Effect of Various Proportions of Rice Husk Powder on Swelling Soil from New Cairo City, Egypt

Abstract

Swelling soil leads to many types of constructional damages, deformations, and failures in the constructions’ roads, shoulders, and foundations. Depending on the amount of swell, they can be insignificant, moderate, or massive. This paper presents a method for swelling soil stabilization by adding rice husk powder (RHP) in variable percentages of 0, 5, 10, 15, 20, and 25 by weight of dry soil. The properties of swelling soil stabilization were investigated by various lab tests such as consistency limits (plastic limit, liquid limit, and plasticity index), swelling potential, swelling pressure, free swelling, and free swell index. The swelling soil was also mineralogically examined using X-ray diffraction of clay mineralogy. This stabilization reduced the plasticity from 56% (extremely high plasticity) to 4.5% (low plasticity). Swelling potential (S) and swelling pressure (SP) decreased by 48% to 45.5, 44.7, and 34.6%, from 1003 kN/m² to 800, 653, and 489 kN/m² for the partial replacement of the soil by 5%, 10%, and 15% RHP, respectively. The results show that the present approach is very efficient for improving the swelling soil properties and that the optimal amount of added RHP of the swelling soil is 15%. It will also be a database aimed at reducing construction risks in the future.

1. Introduction

Swelling soil or expansive soil is qualified by its ability to dilate or shrink when its water content increases or diminishes, and they refer to the climate in Egypt. This property is fundamentally determined by the type of clayey minerals found in soil formation. Clay minerals are mostly composed of montmorillonite, kaolinite, and illite. Montmorillonite has a high swelling property, which indicates a very high swelling potential [1]. The composition of this kind of soil causes damage to buildings. The swelling soil has been called an “engineering cancer” because it is often accompanied by long-term, recurring latent features [2]. Consequently, it is urgent to assess these areas before any development so as to reduce the number of dangers and/or their disastrous impact.

Some solutions for expansive soil must be taken for building purposes in order to decrease the harm caused by expansive soil. Several stabilizing techniques for expansive soil include soil replacement, chemical modification, humidity management, and unique foundation systems [3]. Engineers recommend the chemical alteration because of its large improvement impact and minimal engineering costs.

In recent years, scientists have begun using various forms of solid waste as additives to expand soil stabilization because of environmental challenges that have increased their focus [4], such as fly ash, marble dust, rice husk ash, coir fiber, plastic waste, and nanomaterials [5,6,7,8,9,10,11,12,13]. These enhancements include increased dry unit weight, bearing capacity, durability, and volume changes.

Any country’s development depends on transport installations and construction projects. In order for projects to be successful, foundations need to be strong, requiring better soil properties. The area under investigation is among the most promising areas for cities and tourists and industrial developments in Egypt. New Cairo City is said to be one of the city’s new projects. The study area suffers from several problems, the most important of which is the presence of clay layers in the different geological formations, which have a serious impact on urbanization. As experience from different worldwide places shows [14,15], various clay properties can play a fundamental role in determining geotechnical conditions. The swelling of the soil strongly affected the buildings in the study area, leading to the collapse of many buildings and the presence of numerous cracks in the constructions. The present paper focuses on using RHP to stabilize the swelling soil of the industrial zone of New Cairo City, Egypt.

Rice husk ash (RHA) is one type of solid waste that has gained attention in recent years in rice-growing countries such as Egypt, Indonesia, China, and Pakistan. RHA is made from burning rice husk, which is a common agricultural byproduct. RHA production is around 20% of the weight of the rice. When rice husk is burnt, it removes lignin and cellulose from the silica ash.

