|Year : 2020 | Volume
| Issue : 2 | Page : 68-73
Comparison of clay soils of different colors existing under the same conditions in a location
Ubong Williams Robert1, Sunday Edet Etuk2, Okechukwu Ebuka Agbasi3, Grace Peter Umoren1
1 Department of Physics, Akwa Ibom State University, Mkpat Enin, Akwa Ibom State, Nigeria
2 Department of Physics, University of Uyo, Uyo, Nigeria
3 Department of Physics, Michael Okpara University of Agriculture, Umudike, Nigeria
|Date of Submission||22-Dec-2019|
|Date of Acceptance||16-Mar-2020|
|Date of Web Publication||07-Aug-2020|
Dr. Okechukwu Ebuka Agbasi
Department of Physics, Michael Okpara University of Agriculture, Umudike
Source of Support: None, Conflict of Interest: None
Background: The choice of a suitable soil for an intended application depends, basically on one's thorough knowledge of soil properties. Soil color and thermal properties have been found to vary from place to place. However, there is no scientific information on the properties of a soil type formed with different colors in a location and exposed to the same influence for a reasonable interval of time. Consequently, this leaves room for a great deal of speculation and assumption.
Aims and Objectives: This work was aimed at examining and comparing some vital properties of two soil samples of the same soil type formed in a place of a particular relief but are observed to be completely distinct in their colors. In addition, a model for prediction of temperature variation with the thickness of each sample was considered.
Materials and Methods: Pink clay and yellow clay got from a location were used to prepare six test samples each. The samples were allowed to dry completely under ambient conditions before they were subjected to laboratory- based tests.
Results: The results of each test differed for two clay samples. Apart from values of solar radiation absorptivity and flaking concentration, the mean values of sorptivity, bulk density, specific heat capacity, thermal conductivity and thermal diffusivity were found to be greater for pink clay soil compared to yellow clay soil.
Conclusion: Clay soils of different colors can differ in their other properties even if they exist under same conditions in a particular location. During the time of minimum temperature or the hottest time of the day, pink clay would record a lower temperature than yellow clay.
Keywords: Bulk density, flaking concentration, sorptivity, temperature model, thermal properties
|How to cite this article:|
Robert UW, Etuk SE, Agbasi OE, Umoren GP. Comparison of clay soils of different colors existing under the same conditions in a location. Imam J Appl Sci 2020;5:68-73
|How to cite this URL:|
Robert UW, Etuk SE, Agbasi OE, Umoren GP. Comparison of clay soils of different colors existing under the same conditions in a location. Imam J Appl Sci [serial online] 2020 [cited 2021 Apr 11];5:68-73. Available from: https://www.e-ijas.org/text.asp?2020/5/2/68/291584
| Introduction|| |
Soil is the biologically active porous medium that is formed in the uppermost layer of the earth's crust and consists of different proportions of minerals, organic matter, air, and/or water. For several decades now, soil still remains a valuable natural resource available to human. Factors such as climate, living organisms, topography, parent material, and time affect soil formation and give rise to three major types of soil as loamy, sandy, and clay soils. While loamy soil is known to contain the nutrients that are very necessary for plants growth, sandy soil is viewed as being made up of the largest size of particles, posited that clay soil particle size ranges from 0.002 mm and below.
Like in the case of other kinds of materials, the choice of a suitable soil for an intended application depends basically on one's thorough knowledge of soil properties. As averred by Brady, the physical properties of soil give clues for the prediction of soil temperature of a location. Further, the knowledge of thermal properties of soil samples is very vital in the choice of soil type to be used in building design and planting. It was clearly revealed in the results of the study conducted by Etuk et al. that clay soil samples collected from different locations differ in their thermal properties. In addition, soil colors have been found to vary from place to place due to depth, topographic position, and composition. Again, experience shows that topographic relief and climatic factors play very crucial role in the alteration of soil properties through an interval of time. Therefore, based on the aforementioned findings, there is no doubt that such factors vary from place to place all over the world.
