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Rheological study on influence of mineral composition on viscoelastic properties of clay
Applied Clay Science 187 (2020) 105493
Contents lists available at ScienceDirect
Applied Clay Science journal homepage: www.elsevier.com/locate/clay
Note
Rheological study on influence of mineral composition on viscoelastic properties of clay Hangtian Ni, Yubin Huang
T
⁎
School of Civil Engineering, Chongqing University, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Clay Viscoelasticity Mineral composition Dynamic shear Viscoelastic modulus
Using an oscillating shear rheology experiment and zeta potential analysis to explore the influence of mineral composition on the viscoelastic properties of soil, three pure mineral clays, namely, kaolin, montmorillonite, and illite, and their mixed simulated clays were tested. The results showed that the influence of mineral composition on the viscoelastic properties was larger than the influence of other factors. The contribution of montmorillonite to the viscoelastic properties was much greater than that of kaolin or illite. The influence of the coefficient of montmorillonite on the viscoelasticity of the simulated soil decreased with increase of strain and water content. The zeta potential test results were consistent with theoretical analyses.
1. Introduction
rheological mechanism, and improve rheological analysis theory, this study examined soil viscoelasticity from a mesoscopic perspective. With the aid of the dynamic shearing test and potential analyser, the influence of mineral composition on soil viscoelasticity was evaluated. The experimental results of this study are helpful for revealing the viscoelastic mechanisms of soil, and enriching the research achievements pertaining to viscoelastic properties.
The viscoelastic phenomenon is one of the problems that requires close attention in the application of soil engineering. It has a wide range of manifestations, such as creep, relaxation, and long-term strength. In recent years, many scholars have carried out relevant research from the perspective of rheology, but they have focused mainly on macro and micro aspects (Carotenuto et al., 2015; Terzis and Laloui, 2018; Holthusen et al., 2019). Meso-research can essentially explore the mechanisms of soil rheology from the levels of the material mechanism and behavioural details, but the relevant research that has been carried out focuses mainly on pore water or bound water (Fang and Gu, 2007; Markgraf et al., 2012; Moayeri et al., 2016). Mineral composition, as one of the core aspects at the mesoscopic level of soil, deserves special attention. On one hand, according to the electric double layer theory, mineral particles in soils have an important impact on the properties of soil due to their strong surface electrical characteristics. However, at present, analyses of the relationships between clay mineral composition and viscoelasticity of soil are few and lack systematic research (Ajayi et al., 2013; Ma et al., 2014; Fang et al., 2016; Sun et al., 2017). On the other hand, different mineral particles are certain to have different degrees, or even different directions, of influence on the viscoelasticity of the soil. If studies can accurately grasp the mechanisms, reasons, and laws of influence, the viscoelastic properties of soil could be predicted directly through the composition ratio of the different minerals in the soil. To approach the viscoelastic nature of soil further, reveal the
⁎
2. Materials and experiments 2.1. Experimental materials Three pure mineral clays, namely, kaolin (K), montmorillonite (Mt), and illite (I), were selected for the experiment. The test materials were purchased from a mineral raw material manufacturer in Yueyang, Hunan Province, China. The purity grade of the samples was analytical reagent (AR) grade, and the samples contained only a pure single mineral clay. Additionally, based on a previous investigation (Kao, 2015), the samples were mixed according to the ratio of K:Mt.:I = 37:28:35 to simulate the regional clays, and the test results were compared with the linear combination (LC) of the three pure mineral clays. When mixing, three kinds of dried pure soil were weighed according to the proportion, put into a stirring container and manually stirred for 5 min. In order to prevent the entry of external moisture and the quality loss caused by the soil flying out, the mixed soil was only added to about half of the height of the container, and sealed the container with plastic film. Then inserted the rotor of a small electric stirrer and mechanically stirred for
Corresponding author. E-mail addresses: [email protected] (H. Ni), [email protected] (Y. Huang).
https://doi.org/10.1016/j.clay.2020.105493 Received 19 August 2019; Received in revised form 31 December 2019; Accepted 5 February 2020 0169-1317/ © 2020 Published by Elsevier B.V.
Applied Clay Science 187 (2020) 105493
H. Ni and Y. Huang
viscous deformation, which reflects the continuous process of change from a quasi-elastic solid to a quasi-viscous fluid. The main difference was that the stress of K and I fluctuated in a small range in the viscoelastic stage, whereas the stress of Mt. had an extreme value. During the middle stage, the viscoelastic modulus began to change. Hyun et al. (2002) classified the large strain amplitude shear response of a complex fluid (polymer solution) into four categories: strain thinning, strain thickening, weak strain overshoot, and strong strain overshoot. For K and I, G' and G" both decreased obviously and finally had the same order of magnitude. Under the conditions of the experiment, K and I showed shear thinning behaviour. However, the Mt. soil showed weak strain overshoot behaviour, i.e., G' decreased gradually while G" had a maximum value. The overall decrease of G' and G" was due to a large dissipation of the total energy of the soil with increase of vibration and shear, which weakened the solid property of the soil. However, due to the strong comprehensive action between mineral particles in the Mt. system, which can be verified by the critical shear stress of soil Mt. being much larger than that of soil K or soil I, the initial small shear action could not destroy the Mt. Rather, it disturbed the soil and altered the interaction relationships between particles, such as by changing the relationship between molecular attraction and electric double layer repulsion, thus enhancing the cohesive behaviour and maximising G" at the early stage.
