Experimental and simulation study of the effects of multi-walled carbon nanotubes in clayey soils

• Published in: Applied nanoscience Vol. 13; no. 9; pp. 6249 - 6257
• Main Authors: da Rocha Loures, Fábio Santos, Mortari, Sérgio Roberto, Grison, Tulio Gnoatto, Rossatto, Rafael, de Vargas, Douglas Duarte, Köhler, Mateus Henrique, da Silva, William Leonardo, dos Santos, Cláudia Lange
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.09.2023; Springer Nature B.V
• Subjects: Aluminum oxide; Carbon; Chemical vapor deposition; Chemistry and Materials Science; Clay soils; Consistency tests; Flexible pavements; Maintenance costs; Materials Science; Membrane Biology; Molecular dynamics; Multi wall carbon nanotubes; Nanochemistry; Nanocomposites; Nanotechnology; Nanotechnology and Microengineering; Original Article; Road works; Roads & highways; Shear strength; Silicon dioxide; Simulation; Soil compressibility; Soil strength; Subgrades; Submerging; Water immersion; Carbon nanotubes; Molecular dynamics; Flexible pavements; Clay soils
• ISSN: 2190-5509; 2190-5517
• DOI: 10.1007/s13204-023-02881-8

Flexible pavements are the most used structure to build roads and highways around the world. However, frequent repairs usually related to their low quality, which leads to high maintenance costs, have motivated engineers to explore new alternatives in building new roads and conserving the existing ones. One of the possible solutions for the improvement of these pavements could be the use of carbon nanotubes (CNTs) to reinforce the subgrade soils. The purpose of this work was to investigate the influence of multi-walled carbon nanotubes (MWCNTs) on the shear strength of lower layers of the structure of flexible pavements, consisting primarily of clayey soils (soil 1 and 2). MWCNTs were prepared by the chemical vapor deposition (CVD) method and the nanocomposites (NCs) by the simple mixture of MWCNTs with clayey soils (ranging from 0.5–2.0% w/w). The materials were characterized by geotechnical tests (granulometry, consistency tests and Mini-CBR tests), textural (N 2 porosimetry), chemical, and morphological (SEM–EDS). From geotechnical characterization, soil 1 was denominated as clay of high compressibility (A-7-5) and soil 2 as clay of low compressibility (A-6). NCs with 1% of MWCNTs showed small clusters with a composition predominantly of SiO 2 and Al 2 O 3 . Textural analysis indicated a type IV isotherm, characteristic of mesoporous materials. From the Mini-CBR tests carried out with soil 1, it was observed that the immersion in water significantly reduced the strength of the samples (CPs), this effect being more pronounced for pure soil. In addition, right after molding of the CPs, the pure dry soil showed greater strength. On the other hand, after 5 days, the dry NCs started to present a greater strength showing that the curing time can change the characteristics of the soil. For soil 2, the effect of water immersion was less relevant as compared to soil 1. Moreover, differently from soil 1, the highest strength was observed for the NCs, indicating a positive effect of the addition of MWCNTs. Further classical molecular dynamics (MD) simulations were performed to confirm the experimental results, pointing to a reduction in the average equilibrium distances between the nanocomposites, from ~ 22 to ~ 10 Å, after the addition of CNTs in dry systems. The simulations also highlight the impact of water on the compound's aggregation. These results are promising since a positive signal of its application in flexible pavements could represent an advance in the execution of national and foreign road works.