. Economic Papers. Forms: The weather, the brand of cement used, and theamount of water used in mixing will affect the length of time the formsshould remain in place. As a rule, on reinforced work they shouldremain as long as possible. Ordinarily from 7 to 14 days should beallowed for most reinforced work, although forms on exposed faces maybe removed earlier if the concrete has no load to support. Forms shouldremain under beam bridges 28 days, if possible. No heavy loads shouldbe allowed to cross a bridge having a span over 10 feet within a monthafter placing the concrete, unless the forms su
. Economic Papers. Forms: The weather, the brand of cement used, and theamount of water used in mixing will affect the length of time the formsshould remain in place. As a rule, on reinforced work they shouldremain as long as possible. Ordinarily from 7 to 14 days should beallowed for most reinforced work, although forms on exposed faces maybe removed earlier if the concrete has no load to support. Forms shouldremain under beam bridges 28 days, if possible. No heavy loads shouldbe allowed to cross a bridge having a span over 10 feet within a monthafter placing the concrete, unless the forms supporting the floor are inplace. Finish: On exposed faces, where possible, the forms should be re-moved after 48 hours and bumps rubbed or chiseled off and pocketsfilled with cement mortar of the same proportions as the mortar in theconcrete. In finishing the tops of wing and parapet walls the concreteshould be tamped until the mortar flushes to the surface. A straight N. C. Geological and Economic Survey. ILATK Concrete Pipe Culvert, Made with a Collapsible Form. COUNTRY ROADS IN NORTH CAROLINA 37 edge and short triangular strip of wood may be used to smooth the topand bevel the edges. CONCRETE WATERWAYS Plain and reinforced concrete may be used in all shapes of waterwayswhich usually occur on country roads. The shape to use, whether apipe, box, slab, or arch will usually depend on the location of the struc-ture. Staking Out: In laying out a waterway the length should first bedetermined. This is largely a matter of personal choice, but as a gen-eral rule structures having 25 square feet area of waterway or lessshould extend completely across the graded width, no guard rail beingnecessary; and those having over 25 square feet area of waterway shouldnot be less than 15 feet long, preferably 20 feet. Fig. 13 illustrates amethod of determining the length of small culverts illustrated in thisbulletin. The foundations are laid out according to the dimensions on the small
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