Road infrastructure construction in developing countries such as Vietnam requires an enormous amount of natural sand. The scarcity of river sand is becoming increasingly severe, with predictions indicating a sustained drop in its supply. Hence, it is essential for the construction industry to implement a sustainable strategy by combining waste materials with abundant resources in order to effectively address this challenging situation. The objective of this study is to investigate the mechanical properties and evaluate the potential application of mixtures comprising rock quarry dust and sea sand for the roadbed layers of expressways. The researchers conducted a series of experiments, including the moisture content, specific gravity, angle of repose of material, and triaxial tests to study the composition and mechanical behaviors of mixtures at different ratios. Extensive parametric investigations in conjunction with the calibration in Plaxis' soil-test module obtain the Young's modulus E50 and confining pressure curves. Based on the assessment of materials utilized in roadbed layer of highway, as determined by the California bearing ratio (CBR) coefficient, it demonstrates that combining sea sand and quarry dust can generate the mixtures possessing appropriate properties for application in the construction of the roadbed of highway.

Sea sand exhibits typical features of loose structure, large compressibility and poor consolidation, causing severe challenges for the construction and emergency repair of coastal engineering. A new Hybrid Non-Isocyanate Polyurethane (HNIPU) was utilized as a curing agent to prepare HNIPU-sea sand mixtures (HSM) in this study. A series of uniaxial compression and scanning electron microscopy (SEM) tests were conducted to explore the strength property and microscopic curing mechanism of HSM. As the mass ratio of polyurethane to sea sand increased from 0.1 to 0.7, the uniaxial compressive strength of HSM first increased from 8.75 MPa to 20.09 MPa then decreased to 17.90 MPa. The maximum strength was achieved at a mass ratio of 0.5. The uniaxial compressive strength increased by 79.46% and 58.41% within a temperature range of - 10-60 degrees C and a curing time range of 10-90 min, respectively. Nevertheless, it decreased by 31.06% with an increase from nil to 10% in moisture content. The prediction formula for the uniaxial compressive strength of HSM can be expressed as a function of multiple influencing factors using regression analysis. The main factors affecting the uniaxial compressive strength of HSM are mass ratio, moisture content, curing time, temperature and gradation in sequence. Furthermore, the progressive failure of HSM were identified based on the complete stress-strain curves in conjunction with the failure mode (X-shaped conjugated shear). It is well documented that HNIPU can rapidly fill, encapsulate and cement sea sand and remarkably enhance its strength, ductility and toughness. These research results may provide an effective method for the rapid reinforcement of the beach sand foundation.