Permeable concrete bases protect primary pavement from harmful effects of surface and subsurface water; provide a protective cover over the pavement's aggregate base and a strong working platform for placing concrete pavement; and are easy to place. Permeable concrete bases have been used effectively at the St. Louis-Lambert International Airport on projects costing a total of more than $15 million. CRD Campbell Inc., a St. Louis engineering, architectural and planning firm, has developed a specification for the material. Specifications are included for fine and coarse aggregates, cement, water, water-cement ratio, coefficient of permeability, compressive strength, vibration, subgrade characteristics and placement equipment. Dave Graff of St. Louis' Interface Materials, which supplied recent Lambert projects, warns producers to avoid buildup when supplying permeable concrete. The biggest potential problem is separation of the coarse aggregate from the small amount of mortar used in the mix, which causes material to stick to the drum walls and fins. On the Lambert projects, drivers made sure to remove buildup from these areas after a lane was completed, while the paver was being repositioned. KEYWORDS: permeable concrete bases