Key-Parameters in Chemical Stabilization of Soils with Multiwall Carbon Nanotubes

António Alberto S Correia,Marta S M R Moura,Diogo T R Figueiredo,Maria Graça Rasteiro,Pedro D F Casaleiro

doi:10.3390/app11188754

António Alberto S Correia, Marta S M R Moura + Show 3 more

Open Access

https://doi.org/10.3390/app11188754

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Journal: Applied Sciences	Publication Date: Sep 20, 2021
Citations: 5	License type: CC BY 4.0

Affiliation: University of Coimbra

Abstract

Chemical stabilization is one of the most successful techniques that has been applied to improve the geomechanical behavior of soil. Several additives have been studied to be a sustainable alternative to traditional additives (Portland cement and lime) normally associated with high cost and carbon footprint. Nanomaterials are one of the most recent additives proposed. This work is focused on one type of nanomaterial, multiwall carbon nanotubes (MWCNTs) with unique characteristics, applied to chemical stabilization of soils and aiming to identify the key-parameters affecting the stabilization improvement. It was found that a surfactant should be added in order to oppose the natural tendency of MWCNTs to aggregate with the consequent loss of benefits. The surfactant choice is not so dependent on the charge of the surfactant but rather on the balance between the concentration and the hydrodynamic diameter/molecular weight due to their impact on the geomechanical compression behavior. As time evolves from 7 to 28 days, there is a decrease in the geomechanical benefits associated with the presence of MWCNTs explained by the development of the cementitious matrix. MWCNTs applied in a proper concentration and enriched with a specific surfactant type may be a short-time valid alternative to the partial replacement of traditional additives.

Highlights

Soil is the loose particulate natural material that covers the Earth’s surface
The present work is a contribution to identify the most important or fundamental parameters that control the geomechanical behavior of a chemically stabilized soil additivated with multiwall carbon nanotubes (MWCNTs) dispersed or not in a surfactant solution
Based on the laboratory tests performed, it was found that a simple addition of MWCNTs to the stabilized soil does not produce any improvement of its geomechanical behavior since the nanoparticles are in an aggregate condition, which inhibits its ability to take advantage of the extraordinary properties of MWCNTs

Summary

Introduction

Soil is the loose particulate natural material that covers the Earth’s surface. Soil is a multiphase material containing an aqueous, gaseous and solid phase, each composed of inorganic and organic components. The soil does not meet the safety and stability requirements for construction, and ground improvement techniques are required [3,4,5,6] This is the case of soft soils, characterized by exhibiting low strength and high deformability. The traditional additives most used in chemical stabilization of soft soils are Portland cement and lime, applied alone or in combination in percentages ranging from 5% to 20% w/w (additive/soil) [11,12,13]. These additives have high costs and high environmental impacts associated to their production, which encourages the development of new additives. Industrial byproducts (e.g., slag, fly ash, rice ash), pozzolanic materials (e.g., fly ash, natural pozzolana, silica fume), biobased products (e.g., polymers, enzymes) and nanomaterials (e.g., carbon nanotubes, carbon nanofibers, nano-ashes, nanoclays) are some examples of promising additives that may be used as a total or partial replacement of the traditional additives [11,13,14,15,16,17,18,19,20]

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