WASHING AND GRADING SAND FOR CONCRETE. VII. 
medium, nor fine, but with a mixture of particles of all 
sizes, and that the sand should not be washed, but may 
contain up to 12% of clay, which will not injure but, per- 
haps, improve it.”’ 
The following is an extract from a report on “ Results 
of tests made to determine the strength of concrete when 
cement is mixed with sand and clay, or loam, in varying 
proportions.” The extract was from a report on the 
‘** Defences of Galveston, Texas,’’ by the officer in charge, 
Captain Edgar Jadwin, Corps of Engineers, to the Chief of 
Engineers, printed in the Report of the Chief of Engineers 
for 1905. The cement used was “* Double Anchor ”’ brand, 
the sand standard quality; the clay was taken from the 
cutter of a dredge, working in Galveston channel; the 
loam was heavy black soil from the mainland. Both loam 
and clay were thoroughly pulverized, free apparently from 
all vegetable matter and sand, and sifted to remove lumps. 
All briquettes were made from one sample on the same day, 
under same conditions. Theclay acted so unsatisfactorily 
during the working of the 25% batch, that no more 
briquetttes were made, but the loam was continued to 40%. 
It will be seen from the diagram that at 3 months the 
standard sand and cement mixture was strongest and 
remained so, that 10% clay was almost the same as standard 
at 28 days, and that 5% clay and 5, 10 and 15% loam, were 
all well above standard at 28 days, but fell very rapidly, so 
that at 3 months they had all fallen below the standard, 
and afterwards maintained about the same strength, while 
the standard went on improving. — 
These results do not bear out Professor Sherman’s, 
though they seem to have been very carefully conducted. 
Compare the results of Professor Sherman and Mr. Hain. 
The latter agrees with the former as to admixture of clay 
+ Engineering News, 27th February, 1906. 