However, there is no scientific information on the properties of a soil type formed with different colors in a geographical location where the topography is the same. When considering the fact that at all times, such soils are exposed to the same influence from climatic factors for the same reasonable interval of time, lack of such information leaves room for a great deal of speculation and assumption. Thus, the essence of this study is to examine and to compare some important properties of two soil samples that are of the same soil type formed in a place of a particular relief but are observed to be completely distinct in their colors. In addition, a model for prediction of temperature variation with the thickness of the samples will be presented. Based on the results of the investigation, some suitable applications of such soil samples will be determined. It is hoped that such findings will be useful to pedologists, soil scientists, researchers, farmers, engineers, and others with regard to the present state of global warming affecting us.
| Theory|| |
In addition to many other physical properties, soils can vary in color, sorptivity, and bulk density. Unlike soil colors which can be easily distinguished by careful observation, sorptivity depends on the degree of porosity of dry soil that is in contact with water. Expressed in equation form, the sorptivity of a dry soil measured from horizontal infiltration is such that:
where Sp= sorptivity, d = cumulative infiltration depth, and t = infiltration time.
Being an expression of the level of compactness with existence of interstices, bulk density affects both thermal and mechanical properties of materials. For a given soil sample of mass, M and bulk volume, V, the bulk density ρ, can be calculated as a ratio, thus:
Without internal heat generation in a material that is homogeneous and isotropic, one-dimensional unsteady state heat conduction equation stated by Rajput can be expressed for the soil as:
which on comparison with diffusion equation
where λ = thermal diffusivity, k = thermal conductivity, c = specific heat capacity, and ρc = volumetric heat capacity.
There are several factors that determine soil temperature. However, solar radiation plays the main role and it can be partially absorbed by soil to bring about change in the soil temperature. As noted by Mahrer, the heat budget equation is such that,
Heat flow through the soil = Heat absorbed from atmosphere + Absorbed solar radiation − Re-emitted radiant energy
In one dimension, the energy balance equation becomes
where T = soil temperature, h = heat transfer coefficient of the soil surface, Tatm= atmospheric air temperature, ∝= solar radiation absorptivity at the surface of the soil (and is given as , I = intensity of solar radiation, ∈ = long-wave emissivity of the soil surface, and △R = difference between the incident long wave radiation and the radiation emitted from the soil surface with the solar temperature, Ts expressed as
The following form of general solution to one-dimensional heat condition equation was assumed by Moustafa et al.:
The real part of equation 8 above yields
By modifying equation 9 into a convenient form, the dependency of soil temperature with thickness on the periodic variation of temperature at the soil surface becomes
Where x = thickness of the soil, As= daily temperature amplitude (in °C) at x = 0, t = time of the day (in hours), and to= time of minimum temperature at the surface of the soil (in hours). Tm can be calculated from the hourly soil surface temperature average, Thss(in °C) on 24-h period, as
so that equation 10 now becomes
| Materials and Methods|| |
Two clay soils of different colors, existing with same topographic relief in a place within Uyo Local Government Area, Akwa Ibom State in Nigeria, were collected and used in this study [Figure 1] and [Figure 2]. The latitude and longitude of the location were determined by means of a Global Positioning System (MAP 78 series). For each clay soil gathered, six samples of dimensions 200 mm × 200 mm × 20 mm were prepared. The samples were left to dry naturally under ambient temperature of 28°C and humidity of 47% until there was no reduction in their weight and they became very hard, nonplastic, and brittle. Investigation of the samples' properties was then done through laboratory study.
In performing sorptivity test, three developed samples of each clay color were suspended separately with 3-mm depth from their lower end immersed in cold water contained in a glass vessel at room temperature. After 30 min, the cumulative infiltration depth was determined as the difference between each sample's height and the depth unoccupied by the water. By applying equation 1, the data obtained were used to compute the required sorptivity.
