80 BULLETIN 724, U. S*. DEPARTMENT OF AGRICULTURE. 
as hereinafter specified, all parts of it will serve the required dimensions and 
conform in all respects to the plans and engineer's stakes. Wherever filling is 
necessary in order to bring any part of the trench to the required cross section, 
the material filled in shall be thoroughly tamped, and when the trench is com- 
plete it shall have a compacted and firm bed throughout. 
FOUNDATION. 
(If the climatic and subgrade conditions are such as to make a crushed- 
stone or gravel foundation necessary, the specification already given for the 
foundations of cobble gutters may be inserted here.) 
After the trench and foundation have been prepared as above specified, suit- 
able forms of either wood or steel shall be provided to receive the concrete 
paving. The top edges of the forms shall conform accurately to the line and 
grade required for the gutter. On curves in the alignment of the gutter the 
form sections shall be sufficiently short to give the appearance of a continuous 
arc rather than a succession of chords. The forms shall be sufficiently well 
braced to overcome all tendency to bulge out when the concrete is placed 
against them and shall have a bearing sufficiently uniform and stable to pre- 
vent all sagging while the concrete is being struck off and tamped. The bracing 
shall be so arranged as not to interfere in any way with the striking off and 
finishing of the gutter. The forms shall be clean when used and shall be smooth 
surfaced for all exposed faces. 
CONCEETE. 
The concrete shall be mixed in the volumetric proportion of 1 part cement, 2 
parts of sand, and 4 parts of coarse aggregate, with sufficient water to produce 
a mixture of such consistency that the concrete will hold its shape after being 
placed in the gutter, and finished to the required cross section. The mixing 
shall be thoroughly and uniformly done, either by hand or in a mechanical 
mixer previously approved by the engineer. Hand mixing shall be done upon 
a watertight platform of such area as to afford ample room for turning and 
mixing the largest batch which it is purposed to mix at any one time without 
danger of mortar escaping over the edges of the platform. The procedure in 
mixing concrete by hand shall be as follows for each and every batch: 
1. Mix the cement and sand dry until the mixture is of a uniform color 
throughout. 
2. Spread the coarse aggregate over the mixed sand and cement, add water, 
and turn the whole mass three or more times until every particle of the aggre- 
gate is thoroughly coated with mortar. 
The turning should be systematically done, beginning at one end and turning 
outward from the pile. In this way the entire mass is turned over and no 
core or center left undisturbed. The second turning should be at right angles 
to the firsts and the third again at right angles to the second. 
The concrete shall be placed in the forms immediately after the mixing is 
finished, and shall be spread, struck off, tamped, and finished before sufficient 
time has elapsed for initial set to begin. The foundation shall be moist when 
the concrete is placed. The striking off and tamping shall be done with tem- 
plets shaped to conform with the cross section of the gutter and so operated 
as to insure a uniform surface. The finishing shall be done with a wooden float 
and when completed the surface shall present a uniform mortar surface entirely 
