Evgeny Polyntsev: "We are just at the beginning of the road"

Development of road infrastructure requires expanding the range of building materials. The fact is that materials that are used today in the construction of subgrade and road pavements are expensive and not available in some regions. To reduce the purchase and delivery costs, it is necessary to use more local soils. However, the physical and mechanical properties of these soils often do not meet the regulatory requirements. Therefore, local soils should be strengthened to bring their properties to the required standards.

Post-graduate student of the SPbGASU Department of Roads, Bridges and Tunnels Evgeny Polyntsev has been exploring the issues of strengthening subgrade soils with polyurethane foam sealants for four years. In co-authorship with Associate Professor Alexander Kvitko, PhD, he wrote a number of articles published both in Russian and foreign scientific journals, and submitted a patent application. We asked Evgeny to tell us about the invention and where it can be applied.

– The invention relates to the construction of roads, in particular, to strengthening the soil mass of the subgrade and can be used in new construction, overhaul and/ or reconstruction of roads, railways, streets and driveways. Polyurethane foam sealants have unique properties. They are characterized by good adhesion, a significant increase in volume (20–70 times) in the interval from injection to the completion of polymerization process; they are easy to apply and can be used at low temperatures. They are also distinguished by a fairly rapid solidification – within 4-8 hours, water and vapour impermeability, hardening of the material due to the absorption of water from the soil and a low coefficient of thermal conductivity. Thanks to all these features, the invention can be in demand in other construction areas.

Globally, considerable experience has been accumulated in strengthening soil foundations and structural layers of highways. Soil strengthening methods are varied. The most common and affordable are those using inorganic (cement, lime) and organic (bitumen, emulsion) binders. However, these methods have quite a large range of restrictions on their use. An alternative way can be soil strengthening with polyurethane foam sealants. 

– Evgeny, please tell us how you conducted your research. 

– First of all, we collected and analyzed information on soil strengthening and polyurethane foam sealants. Practical studies were carried out in the laboratory of the Department of Roads, Bridges and Tunnels. In the course of the experimental part, cohesive soil was reinforced with a sealant. A one-component, all-season polyurethane foam was chosen as the binder.

The experiment showed that when the binder is injected into the soil to a depth of 10-15 cm, an active interaction (sticking) of the soil and the sealant occurs. In the process of the primary and secondary expansion of the binder, the foam is wedged into the soil. The soil is “absorbed”, forming a single “soil–binder” system. The expansion of the sealant took place evenly in all directions and amounted to about 10 cm from the puncture. At the same time, a cylindrical layer of hardened soil with irregularly shaped edges, about 20 cm in diameter, was formed, which is a monolith of solidified foam interspersed with soil. In addition, the foam was partially ejected onto the surface with the formation of a hardened foam cap. 

– What conclusions have you arrived at?  

–Based on the results of our work, we can conclude that strengthening the soil with polyurethane foam sealant is a more effective method compared to those that are applied now. Due to its simplicity, extensive scope of application, fast and high-quality final results, the method will be in high demand in the field of road and civil construction. The resulting building material is characterized by a low coefficient of thermal conductivity and can significantly reduce the thickness of the additional layer of road pavements, ensure a stable water-thermal regime of the subgrade, maintain high strength characteristics of the subgrade at the level of strength of the soil components at optimal humidity, and prevent frost heaving of the subgrade. The conducted research allowed us to prepare structural schemes with a description of possible applications of the studied method.

– Will you please share your future plans? 

– The research we are doing goes far beyond road construction. Therefore, we are only at the beginning of our journey.

Text: Tatyana Petrova
Photos: Evgeny Polyntsev, Alexander Kvitko

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