80 BULLETIN- 724, U. S*. DEPARTMENT OH AGRtCULTUEE. 



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. 



FOUNDATTON. 



(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.) 



FOBMS. 



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. 



CONCRETE. 



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 Uie largest batch which it is purposed to mix at any one time without 

 danger of mortar escaping over tlie 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. 



Tile 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 firstj 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 shiill be moist when 

 the conci-ete is placed. Tho striking off and tamping shall' be done with tem- 

 plets shaped to confoi-ni with the. cross section of the gutter and so operated 

 as to insure a uniform surface. The finishing shall be dono with a wooden float 

 and when completed the surface shtiU present a uniform mortar surface entirely 



