is clear that 
any variation in weight due to carelessness in manufacture or to changes 
brought about by the replacement of the original needle will most seri¬ 
ously affect the smaller loads—that is, a difference of 1 gm. should pro¬ 
duce proportionately a more marked effect where the 50-gm. load is 
employed than with heavier loads. A variation of 1 gm. is, of course, 
much larger than would ordinarily be expected to exist in different in¬ 
struments, but as great a variation as this has been noted by the writers. 
In order to determine the effect of variation in load, penetration tests 
were made upon all of the 12 samples with i-gm. variations from the 
50- and 100-gm. loads, and in addition to this the penetrations at inter¬ 
mediate loads between 50 and 200 gm. were determined in order to ascer¬ 
tain just what effect would be produced in the penetration of different 
types of asphalt cements by changes in load when the penetrations were 
all made for 5 seconds at a temperature of 25 0 C. The results of these 
tests are given in Table VI. 
Table; VI .—Effect of variations in bad on penetration of asphalt cements , 2§° C., 5 
seconds 
Load. 
California. 
Mexican. 
Blended. 
Blown. 
8961 
8962 
8963 
8948 
8949 
8950 
8994 
8995 
8996 
8956 
8957 
8958 
Gm . 
49 . 
31 
59 
89 
32 
60 
96 
40 
60 
106 
26 
53 
83 
32 
60 
90 
32 
61 
97 
40 
60 
106 
26 
54 
83 
32 
61 
91 
33 
62 
98 
40 
60 
106 
26 
54 
83 
35 
67 
98 
36 
67 
no 
43 
63 
120 
29 
63 
94 
40 
76 
112 
41 
77 
123 
48 
75 
133 
36 
72 
hi 
43 
85 
123 
45 
85 
134 
54 
84 
147 
39 
82 
124 
46 
9 i 
132 
48 
90 
140 
60 
90 
155 
4 i 
89 
134 
100.... 
46 
92 
132 
49 
90 
142 
60 
90 
155 
42 
90 
134 
IOI... 
46 
92 
132 
49 
9 i 
142 
60 
90 
156 
43 
90 
135 
125. 
Si 
IOI 
146 
54 
IOI 
159 
65 
IOI 
173 
51 
105 
157 
iso. 
59 
113 
160 
60 
113 
178 
76 
113 
192 
58 
118 
182 
200. 
68 
134 
178 
72 
129 
211 
90 
134 
218 
72 
153 
231 
