Biochar (BC) is an eco-friendly material produced through coal pyrolysis and can improve the mechanical properties of cement-based construction and building materials. This research study explored the effects of BC and natural sand (Sand) replacement on the improved static and cyclic response of blended hydraulic cement (BHC) stabilized soft clay (SC) as a greener subgrade material. Unconfined compressive strength (UCS), indirect tensile stress (ITS), and indirect tensile fatigue life (ITFL) of the BHC-stabilized SC-BC-Sand samples were examined. Adding 10% BC to the BHC-stabilized samples was found to enhance cementitious products due to its porous structure and high water absorbability. The UCS, ITS and ITFL at this optimum ingredient were improved up to 315%, 347% and 862%, respectively, compared to the BHC-stabilized SC. Fourier transform infrared spectrometer, thermogravimetry differential thermal analysis and a scanning electron microscope with energy- dispersive-ray spectroscopy analyses the BHC-stabilized sample at the optimum ingredient showed the highest C-S-H and Ca(OH)2 2 in the pores. This investigation will encourage the utilization of BC to create both environmentally friendly and durable stabilized subgrade material.

Road infrastructure plays an important role in strengthening transportation and driving the economic advancement of countries. However, the increasing traffic volume has accelerated road deterioration, particularly at critical points like bridge-road junctions. Traditional repair methods involving demolition and reconstruction lead to extended closures and high costs. This study explores the polyurethane (PU) foam injection technique as an alternative solution, which can reduce both repair time and costs. The research evaluates the application of PU foam in various road projects across Thailand, highlighting its ability to repair pavement surfaces and structures, even in severely damaged areas. Despite its advantages, the use of PU foam faces challenges due to a lack of standardized quality control. This paper proposes a set of working guidelines for PU foam injection, aimed at key stakeholders such as the Department of Highways, the Department of Rural Roads, and the Department of Local Administration. The findings underline the importance of establishing standardized methods to ensure the long-term effectiveness of PU foam in road maintenance. Future research should focus on refining these guidelines for diverse road conditions to support the sustainable development of national transportation infrastructure.

Municipal solid waste (MSW) is the largest group of non-hazardous waste. Four percentages of MSW replacement (15 %, 25 %, 35 %, and 45 % by weight) were used for chemical modification of soft clay at 1, 14, and 28 days of curing. The MSW replacement at optimum (15 % and 25 %) to the clay enhanced unconfined compressive strength (UCS) and California bearing ratio (CBR) by 1.28 and 3.34 times, respectively. Also, the nanomagnesium (Nano-MgO) was used as an additive at small contents i.e., 0.25, 0.5, 0.75, and 1 % to improve the mechanical properties of MSW-soft clay blends. The optimum MSW replacement ratios with 1 % Nano-MgO significantly improves UCS and CBR of the soft clay when compared to clay stabilized with 1 % Nano-MgO. The UCS and CBR improvement mechanism was investigated via microstructural analysis of the MSW-soft clay stabilized with Nano-MgO. The improved structure of stabilized specimens was found to be due to flocculation, cation exchange, and cementation bond formation with brucite mineral. However, the X-ray diffraction tets results indicated the presence of the Palygorskite mineral in the specimen containing very high MSW replacement ratio, which retarded the Nano-MgO stabilization process. At optimum MSW replacement ratio (15 % and 25 %), Nano-MgO could effectively improve mechanical properties of soft clay for sustainable road construction.