Table 1 Basic parameters of four soil samples. Soil samples
Specific gravity
Plastic limit (%)
Liquid limit (%)
Kaolin (K) Montmorillonite (Mt) Ilite (I) Simulated soil (S)
2.33 2.18 2.23 2.21
16.2 19.1 18.0 17.1
29.2 34.5 29.7 34.3
3 min to obtain evenly dried mixed soil. The basic parameters are listed in Table 1, and the particle size analysis is listed in Table 2. 2.2. Experimental instruments and test procedures The oscillating shear rheology test was conducted using an MCR102 large particle rheometer developed by Anton-Paar (Austria), which was equipped with a coaxial cylinder measuring system and a stainless-steel double-plate rotor. Before testing, the soil was passed through a 0.5 mm geotechnical sieve and dried in an oven. According to the experimental design, the cooled soil and the calculated water were mixed evenly to obtain samples with the target water content (ω). The mixing process was the same as the steps for preparing simulated clay, i.e. put the accurately weighed soil and water into a stirring container (only about half the height), and sealed with plastic film. Manually stirred for 5 min, and then 3 min by the machine, to obtain the evenly mixed test samples. For each group of tests, two samples were prepared for measurement, and the third measurement was conducted for verification if there is an error. Meanwhile, in order to ensure the accuracy of ω, the next group shall be prepared after the former test is completed. The test ω is controlled according to the liquid limit (LL) of soils, and three water contents are designed for each soil, i.e. 1 time, 1.25 times and 1.5 times of the LL. The soil with the designed ω was poured into the instrument cylinder and allowed to stand for 10 min. Then, the rotor was inserted into the soil, and the soil was allowed to stand for 10 min before the experiment was started. Finally, the instrument was operated according to the oscillating shear mode to complete the experiment.
3.1.2. Frequency scanning and time scanning To understand fully the effects of shear frequency and time on the viscoelastic modulus, the four pure mineral soils were scanned with frequencies ranging from 0.01 Hz to 10 Hz, and the results are shown in Table 3. Meanwhile, the strain amplitude and shear frequency were fixed at 0.01% and 1 Hz for time scanning, respectively. These data are summarised in Table 4. The results showed that the frequency had a limited effect on the viscoelastic modulus, and the stability of the data over time proved the validity of the test results. 3.1.3. Influence of water content Water content (ω) is one of the important factors affecting soil properties. The changes of viscoelastic modulus under different ω are shown in Fig. 2. For K and I, under the action of shear, the infiltration of water intensified destruction of the soils, so the modulus was reduced greatly. However, for Mt., G' was basically stable, and G" showed an increase phenomenon. This occurred because the initial energy between mineral particles in the Mt. was relatively large. Therefore, water infiltration under weak shear could not destroy the soil, so G' was basically unchanged. However, for the increase of G", the influencing factors are complex. The main reason for the increase is that the weak shearing action adjusted the soil particles system, meanwhile, clay particles
3. Results and discussion 3.1. Analysis of pure mineral clays 3.1.1. Strain amplitude scanning The stress–strain relationship of the three pure mineral soils (Fig. 1) successively showed elastic deformation, viscoelastic deformation, and Table 2 Particle size distribution of four soil samples. Particle size (μm)
K (%)
Mt (%)
I (%)
S (%)
Particle size (μm)
K (%)
Mt (%)
I (%)
S (%)
0–1.031 1.031–1.207 1.207–1.414 1.414–1.655 1.655–1.938 1.938–2.269 2.269–2.657 2.657–3.11 3.11–3.642 3.642–4.264 4.264–4.992 4.992–5.845 5.845–6.843 6.843–8.013 8.013–9.381
0 0.24 1.01 2.13 3.52 5.05 6.59 7.99 9.15 9.94 10.23 9.98 9.18 7.93 6.36
0 0 0.01 0.32 0.71 1.18 1.7 2.25 2.84 3.46 4.11 4.76 5.41 6.05 6.62
0 0 0.01 0.31 0.56 0.86 1.21 1.65 2.18 2.82 3.55 4.35 5.17 5.93 6.57
0 0.01 0.55 1.16 1.81 2.47 3.11 3.73 4.32 4.87 5.36 5.77 6.08 6.27 6.33
9.381–10.984 10.984–12.86 12.86–15.057 15.057–17.629 17.629–20.641 20.641–24.167 24.167–28.295 28.295–33.129 33.129–38.788 38.788–45.414 45.414–53.173 53.173–62.256 62.256–72.891 72.891–85.343 85.343–2000
4.69 3.12 1.78 0.85 0.23 0.02 0 0 0 0 0 0 0 0 0
7.1 7.42 7.54 7.4 6.98 6.3 5.4 4.36 3.3 2.32 1.48 0.78 0.19 0 0
6.99 7.15 7.01 6.58 5.94 5.16 4.37 3.67 3.12 2.73 2.47 2.27 2.07 1.81 3.48
6.25 6.02 5.66 5.19 4.65 4.06 3.47 2.91 2.4 1.95 1.57 1.24 0.97 0.73 1.08
2
Applied Clay Science 187 (2020) 105493
H. Ni and Y. Huang
Fig. 1. Variation laws of viscoelastic parameters of the four soils. τ is shear stress, G' for storage (elastic) modulus, G" for loss (viscous) modulus, f is frequency, and θ is phase angle. 1, 1.25 and 1.5 after the soil code number represent water content (ω), which controlled according to the liquid limit (LL) of soil. For example, K-1.25-G" represents the loss modulus of kaolin, which water content with respect to liquid limit is 1.25 times, and so on.
viscoelastic modulus decreased.
