Complex modification of soil cement for road pavements

The study's relevance is justified by the need to ensure the required strength and frost resistance of soil-cement layers of road pavements in road-climatic zones with seasonal and daily temperature changes, especially with frequent transitions through 0 °C. The object of research is modified soil cement for road pavements. This work aims to develop soil-cement compositions with complex modification with an organosilicon compound, a polycarboxylate superplasticizer, and an electrolyte. Method. The compositions of complex-modified soil cement were optimized using the second-order rotatable planning method. Potassium methylsiliconate, polycarboxylate superplasticizer, and sodium hydroxide percentages were selected as variable factors. The X-ray phase analysis method used an automatic X-ray diffractometer Bruker D8 Advance to determine the mineralogical composition and identify the products of new formations during the hardening of modified soil cement. The construction and analysis of diffraction patterns were performed using the Bruker Diffrac Eva program. Results. It was established that the complex modification of soil-cement with potassium methyl silicone, polycarboxylate superplasticizer, and sodium hydroxide provided an increase in the compressive strength by 95 %, the tensile strength in bending by 132 %, and the frost resistance coefficient by 129 % with a Portland cement content of 8 %. Strength grade M40 and frost resistance grade F15 were achieved with the introduction of Portland cement in an amount of 8 % and a complex of modifiers: potassium methyl siliconate – 0.4 %, polycarboxylate superplasticizer – 0.35 %; sodium hydroxide – 0.1 %. X-ray phase analysis was used to establish that introducing a complex of modifiers into cement soils increases the amount of portlandite by 81 %, calcium hydrosilicates by 50 %, and reduces the content of residual clinker minerals C₃S and C₂S by 61 %. An increased amount of amorphous phase from 27 % to 29.9 % in the form of tobermorite gel in cement soils indicates a more significant number of new formations. The main reflection of calcite CaCO₃, as a product of calcium hydroxide carbonation, is reduced in the modified cement soil sample by 18.9 %.