Contrastive study on mechanical and microstructure properties of silt improved by nano material stabilizers

Abstract

Silt is generally stabilized with industrial waste for subgrade filler material. However, problems such as high cost, poor water stability, and easy shrinkage hinder the use of industrial waste-stabilizing materials. Experiments are conducted to compare the effect of nano-silica (NS) and nano-MgO (NM) on the unconfined compressive strength (UCS) of silt. It is undertaken by stabilized silt with NM and NS in four different concentration grades of NM(S)-3, NM(S)-4, NM(S)-5, NM(S)-6 ( 0.3%, 0.4%, 0.5%, 0.6% by weight of silt). XRD, FT-IR, and SEM tests are carried out to discern the latent mechanisms so that the mineral composition and pore structure within the soil matrix can be explained. The results demonstrate that the increase in different grades of nano-MgO and nano-silica stabilized silt plays an important role in improving the mechanical properties of the silt. Nano-silica is more conducive to strength and water resistance enhancement due to the formation of ettringite and C-S-H gel. Nevertheless, a small amount of nano-MgO can better improve the water stability of stabilized silt in the early stage. Optimal results are obtained for silt treated with NS-5 (2% cement, 2% GGBS, 1% FA, 0.5% nano-silica) and NM-5 (2% cement, 2% GGBS, 1% FA, 0.5% nano-MgO). XRD, FT-IR, and SEM analysis of the samples show, respectively, that the amorphous (C-S-H) structure and the soil particles embedded in the cementitious matrix comprise the strength of the silt. Nano-MgO is mainly involved in carbonation and pozzolanic reactions. The cement hydration reaction and ettringite formation, which unite smaller particles to produce larger particles, are enhanced by the addition of SiO2. In summary, this paper recommends the use of nano-MgO to improve the early strength of stabilized silt, and the use of nano-silica to improve the long-term strength.