hydrated and expanded after being exposed to water, so the interaction between different clay particles changed. Furthermore, the infiltration of water reduced the ion concentration in the electric double layer and decreased the repulsive force between particles, thus increasing the viscosity. At the later stage of shearing, the infiltration of water and strong shearing action intensified the destruction of the soil, so the
3.2. Influence of mineral composition Combining with the results from Fig. 1 for analysis, soil S also underwent three stages. Among the three kinds of pure mineral clays, the
Table 3 G' and G" of four soil samples under frequency scanning. Angular frequency (rad/s)
K-1.25-G'(Pa)
K-1.25-G"(Pa)
M-1.25-G'(Pa)
M-1.25-G"(Pa)
I-1.25-G'(Pa)
I-1.25-G"(Pa)
S-1.25- G'(Pa)
S-1.25- G"(Pa)
0.0628 0.0996 0.158 0.25 0.396 0.628 0.996 1.58 2.5 3.96 6.28 9.96 15.8 25
0.18 0.25 0.32 0.67 0.51 0.82 0.70 1.04 1.02 1.12 1.43 1.27 0.91 2.83
0.14 0.21 0.27 0.33 0.31 0.57 0.41 0.59 0.64 0.36 1.08 1.26 2.33 5.46
245,000 245,000 248,000 250,000 253,000 254,000 256,000 258,000 258,000 260,000 260,000 261,000 262,000 262,000
9987 9974.6 8211.9 7510.5 7116.1 5609.3 5130 3806.9 4307 3475 2904.5 2837.2 2541.5 2413.2
429.4 1148.8 1858.7 2519.2 3317 3967.8 4435.6 4829.5 5154.8 5482.1 5697.4 5853.2 5936.1 5823.9
658.9 1572.1 2214.2 2673.3 3066.6 3252.5 3320.7 3311 3249.8 3152.6 2917.7 2716.9 2550.5 2419.6
127,000 147,000 155,000 159,000 163,000 166,000 170,000 173,000 177,000 180,000 182,000 185,000 187,000 189,000
47,003 29,521 24,195 21,067 19,213 18,021 16,933 16,476 15,833 14,130 12,644 11,565 10,292 9588.8
3
Applied Clay Science 187 (2020) 105493
H. Ni and Y. Huang
at the meso and micro levels, such as by changing the relationship between molecular attraction and electric double layer repulsion, so the cohesive behaviour of the soil was enhanced and a maximum value of G" appeared. For these reasons, S showed strain overshoot behaviour that similar to that of Mt. The test results with varying water content were also evaluated. According to Fig. 2, the variation law of the viscoelastic modulus of S under different moisture contents was also the same as that of Mt., but it differed from those of K and I. In the result, the strain corresponding to the maximum point of S was only about one-tenth that of Mt., which was mainly due to the reduction of the content of strongly acting mineral particles (Mt) and the interaction coupling between various mineral particles. Based on the analysis above, it can be inferred preliminarily that the degree of influence of mineral composition on the viscoelastic property of the soil was higher than those of other factors.
Table 4 G' and G" of four soil samples under time scanning. T(min)
K1.25G'(Pa)
K1.25G"(Pa)
M-1.25G'(Pa)
M1.25G"(Pa)
I1.25G'(Pa)
I-1.25G"(Pa)
S-1.25G'(Pa)
S-1.25G"(Pa)
1 1.17 1.33 1.5 1.67 1.83 2 2.17 2.33 2.5
250 207 228 246 240 277 242 212 239 247
51 49 46 55 59 65 50 47 53 60
208,000 210,000 206,000 208,000 208,000 207,000 209,000 211,000 208,000 209,000
7814 8315 7643 8222 7835 8448 7804 8387 8250 7844
4592 5054 4868 5176 5171 5088 5321 5345 5443 5598
2783 3113 2911 3028 3071 3047 3123 3175 3140 3185
135,000 134,000 135,000 134,000 133,000 135,000 134,000 135,000 134,000 135,000
13,221 12,873 13,001 13,205 13,079 12,862 13,011 13,270 12,958 13,100
interaction between Mt. particles was much stronger than that for K or I, so it played a major role in the viscoelastic properties of the mixed soil. Due to the strong effect of Mt. particles and the mixed particle sizes, which caused the soil to be denser, the initial small shear action could not destroy the soil mass but only disturb the soil mass and slightly adjust the system, so the G' of S changed little. However, the shearing action still affected the complex relationships among particles
3.3. Double electric layer analysis The electric double layer, as the embodiment of the complex relationship within a soil, is directly related to a series of physical and chemical properties of the soil and essentially affects the viscoelastic behaviour of the soil. In the theory of the electric double layer, the zeta
Fig. 2. G'/G" of the four soils at different water contents. K-kaolin, Mt-montmorillonite, I-illite. G' for storage (elastic) modulus, G" for loss (viscous) modulus. 1, 1.25 and 1.5 after the soil code number represent water content (ω), which controlled according to the liquid limit (LL) of soil. For example, K-1.25-G" represents the loss modulus of kaolin, which water content with respect to liquid limit is 1.25 times, and so on. 4
Applied Clay Science 187 (2020) 105493
H. Ni and Y. Huang
1. Dynamic shear rheology tests could better characterise the viscoelasticity of the soils. The obtained elastic modulus (G'), viscous modulus (G"), and phase angle (θ) could effectively measure the elastic temporary deformation, viscous permanent deformation, and viscoelastic proportion change of the soils. The effects of water content, strain amplitude, and frequency on the parameters were also studied. 2. Through an analysis of the results, kaolin (K) and illite (I) showed strain thinning behaviour. However, due to the strong interaction between mineral particles, Mt. behaved differently from K and I under various moisture contents and shear effects, showing weak strain overshoot behaviour and larger corresponding shear stress. 3. The viscoelasticity of the mixed clay (S) was affected mainly by Mt. and showed the same weak strain overshoot behaviour as Mt. under all conditions. However, the critical strain was only one-tenth that of Mt., mainly due to the lower content of strongly acting mineral particles (montmorillonite) and the interaction coupling between various mineral particles. At the same time, the influence of montmorillonite decreased with increase of shear and water. 4. The variation laws of the soil viscoelastic properties were consistent with the zeta (ζ) potential results, which confirms the effectiveness of ζ potential and electric double layer theory for revealing soil viscoelastic properties. Meanwhile, it was pointed out as a result of the analysis that the mineral composition, as the most essential feature of the soils, had a greater influence on the viscoelasticity of the soils than other factors.
