The cost of laying such sidewalk or sidewalks, roadway or roadways, shall be apportioned and assessed by the county commission or commissions against the abutting property on the basis per front foot ascertained by dividing the cost of the work by the total frontage of the abutting property, and such assessments shall be known as special assessments for improvements and shall be levied and collected as a special tax, and a special tax bill, to be prepared by the county clerk of the county, shall issue therefor. Said special tax bills are to be issued upon the completion, approval and acceptance by the county commission, and may bear interest, after thirty days, at the rate of eight percent per annum, and every such special tax bill shall be a lien against the lot or piece of ground described in the same until the same is paid.