It shall be the duty of the commissioners, in every case where damages are allowed as aforesaid, to provide for the payment of such damages by assessing against the city the amount of benefit, if any, to the public generally by reason of the change, enlargement or improvement aforesaid, and the balance, if any, against all property which shall, in the opinion of the commissioners, be especially benefitted by the proposed change, enlargement or improvement, to the amount that each lot or tract of ground shall be benefitted thereby. The sum to be paid by the owners of the property especially benefitted as aforesaid shall be a lien on the property charged from the date of the final decree of the circuit court, and the court, when it makes such decree and confirms the report of the commissioners, shall render a special judgment against each tract or parcel of private property assessed in said report for benefits, to the amount assessed against each tract and parcel, which judgment shall be a special judgment and bind the property and the interests of the defendant therein. If said judgment is not paid within ten days thereafter, then there shall be issued from said court in favor of the city a special execution against each tract or parcel separately, and the same shall be sold in the same manner as is now provided by law for sales of real estate under execution. Said judgment shall bear fifteen percent interest from ten days from the rendition thereof; and the cost of such execution and proceedings thereunder shall be taxed against the defendants.