Table 5 Zeta potential of four soil samples. Soil sample
Refractive index
Average potential (mV)
K M I S
1.55 1.56 1.57 1.56
−8.04 −20.5 −27.2 −23.6
potential (ζ) can provide a lot of information pertaining to the structure and properties of the electric double layer. It is generally believed that ζ potential is a measure of the strength of mutual repulsion or attraction between particles. When the absolute value of ζ potential is lower, the soil particles are more inclined to condense, or agglomerate, that is, the interaction force between soil particles is stronger. Using the nanoparticle size and ζ potential analyser (Malvern Company, England), a 5 wt% suspension was prepared under the temperature of 25 °C, and the zeta potentials of the four kinds soil samples were tested. The results are listed in Table 5. Under the conditions of shearing action and water infiltration, according to Fig. 1, the magnitude relation of G" for the four soils was G" (K) < G” (I) < G” (S) < G” (Mt). According to ζ potential theory, the absolute value relation of the potential ζ should be ζ (Mt) < ζ (S) < ζ (I) < ζ (K), while the actual result was ζ (K) < ζ (Mt) < ζ (S) < ζ (I). As analyzed above, when the absolute value of the potential is lower, the soil tends to coagulate, or agglomerate, it depends on the interaction between soil particles, and can be used to measure the viscosity of soil particles to a certain extent. For soil samples S and Mt., with particle sizes of the same magnitude, this conclusion is consistent with the result. However, because the particle size of soil sample K was smaller, under the conditions of shearing action and water infiltration, the distance between particles was too large, which minimised the interaction between K particles of the soil; therefore, although the absolute value of the potential was smallest, the viscosity was instead lowest. On the other hand, for soil sample I, the absolute value of the potential was larger than that of soils S and Mt., so it can be inferred that the G" of I would be lower than that of S and Mt. This is exactly what was observed. However, soil I had the largest particle size. Under the test conditions, the particle spacing would be the smallest, which is conducive to interaction between particles. Nevertheless, from the results, the relative relationship between G" was not changed. Therefore, to some content (the change range of particle size in this study was not large enough), it can be considered that the degree of influence of the viscosity layer of the double electric layer between particles was larger than the that of the particle size distribution. Similarly, the stress relation of the soils shown in Fig. 1A is τ (I) < τ (S) < τ (M), which also indicates that the strongly viscous layer makes an important contribution to the energy of the soil system and, to a certain extent, determines the viscoelastic properties of the soil.
Declaration of Competing Interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References Ajayi, A.E., Dias Junior, M.S., Curi, N., Oladipo, I., 2013. Compressive response of some agricultural soils influenced by the mineralogy and moisture. Int. Agrophy. 27 (3), 239–246. Carotenuto, C., Merola, M.C., Álvarez-Romero, M., Coppola, E., Minale, M., 2015. Rheology of natural slurries involved in a rapid mudflow with different soil organic carbon content. Colloids Surf. A Physicochem. Eng. Asp. 466, 57–65. Fang, Y.G., Gu, R.G., 2007. Experiment study on the effects of adsorbed water on rheological characteristics of soft clayey soil. Sci. Technol. and Eng. 7 (1), 73–78. Fang, Y.G., Peng, Z.Q., Gu, R.G., Hu, Y.G., Ou, Z.F., Li, B., 2016. Analysis of creep test on effect of rheological material on soft soil rheological parameter. Rock Soil Mech. 37 (S2), 257–262. Holthusen, D., Pértile, P., Reichert, J.M., Horn, R., 2019. Viscoelasticity and shear resistance at the microscale of naturally structured and homogenized subtropical soils under undefined and defined normal stress conditions. Soil Tillage Res. 191, 282–293. Hyun, K., Kim, S.H., Ahn, K.H., Lee, S.J., 2002. Large amplitude oscillatory shear as a way to classify the complex fluids. J. Non-Newtonian Fluid Mech. 14, 49–55. Kao, Y.Z., 2015. Effect of Clay Mineral Composition on Polycarboxylate Superplasticizer Dispersibility [D]. Chongqing University, Chongqing. Ma, W.B., Rao, Q.H., Rong, H.Y., Guo, S.C., Li, P., 2014. Macroscopic properties and microstructure analyses of deep-sea sediment. Rock Soil Mech. 35 (6), 1641–1646. Markgraf, W., Watts, C.W., Whalley, W.R., Hrkac, T., Horn, R., 2012. Influence of organic matter on rheological properties of soil. Appl. Clay Sci. 64, 25–33. Moayeri, K.M., Hin, L.S., Ibrahim, S.B., Nik Sulaiman, N.M.B., Teo, F.Y., 2016. An investigation into the effects of particle texture, water content and parallel plates' diameters on rheological behavior of fine sediment. Int. J. Sediment Res. 31 (2), 120–130. Sun, W.J., Wang, L.B., Wang, Y.Q., 2017. Mechanical properties of rock materials with related to mineralogical characteristics and grain size through experimental investigation: a comprehensive review. Front. Struct. Civ. Eng. 11 (3), 322–328. Terzis, D., Laloui, L., 2018. 3-D micro-architecture and mechanical response of soil cemented via microbial-induced calcite precipitation. Sci. Rep. 8 (1), 1416.
