SPECIFICATIONS FOR CONCRETE RETAINING WALLS. 243 



27. Placing of Concrete.-^-Conctete after the addition of water to the mix, shall be handled 

 rapidly from the place of mixing to the place of final deposit, and under no circumstances shall 

 concrete be used that has partially set before final placing. 



28. The concrete shall be deposited in such a-manner as will prevent the separation of the 

 ingredients and permit the most thorough compacting. It shall be compacted by working with 

 a straight shovel or slicing tool kept mqying* up and down until all the ingredients have settled 

 in their proper place, and the surplus water i forced to the surface. All concrete must be de- 

 posited in horizontal layers of uniform thickness throughout. Temporary planking shall be placed 

 at rnds of partial layers so that the concrete shall not run out to a thin edge. In placing concrete 

 it shall not be dropped through a clear space of over 6 ft. vertical, For greater heights a trough 

 or other suitable device must be used to deliver the concrete in place, and in depositing each 

 batch this trough or other device must first be carefully filled with concrete and then as fast as 

 concrete is removed at the bottom it shall be replenished at the top. 



29. The work shall be carried up in alternate sections of approximately 32 ft. in length as 

 shown on the plans, and each section shall be completed without intermission. In no case shall 

 work on a section stop within 18 in. of the top. 



30. Before depositing concrete, the forms shall be thoroughly wetted, except in freezing 

 weather, and the space to be occupied by the concrete cleared of debris.. 



31. Expansion Joints. Expansion joints shall be provided (sections were approximately 

 32 ft. long) as shown on the plans. The wall shall be constructed in alternate sections, the ends 

 of the sections being formed by vertical end forms, the section being completed as though it were 

 the end of the structure. Before placing the remaining sections the end forms shall be removed 

 and the surface of the concrete shall be painted with coal tar paint, composed of sixteen (16) 

 parts coal tar, four (4) parts Portland cement and three (3) parts kerosene oil. The expansion 

 joints shall be finished on the exposed side by the insertion in the forms of a metal mold that will 

 give a groove i in. wide, I in. deep and shall have a draft of I in. The wall sections shall be 

 locked together by means of bars as shown on the plans. 



32. Forms. Forms shall be substantial and unyielding and built so that the concrete shall 

 conform to the design, dimensions and contours, and so constructed as to prevent the leakage of 

 mortar. Where corners of the masonry and other projections liable to injury occur, suitable 

 moldings shall be placed in the angles of the forms to round or bevel them off. Material once 

 used in forms shall be cleaned before being used again. 



33. The forms must not be removed within 36 hours after all the concrete in that section 

 has been placed; in freezing weather they must remain until the concrete has had sufficient time 

 to become thoroughly set. 



34. Proportioning. In proportioning concrete, a barrel or 4 sacks of Portland cement shall 

 be assumed to contain 3.8 cu. ft., while the sand and gravel shall be measured loose in a measuring 

 vessel. The proportions required for concrete are as follows: 



For footings, walls of retaining walls, abutments, and pedestals, one (i) part Portland cement, 

 three (3) parts sand and five (5) parts gravel. For bridge seats and copings, one (i) part Portland 

 cement, two (2) parts sand and four (4) parts gravel. 



35. The tops of the bridge seats, pedestals, and copings, shall be finished with a smooth 

 surface composed of one (i) part Portland cement and two (2) parts sand applied in a layer I in. 

 thick. This must be put in place with the last course of concrete. 



36. Water-Proofing. The expansion joints in the retaining walls and abutments shall be 

 water-proofed as follows: After the forms have been removed and the concrete is thoroughly 

 dried, the back of the wall for a distance of 18 in. on each side of the expansion joints shall be 

 mopped with hot refined coal tar pitch. A layer of burlap shall then be placed so as to cover the 

 expansion joints, and the burlap shall be mopped with coal tar pitch. In the same manner two 

 additional layers of burlap shall be applied, making a 3-ply water-proofing. 



37. Reinforcing Bars. Reinforcing bars, where used, shall be placed 3 in. clear from the 

 outside surface of the concrete, and shall be placed in the position shown on the plans. Care 

 must be taken to insure the coating of the metal with mortar, and a thorough compacting of 

 concrete around the bars. All reinforcing bars shall be clean and free from all dirt or grease. 



38. Freezing Weather. Concrete shall not be mixed or deposited at a freezing temperature, 

 unless special precautions are taken to avoid the use of materials containing frost or covered 

 with ice, and means are provided to prevent the concrete from freezing. Where the temperature 

 of the air during the time of mixing and placing concrete is below 40 Fahr. the water used in 

 mixing the concrete shall be of such a temperature, that the temperature of the concrete when 

 delivered in the forms shall not be lower than 60 Fahr. Special precautions shall be taken not 

 to scald the cement. 



39. Placing in Water. Concrete shall not be deposited under water except on the approval 

 of the Consulting Engineers. Where water is encountered without current, but in such quantity 

 that it cannot be lowered to the required depth and maintained there, or where such lowering 





