Physical, microstructure and leaching assessments for pavement road base containing mixed steel slag and cathode ray tube glass

Use of by-product materials, such as steel slag and cathode ray tube glass, as alternative recycled materials in the construction of roads, could reduce the demand for natural aggregates. Measurements of the physical properties (specific gravity, water absorption, Los Angeles abrasion value and soundness) and microstructure characteristics were made to evaluate the effectiveness of using these materials in pavement road base. The laboratory assessments were also conducted using California bearing ratio, unconfined compression strength and indirect tensile strength tests. Leaching tests were performed on six elements (arsenic, barium, cadmium, lead, silver and mercury) to determine the leaching potential of hazardous metals. Element concentration release limits were determined based on the Toxicity Characteristic Leaching Procedure (TCLP). The results indicate that the alternative recycled materials are suitable for use in aggregates and meet the requirements for natural aggregates used for similar purposes. Microstructure analysis shows that the steel slag is more porous and rougher than granite and cathode ray tube glass. The higher percentage of steel slag produces higher California bearing ratio test values for both the soaked and unsoaked samples. Findings from unconfined compression strength and indirect tensile strength tests show that the performance of the mixture was enhanced significantly upon incorporating a higher percentage of steel slag. The samples show a significant strength improvement between 2 and 17%. The concentration of leached barium and lead is higher than that of the other elements, however it is still less than 1% of the TCLP regulatory limit, hence the concentration of the leached elements does not pose an environmental risk. The laboratory test results indicate that mixtures consisting of granite, steel slag and cathode ray tube glass are both environmentally safe and suitable for use as aggregate in pavement road base.