Microwave-Mediated Polymer Bonding of Sands: Experimental Study

Bonding of soil grains can be achieved by melting added polymer particles initially mixed with dry soil. Salient challenges associated with conventional external heating via boundary conduction include long treatment durations and inhomogeneous bonding. The current study aims to overcome these challenges via the use of microwaves to induce quick internal heating. Results of experiments on sand-silt specimens that contain a 10% fraction of natural microwave susceptor grains confirmed that internal heating produces homogeneous bonding much quicker than external heating (by a factor of 20), particularly when the target soil mass is relatively large. The tensile strength ($q_t$) of specimens bonded via microwave heating was found to be inversely proportional to their fines content (FC), although the temperatures sustained by soils increased with increasing FC. Bonded specimens subject to a wetting–drying cycle exhibited lower tensile strengths than the unwetted counterparts. Yet, specimens subject to reexposure to microwaves after a wetting–drying cycle exhibited tensile strengths of at least 85% that of analogous unwetted specimens. The power penetration depth for 2.45 GHz microwaves was calculated to be $0.5\mathrm{m}<{\mathrm{S}}_{\mathrm{p}}<0.8\mathrm{m}$ for dry soils. Therefore, applications deemed worthy of future consideration include large brick manufacturing, rapid repair of temporary runways, and treatment of polymer particle-laden rammed-earth walls.