Use of zinc coated steel CNC milling waste for road pavement subgrade

Abstract The reuse of Computer Numerical Control (CNC) milling waste spirals is becoming a challenging task for numerous countries because of the annual increase in steel production integrated with the CNC machines. This paper presents the results of a study of some geotechnical properties of a low plasticity clay (CL) mixed with steel CNC milling waste spirals. The spirals had been first coated with zinc (galvanization) in order to decrease the corrosion rate, and then mixed with the CL at different ratios (5%, 10%, 15%, 20%, and 25% by dry weight). The response of the mixtures has been investigated using an intensive series of laboratory experiments including compaction, permeability, consolidation, unconfined compressive strength (UCS), and California bearing ratio (CBR) tests. The test results indicated a considerable decrease in optimum moisture content (wopt), and an increase in maximum dry unit weight (γDmax) with an increase in the amount of waste spirals in the mixtures. A decrease of about 34% in coefficient of permeability (k) was observed from a 25% addition of waste spirals in the soil. The consolidation tests indicated various levels of decrease in the swelling index (cs), and compression index (cc) values as a result of the addition of the waste spirals. It was also observed that the highest CBR value of 11.22% was obtained for a mixture with 20% waste, whilst the maximum UCS value of 390.11 kPa was achieved for a mixture with 15% waste.