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1. Influence of the coefficient of uniformity on bio-cemented sands: a microscale investigation

   Reed, Marlee; Montoya, Brina M. (September 2023, Proceedings of the 8th International Symposium on DEFORMATION CHARACTERISTICS OF GEOMATERIALS)

   Viana da Fonseca, António; Ferreira, Cristiana (Ed.)

   Microbially induced carbonate precipitation (MICP) is a bio-mediated ground improvement technique that can increase soil stiffness and produce cohesion within granular material. Most experimental investigations on MICP-treated soils are performed on idealized granular materials. Evaluating a narrow range of particle sizes dismisses the potential influence of soil fabric on MICP treatment efficiency. Therefore, little is known regarding the influence of soil fabric on the level of improvement achievable post-MICP treatment. We investigate the influence of the coefficient of uniformity (Cu) on the level of improvement that can be obtained from MICP treatment. This study couples unconfined compression testing with microscale observations obtained from x-ray computed tomography (CT) of two sand mixtures with different Cu values. A soil column and CT specimen of each sand mixture were prepared and received the same number of MICP- injections. The shear wave velocity (Vs) of the soil columns was monitored to evaluate the increase in soil stiffness over time. After MICP treatment, the bio-cemented columns were subjected to unconfined compressive strength testing. Results indicate that for a similar mass of carbonate, the soil with a larger Cu experienced a greater increase in Vs but a lower maximum unconfined compressive strength. Through CT imaging, the soil with a smaller Cu was observed to have a more uniform distribution of carbonate within the sand matrix whereas the soil with a larger Cu has more sporadic MICP trends. This study elucidates the influence of soil fabric on the level of improvement that can be achieved through MICP treatment and assesses the reliability of x-ray CT scanning of MICP-treated sands with moderate carbonate content. 

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2. The impacts of biomineralization and oil contamination on the compressive strength of waste plastic-filled mortar

   https://doi.org/10.1038/s41598-022-25951-3  

   Rux, Kylee; Kane, Seth; Espinal, Michael; Ryan, Cecily; Phillips, Adrienne; Heveran, Chelsea (December 2022, Scientific Reports)

   Abstract Researchers have made headway against challenges of increasing cement infrastructure and low plastic recycling rates by using waste plastic in cementitious materials. Past studies indicate that microbially induced calcium carbonate precipitation (MICP) to coat plastic in calcium carbonate may improve the strength. The objective of this study was to increase the amount of clean and contaminated waste plastic that can be added to mortar and to assess whether MICP treatment enhances the strength. The performance of plastic-filled mortar was investigated at 5%, 10%, and 20% volume replacement for cement. Untreated, clean plastics at a 20% cement replacement produced compressive strengths acceptable for several applications. However, a coating of MICP on clean waste plastic did not improve the strengths. At 10% replacement, both MICP treatment and washing of contaminated plastics recovered compressive strengths by approximately 28%, relative to mortar containing oil-coated plastics. By incorporating greater volumes of waste plastics into mortar, the sustainability of cementitious composites has the potential of being improved by the dual mechanisms of reduced cement production and repurposing plastic waste. 

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3. Utilizing Recycled Concrete Aggregate Fines as Co-Additives in Low-Carbon Cement for Problematic Soil Stabilization

   https://doi.org/10.1177/03611981251347627  

   Sanei, Muddassir; Biswas, Nripojyoti; Chou, Sopharith; Puppala, Anand J (October 2025, Transportation Research Record: Journal of the Transportation Research Board)

