Sidewalks shall have minimum width of four feet and four inches thickness except at driveways and aprons where the sidewalks shall be six inches in thickness. The sidewalk at driveways and aprons shall be reinforced with six-inch #6 gauge welded mesh reinforcement or equivalent placed four inches below the finished sidewalk surface. Sidewalks shall be constructed at the locations and to the prescribed lines and grades as approved on the preliminary plat, but sidewalks shall be constructed after the adjacent curb has first been installed. The subgrade shall be smooth and even and shall be compacted by rolling and three-quarter-inch broken stone shall be spread to a depth of not less than four inches and compacted where directed by Borough Engineer. Concrete for sidewalks shall be State Mix Class "B" air entrained 4,000 PSI concrete, and shall be manufactured in accordance with New Jersey State Highway Department's Standard Specifications for Road and Bridge Construction-1961 and addenda, and shall originate in a ready-mixed plant that has been certified and approved by the National Ready-Mixed Concrete Association.