Chemical and Biomolecular Engineering
Volume 1, Issue 2, December 2016, Pages: 32-39

Influence of Nano Additives on Unconfined Compressive Strength of Asphaltic Soil

Saad Issa Sarsam*, Aamal A. Al Saidi, Afaq H. AL Taie

Department of Civil Engineering, College of Engineering, University of Baghdad, Baghdad, Iraq

Email address:

(S. I. Sarsam)

*Corresponding author

To cite this article:

Saad Issa Sarsam, Aamal A. Al Saidi, Afaq H. AL Taie. Influence of Nano Additives on Unconfined Compressive Strength of Asphaltic Soil. Chemical and Biomolecular Engineering. Vol. 1, No. 2, 2016, pp. 32-39. doi: 10.11648/j.cbe.20160102.11

Received: December 6, 2016; Accepted: December 19, 2016; Published: January 14, 2017


Abstract: Collapsible behaviour of soil is considered as one of the major problems in the stability of roadway embankment, the lack of cohesion between soil particles and its sensitivity to the change of moisture content are reasons for such problem. Creation of such cohesion may be achieved by implementation of liquid asphalt and introduction of Nano additives. In this work, silica fumes, fly ash and lime have been implemented with the aid of asphalt emulsion to improve the unconfined compressive strength of the collapsible soil. Specimens of 38 mm in diameter and 76 mm height have been prepared with various percentages of each type of Nano additive and fluid content. Specimens were subjected to unconfined compressive strength determination at dry and absorbed test conditions. It was concluded that the unconfined compressive strength increases by (13-25) folds after stabilization with asphalt emulsion at dry test condition. The implementation of lime shows that the cohesive strength is increased by a range of (93-517)% for absorbed condition, while it decreased by a range of (50-31)% at dry test conditions. When 5% silica fumes was introduced, the compressive strength increased by 9.2% in dry test condition while it decreases in a range of (31.5-63.8)% for other percentages. When fly ash class F was introduced, the reduction in the strength was in the range of (100-120)% for various fly ash content at dry test condition.

Keywords: Nano Additives, Liquid Asphalt, Collapsible Soil, Unconfined Compressive Strength


1. Introduction

Collapsibility of granular soil has been an issue in many research work, the major cause of such engineering problem is the loss of cohesion between soil particles due to change of the moisture content. An example of such soil is the sand, silty sand, and Gypseous soil, [1]. When such soil is intended to be used in the construction of roadway embankment, it should be treated with other materials that supports the cohesion such as liquid asphalt, or with fine grained additive or both, [2]. Implementation of Nano materials to improve the geotechnical properties of asphalt stabilized granular soil was investigated by [3], the silica fumes shows positive impact in of (49.9, 25.7, and 22.2)% on deformation in (mm) for all the percentages tried of (0.5, 1.5, and 2)% respectively. Hydrated lime exhibits the highest reduction of deformation of 66.6% at 0.5% content, 1.5% of coal fly ash exhibits 63.1% reduction of deformation. Another investigation by [4] had concluded that the tensile strength was increase by (6.6% and 39.6%) when (2%) of silica fumes or lime were implemented respectively. Punching shear for asphalt stabilized soil increases by (47.4%) when (2%) lime was added, while it decrease by (10.5%) when (2%) of silica fumes was added. [5] investigated the of effect cutback asphalt and lime on Gypseous soil, it was found that addition (5% cutback asphalt+11% water+7% lime) increase the strength of Gypseous soil, causes reduction in the coefficient of permeability and increases C. B. R. values as compared with untreated soil. [6] Used emulsified asphalt to stabilize the soil; it was concluded that the unconfined compressive strength for unsoaked samples increased with the increase in binder content up to an optimum value and then it gradually decreased. For the soaked samples, strength increased with the increase in binder content. [7] Used emulsified asphalt and treated the soil by 4%, 6% and 8% of its dry weight. The test results showed that the unconfined compressive strength for the treated soil without soaking increases as the binder content increases up to an optimum value and then decreases. [8] Showed that the unconfined compression test results of the treated Gypseous soil by different percentages of emulsified asphalt content increased with increasing emulsified asphalt content up to an optimum limit and then the compressive strength decreased. The aim of this investigation was to assess the influence of Nano additives (lime, silica fumes, and fly ash) on the unconfined compressive strength of asphalt stabilized soil under dry and absorbed testing conditions.

