The cash prepayments and the bonds in the amount that may be necessary for the purpose shall be turned over and delivered to the contractor or assigns at par and accrued interest in payment of the amount due, including advertising, engineering and appraising costs, in accordance with the terms of the contract. The bonds shall be executed and held by the municipality and delivered in parcels from time to time upon the completion and approval of the work, or any part thereof not less than one (1) block, in an amount equal to the improvement so completed and accepted.