4. Conclusion In traditional soil mechanics, research on soil viscoelasticity has concentrated mostly on the macro and micro levels. From the mesoscopic and material levels, this study mainly examined the influence of mineral composition on soil viscoelasticity through a series of oscillatory shear rheology experiments on three pure mineral clays (kaolin, montmorillonite, and illite) and a mixed clay. At the same time, based on ζ potential tests and electric double layer theory, this study theoretically analyzed the viscoelastic properties and revealed the viscoelastic mechanisms of the soils. The conclusions of the study follow:
5
Contents lists available at ScienceDirect
Applied Clay Science journal homepage: www.elsevier.com/locate/clay
Note
Rheological study on influence of mineral composition on viscoelastic properties of clay Hangtian Ni, Yubin Huang
T
⁎
School of Civil Engineering, Chongqing University, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Clay Viscoelasticity Mineral composition Dynamic shear Viscoelastic modulus
Using an oscillating shear rheology experiment and zeta potential analysis to explore the influence of mineral composition on the viscoelastic properties of soil, three pure mineral clays, namely, kaolin, montmorillonite, and illite, and their mixed simulated clays were tested. The results showed that the influence of mineral composition on the viscoelastic properties was larger than the influence of other factors. The contribution of montmorillonite to the viscoelastic properties was much greater than that of kaolin or illite. The influence of the coefficient of montmorillonite on the viscoelasticity of the simulated soil decreased with increase of strain and water content. The zeta potential test results were consistent with theoretical analyses.
1. Introduction
rheological mechanism, and improve rheological analysis theory, this study examined soil viscoelasticity from a mesoscopic perspective. With the aid of the dynamic shearing test and potential analyser, the influence of mineral composition on soil viscoelasticity was evaluated. The experimental results of this study are helpful for revealing the viscoelastic mechanisms of soil, and enriching the research achievements pertaining to viscoelastic properties.
The viscoelastic phenomenon is one of the problems that requires close attention in the application of soil engineering. It has a wide range of manifestations, such as creep, relaxation, and long-term strength. In recent years, many scholars have carried out relevant research from the perspective of rheology, but they have focused mainly on macro and micro aspects (Carotenuto et al., 2015; Terzis and Laloui, 2018; Holthusen et al., 2019). Meso-research can essentially explore the mechanisms of soil rheology from the levels of the material mechanism and behavioural details, but the relevant research that has been carried out focuses mainly on pore water or bound water (Fang and Gu, 2007; Markgraf et al., 2012; Moayeri et al., 2016). Mineral composition, as one of the core aspects at the mesoscopic level of soil, deserves special attention. On one hand, according to the electric double layer theory, mineral particles in soils have an important impact on the properties of soil due to their strong surface electrical characteristics. However, at present, analyses of the relationships between clay mineral composition and viscoelasticity of soil are few and lack systematic research (Ajayi et al., 2013; Ma et al., 2014; Fang et al., 2016; Sun et al., 2017). On the other hand, different mineral particles are certain to have different degrees, or even different directions, of influence on the viscoelasticity of the soil. If studies can accurately grasp the mechanisms, reasons, and laws of influence, the viscoelastic properties of soil could be predicted directly through the composition ratio of the different minerals in the soil. To approach the viscoelastic nature of soil further, reveal the
⁎
2. Materials and experiments 2.1. Experimental materials Three pure mineral clays, namely, kaolin (K), montmorillonite (Mt), and illite (I), were selected for the experiment. The test materials were purchased from a mineral raw material manufacturer in Yueyang, Hunan Province, China. The purity grade of the samples was analytical reagent (AR) grade, and the samples contained only a pure single mineral clay. Additionally, based on a previous investigation (Kao, 2015), the samples were mixed according to the ratio of K:Mt.:I = 37:28:35 to simulate the regional clays, and the test results were compared with the linear combination (LC) of the three pure mineral clays. When mixing, three kinds of dried pure soil were weighed according to the proportion, put into a stirring container and manually stirred for 5 min. In order to prevent the entry of external moisture and the quality loss caused by the soil flying out, the mixed soil was only added to about half of the height of the container, and sealed the container with plastic film. Then inserted the rotor of a small electric stirrer and mechanically stirred for
Corresponding author. E-mail addresses: [email protected] (H. Ni), [email protected] (Y. Huang).
https://doi.org/10.1016/j.clay.2020.105493 Received 19 August 2019; Received in revised form 31 December 2019; Accepted 5 February 2020 0169-1317/ © 2020 Published by Elsevier B.V.
Applied Clay Science 187 (2020) 105493
H. Ni and Y. Huang
viscous deformation, which reflects the continuous process of change from a quasi-elastic solid to a quasi-viscous fluid. The main difference was that the stress of K and I fluctuated in a small range in the viscoelastic stage, whereas the stress of Mt. had an extreme value. During the middle stage, the viscoelastic modulus began to change. Hyun et al. (2002) classified the large strain amplitude shear response of a complex fluid (polymer solution) into four categories: strain thinning, strain thickening, weak strain overshoot, and strong strain overshoot. For K and I, G' and G" both decreased obviously and finally had the same order of magnitude. Under the conditions of the experiment, K and I showed shear thinning behaviour. However, the Mt. soil showed weak strain overshoot behaviour, i.e., G' decreased gradually while G" had a maximum value. The overall decrease of G' and G" was due to a large dissipation of the total energy of the soil with increase of vibration and shear, which weakened the solid property of the soil. However, due to the strong comprehensive action between mineral particles in the Mt. system, which can be verified by the critical shear stress of soil Mt. being much larger than that of soil K or soil I, the initial small shear action could not destroy the Mt. Rather, it disturbed the soil and altered the interaction relationships between particles, such as by changing the relationship between molecular attraction and electric double layer repulsion, thus enhancing the cohesive behaviour and maximising G" at the early stage.
