Performance enhancement of cementitious soil stabilizers using incorporated nanosilica

This investigation aims to study the performance of different hybrid binders as environmentally-friendly cementitious soil stabilizers as well as Nanosilica as a reactive powder. Mechanical properties and microstructural analysis in addition to the molecular and mineralogical specifications were investigated to evaluate the performance of stabilized soil samples. For this purpose, a series of experimental tests including scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) are considered as well as mechanical tests to investigate the various aspects of the material. The results showed that the incorporation of Nanosilica not only improved the unconfined compressive strength (UCS) of the stabilized samples, but also the elastic modulus which is indicative of Nanosilica's tendency to increase the ductility of samples. In Portland cement (PC) and phosphorus slag blended cement (SBC)-based samples, the results confirmed that samples containing Nanosilica possess an intensified C–S–H phase compared to other samples. It appeared that the supplied reactive Nanosilica to the matrix showed better participation reaction of Ca2+ of Portlandite for formation of extra C–S–H phase due to the observed phase change of needle-like crystals of Portlandite in lower amount with smaller particles. Moreover, the microstructure results revealed that the presence of Nanosilica leads to more densified binder matrix with more coverage of soil particles. The incorporation of Nanosilica in SBC exhibited a more densified matrix with higher UCS values compared to PC samples. The presence of 2 wt% of Nanosilica in the alkali-activated phosphorus slag cement (AAC)-based samples resulted in lengthening the aluminosilicate chain with more substituted Al with reactive Si. In AAC-based samples, with incorporated Nanosilica a compact interfacial bond of matrix and soil particles was observed.