2. Materials and Methods

2.1. Subgrade Soil

Soil was brought from AL-Nasiriya city, 380 km south of Baghdad. The soil was obtained from a depth of (1.0 upto1.5) m below the natural ground level after removing the top soil. The physical properties of the soil are shown in Table 1. The chemical composition of the soil is shown in Table 2. Figure 1 shows the grain size distribution of the soil.

Table 1. Physical properties of the soil.

Physical properties Test results
Liquid limit (%) 47
Plastic limit (%) 23
Plasticity index (%) 24
Specific gravity (Gs) 2.730
Clay (%) 42
Silt (%) 57
Sand (%) 1
Unified classification system CL
AASHTO classification system A-7-6
Maximum Dry Unit Weight (kN/m3) (Standard proctor) 16.6
Optimum Moisture Content (%) (Standard proctor) 20
Collapse potential 5.5%

Table 2. Chemical composition of the soil.

Chemical composition Test result
Organic content (%) 0.56
SiO2 40.24
Fe2O3 6.0
Al2O3 11.24
CaO 17.36
MgO 5.9
Na2O 1.18
L. O. I. 15.99
TSS 1.2
PH Value 8.2

Figure. 1. Grain size distribution of the soil.

2.2. Asphalt Emulsion

This type of liquid asphalt was brought from Al-Daura refinery. As previously assessed, asphalt emulsion provides easy cold mixing with soil, and ultimately a homogenous mixing is obtained. Properties of asphalt emulsion are given in Table 3 as supplied by refinery.

Table 3. Properties of asphalt emulsion.

Property Test results
Particle charge +ve
Viscosity (Cst) 45
Cement mixing 1.2
Settling time (hour) 19
Coating ability and water resistance Good
Coating dry and wet aggregates Fair

2.3. Lime

In this study, hydrated lime was used. The major chemical and physical properties of lime are shown in Table 4.

Table 4. Chemical composition of lime.

Composition Percent
SiO2 1.51
Fe2O3 0.11
Al2o3 0.93
CaO 92.01
Loss on ignition 8.9
% passing sieve No. 200 89

2.4. Silica Fumes

In this study used, a grey-coloured densified silica fumes is implemented. The chemical properties of silica used is shown in Table 5.

2.5. Fly Ash

Class F fly ash According to [9], was implemented in this investigation. The chemical composition of fly ash used are shown in Table 5.

Table 5. Chemical composition of Nano additives.

Content Silica fumes Fly ash
Percent content
SiO3 90 90
Al2O3 3.0 2.2
CaO 1.2 3.5
Fe2O3 1.0 0.3
MgO 1.0 0.5
Loss on ignition (LOI) < 6 3.5

2.6. Specimen's Preparation

The pulverized and homogenous soil passing No.10 sieve was oven dried at a temperature of (105°C).

The first group of specimens was prepared from soil asphalt emulsion mixture, soil was mixed thoroughly by hand with the predetermined weight of water and emulsion (optimum fluid content) which gives the maximum standard dry unit weight of 16.6 (kN/m3). Different percentage of emulsified asphalt was added, as shown in Table 6. to the soil and mixed by rubbing the mixture between palms for two minutes so that the mixture had a homogenous character and proper coating of soil particles with asphalt occurred. The mix was allowed to aeration for two hours at room temperature as recommended by [10] before compaction. Specimens were allowed to cure for seven days at room temperature as advised by [5]. Duplicate specimens have been prepared for each percentage of emulsion, and the average value of the unconfined compressive strength for each duplicate specimens was calculated and considered for analysis. Figure 2 shows the mixture under aeration process, while Figure 3 shows part of the prepared unconfined compression strength test Specimens. The second group of specimens were prepared using the first type of Nano additives (hydrated lime) in addition to asphalt emulsion. The required amount of lime was added to the soil at different percentage of (2, 4, 6, 8, and 10)%, then the required percentage of water was introduced followed by the predetermined amount of asphalt emulsion, and mixed thoroughly by hand for two minutes so that the mixture had a homogenous character.