The burning of rice husks causes difficult problems for the government and may impact the environment in general. It has significant negative effects on human health because it absorbs a large number of environmental perturbations and creates what is known as cloud black. This leads to contaminated rainfall, which affects the environment and causes many diseases due to consuming foods contaminated by harmful gases present in the rain. The government should strengthen agricultural waste development through recycling to take full advantage of the increase in pollutants at an abnormal rate. The pollution caused by the rice husk combustion costs the Egyptian economy tens of billions of dollars each year. For the above reasons, the author of this paper used RHP to stabilize swelling soils and convert them from harmful substances to beneficial substances. There is plenty of scientific research to take advantage of rice husk. It is available as an organic fertilizer or as animal feed. It can also be utilized to make paper, compressed wood, concert, and is made of light walls that are resistant to high temperatures. It can also be utilized to increase soil fertility and power generation [16,17,18,19].

Canakci et al. [20] This paper presents the results of a laboratory study on the feasibility of using waste, lignin, and rice husk in the form of powder (RHP) and ash (RHA) to improve the strength and consistency of an expanding soil. Soil mixed with RHP ranged from 5% to 20%. The LL decreased from 148% to 132.2%, PI from 119.28% to 99.28%, swelling percent decreased from 11% to 8.25%, while the PL increased from 24.72% to 32.94%. The ideal value of RHP was 20%.

Robert [21] utilized RHA and fly ash to stabilize the expansive soil. After it was set up, the California Bearing Ratio (CBR) improved 47% by adding RHA from 0 to 12%. In contrast, by adding 0 to 25% fly ash, stress and strain increased from 106% to 50%, respectively. In conclusion, in this study, the optimal value of fly ash and RHA is 25% and 12%, respectively. Rahman and Ahmed [22] compared the influence of RHA and lime on the geotechnical characteristics of the lateritic soil. Soil mixed with RHA ranged from 4% to 24% and lime from 2% to 12%. The plasticity index (PI) was decreased from 27.2% to 15.7%. The CBR value of RHA and lime was 77% and 59.4%, respectively. Liu et al. [23] utilized RHA-lime to treat expansive soils. They added the RHA/lime 4:1 by weight for soil stabilization. The S and the SP decreased from 25.8% to 4.6%, 386 kPa to 32.1 kPa, respectively, by adding 20% RHA/lime. The compression index decreased from 0.244 to 0.067. Cohesion and the internal friction angle increased from 51.5 kPa to 189.3 kPa, 7° to 31.7° respectively.

Recycled materials have reduced landfill space and opened a new portal for sustainable building practices in engineering applications. The primary goal of this work is to assess the improvement of the geotechnical characteristics of swelling soil by adding RHP in different percentages from 5% to 25% and testing the physicomechanical characteristics of this mixture to reduce the cost of construction and the number of hazards. Furthermore, it provides a cost-effective solution for pollution prevention by converting harmful agricultural waste substances into useful products.

2. Materials and Methods

2.1. Geological Setting

The following coordinates define the examined area: Longitudes 31°20 and 31°40 E, and latitudes 29°55 and 30°05 N. It was limited to the north by the Cairo, Suez desert route, to the south by the El-Qattamiya-Ain El-Sokhna road, to the west of the Ring road, and to the east by the Gebel El-Anqaabiya road (Figure 1).

Stratigraphically, the work area is basically made of sedimentary rocks in addition to close to patches of basaltic flows in various localities, ranging in age from Middle Eocene to Upper Miocene according to [24,25,26]. The Eocene succession is unconformable and rests on the Upper Cretaceous beds. The Oligocene sequence is divided into loose sands and gravels at the base represented by the Gebel Ahmer Formation and basalt flows at the top. The Oligocene sediment thickness increases significantly from east to west. In several places, unconformable Miocene sediments overlie Oligocene rocks. The Miocene sequence differs in two units: the marine Miocene sediments at the base and the non-marine Miocene sediments at the top. An unconformity surface separates these two units from one another. The marine Miocene rocks represented by the Hommath Formation are primarily composed of limestone, sandstone, and shale that has become more calcareous both temporally and eastward. The non-marine Miocene rocks are made up of gravels, sandstones, clays, and a few limestones represented by the Hagul Formation that can be distinguished from the Oligocene sediments by their lighter color and finer grain size (Figure 2). The studied samples are represented by the marine Miocene (Hommath Formation). Mudstones are middle to thick layers that are interpreted as representing a fluvial-fluviomarine deposition system [27]. The clay layer in the north-south directions is thicker from 10.3 to 10.9 m, but the thickness and depth decrease [28].

