No person shall mix concrete or mortar or any mixture or substance containing cement on any existing pavement on public property nor leave or cause to be left any excess concrete or mortar or any mixture or substance containing cement on any existing pavement on public property, nor allow same to leak or fall from any container or receptacle onto pavement on public property. If any concrete, mortar or any mixture or substance containing cement is accidentally dropped or placed upon any pavement on public property within the city, the person responsible shall immediately remove same before such substance hardens or sets on the pavement. (Ord. 8590)