Micro- and nano- bentonite to improve the strength of clayey sand as a nano soil-improvement technique.

Nano-additives results in the formation of nano-cementation (NC). This process is recently used to improve the durability of various building materials. NC used to improve the strength of untreated soil materials, also known as nano soil-improvement (NSI). In few years, the role of nano-additives in various types of soils were developed. In this research, the role of micro- and nano- size of bentonite as soil stabilizer was evaluated as first few research to improve geotechnical properties of soils. Nano-additives prepared by micro- and nano- sizes of bentonite were blend with four formulations. These formulations of micro- and nano- additives at concentrations of 0, 1, 2, and 3%, namely 0% Micro-Bentonite, 1% Micro-Bentonite, 2% Micro-Bentonite, 3% Micro-Bentonite, 0% Nano-Bentonite, 1% Nano-Bentonite, 2% Nano-Bentonite, and 3% Nano-Bentonite, respectively. These formulations of micro- and nano- additives were separately added to soil. Specimens with 3% nano-bentonite showed significant improvement in unconfined compressive strength (UCS) of soil that was more than 2.3-times higher than control specimen in 7-d curing time. Also the performance of micro-bentonite resulted in improvement in UCS of soil that was more than 1.1-times higher than control specimen at 7-d curing time. The secant modulus at 50% of peak stress (E50) of the samples treated with micro- and nano- additives increased in comparison to untreated specimens. Further, X-ray fluorescence (XRF), scanning electron microscopy, and X-ray diffraction analyses characterized micro- and nano- structures of soil specimens, and showed the performance of nano-additives in improving strength of soils. Results show that nano-bentonite as a type of nano-additives is an effective means of increasing the strength of soils. This research shows the significant of nano-bentonite in soil improvement, as a NSI technique.