Standard Rules for Bridge Masonry Construction

5. Water. The water shall be clean and free from acids or strong alkalis.

6. Classification. Concrete masonry will be of three classes, determined by the proportions of the materials, as follows : Class made in the proportions of one sack of cement to cubic feet of sand and 5 cubic feet of broken stone.

Class made in the proportions of one sack of cement to 3 cubic feet of sand and 6 cubic feet of broken stone.

Class made in the proportions of one sack of cement to cubic feet of sand and 7 cubic feet of broken stone.

In general, the class of concrete to be used in any given structure will be stated on the masonry plan ; but, when not stated, will be as follows unless otherwise di rected by the Engineer-in-Charge : Class A concrete will be used in the covers of culverts, arch-rings, copings of piers and abutments, foundations laid under water, walls subject to water pressure, when desired to make impervious, and for all concrete which is fully reinforced.

Class B concrete will be used in retaining walls, piers, abutments, pedestals, foundations subject to vibration, walls, footings of structures where piles are used or where a wet foundation is encountered, and in all concrete that is only partially reinforced, provided this classification does not conflict with the conditions specified for Class A concrete.

Class C concrete will be used in the footings of struc tures on dry foundations, and in the neatwork of unim portant structures.

7. Proportioning. One sack of cement (one-fourth of a barrel) is taken as the unit of measurement, and as sumed as containing one cubic foot.

The sand and broken stone in each batch shall be ac curately measured by volume in boxes, or by frequently checked gauge-marks on the barrows or cars. Gravel may be used in place of sand, in which case the amount of pebbles exceeding one-quarter-inch in diameter, in the gravel, is to be determined by screening, and the relative proportions of gravel and broken stone changed to corre spond.

S. Consistency. For concrete fully reinforced, thin building walls and columns, a mushy concrete, so soft that it must be handled quickly or it will run off the shovel, should be used.

For ordinary mass concrete, such as large walls, foun dations, piers, and abutments, use a medium wet concrete of such consistency that when dumped into place it will not require tamping, and will be wet enough to cause the workmen to sink into it ankle deep.

9. Hand-Mixing. If the concrete is mixed by hand, it shall be done as follows : The sand or gravel and cement shall be thoroughly mixed dry by being deposited in alternate layers on a water-tight platform, and then turned with a shovel or a hoe not less than twice, so that the mass will be of a uniform color, showing no streaks of sand, after which the amount of water required shall be added, and the mass again mixed to a uniform consist ency.

In the meantime, the broken stone shall have been spread on a water-tight platform in a thin layer and wetted down. On this thin layer of stone, the mortar is to be uniformly spread, and the mass turned with shovels until each particle is entirely surrounded with mortar and the mass is of a uniform consistency before it is shov eled into the barrows.

10. Machine-Mixing. If the concrete is mixed by a machine, the machine shall be of a design approved by the Engineer. The size of each batch mixed shall not exceed the rated capacity of the mixer; and no batch will be dis charged from the mixer until a sufficient number of revo lutions have been made after all of the ingredients have been deposited in the mixer to insure a first-class concrete of uniform consistency. The use of a continuous mixer will not be permitted.

11. Placing. The concrete shall be conveyed and de posited in such a manner that there shall be no distinct separation of the different ingredients, and shall be used so soon after mixing that it can be worked or puddled in place as a plastic, homogeneous mass.

All exposed surfaces and those required to be water proofed shall be well spaded, to force back the broken stone and secure a finished mortar surface; and in all cases the entire mass shall be puddled and worked as de posited, so as to expel the air and surplus water.