2.2. Sampling

2.2.1. Swelling Soil

Swelling soil samples were collected from construction sites in an open-pit excavation in the Abu El Hole region of New Cairo City, Egypt. The soil is very dark gray and was taken from a depth of 1.5 m to 3 m below the ground surface. The depths chosen reflect the shallow depth of most foundations and the expected depth of the active zone in the study area. The pits were dug by hand using picks and shovels. Samples of high-quality undisturbed blocks from the pits were collected from a variety of carefully delineated depths using hand tools such as knives and trowels—the original properties of a swelling soil sample as stated in

Table 1. Engineering properties of the parent soil.

Parameter No.	Index Properties	Results
1	Specific gravity	2.6
2	Initial water content (%)	25
3	Passing sieve No 40 (%)	99.5
4	Passing sieve No 200 (%)	92
5	Liquid limit (%)	92
6	Plastic limit (%)	36
7	Plasticity index (%)	56
8	Shrinkage limit	13.6
9	Free swell (%)	200
10	Free swell index	100
11	Swelling pressure (kN/m2)	1003
12	Swelling potential %	48.5
13	Soil classification according to (USCS)	EH

. The soil granulation curve is shown in Figure 3.

2.2.2. Rice Husk Powder (RHP)

RHP was collected from certain farmers and then crushed by grinding machines for 4 min at less than 1000 turns per minute. Particle sizes vary between 0.6 mm and 0.063 mm.

Table 2. Chemical composition of rice husk powder.

Compound	SiO2	Al2O3	Fe2O3	CaO	MgO	SO3	K2O	Na2O	Cl
As received husk	82.55	0.87	2.05	0.25	3.15	0.14	5.28	0.87	0.07
Washed husk	90.89	1.20	2.42	0.73	1.54	0.11	1.52	0.35	0.01

sets out the chemical composition of RHP determined by an atomic absorption spectrophotometer in the laboratories of the Nuclear Materials Authority (NMA).

2.2.3. Soil Sample Preparation

Before mixing, the swelling soil was dried and passed through a 0.425 mm sieve. Afterward, RHP was mixed in varying percentages with swelling soil ranging from 5, 10, 15, 20, and 25% dry soil weight. The mixture was mixed in a laboratory mixer for a minimum of 3 min after adding water (required for determination of Atterberg limits). The percentage of RHP should be determined based on a pH value of approximately 12. Treated samples were performed by mixing a pre-calculated quantity of RHP and an expansion soil with a moisture content of 25%.

2.3. Analysis

The lab experiments performed on the soil samples are Atterberg limits, natural water content (one sample before treating), specific gravity (one original sample), swelling pressure, swelling potential, and free swelling tests, as reported by the American Society for Testing Material (ASTM). Noting that the plastic limit (PL) and liquid limit (LL) were applied in accordance with ASTM D-4318 [29], swelling pressure was determined in compliance with ASTM D-2435 [30]. The following tests are discussed.

2.3.1. Free Swell (FS) Test

FS tests comprise of putting a known volume of dry soil in water and noticing the expanded volume after the material settles, with no extra charge to the base of a graduated cylinder. The FS value is the contrast between the final and initial volume, expressed as a percentage of the initial volume. According to Holtz and Gibbs [31], soils having free swelling an incentive as high as 100% can cause significant harm to softly stacked structures, and soils with an incentive beneath the half only occasionally display apparent volume change under extremely light loading. The percentage of FS is expressed as follows:

$$\mathrm{F}.\mathrm{S}. \% =\frac{v_f-v_i}{v_i}\times 100$$

(1)

where: v_f = Final volume of a soil sample after wetting for 24 h and v_i = Initial volume of air-dry soil.

