70 ILCS 15/8
All contracts let for the construction of any work authorized to be done under the provisions of this Act, where the amount thereof exceeds $5,000, shall be let to the lowest responsible bidder or bidders on open, competitive bidding after public advertisement made at least 15 days before the opening of bids, in a newspaper of general circulation in a county in which an Authority airport is located, in such manner and at such intervals as may be prescribed by the Authority. The successful bidders for such work shall enter into contracts furnished and prescribed by the Authority. Such contracts shall contain a provision that such successful bidder shall indemnify and save harmless the State of Illinois for any accidental injuries or damages arising out of his negligence in the performance of such contract, and shall, in addition, execute and give bonds, payable to the Authority, with a corporate surety authorized to do business under the laws of the State of Illinois, equal to at least 50% of the contract price, one conditioned upon faithful performance of the contract and the other for the payment of all labor furnished and materials supplied in the prosecution of the contracted work.
70 ILCS 15/8