Enhancing the mechanical and hydraulic properties of coarse quartz sand using a water-soluble hydrogel based on bacterial alginate for novel application in agricultural contexts

Climate change is generating severe changes in the physical behavior of soils (i.e., soil structure, mechanical resistance, and water conductivity), causing negative impacts on different agricultural systems and, therefore, threatening food security. To cope with this situation, hydrogels based on biopolymers have been proposed to modify the mechanical and hydraulic behavior of complex porous materials such as soils, yet most of them are nonsoluble, making their application at field level laborious. In this study, we investigated the effect of a water-soluble hydrogel based on bacterial alginate on the mechanical and hydraulic behavior of coarse quartz sand. The results from unconfined uniaxial compression test showed that the strength of the sand treated with hydrogel increased by 94.5%, whereas hydraulic conductivity decreased 33%. Interestingly, we observed that bacterial alginate and hydrogel shifted the mechanics of the fluid phase toward a Darcy regime. The aggregate stability tests showed that coarse quartz sand treated with hydrogel displays larger mean weight diameter, reaching 1.5 mm compared with 0.12 mm of the control (i.e., coarse quartz sand). Finally, transmission light microscopy imaging of the hydrogel treatment revealed a new three-dimensional matrix between the quartz sand particles, changing the microaggregates and macroaggregates and providing a modified structure of the sand material. Our findings suggest that the use of the water-soluble hydrogel improves the mechanical and hydraulic behavior of coarse quartz sand, allowing better soil conservation against climate change-related phenomena, and is also potentially applicable in agricultural systems facing water scarcity.