Recent research, development, and applied utilization activities conducted by the author for the increased use of ferrous and nonferrous slags in civil and highway construction are presented. Quantification work that leads to usability criteria has been conducted to ensure its appropriate use of slag in highway construction. Criteria and guidelines on slag expansivity to further the use of appropriate quality steel slags, with demonstrated acceptable performance, in granular subbase/base, hot-mix asphalt, concrete, and cementitious applications are outlined. Examples are presented for each usability criterion. The use of air-cooled nickel slag is also presented, based mainly on recent positive developments in the Dominican Republic with ferronickel slag. It has been shown in the laboratory, and more importantly during highway construction, that air-cooled, crushed nickel slag is an excellent aggregate in granular base, engineered fill, and hot-mix asphalt.