Table 1 Basic parameters of four soil samples. Soil samples
Specific gravity
Plastic limit (%)
Liquid limit (%)
Kaolin (K) Montmorillonite (Mt) Ilite (I) Simulated soil (S)
2.33 2.18 2.23 2.21
16.2 19.1 18.0 17.1
29.2 34.5 29.7 34.3
3 min to obtain evenly dried mixed soil. The basic parameters are listed in Table 1, and the particle size analysis is listed in Table 2. 2.2. Experimental instruments and test procedures The oscillating shear rheology test was conducted using an MCR102 large particle rheometer developed by Anton-Paar (Austria), which was equipped with a coaxial cylinder measuring system and a stainless-steel double-plate rotor. Before testing, the soil was passed through a 0.5 mm geotechnical sieve and dried in an oven. According to the experimental design, the cooled soil and the calculated water were mixed evenly to obtain samples with the target water content (ω). The mixing process was the same as the steps for preparing simulated clay, i.e. put the accurately weighed soil and water into a stirring container (only about half the height), and sealed with plastic film. Manually stirred for 5 min, and then 3 min by the machine, to obtain the evenly mixed test samples. For each group of tests, two samples were prepared for measurement, and the third measurement was conducted for verification if there is an error. Meanwhile, in order to ensure the accuracy of ω, the next group shall be prepared after the former test is completed. The test ω is controlled according to the liquid limit (LL) of soils, and three water contents are designed for each soil, i.e. 1 time, 1.25 times and 1.5 times of the LL. The soil with the designed ω was poured into the instrument cylinder and allowed to stand for 10 min. Then, the rotor was inserted into the soil, and the soil was allowed to stand for 10 min before the experiment was started. Finally, the instrument was operated according to the oscillating shear mode to complete the experiment.
3.1.2. Frequency scanning and time scanning To understand fully the effects of shear frequency and time on the viscoelastic modulus, the four pure mineral soils were scanned with frequencies ranging from 0.01 Hz to 10 Hz, and the results are shown in Table 3. Meanwhile, the strain amplitude and shear frequency were fixed at 0.01% and 1 Hz for time scanning, respectively. These data are summarised in Table 4. The results showed that the frequency had a limited effect on the viscoelastic modulus, and the stability of the data over time proved the validity of the test results. 3.1.3. Influence of water content Water content (ω) is one of the important factors affecting soil properties. The changes of viscoelastic modulus under different ω are shown in Fig. 2. For K and I, under the action of shear, the infiltration of water intensified destruction of the soils, so the modulus was reduced greatly. However, for Mt., G' was basically stable, and G" showed an increase phenomenon. This occurred because the initial energy between mineral particles in the Mt. was relatively large. Therefore, water infiltration under weak shear could not destroy the soil, so G' was basically unchanged. However, for the increase of G", the influencing factors are complex. The main reason for the increase is that the weak shearing action adjusted the soil particles system, meanwhile, clay particles
3. Results and discussion 3.1. Analysis of pure mineral clays 3.1.1. Strain amplitude scanning The stress–strain relationship of the three pure mineral soils (Fig. 1) successively showed elastic deformation, viscoelastic deformation, and Table 2 Particle size distribution of four soil samples. Particle size (μm)
K (%)
Mt (%)
I (%)
S (%)
Particle size (μm)
K (%)
Mt (%)
I (%)
S (%)
0–1.031 1.031–1.207 1.207–1.414 1.414–1.655 1.655–1.938 1.938–2.269 2.269–2.657 2.657–3.11 3.11–3.642 3.642–4.264 4.264–4.992 4.992–5.845 5.845–6.843 6.843–8.013 8.013–9.381
0 0.24 1.01 2.13 3.52 5.05 6.59 7.99 9.15 9.94 10.23 9.98 9.18 7.93 6.36
0 0 0.01 0.32 0.71 1.18 1.7 2.25 2.84 3.46 4.11 4.76 5.41 6.05 6.62
0 0 0.01 0.31 0.56 0.86 1.21 1.65 2.18 2.82 3.55 4.35 5.17 5.93 6.57
0 0.01 0.55 1.16 1.81 2.47 3.11 3.73 4.32 4.87 5.36 5.77 6.08 6.27 6.33
9.381–10.984 10.984–12.86 12.86–15.057 15.057–17.629 17.629–20.641 20.641–24.167 24.167–28.295 28.295–33.129 33.129–38.788 38.788–45.414 45.414–53.173 53.173–62.256 62.256–72.891 72.891–85.343 85.343–2000
4.69 3.12 1.78 0.85 0.23 0.02 0 0 0 0 0 0 0 0 0
7.1 7.42 7.54 7.4 6.98 6.3 5.4 4.36 3.3 2.32 1.48 0.78 0.19 0 0
6.99 7.15 7.01 6.58 5.94 5.16 4.37 3.67 3.12 2.73 2.47 2.27 2.07 1.81 3.48
6.25 6.02 5.66 5.19 4.65 4.06 3.47 2.91 2.4 1.95 1.57 1.24 0.97 0.73 1.08
2
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H. Ni and Y. Huang
Fig. 1. Variation laws of viscoelastic parameters of the four soils. τ is shear stress, G' for storage (elastic) modulus, G" for loss (viscous) modulus, f is frequency, and θ is phase angle. 1, 1.25 and 1.5 after the soil code number represent water content (ω), which controlled according to the liquid limit (LL) of soil. For example, K-1.25-G" represents the loss modulus of kaolin, which water content with respect to liquid limit is 1.25 times, and so on.
viscoelastic modulus decreased.
