Cement and Concrete Fence Posts. 5 
ten necessary to make a rough determination of the percentage of 
voids to the total aggregate. Where maximum strength is required 
about 10 per cent, more cement should be used than the total voids. 
The determination may be made as follows: Secure a water 
tight box or pail of known capacity, fill it with the aggregate to be 
used so that when it has been well shaken it will smooth off even 
at the top. Pour water of known amount into this until full. The 
volume of water used in proportion to the total volume of the re¬ 
ceptacle determines the total voids. 
For example, suppose the total volume of the receptacle in 
which the aggregate is placed is 2,032 cubic inches and that it takes 
two gallons of water to fill it. One gallon of water contains 231 
cubic inches and two gallons would contain 462 cubic inches. The 
total volume of water used, divided by the volume of the receptacle 
holding the aggregate represents the proportion of voids. Thus, 
462 divided by 2,032 equals 22.73, or the voids make up 22.73 per 
cent, of the total volume. For the maximum, strength 10 per cent, 
should be added to this. Ten per cent, of 22.73 equals 2.27. By 
adding this 2.27 to 22.73 we obtain 25, or in other words, 25 per 
cent, of the total volume should be cement. The mixture in this 
case would be represented by one part of cement to four parts of 
aggregate. 
The proportions used in the constructions of the fence posts 
in this bulletin varied from 1 part cement and 3 parts of sand to 1 
part of cement and 5 parts of sand. In others gravel was used in 
the proportion of 1 part cement, 3 parts sand, and 3 parts gravel. 
It is a difficult matter to use broken stone or gravel in large quan¬ 
tity and place the reinforcement properly. 
Measure all materials in correct proportions. This may be 
done with a shovel, a pail, wheel barrow, or barrel. It will usually 
be advantageous to measure the water, especially where small quan¬ 
tities are mixed or where the same amount of mixture is made 
several times. 
MIXING. 
Hand Mixing .—Where the mixing is done by hand, a flat 
water-tight platform, or shallow box is convenient. Measure the 
sand and place it in a uniform layer and over this spread the proper 
amount of cement. Mix this thoroughly before adding water until 
it shows a uniform color. The rule is to shovel it over at least three 
times. Now spread out the mixture, making a sort of basin in 
the middle into which the greater part of the water may be poured. 
Work in the dry edges until the water disappears, then add enough 
more water in small amounts to make the mixture of the desired con¬ 
sistency. Do not mix more material than can be used in twenty 
minutes. 
