Investigating the effect of nanoparticles on the self-healing process of clay soils

Master's Thesis in Civil-Soil Engineering

Abstract

Dense clay layers are used as one of the most common impermeable layers in most geotechnical structures such as earthen dams and municipal and radioactive waste disposal centers. Due to the special geotechnical characteristics, these layers are damaged by cracking during their lifetime. These cracks increase the permeability of the layer and reduce its efficiency.

Regarding the necessity of knowing and knowing the factors affecting the stability of geotechnical structures built with these layers, in this research, an attempt has been made to use the self-healing properties of clay soils to take a step towards improving the performance of soils in different conditions.

In this research, by conducting Numerous tests have shown that the speed of crack repair can be increased by increasing the resistance of clay soils. The obtained results show that the addition of montmorillonite nanoclay to the soil increases its final strength; The passage of time fully reveals the effect of this increase in strength in the process of repairing the crack created by the device in the samples. Chapter 1 Generalities 1- Introduction Clay soils often have problems such as high settlement, low shear strength and difficulty in compaction. To provide proper soil strength, soil diversification, preloading, mixing, and soil stabilization are the methods. Depending on the type of project and conditions, there are various improvement methods. Some of these methods include compacting the construction, one of these methods is chosen as a suitable method for stabilization [1].

Clay stabilization using common additives such as cement, lime, fly ash, etc. It has always been studied by researchers. Besides that, nanomaterials that have unique features have been given less attention. [2]. The results of previous experiments show that adding a small percentage of montmorillonite nanoclay to clay significantly increases its resistance [2] and [3]; (For this reason, unmodified montmorillonite nanoclay was selected as the additive used in this research). The crack repair property of clay means closing the cracks created in it [15] and [23] and [24]. Factors affecting the self-healing of clay, especially the pasty properties of soils in different compaction-consolidation and humidity conditions cause specific behaviors related to clay [4].

Most of the tests performed in the field of self-healing of clays were permeability tests and were limited to cracks caused by contraction and expansion in landfills [15] and [24], or cracks caused by internal erosion in earthen dams. [4] and [23]. While these properties of clays can be used in other geotechnical phenomena that occur under a specific and predictable load. To achieve this goal in this research by creating a crack by testing the unenclosed compressive strength in the soil reinforced with montmorillonite nanoclay and keeping it in order to be repaired for a certain period of time, we are trying to investigate the effect of increasing resistance in the process of this phenomenon. Turkey

- Investigating the physical properties of soil and their modification

- Investigating the role of unmodified montmorillonite nanoclay on the self-healing rate of soils over time

- Obtaining an optimal percentage of nanoclay additive that, in addition to increasing resistance, will accelerate self-healing.

1-3- Research structure

This research is organized in the form of separate chapters that generally include topics related to the research topic.

In this research, after giving explanations related to the conducted research and the results obtained so far by examining clay soils, we have evaluated the impact of clay soils on physical properties including self-healing of soils, and after knowing the effect of clay soils by conducting experiments, we have measured the issue of self-healing of clay soils and evaluated and investigated the research objectives and presented the results in the conclusion and suggestions section.

2-1- Introduction

In this chapter, at the beginning, we have given explanations regarding the history of nanotechnology and the need to use it in geotechnics, then we have stated the studies conducted in relation to the research subject so far.

2-2- History of nanotechnology

The first spark of nanotechnology (although it was not yet known by this name at that time) was struck in 1959. In this year, Richard Feynman introduced the idea of ??nanotechnology during a speech entitled "There is a lot of space at low levels". He presented the theory that in the near future we will be able to directly manipulate molecules and atoms [5]. He stated that with the increase of scientists in the field of making transistors and other small scale sizes, we will be able to constantly make them smaller and smaller so that they finally approach their natural range at the edges of quantum uncertainty and stop where the atoms themselves become very slippery, unrecognizable and mechanically reliable. It was in the early 1990s that our attention to what we call today "nano-technology" gained tremendous momentum [6].

In the 1980s, measuring devices that have the characteristics and capabilities desired by Feynman were invented. These devices, which include scanning tunneling microscopes, atomic microscopes, and near-field microscopes, provided the necessary "eyes" and "fingers" for measuring and manipulating nanostructures. At the same time, the expansion of computing power has made it possible to simulate the complex behavior of materials at the nanoscale [7]. The word nanotechnology was first introduced by Noriyo Tainguchi, a professor at the Tokyo University of Science in 1974. He used this term to describe the manufacturing of precise materials (devices) whose dimensional tolerance is in the range of nanometers. In 1986, this term was recreated and redefined by K. Eric Drexler in a book titled "The Engine of Creation: The Beginning of the Era of Nanotechnology". He examined this term in a deeper way in his doctoral thesis and later developed it in a book entitled "Nanosystems, molecular machines, how to make and calculate them" [5].

2-3-Reasons for using nanotechnology

Maybe this question arises in the mind, what is there in the nanometer scale that a technology is based on. What has caused the emergence of nanotechnology is the high ratio of surface to volume of materials. This issue is one of the most important properties of materials produced at the nanoscale (nanomaterials or nanomaterials). At the nanoscale, objects begin to change their behavior and the behavior of surfaces overcomes the bulk behavior of matter. At this scale, some physical relationships that apply to ordinary materials are violated. For example, a wire or components of a nanoscale circuit do not necessarily obey Ohm's law. Ohm's law depends on voltage current and resistance. But at the nanoscale, when the width of the wire is only one or more atoms, the electrons must necessarily pass through the wire in order and one by one. Therefore, Ohm's law may be violated to some extent on this scale. In fact, at this scale, the laws of quantum physics enter the scene and it will be possible to control the inherent properties of the material, including the melting temperature, magnetic properties, charge capacity, and even the color of the material without changing the chemical composition of the material. Each smaller cube is still gold, yellow, shiny and heavy. All these cubes are soft, they are an electrically conductive metal, with the same melting point as they had before being divided into these smaller cubes. If we continue this process and keep making the gold cubes smaller and smaller, eventually we will not be able to see the crushed pieces of gold with the naked eye. But still the physical and chemical properties of gold pieces remain unchanged.

When we reach the nanoscale, almost everything changes, even the color of gold. Its melting point and chemical properties change completely.