   Subgrade treatment has traditionally been achieved using calcium-based cement. However, it does not necessarily enhance sustainable design. Recently, low-carbon alternatives such as portland limestone cement (PLC) have gained attention as substitutes for traditional cement. In addition, recycled concrete aggregate fines (fRCA), a waste product, have shown potential for application in transportation infrastructure because of their enhancements in pavements. This study investigates the effectiveness of PLC and fRCA in improving soil properties under different environmental stressors. Clayey soil was treated with PLC (10% PLC or 10C) and PLC-fRCA mixtures at different ratios (8% PLC/15% fRCA or 8C_15fRCA and 8% PLC/30% fRCA or 8C_30fRCA). Improvements in strength, stiffness, and volumetric changes were evaluated through unconfined compressive strength and repeated load triaxial tests after exposure to various environmental conditioning cycles (0, 6, and 12 cycles of wet–dry or freeze–thaw) in the laboratory. Results indicated that untreated soil collapsed within two cycles of environmental conditioning. In contrast, treated soils exhibited significant improvements in strength and resilience to environmental stressors. Stiffness also improved with treatment, and despite some reduction after exposure to environmental conditioning, treated specimens maintained relatively higher stiffness values. These enhancements are attributed to the formation of strong binding gels from hydration and secondary reactions among PLC, fRCA, and soil, which exhibit strong resistance to moisture intrusion, helping to preserve their engineering properties. Overall, this study provides a comprehensive understanding of the potential of using fRCA as a co-additive to PLC, offering a more sustainable and durable alternative for the long-term performance of transportation infrastructures. 

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4. Post-wildfire soil hydrophobicity and slope erosion remediation by applying environmentally friendly modifiers

   https://doi.org/10.1016/j.gete.2025.100740  

   Ma, Wenpei; McKlin, Henry; Chan, Russel; Kim, Caitlin; DePoint-Spang, Teagan; Tomac, Ingrid (September 2025, Geomechanics for energy and the environment)

   This paper investigates the use of environmentally friendly remediation materials and techniques for rain-induced post-wildfire soil erosion on burned slopes. During wildfires, vegetation and organic matter combust and release hydrophobic chemicals on soil grains. Hydrophobicity reduces the water infiltration rate, prolongs the wetting process, increases erosion, and causes severe debris flows over watersheds. This comparative study presents the most effective approaches for mitigating hydrophobicity effects through environmentally friendly biopolymers and surfactants. Experimental techniques evaluate the dynamics of water drop penetration into treated and untreated soil, downhill water drop mobility, and erosion. The waterdrop contact angle measurements indicate that biopolymer Xanthan Gum (XG) slightly reduces hydrophobicity, whereas surfactant Sodium Cocoyl Isethionate (SCI) reduces it by a factor of a thousand. In addition, SCI can decrease slope erosion at low-inclined and moderate-inclined slopes. Sands' infiltration rates (IR) are very fast due to high permeability in normal conditions; however, surface hydrophobicity significantly reduces IR. Results from artificially treated extremely water-repellent samples of mixed sand show a six orders of magnitude decrease in IR. Then, after treatments XG and SCI modifiers, the IR increased by an order of magnitude after the XG treatments, and by four orders of magnitude under SCI treatment. Although XG is wettable and attractive to water, the crust and webs it forms between sand particles prevent effective water infiltration. Mild slopes exhibit similar IR rates as horizontal surfaces for all the cases; however, steeper slopes reduce IR for treated hydrophobic soils because they allow for downhill motion of water that is faster relative to the infiltration speed. 

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5. Sustainable Solution on Desiccation Crack Mitigation with Recycled Glass Sand

   https://doi.org/10.1088/1755-1315/1337/1/012050  

   Zhang, Bin; Wen, Kejun; Li, Junjie; Huang, Wei (May 2024, IOP Conference Series: Earth and Environmental Science)

   Abstract Desiccation cracking is a frequent natural phenomenon that occurs in drying soil and has a significant negative impact on the mechanical and hydraulic properties of clay or geomaterials in various engineering applications. In this study, recycled glass sand (RGS) was used to reduce the plasticity of clay soil and mitigate desiccation cracks in clay soils. The effect of the RGS particle size and content was investigated using a desiccation crack observation test. Digital image processing technology was used to evaluate the crack rate, length, width, and area during the observation test. The results reveal that the cracking rate was inversely proportional to the RGS content and directly proportional to the RGS particle size. For instance, the cracking rate of clay soil treated with 25% RGS with a particle size of 0.15 mm was reduced to 0.17% compared with untreated soil. The strengths of the untreated and RGS-treated soils were evaluated through unconfined compression tests. The unconfined compressive strength of the RGS-treated clay soil decreased slightly with the addition of RGS. In general, the addition of RGS has great potential for mitigating desiccation cracks in clay soils. 

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