Figure 2. The aeration process.

Figure 3. Part of the prepared specimens.

The mixtures were subjected to aeration for two hours at room temperature. The third group included the specimens stabilized with 17% emulsion asphalt and with different percentage of silica fumes content of (1%, 3%, 5%, 7% and 9%). The soil was mixed with silica fumes, then water content was added followed by asphalt emulsion. The mixture was rubbed between palms for several minutes to get a homogenous character, then subjected aeration for two hours at room temperature. The fourth group includes soil stabilization with emulsion asphalt and with different percentage of class C fly ash content of (4%, 6%, 8% and 10%). Soil was mixed with fly ash and then water content was added followed by emulsified asphalt. After thoroughly mixing, the mixture was allowed to aeration for two hours at room temperature. After aeration, all mixes were compacted statically in a cylindrical mould of a split type of 38 mm in diameter, and 76 mm height. Then all specimens were allowed to cure for seven days at room temperature and tested, the average value of the unconfined compressive strength for each duplicate specimens was considered.

Table 6. Moisture and emulsion percentages implemented for optimum fluid content determination.

Moisture% 1 3 5 7 9 11 13 15 17 19
Emulsion% 19 17 15 13 11 9 7 5 3 1

The unconfined compression test was carried out according to the ASTM standard, [9] using a constant strain compression machine with a loading rate of 1.52 mm per minute. A calibrated proving ring of (5kN) capacity and (0.01mm) precision dial gauge for vertical deformation reading were used. From the unconfined compression strength test of the first group, the optimum fluid content was determined to be (3% water and 17% emulsion). The prepared specimens were divided into two sets, the first set was tested under dry condition, while the second set was subjected to water absorption by capillary rise for 24 hours, then tested for unconfined compressive strength. Figure 4 demonstrates specimens with various additives.

2.7. Absorption Technique

The absorption technique apparatus consisted of a container filled with 10 cm thickness of fully saturated sand passing 6 mm sieve as was used by [11], and [12]. This sand layer was kept saturated throughout the absorption period with distilled water and checked visually.

Figure 4. Asphalt stabilized specimens with various Nano additives.

2.8. Testing of Specimens After Absorption

The prepared unconfined compression test specimens were weighted and then were placed in the absorption apparatus over the saturated sand layer for 24 hours. The whole container was tightly covered by polyethylene sheets to retain the moisture in the sand and specimens. The water will be absorbed through capillary rise action. The weight of absorbed water was then determined after 24hours by successive weighting of specimens at this age. After an absorption period, the specimens were subjected to unconfined compressive strength determination. It was found that the specimens with silica fumes or fly ash placed in the container collapsed because of the water absorbed in the voids of sample by capillary raise. Figure 5 exhibits specimens under water absorption.

Figure 5. Specimens under absorption technique.

3. Results and Discussion

Figure 6 present the failure mode of the untreated soil after testing for unconfined compression strength at dry and absorbed conditions. It can be observed that a typical brittle shear failure could be achieved at the dry test condition. However, the absorbed test exhibits a plastic type of failure.

Figure 6. Failure mode of untreated soil specimens.

The main objective of this test was to find the optimum percentages of asphalt emulsion which contribute to the shear strength of soil that can achieve through the unconfined shear strength. Figure 7 shows the stress-strain relationship of the unconfined compression test, the optimum fluid content (emulsified asphalt and water) that can achieve the unconfined shear strength in dry condition could be observed to be (17% asphalt emulsion + 3% water). The stress increases gently at early stages of loading up to 2% strain, then it increases sharply with further increments in the strain until it reaches a peak value (indicating the limit of failure), then it decreases as the strain increases. Figure 7 also shows that the unconfined compressive strength increases with increasing emulsified asphalt content up to 17% of asphalt, this increase may be attributed to the gain in cohesion which is provided by continuous film of asphalt coating the soil particles. Further increment in asphalt content could increase the asphalt film thickness and spread soil particles apart, this will causes a high reduction in friction, and reduces the compressive strength of the stabilized soil.

Figure 7. Stress-strain relationship for emulsified asphalt stabilized soil.

