104. Foundation.[[56]]—The foundation for bituminous concrete pavement shall be a properly prepared old pavement, or hydraulic concrete, or compressed broken stone, as determined by the engineer.
105. Old macadam pavement or road to be utilized for foundation, shall be prepared in the following manner:
All high places or humps shall be dressed down to a plane two (2) inches below the pavement datum, the work being done with care so as to disturb as little as possible the macadam that is to remain. Depressions in the old macadam shall be carefully cleaned out so as to remove all earth and other débris and loose material, and filled with hydraulic concrete. Newly dug or filled trenches and holes extending through the macadam shall be excavated and cleaned out so as to admit the use of at least four (4) inches of hydraulic concrete. The hydraulic concrete for thus leveling up the roadway shall be composed of one (1) part of approved Portland cement, four (4) parts of clean sand and nine (9) parts of sound, hard crushed stone, well mixed into a wet concrete. After placing, the concrete shall be well tamped so as to form a compact body, conforming to a plane two (2) inches below the pavement datum. The concrete shall be protected from travel and allowed to become well set before the surface of bituminous concrete is applied.
106. Old stone block or brick pavement may be utilized for foundation, provided that the blocks or bricks do not require to be taken up and reset, or, if so taken up and reset, that the joints shall be completely filled with grout composed of one (1) part Portland cement and two (2) parts of good sand. Depressions, trenches and holes shall be treated as specified in Section 105.
107. Hydraulic concrete foundation shall be constructed in compliance with the requirements of Sections 28, 29, 30, 31, 32, 33, 34, 35, 36 and 37 of these specifications. Its depth or thickness shall be ... inches.
108. Broken stone foundation shall be ... inches in thickness after completion. It shall be constructed in accordance with Section 40 of these specifications.[[57]]
109. When completed the upper surface of the foundation shall nowhere be more than two and one-half (2½) inches nor less than one and three-fourths (1¾) inches below the pavement datum. No travel shall be permitted upon the foundation until the bituminous concrete shall have been laid.
110. Bituminous Concrete.—The bituminous concrete shall be composed of crushed stone, sand, pulverized stone, and asphaltic cement.
A typical composition for the bituminous concrete, to be as closely approximated as practicable, is as follows, the percentages being by weight:
| Pure bitumen in asphaltic cement. | 8.5% |
| Pulverized stone passing No. 200 sieve. | 8.5% |
| Sand passing No. 80 sieve. | 10.0% |
| Sand passing No. 40 sieve. | 23.0% |
| Sand and fine stone passing No. 10 sieve. | 15.0% |
| Crushed stone passing a screen having four meshes to the linear inch. | 25.0% |
| Crushed stone passing a screen having two meshes to the linear inch. | 10.0% |
| 100.0% | |