It shall be unlawful for any person, either as owner, agent, servant, contractor or employee to construct any permanent sidewalk in Provo City, without having first obtained from the City Engineer a permit so to do. The acceptance of such permit shall be deemed an agreement upon the part of such person to construct said sidewalk in accordance with the specifications and grades furnished by the City Engineer as to the character and quality of the work; and if the sidewalk is constructed of cement, the character and quality of the cement, the constituent parts of the mixture, and the thickness of the walk. When the walk is extended from the main sidewalk to the back of the curb already constructed, there shall be placed between the back of the curb and walk, an expansion joint designated by the City Engineer. It shall be unlawful to construct any such sidewalk in violation of the specifications given by the City Engineer.