Bai, et al (2024) Geopolymer stabilization of carbon-negative gasified olive stone biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More as a subgrade construction material. Construction and Building Materials. https://doi.org/10.1016/j.conbuildmat.2024.137617

Biochar, a carbon-rich material derived from biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More, offers significant environmental benefits by capturing and storing carbon. Recent research explored the potential of using olive stone biochar (OSB) as a component in geopolymer composites for road subgrade construction. The study utilized industrial residues like fly ashAsh is the non-combustible inorganic residue that remains after organic matter, like wood or biomass, is completely burned. It consists mainly of minerals and is different from biochar, which is produced through incomplete combustion.   Ash Ash is the residue that remains after the complete More (FA) and ground granulated blast furnace slag (S) as precursors in the geopolymerization process. The resulting OSB-based geopolymers demonstrated impressive mechanical properties, making them viable alternatives to traditional construction materials while also contributing to carbon sequestration.

The research assessed the unconfined compressive strength (UCS) of these geopolymer composites. Samples stabilized with FA and S-based geopolymers showed higher UCS values compared to traditional methods. S-based geopolymers generally exhibited superior strength, with UCS values peaking around 6 MPa. The study identified that curing time and temperature significantly influenced the UCS, with longer curing periods or higher temperatures yielding better results. For practical application, FA or S-based geopolymers with 30% precursor content, cured at 20°C for 7 days, provided optimal performance, surpassing the local requirement of 700 kPa UCS for stabilized road subgrades.

The California Bearing Ratio (CBR) test results further validated the effectiveness of the optimal blends, showing enhanced CBR values with the addition of FA or S-based geopolymers. This improvement reduced the required pavement thickness and construction costs. The repeated load triaxial (RLT) test confirmed the dynamic strength of the geopolymer-stabilized OSB composites, demonstrating their ability to withstand simulated traffic loads.

Economic analysis revealed that the cost of OSB is comparable to natural aggregates when considering volume. The carbon footprint assessment indicated that the geopolymer stabilization of OSB using 30% FA or S resulted in carbon-negative materials. This dual benefit of cost-effectiveness and environmental sustainability positions OSB-based geopolymers as a promising solution for green infrastructure.

In terms of production, the olive stone biochar used in this study was sourced from a biomass gasificationGasification is a high-temperature, thermochemical process that converts carbon-based materials into a gaseous fuel called syngas and solid by-products. It takes place in an oxygen-deficient environment at temperatures typically above 750°C. Unlike combustion, which fully burns material to produce heat and carbon dioxide (CO2​), gasification More facility. The process involved dehydrating the olive stones, followed by pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More in a low-oxygen environment, resulting in a solid by-product rich in carbon. Elemental analysis of the OSB revealed a high carbon content, indicating its potential for long-term carbon sequestration.

Morphological analysis using scanning electron microscopy (SEM) showed that increasing the precursor dosage improved the microstructural integrity of the geopolymer composites. Higher dosages led to better encapsulation of OSB particles and reduced voids, resulting in stronger composites. The study also highlighted the importance of curing conditions, with higher temperatures and longer durations leading to more robust microstructures.

This research contributes to the field of sustainable construction by demonstrating the feasibility of using geopolymer-stabilized OSB composites as road subgrade materials. By incorporating biochar, a renewable resource, and reducing reliance on natural aggregates, this approach supports the development of eco-friendly infrastructure. The findings underscore the potential of biochar as a versatile material in civil engineering applications, promoting both environmental and economic benefits.