10. Depositing. (a) Each layer should be left somewhat rough to insure bond ing with the next layer above; and, if the concrete has already set, it shall be thoroughly cleaned by scrubbing with coarse brushes and water before the next layer is placed upon it.
(b) Concrete shall be deposited in the moulds in layers of such thickness and position as shall be specified by the engineer in charge. Temporary planking shall be placed at the ends of partial Layers, so that none shall run out to a thin edge. In general, excepting in arch work, all concrete must be deposited in horizontal layers of uniform thickness throughout.
(c) The work shall be carried up in sections of convenient length and the eections shall be completed without intermission.
(d) In no case shall work on a section stop within 18 inches of the top.
(e) Concrete shall be placed immediately after mixing, and any having an initial set shall be rejected.
11. Expansion Joints. In exposed work, expansion joints may be provided at intervals of thirty to one hundred feet, as the character of the structure may require.
(6) A temporary vertical form or partition of plank shall be set up, and the section behind shall be completed as though it were the end of the structure. The partition shall be removed when the next section is begun, and the new concrete shall be placed against the old without mortar flushing. Locke shall be provided, if directed or called for by the plans.
(c) In reinforced concrete the length of these sections may be materially in creased at the option of the engineer.
12. Facing. (a) The facing may be made by carefully working the coarse stone back from the form by means of a shovel, bar or similar tool so as to bring the excess mortar of the concrete.
(b) About one inch of mortar (not grout) of the same proportions as used in the concrete may be placed next to the forms immediately in advance of the concrete, in order to secure a perfect face.
(c) Care must be taken to remove from the inside of the forms any dry mortar in order to secure a perfect face.
13. Proportions. The proportions of the materials in the concrete shall be as specifically called for by the contract, or as set forth herein, upon the lines left for that purpose, the volume of cement to be based upon the actual cubic contents of one barrel of specified weight.
14. Finishing. (a) After the forms are removed, which should generally be as soon as possible after the concrete is sufficiently hardened, any small cavities or openings in the face shall be neatly filled with mortar, if necessary in the opin ion of the engineer. Any ridges due to cracks or joints in the lumber shall be
rubbed down with chisel or wooden float. The entire face may then be washed with a thin grout of the consistency of whitewash, mixed in the same proportion as the mortar of the concrete. The wash shall be applied with a brush. The earlier the above operations are performed the better will be the result.
(6) The tops of bridge seats, pedestals, copings, wing walls, etc., when not finished with natural stone coping, shall be finished with a smooth surface composed of one part cement to two parts of granite or other suitable screenings or sand, applied in a layer } to 1 inch thick. This must be put in place with the last course of concrete.
15. Waterproofing. Where waterproofing is required, a thin coat of mortar or grout shall be applied for a finishing coat, upon which shall be placed a covering of suitable waterproofing material.
16. Freezing Weather. Ordinarily concrete to be left above the surface of the ground shall not be constructed in freezing weather Portland-cement concrete may be built under these conditions by special instructions. In this case the sand, water and broken stone shall be heated; and in severe cold, salt shall be added in the proportion of about 2 pounds per cubic yard.
17. Reinforced Concrete. Where concrete is deposited in connection with metal reinforcing, the greatest care must be taken to insure the coating of the metal with mortar and the thorough compacting of the concrete around the metal. Whenever it is practicable,' the metal shall be placed in position first. This can usually be done where the metal occurs in the bottoms of the forms, by supporting the metal on transverse wires or otherwise, and then flushing the bottoms of the forms with cement mortar, so as to get the mortar under the metal and depositing the concrete immediately afterward. The mortar for flush ing the bars shall be composed of one part cement and two parts sand. The metal, used in the concrete shall be free from dirt, oil or grease. All mill scale shall be removed by hammering the metal, or preferably by pickling the same in a weak solution of muriatic acid. No salt shall be used in reinforced concrete when laid in freezing weather.