## 4 Conclusions  
The mixing of anionic BSMs and aqueous solutions of cationic PDADMAC was accompanied by complexation between these oppositely charged components. At the weight fraction of PDADMAC W = 0.036, the saturated positively charged BSMs-PDADMAC complex was formed. An increase in W up to 0.5 resulted in the accumulation of unbound PDADMAC in aggregately stable BSMs-PDADMAC aqueous formulations. For the films prepared from the binary BSMs-PDADMAC formulations, with increasing W, the growth in the rigidity of the material (20-fold growth in elastic modulus, 2-fold growth in strength and 2-fold decrease in ultimate strain) was attributed to the accumulation of unbound PDADMAC. Treatment of the sand with BSMs-PDADMAC formulations is accompanied by polymer binding to sand particles and the formation of ternary BSMs-PDADMAC-sand surface coating (crust) on the soil with porosity comparable to that for the virgin sand. With an increasing weight fraction of PDADMAC from 0 to 1, the growth in the crust strength from 0.8 to 45.0 MPa was observed when crust elasticity was estimated as the bending angle fell down. In parallel to this evolution of the mechanical characteristics, the water-resistance of  
Figure 6: A Petri dish with moistened sand treated by PDADMAC (**a**) and BSM–PDADMAC formulation with W = 0.2 (**b**). Figure 7: Micrographs outside the surface (**a**), edge of crust (**b**) and transverse fault (**c**) of the polymer-sand crust prepared with a PDADMAC–BSM formulation (W = 0.2). the crust decreases. The protective coatings with high strength and water-resistance were shown to be formed at 0.05 < W < 0.2. Comparative studies in the mechanical behavior of the binary BSMs-PDADMAC films and ternary BSMs-PDADMAC-sand crusts revealed the following roles of the polymer components: rubbery BSMs contribute to the elasticity of the materials, while unbound PDADMAC controls their rigidity. From this standpoint, the change in weight fraction of PDADMAC allowed one to control \"rigidity-elasticity\" balance of both polymer-colloid films and sand surface coatings. Electron microscopic studies of polymer-sand crusts evidenced the following \"structure-property\" correlation for them. The treatment of sand with the BSMs-PDADMAC formulations does not influence a sand porous structure, and the role of the polymeric binder is associated with the appearance of the polymer film on the surface of the sand particle with the thickness of 0.25-1 \(\upmu\)m. The latter factor is responsible for the binding of sand particles with each other at the points of inter-particle contacts. In other words, the formation of a strong polymer-sand crust is associated with the binding of sand particles by polymeric \"bridges\" with no influence on the porous sand structure. These observations can be supplemented by the literature data on the stability of ionic polymers which are the initial components of the stabilizing IPEC formulations. The shelf life of polymers and the relevant IPECs have been actively tested previously. Particularly, the long-term stability for the initial polymers was shown under different weather conditions (frost, hot weather, rain and etc.) [53; 54]. Polymer-soil coatings withstood multiple repeated freezing-thawing and wetting-drying cycles. However, these works were mainly carried out with linear polymers, which, being bonded to soil and sand, form rather rigid coatings. This approach has proved to be excellent when treating vast flat areas, such as fields, slopes of wide ravines, etc. Problems appear when these conventional formulations are used for stabilizing sites with a more complicated relief, e.g., decorative zones and open-air museums. In this case, different formulations are required which are capable of forming elastic coatings and which maintain integrity for a long time. As follows, from the above, the elasticity of the polymer-soil coating can be increased via using latex, an aqueous suspension of rubbery polymeric microspheres.