The remaining samples were then used for other tests. Thermal conductivity was measured for each sample by means of a heat flow meter (100 series) in accordance with the standard procedure outlined in previous study. For flaking test, the initial mass of the samples was measured after which a very hard shoe brush was used to rub against the two surfaces of each sample. After making 50 strokes of forward and backward movements against each surface, the mass of each flaked sample was weighed and the flaking concentration was computed as the ratio of decrease in the sample's mass to its initial mass. Then after, the same samples were cut to reasonable sizes and the mass of each of them was measured with the aid of analytical balance (TOLEDO PL203). While the bulk volume of each sample was determined by modified water displacement method, the corresponding bulk density was calculated using equation 2. Further, the specific heat capacity of each sample was measured by mixture method of calorimetry employing temperature-cooling correction as described elsewhere., Again, the data obtained for thermal conductivity, bulk density, and specific heat capacity were used to compute the thermal diffusivity and then absorptivity of each sample. Each test was performed three times in this study, and the mean values of the results obtained were tabulated with their corresponding standard error.
| Results and Discussion|| |
The particulars that describe the as-collected clay soils used in this work are presented in [Table 1]. In addition, the experimental results obtained per test carried out on the samples developed from the clay soils are registered in [Table 2].
|Table 2: Results of test properties obtained at room temperature with ±2°C variations|
Click here to view
From [Table 1], it can be seen that out of the two clay soils used in this work, one has pink color (which is a light shade of red) whereas the other clay soil has yellow color, but they exist on Latitude 5°02'N and Longitude 7°57'Es.
This shows that the clay soil samples developed and investigated in this work are very distinct in terms of color, yet they exist in the same place and are exposed to the same conditions for the same interval of time. As revealed in the work, the pink color observed is indicative of high contents of alumina and iron oxides with low silica proportion in the clay soil. Further, in line with the remark by Brady and Weil, the yellow color indicates the presence of oxidized ferric iron oxides in the clay soil. In the wet form, both clay soils are plastic in nature due to their particle size and geometry. This means that they can be molded into any shape if there is a reasonable quantity of water in them.
From [Table 2], it can be seen that the mean sorptivity value of the pink clay sample is higher than that of the yellow clay sample. This is suggestive of the fact that the yellow clay is more porous than the pink one. As such, under capillary suction, the rate of movement of water front through the prink clay is higher than in the case of the yellow clay. It thus portrays that if the two clay soils are exposed to an aggressive environment, the yellow clay soil will be more resistive and durable than the pink clay soil.
In the case of bulk density, the mean value obtained for the pink clay sample is observed to be greater than that of the yellow clay sample, thereby indicating that the pore in the pink clay is smaller in size than how it is in the yellow clay. Stating in another way, the degree of particles compactness is greater in the pink clay than in the case of yellow clay and thus reveals that the pink clay is of lower aeration as well as permeability level than the yellow soil. This may further account for a higher sorptivity value earlier observed with the pink clay sample.
Further, the mean specific heat capacity value obtained for the pink clay in this work is (207.547 ± 2.674) J/kg/K greater than that of the yellow clay sample. Since the specific heat capacity of the soil is governed by the heat capacity of its constituents, it can be understood that the higher value of mean specific heat capacity observed in the case of the pink clay soil sample is due to the presence of high content of alumina in it. This is obvious when comparing oxidized ferric iron oxide mineral like geothite that exists in the yellow clay soil with alumina, which is known to be a compound of higher specific heat capacity. Using the results of bulk density and specific heat capacity presented, it can be deduced that the mean volumetric heat capacity of the pink clay sample is 4.271 ± 0.005 MJ/m3/K while that of the yellow clay sample is 3.643 ± 0.005 MJ/m3/K. By implication, more heat is required by pink clay than yellow clay to change the temperature of their unit mass or unit volume by one Kelvin.
