Concrete curbs may be one of two types, depending on the slope of the street. An integral curb and gutter shall be placed in all instances where the slope is less than one foot per one hundred feet. When the slope is more than one foot per one hundred feet, and independent-type curb may be used. Both types shall contain not less than one cubic foot of concrete per lineal foot, and shall be poured monolithically of concrete having a 28-day compressive strength of not less than two thousand pounds per square inch. Expansion joints shall be placed at each break in alignment and not further than 45 feet apart in the length of the curb. Contraction joints shall be placed not further than 15 feet apart in the length of the curb. All concrete curbs, whether placed by contractors or private owners, shall be constructed as specified by the city engineer and accepted by him upon completion. Rejected curbs shall be patched or broken up and replaced as the city engineer may direct. (Ord. 2763 §11, 1958).