2.3.2. Swelling Potential (S)

This experimental study used the swelling method to detect the level of swelling. Each sample was prepared 60 g dry weight 15 mL water was added to the sample to achieve 25% moisture content. The disturbed soil sample is cut to its moisture content in situ placed on an oedometer. Additional loading of approximately 6.9 kPa is applied to measure the initial swelling as per the Egyptian code. Water is added to the sample, and sample volume expansion is measured until equilibrium achieves. The S is calculated as follows:

S (%) = ∆H/H × 100

(2)

where: ∆H = height of swell due to the saturation; H = original height of the specimen

When the soil reaches its maximum heave, the final heave is measured, and the S% was calculated according to Equation (2).

2.3.3. Swelling Pressure (SP)

SP is measured in the lab with a one-dimensional consolidometer. The soil sample (typically 75 mm in diameter and 20 mm in thickness) is enclosed in a steel cutter ring. The soil sample is placed in a metallic ring, and pore stone discs are placed on the top and bottom of the sample. The test sample is allowed to consolidate under a number of vertical stress increments, with each stress remaining constant until the end of compression (generally for a 24-h period). The stresses normally used are 0.25, 0.5, 1, 2, 4, 8 and 16 kg/cm2.The percent of vertical deformation is then calculated in relation to the applied vertical pressure. SP is the pressure corresponding to the zero volume change of the sample.

2.3.4. X-ray Diffraction Analysis

The mineralogical studies were carried out with the aid of a Philips X-ray diffractometer (9 types PW 3710) and Ni-filter cake radiation. The samples were analyzed from 2 to 50 with a current of 40 ma and a voltage of 40 KV. To identify the mineral composition of the clay, three oriented particle assemblies were prepared from the pure clay fraction (<2 um) and X rayed for the semi-quantitative identification of clay minerals. Pipetting a clay suspension onto the glass slides was utilized to prepare them. The first slide was used for an X-ray in its initial (untreated) state. The second slides were X-rayed after saturation with ethylene glycol (glycolate) and the third slide after heating at 550 °C for two hours (heated) as represented by Gibb [32].

3. Results and Discussion

3.1. Geotechnical Characteristics Evaluation before Using RHP

The parent soil in the study area can swell as a result of the free swelling ratio is 200% (Table 1). According to the Egyptian Code [33], this ratio leads to many expected problems. The PI of the parent soil is more than 50% exactly 56% (Table 1), so this soil is very high in plasticity as per Chen [34] (

Table 3. Classification of expansive soil according to plasticity index [34], swelling potential [35], swelling pressure [36].

PI (%)	S (%)	SP (kPa)	Degree of Expansion
≤15	0–1.5	˂196	Low
15–30	1.5–5	196–392	Medium
30–50	5–25	392–687	High
<50	˃25	˃687	Very High

).

Touching on the PI of the studied soil with the above-given range reveals that the parent soil falls in the range of extremely high plastic (EH) in accordance with the Unified Soil Classification System (USCS). In addition, Laboratory determination of LL and PI for a soil sample enables fine-grain soils to be assigned to the appropriate group using the plasticity diagram [37]. The plasticity diagram shows that the clay specimens studied can be classified as extremely high inorganic plastic clay (Figure 4).

Seed et al. [35] and Geraid [36] introduced the classification of expansive soil, according to values of S and SP as indicated in Table 3. Based upon such classifications, the soils studied are considered highly expansive, where the value of the S is 48.5%, and the SP is 1003 kN/m² (Table 1). Clearly, all soil classification methods agree that the soil in the study area has a high degree of expansion.

The mineralogical analysis of the studied samples presents the basis for understanding their engineering behavior. It also identifies the types of clayey minerals, which vary from relatively inactive kaolinite to very active montmorillonite.

