The impact of lignin as soil stabilizer on the characteristics of treated base through full-depth recycling of pavement

This study explores the application of calcium lignosulfonate (CLS), derived from paper mill waste, as a sustainable stabilizing agent in Full Depth Reclamation (FDR) of asphalt pavement. The use of conventional stabilizing agents in FDR poses environmental challenges, while CLS offers a sustainable alternative by reducing the use of bitumen and cement, minimizing greenhouse gas emissions, and energy consumption. The paper evaluates the performance of CLS in FDR, comparing its use alone and in combination with Portland cement. Assuming the same thickness, two mix designs were considered in this study. One mix design consisted of 85 % RAP and 15 % base soil, while the other mix design comprised 60 % RAP and 40 % base soil. Various combinations of cement and lignin were then considered. Each combination included a percentage of the optimal cement (100 %, 75 %, 50 %, 25 %, and 0 %) and a percentage of the optimal lignin (0 %, 25 %, 50 %, 75 %, and 100 %). Through various tests, it was found that CLS, when combined with Portland cement, enhances the performance of stabilization and increases the Unconfined Compressive Strength (UCS) compared to using only Portland cement or CLS. The study concludes that CLS, especially when combined with Portland cement, significantly improves the environmental and mechanical performance of FDR, making it a more sustainable maintenance and repair method. Moreover, the findings indicate that a higher RAP content leads to a rise in the optimal cement percentage while reducing the optimal percentage of CLS. Also, for the 28-day cured samples, 85 % RAP with 50 % cement and 50 % lignin, and 60 % RAP with 75 % cement and 25 % lignin, have UCS values that are 10.6 % and 5.8 % higher, respectively, compared to the samples stabilized only with the optimal percentage of cement without lignin.