Again, the rate of heat transmission through a soil depends on the composition and condition of the soil. In the instant case, pore spaces play a major role in determining heat conduction across the thickness of the clay samples under the study. With the recorded mean thermal conductivity value being greater for the pink clay sample than in the case of the yellow clay sample, it simply implies that more interstices occupied by air exist in the yellow clay than in the pink clay. Consequently, the exchange of thermal energy by conduction between the adjacent particles is enhanced more in the pink clay sample than in the yellow clay sample. This is possible because air is a poor conductor of heat, and as such, the more porous a soil is, the greater ability it has to impede heat flow through its cross-section and across its depth/thickness. However, the values of mean thermal conductivity for both clay samples in this work lie between 0.023 W/m/K and 2.900 W/m/K being the range recommended by Twidell and Weir for good heat-insulating and construction materials.
More so, the pink clay sample has a mean thermal diffusivity value of 6.413 ± 0.014 10−8 m2/s against the mean value of 6.139 ± 0.006 10−8 m2/s obtained for the yellow clay sample. This points to the fact that pink clay soil has a greater tendency than yellow clay soil to respond faster to a change in temperature. In other words, if pink clay and yellow clay soils of same dimensions are subjected simultaneously to thermal influence under the same conditions, a longer time would be taken for heat to spread within the yellow clay soil than in the case of the pink clay soil. The reason for this observation may be attributed to pink clay having a higher thermal conductivity value than yellow clay. Such direct relationship between thermal conductivity and thermal diffusivity is evident in the mathematical formula employed as equation 5 in this work.
In terms of solar radiation absorptivity, the pink clay sample has a mean value of 23.813 ± 0.025/m whereas the yellow clay sample has mean value of 24.338 ± 0.012/m. With respect to the recorded value for the yellow clay, the results show about 2.2% ±0.1% decrease in the value for the pink clay. Though it is a small decrease, the mean values presented actually depict that under conditions in which the path of solar radiation has unit length and the boundaries of the layer have no influence, yellow clay is better than pink clay in their ability to absorb radiation equal to the internal absorptance of their homogeneous layer.
Soil temperature variability depends on the amount of solar radiation received and absorbed by the soil. Now, substituting the respective mean values of solar radiation absorptivity into equation 12 yields the required model for predicting temperature variation with thickness, x of each of the clay soil samples at any given time, t of the day as follows:
For pink clay soil:
For yellow clay soil:
The study of equation 13 (a) and equation 13 (b) reveals that at a thickness of 18 cm, pink clay would record a lower temperature than yellow clay during either the time of minimum temperature (i.e., 06 h, Nigerian time) or the hottest time of the day (i.e., 13 h, Nigerian time) if both soils are exposed to the same conditions. Since soil is heated through atmospheric, geothermal, and radiative processes and soil temperature depends on the content of soil mass, it can be deciphered that the lower temperature pink clay would record is mainly due to its higher heat capacity when compared with the yellow clay. It is noteworthy that the same minerals which determine soil color and affect the soil heat capacity also affect the amount of heat supplied to the surface of the soil. This view that soil heat capacity influences soil temperature is in agreement with the assertion by Nusier and Abu-Hamdeh, concerning the management of soil temperature regimen.
There is no doubt that the surface of dry clay soil can possibly show uneven wear. In this work, the mean value of flaking concentration is revealed to be lower for the pink clay sample than the yellow clay sample. This means that pink clay soil is better than yellow clay soil in maintaining their original structure and appearance by resisting mechanical wear. Thus, it can be remarked that pink clay is more cohesive and less porous than yellow clay.
| Conclusion|| |
This study aimed at evaluating and comparing important properties of two clay soil samples of distinct colors formed in a place of a particular relief and exposed to the same conditions. From the results of the investigation, the mean value of thermal conductivity of yellow clay soil was found to be 18.33% ± 0.15% lower than that of pink clay soil. In addition, the results obtained revealed the values of solar radiation absorptivity and flaking concentration to be lower for pink clay soil than for yellow clay soil used by 0.525 ± 0.028/m and 1.226% ± 0.001%, respectively. Again, lower values of sorptivity, thermal conductivity, and thermal diffusivity obtained in the case of yellow clay soil portrayed it to be better than pink clay as a choice material for passively cooled building design. Generally, it was observed that clay soils of different colors in a particular location exposed to the same conditions for a reasonable time interval could also differ in their other properties.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2]