The county board shall not let or enter into any contract or contracts for the erection of any bridge, the estimated cost of which bridge shall exceed the sum of five hundred dollars, except upon uniform plans and specifications and bidding blanks prepared by the Director-State Engineer, or such other officers who may have charge of such matters in this state, which plans shall be drawn to scale and shall show the outline of the bridge or bridges as it or they will appear when completed. The plans and specifications shall also show at least one cross-sectional view of each. They shall show the name, number, size, grade, dimensions, mixture or other quality of all work and material to be used in the construction of the bridge or bridges. It shall be the duty of the Director-State Engineer or such other officer who may have charge of such matters in this state, to inspect and check the completed work when called upon so to do by the county board, or by the written request of five resident freeholders of the county.