Utilization of Industrial Sludge and Fly Ash in Highway Construction: A Feasibility and Performance Study

The growing demand for sustainable and cost-effective construction materials has intensified interest in utilizing industrial by-products as partial replacements for cement in pavement-quality concrete. Among these, Fly Ash (Class-F) from thermal power plants and Hypo Sludge from the paper recycling industry offer significant potential due to their pozzolanic and cementitious characteristics. This study investigates the performance of concrete incorporating Fly Ash and Hypo Sludge as Supplementary Cementitious Materials (SCMs) for rigid pavement applications, with a focus on M25 and M40 grade concrete mixes. Replacement levels of 10%, 20%, 30%, and 40% were explored individually and in hybrid combinations to evaluate their effects on mechanical properties, particularly compressive strength. Comprehensive laboratory testing was conducted on cube, cylinder, and beam specimens to determine compressive strength, split-tensile strength, and flexural strength at different curing ages. Results indicate that both Fly Ash and Hypo Sludge contribute to strength gain, especially beyond 28 days due to their slow pozzolanic reaction. Optimum performance was observed at 20% hybrid replacement (Fly Ash + Hypo Sludge) for M25 grade and 10% hybrid replacement for M40 grade concrete. At these levels, the mixes achieved targeted 28-day strength while exhibiting progressive strength gain up to 90 days. Higher replacement percentages resulted in significant reductions in early and ultimate strength. The study further extends its findings to pavement design for rural roads and national highways in Gujarat, considering CBR values of 2%, 4%, and 6%, and wheel loads of 30 kN and 51 kN. Analysis reveals that optimized SCM-based concrete mixes can reduce pavement thickness and construction cost, particularly for rural roads under lower wheel loads. The 20% hybrid mix demonstrated cost savings of up to 14% without compromising structural adequacy. Overall, the research establishes Fly Ash and Hypo Sludge as viable materials for producing eco-efficient, economical concrete suitable for rigid pavements. Their use promotes sustainable waste management, conserves natural resources, and contributes to the development of durable, long-lasting road infrastructure.