hydrated and expanded after being exposed to water, so the interaction between different clay particles changed. Furthermore, the infiltration of water reduced the ion concentration in the electric double layer and decreased the repulsive force between particles, thus increasing the viscosity. At the later stage of shearing, the infiltration of water and strong shearing action intensified the destruction of the soil, so the
3.2. Influence of mineral composition Combining with the results from Fig. 1 for analysis, soil S also underwent three stages. Among the three kinds of pure mineral clays, the
Table 3 G' and G" of four soil samples under frequency scanning. Angular frequency (rad/s)
K-1.25-G'(Pa)
K-1.25-G"(Pa)
M-1.25-G'(Pa)
M-1.25-G"(Pa)
I-1.25-G'(Pa)
I-1.25-G"(Pa)
S-1.25- G'(Pa)
S-1.25- G"(Pa)
0.0628 0.0996 0.158 0.25 0.396 0.628 0.996 1.58 2.5 3.96 6.28 9.96 15.8 25
0.18 0.25 0.32 0.67 0.51 0.82 0.70 1.04 1.02 1.12 1.43 1.27 0.91 2.83
0.14 0.21 0.27 0.33 0.31 0.57 0.41 0.59 0.64 0.36 1.08 1.26 2.33 5.46
245,000 245,000 248,000 250,000 253,000 254,000 256,000 258,000 258,000 260,000 260,000 261,000 262,000 262,000
9987 9974.6 8211.9 7510.5 7116.1 5609.3 5130 3806.9 4307 3475 2904.5 2837.2 2541.5 2413.2
429.4 1148.8 1858.7 2519.2 3317 3967.8 4435.6 4829.5 5154.8 5482.1 5697.4 5853.2 5936.1 5823.9
658.9 1572.1 2214.2 2673.3 3066.6 3252.5 3320.7 3311 3249.8 3152.6 2917.7 2716.9 2550.5 2419.6
127,000 147,000 155,000 159,000 163,000 166,000 170,000 173,000 177,000 180,000 182,000 185,000 187,000 189,000
47,003 29,521 24,195 21,067 19,213 18,021 16,933 16,476 15,833 14,130 12,644 11,565 10,292 9588.8
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H. Ni and Y. Huang
at the meso and micro levels, such as by changing the relationship between molecular attraction and electric double layer repulsion, so the cohesive behaviour of the soil was enhanced and a maximum value of G" appeared. For these reasons, S showed strain overshoot behaviour that similar to that of Mt. The test results with varying water content were also evaluated. According to Fig. 2, the variation law of the viscoelastic modulus of S under different moisture contents was also the same as that of Mt., but it differed from those of K and I. In the result, the strain corresponding to the maximum point of S was only about one-tenth that of Mt., which was mainly due to the reduction of the content of strongly acting mineral particles (Mt) and the interaction coupling between various mineral particles. Based on the analysis above, it can be inferred preliminarily that the degree of influence of mineral composition on the viscoelastic property of the soil was higher than those of other factors.
Table 4 G' and G" of four soil samples under time scanning. T(min)
K1.25G'(Pa)
K1.25G"(Pa)
M-1.25G'(Pa)
M1.25G"(Pa)
I1.25G'(Pa)
I-1.25G"(Pa)
S-1.25G'(Pa)
S-1.25G"(Pa)
1 1.17 1.33 1.5 1.67 1.83 2 2.17 2.33 2.5
250 207 228 246 240 277 242 212 239 247
51 49 46 55 59 65 50 47 53 60
208,000 210,000 206,000 208,000 208,000 207,000 209,000 211,000 208,000 209,000
7814 8315 7643 8222 7835 8448 7804 8387 8250 7844
4592 5054 4868 5176 5171 5088 5321 5345 5443 5598
2783 3113 2911 3028 3071 3047 3123 3175 3140 3185
135,000 134,000 135,000 134,000 133,000 135,000 134,000 135,000 134,000 135,000
13,221 12,873 13,001 13,205 13,079 12,862 13,011 13,270 12,958 13,100
interaction between Mt. particles was much stronger than that for K or I, so it played a major role in the viscoelastic properties of the mixed soil. Due to the strong effect of Mt. particles and the mixed particle sizes, which caused the soil to be denser, the initial small shear action could not destroy the soil mass but only disturb the soil mass and slightly adjust the system, so the G' of S changed little. However, the shearing action still affected the complex relationships among particles
3.3. Double electric layer analysis The electric double layer, as the embodiment of the complex relationship within a soil, is directly related to a series of physical and chemical properties of the soil and essentially affects the viscoelastic behaviour of the soil. In the theory of the electric double layer, the zeta
Fig. 2. G'/G" of the four soils at different water contents. K-kaolin, Mt-montmorillonite, I-illite. G' for storage (elastic) modulus, G" for loss (viscous) modulus. 1, 1.25 and 1.5 after the soil code number represent water content (ω), which controlled according to the liquid limit (LL) of soil. For example, K-1.25-G" represents the loss modulus of kaolin, which water content with respect to liquid limit is 1.25 times, and so on. 4
Applied Clay Science 187 (2020) 105493
H. Ni and Y. Huang
1. Dynamic shear rheology tests could better characterise the viscoelasticity of the soils. The obtained elastic modulus (G'), viscous modulus (G"), and phase angle (θ) could effectively measure the elastic temporary deformation, viscous permanent deformation, and viscoelastic proportion change of the soils. The effects of water content, strain amplitude, and frequency on the parameters were also studied. 2. Through an analysis of the results, kaolin (K) and illite (I) showed strain thinning behaviour. However, due to the strong interaction between mineral particles, Mt. behaved differently from K and I under various moisture contents and shear effects, showing weak strain overshoot behaviour and larger corresponding shear stress. 3. The viscoelasticity of the mixed clay (S) was affected mainly by Mt. and showed the same weak strain overshoot behaviour as Mt. under all conditions. However, the critical strain was only one-tenth that of Mt., mainly due to the lower content of strongly acting mineral particles (montmorillonite) and the interaction coupling between various mineral particles. At the same time, the influence of montmorillonite decreased with increase of shear and water. 4. The variation laws of the soil viscoelastic properties were consistent with the zeta (ζ) potential results, which confirms the effectiveness of ζ potential and electric double layer theory for revealing soil viscoelastic properties. Meanwhile, it was pointed out as a result of the analysis that the mineral composition, as the most essential feature of the soils, had a greater influence on the viscoelasticity of the soils than other factors.