Mineralogical analysis of samples examined through X-ray diffraction analysis indicated that the sediments are composed of montmorillonite as a primary component at about 59 % and kaolinite as a minor component at about 41%. Montmorillonite is characterized by high swelling property, where the value of the free swelling was 200% very high expansive soil, which contributed to a pile of damage to the structure when construction of this type of soil. The results of the mineralogical analysis of the samples under investigation are shown in Figure 5.

3.2. Geotechnical Characteristics Evaluation after Using RHP

3.2.1. Effect of RHP on Atterberg Limits

Smaller ratios of RHP are more efficient in thinning out the PI, but with an increase in the proportion of RHP, the result becomes less efficient. The results of the Atterberg limits of swelling soil with different percentages of RHP are shown in

Table 4. Effect of stabilizer on Atterberg limits of the studied samples.

S.No.	RHP (%)	Liquid Limit (%)	Plastic Limit (%)	Plasticity Index (%)
1	0	92	36	56
2	5	89.5	53.8	35.7
3	10	87	61	32
4	15	85	80.5	4.5
5	20	100	53	37
6	25	103	60	40
Mean value		92.75	57.4	34.2
Standard deviation		6.60	13.19	15.30
Variance		44	174	235

.

The variety of LL, PL, and PI with different percentages of RHP are presented in Figure 6. As seen in this figure, the LL decreases as the percentage of RHP increases. Moreover, PL increases with the increase in additives. The LL was reduced from 92% of the parent soil to 89.5%, 87%, and 85% partial replacement of soil with RHP, 5%, 10%, and 15%, respectively. This can be seen as the result of soil particle bonding and dispersal of the clay fraction by RHP, which acts as a binding agent to stick soil particles together. In addition, this may be due to the substitution of soil swelling with RHP, which has a small water attraction capability. The highest LL variation was achieved at 15% of the RHP. For example, 15% of RHP decreased LL versus LL in the control sample. Consequently, 15% is considered the optimal percentage of RHP for this study. This is obvious from Figure 6 that up to 5% RHP, the LL reduction is significant enough to become straight. This finding indicates that, above 5%, the LL reduction increases slightly. Therefore, the lowest value and the maximum LL reduction were obtained at 15% RHP.

In addition, this figure shows the change in the PL with additive materials. It is clear from the curves that RHP has a substantial effect on the PL of the expansive soil. The PL of the stabilized soil has increased from 36% for parent soil to 53.8%, 61%, and 80.5% for the partial replacement of the soil by 5%, 10%, and 15% RHP, respectively. This increase in the PL means that the soil treated with RHP requires more water to transform it into a semi-solid plastic state. The same behavior was reported by Canakci et al. [20]. It is indicated from Figure 6 (PI) that all processed samples showed a decrease in any additive content. The PI has decreased from 56% (extremely high plasticity) to 4.5% (low plasticity), with an RHP increase from 0% to 15%. The increase in PL and a decrease in PI are primarily caused by the flocculation of clay particles and the increasing number of coarse particles in the mixture. The reaction compounds decrease the repulsion forces between clay particles transmitting the flocculated structure with some cementing or bonding, which should have been responsible for the decrease of the free swell and PI. In addition, the reduction in swelling is attributed to the reduction in the thickness of the diffuse double layer (DDL), which results in the flocculation of clay particles. In terms of the order, the reduction in DDL thickness makes the soil skeleton shrink. It causes a decrease in repellent forces, thereby contributing to the flocculation of clay particles, which later became granular or formed hydrogen bonds [38]. The bond is sufficiently strong that van der Waals forces, so there is no interlayer swelling in the presence of water [39]. Only the increased proportion of RHP between 20% and 25% increases the plasticity index. The primary reason for these changes is the reduction in clay content in the soil mixture or maybe an excessive accumulation of cations on the clay [7]. In addition, based on the PI results, 15% of RHP have the most impact on the expansive soil.

3.2.2. Effect of RHP on S and SP

The SP and soil S results in different percentages of RHP are presented in

Table 5. Effect of stabilizers on swelling pressure and swelling potential.

S.No.	RHP (%)	Swelling Pressure kN/m2	Swelling Potential (%)
1	0	1003	48
2	5	800	45.5
3	10	653	44.7
4	15	489	34.6
5	20	593	38
6	25	624	40.8

. The variables of SP and S of the soil with different parentages of RHP are presented in Figure 7 and Figure 8. The SP and S of the test sample were reduced by adding 5% to 15% of the RHP. For example, Figure 7 and Figure 8 show that the SP decreases from 1003 kN/m² to 800, 653, and 489 kN/m², while S decreases from 48% to 45.5, 44.7, and 34.6% by adding the RHP from 0 to 15%. The addition of the stabilizer shows an unmistakable decrease in S and SP. The reduction in S and SP values for stabilizing soils was due to the addition of low-plastic content materials (RHP). As a result, the physical properties of the original expansion soil were changed.

RHP contains 90 percent silicon dioxide. Where the total percentage composition of silicon dioxide, aluminum oxide, and ferric oxide was 94.51 so, this value was well in excess of the minimum requirement of 70% of ASTM C618 pozzolans [40]. Once added to the RHP, the granular structure of the expanding soil changes. This high amount of silica provides good pozzolanic action, which leads to a significant improvement in soil characteristics. RHP has a certain degree of replacement effect when added to expansive soil. On the one hand, due to the low plasticity and low expansion and water absorption, expansive soil’s physical properties, particularly PI and S, will change.

3.3. Comparison of other Research Studies

As noted above, there were a few findings on stabilizing swelling or clayey soils using RHP. This was achieved by comparing the engineering properties of stabilized soils, as shown in Figure 9. RHP was added at rates from 5% to 25% in the current paper, while in the other paper, it was added at rates from 5% to 20%. In this paper, the maximum reduction in LL, PI, and S % was 7.6%, 92%, and 28%, respectively for 15% RHP, while in the second paper was 10.7%, 21%, and 36.5 for 20% RHP. The RHP was optimized at 15% in this study and 20% in the other article. Applying this method solves the problem of environmental pollution by waste and reduces the cost of construction in expanding soil areas.

4. Conclusions

The study provides a soil stabilization method by replacing it with RHP at the ratio of 5%, 10%, 15%, 20%, and 25%. The RHP could be argued as an efficient agent for improving the properties of swelling soils. The current study concluded that the ideal ratio of RHP stabilizers is 15%. This percentage is very useful for inhibiting soil expansion. In contrast, mineralogical studies of X-ray diffraction analysis showed that sediments in the study area are comprised of montmorillonite and kaolinite. The montmorillonite in the soil indicates the swelling potential and is not allowed to direct the foundations above it. The LL of the stabilized soil is decreased from 92% for parent soil to 89.5%, 87%, and 85% partial replacement of soil with RHP, 5%, 10%, and 15%, respectively. The PL of the stabilized soil has increased from 36% for parent soil to 53.8%, 61%, and 80.5% for the partial replacement of the soil by 5%, 10%, and 15% RHP, respectively. The PI was reduced with the increase in RHP from 56% (high plasticity) to 4.5% (low plasticity). This decrease in plasticity rate indicates that the soil is improving. The SP of the stabilized soil is decreased from 1003 kN/m² for parent soil to 800 kN/m², 653 kN/m^2, and 489 kN/m² for the partial replacement of the soil by 5%, 10%, and 15% RHP respectively. The S of the stabilized soil is decreased from 48% for parent soil to 45.5%, 44.7%, and 34.6% partial replacement of soil with RHP 5%, 10%, and 15%, respectively. According to the above study, it is clear that RHP can be used as a soil stabilizer. The stabilization process has proven to be a fiscally efficient and environmentally efficient solution for such large and important construction works. The results of the laboratory tests highlight the need for a thorough study of the characteristics of clay soils if they are to be used in road construction work.

This study recommends further investigation through triaxial CD tests under monotonous and cyclic loading to expand our understanding of the effect of RHP on pore pressure, permeability, and cyclic behavior.