Table 5 Zeta potential of four soil samples. Soil sample
Refractive index
Average potential (mV)
K M I S
1.55 1.56 1.57 1.56
−8.04 −20.5 −27.2 −23.6
potential (ζ) can provide a lot of information pertaining to the structure and properties of the electric double layer. It is generally believed that ζ potential is a measure of the strength of mutual repulsion or attraction between particles. When the absolute value of ζ potential is lower, the soil particles are more inclined to condense, or agglomerate, that is, the interaction force between soil particles is stronger. Using the nanoparticle size and ζ potential analyser (Malvern Company, England), a 5 wt% suspension was prepared under the temperature of 25 °C, and the zeta potentials of the four kinds soil samples were tested. The results are listed in Table 5. Under the conditions of shearing action and water infiltration, according to Fig. 1, the magnitude relation of G" for the four soils was G" (K) < G” (I) < G” (S) < G” (Mt). According to ζ potential theory, the absolute value relation of the potential ζ should be ζ (Mt) < ζ (S) < ζ (I) < ζ (K), while the actual result was ζ (K) < ζ (Mt) < ζ (S) < ζ (I). As analyzed above, when the absolute value of the potential is lower, the soil tends to coagulate, or agglomerate, it depends on the interaction between soil particles, and can be used to measure the viscosity of soil particles to a certain extent. For soil samples S and Mt., with particle sizes of the same magnitude, this conclusion is consistent with the result. However, because the particle size of soil sample K was smaller, under the conditions of shearing action and water infiltration, the distance between particles was too large, which minimised the interaction between K particles of the soil; therefore, although the absolute value of the potential was smallest, the viscosity was instead lowest. On the other hand, for soil sample I, the absolute value of the potential was larger than that of soils S and Mt., so it can be inferred that the G" of I would be lower than that of S and Mt. This is exactly what was observed. However, soil I had the largest particle size. Under the test conditions, the particle spacing would be the smallest, which is conducive to interaction between particles. Nevertheless, from the results, the relative relationship between G" was not changed. Therefore, to some content (the change range of particle size in this study was not large enough), it can be considered that the degree of influence of the viscosity layer of the double electric layer between particles was larger than the that of the particle size distribution. Similarly, the stress relation of the soils shown in Fig. 1A is τ (I) < τ (S) < τ (M), which also indicates that the strongly viscous layer makes an important contribution to the energy of the soil system and, to a certain extent, determines the viscoelastic properties of the soil.
Declaration of Competing Interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References Ajayi, A.E., Dias Junior, M.S., Curi, N., Oladipo, I., 2013. Compressive response of some agricultural soils influenced by the mineralogy and moisture. Int. Agrophy. 27 (3), 239–246. Carotenuto, C., Merola, M.C., Álvarez-Romero, M., Coppola, E., Minale, M., 2015. Rheology of natural slurries involved in a rapid mudflow with different soil organic carbon content. Colloids Surf. A Physicochem. Eng. Asp. 466, 57–65. Fang, Y.G., Gu, R.G., 2007. Experiment study on the effects of adsorbed water on rheological characteristics of soft clayey soil. Sci. Technol. and Eng. 7 (1), 73–78. Fang, Y.G., Peng, Z.Q., Gu, R.G., Hu, Y.G., Ou, Z.F., Li, B., 2016. Analysis of creep test on effect of rheological material on soft soil rheological parameter. Rock Soil Mech. 37 (S2), 257–262. Holthusen, D., Pértile, P., Reichert, J.M., Horn, R., 2019. Viscoelasticity and shear resistance at the microscale of naturally structured and homogenized subtropical soils under undefined and defined normal stress conditions. Soil Tillage Res. 191, 282–293. Hyun, K., Kim, S.H., Ahn, K.H., Lee, S.J., 2002. Large amplitude oscillatory shear as a way to classify the complex fluids. J. Non-Newtonian Fluid Mech. 14, 49–55. Kao, Y.Z., 2015. Effect of Clay Mineral Composition on Polycarboxylate Superplasticizer Dispersibility [D]. Chongqing University, Chongqing. Ma, W.B., Rao, Q.H., Rong, H.Y., Guo, S.C., Li, P., 2014. Macroscopic properties and microstructure analyses of deep-sea sediment. Rock Soil Mech. 35 (6), 1641–1646. Markgraf, W., Watts, C.W., Whalley, W.R., Hrkac, T., Horn, R., 2012. Influence of organic matter on rheological properties of soil. Appl. Clay Sci. 64, 25–33. Moayeri, K.M., Hin, L.S., Ibrahim, S.B., Nik Sulaiman, N.M.B., Teo, F.Y., 2016. An investigation into the effects of particle texture, water content and parallel plates' diameters on rheological behavior of fine sediment. Int. J. Sediment Res. 31 (2), 120–130. Sun, W.J., Wang, L.B., Wang, Y.Q., 2017. Mechanical properties of rock materials with related to mineralogical characteristics and grain size through experimental investigation: a comprehensive review. Front. Struct. Civ. Eng. 11 (3), 322–328. Terzis, D., Laloui, L., 2018. 3-D micro-architecture and mechanical response of soil cemented via microbial-induced calcite precipitation. Sci. Rep. 8 (1), 1416.
4. Conclusion In traditional soil mechanics, research on soil viscoelasticity has concentrated mostly on the macro and micro levels. From the mesoscopic and material levels, this study mainly examined the influence of mineral composition on soil viscoelasticity through a series of oscillatory shear rheology experiments on three pure mineral clays (kaolin, montmorillonite, and illite) and a mixed clay. At the same time, based on ζ potential tests and electric double layer theory, this study theoretically analyzed the viscoelastic properties and revealed the viscoelastic mechanisms of the soils. The conclusions of the study follow:
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