Such results are in agreement with those of many researchers work [1], [2] and [11]. On the other hand, during the absorbed test condition, all samples were collapsed in the absorption apparatus. This failure may be attributed to the weak adhesion between soil particles and asphalt emulsion or the weak cohesive bond between the asphalt-particles system. This result confirmed that of [13], [14], and [15]. Table 7 shows the result of unconfined compression strength for specimen’s stabilized with emulsion in dry test condition. It can be observed that the unconfined compressive strength increases by (13-25) folds after stabilization with asphalt emulsion at dry test condition. It was noted that the optimum percentage of fluid content 20% (17%emulsion asphalt+3%water content) increases the unconfined compressive strength of soil in about 23 folds as compared to untreated soil in dry test condition. At this stage of the experimental program, it was decided to implement the Nano additives to change the overall gradation of the soil, reduce the voids content, and to create some kind of reaction into the soil structure which may be beneficial to the strength behaviour at absorbed test condition.

Table 7. Impact of fluid content on unconfined compressive strength.

Water content (%) Asphalt emulsion content (%) Unconfined compressive strength (kPa)
20 0 121
17 3 1737
15 5 1888
13 7 1892
11 9 2123
9 11 2298
7 13 2257
5 15 2495
3 17 2909
1 19 3155

Figure 8 present the stress-strain relationship of unconfined compressive strength of soil stabilized with 17% emulsion asphalt mixed with lime contents of (2%, 4%,6%,8% and 10%), in both dry and absorption test. It can be noticed that the unconfined compressive strength increases with increasing lime content until (6%) lime content and then decreased when increasing the percentage of lime to (8%, 10%) at dry test condition, while 8% of lime exhibits lower axial strain accompanied with high stress level. This behavior may be attributed to the role of possible chemical reaction of lime additive with soil in improving the cementation, and water proofing action of the soil emulsion mixture thus the effect of water damage on soil emulsion mixture is reduced. The role of lime additive in changing the gradation, filling the voids, increasing the bond between soil particles, and improving the particle coating with asphalt, is pronounced, thus the capillarity rise action is decreased.

Figure 8. Impact of lime on unconfined compression strength of asphalt stabilized soil.

Table 8 summarizes the impact of lime additive content on the unconfined compressive strength of the soil emulsion mixture in both dry and soaked conditions. It can be noted that the cohesive strength is increased by a range of (93-517) % for absorbed condition as compared with asphalt stabilized soil. This may be attributed to chemical reaction between soil and lime during the aeration period which improves the cohesion property of the mixture. However, the unconfined compressive strength was reduced by a range of (50-31) % at dry test conditions. Such behaviour could be attributed to the lower unite weight of the specimens after digestion with lime as compared to asphalt stabilized soil. Figure9 illustrates the stress-strain relationship of unconfined compressive strength of soil stabilized with 17% emulsion asphalt mixed with silica fumes at different percentage contents of (1%, 3%, 5%, 7% and 9%) at dry test. It can be noticed that the unconfined compressive strength increases with increasing silica fumes content until it reach 5%, and then decreases with further increase in the percentage of Silica fumes.

Table 8. Influence of lime on unconfined compressive strength of asphalt stabilized soil.

Mixture type Unconfined compressive strength –
dry (kPa)
Unconfined compressive strength –
absorbed (kPa)
20% fluid + 0% lime 2909 Zero
20% fluid +2% lime 1456 94
20% fluid +4% lime 1545 305
20% fluid +6% lime 1995 517
20% fluid +8% lime 1526 483
20% fluid +10% lime 1485 122

The optimum percentage of silica fumes with emulsified was (5%) in dry test. On the other hand, Figure 9 also illustrates the stress-strain relationship of unconfined compressive strength of soil stabilized with 17% emulsion asphalt mixed with fly ash at different percentage of (2%, 4%, 6%, 8% and 10%) in dry test. It can be noticed that the compressive strength increases as fly ash increase up to 4%, then it decreases with further increments in fly ash content.

Figure 9. Influence of silica fumes and fly ash on unconfined compressive strength.

Table 9. Illustrate that the cohesive strength for soil stabilized with optimum percentage emulsion of 17% and 5% silica fumes increased about 9.2% in dry test condition as compared with untreated soil, while it decreases in a range of (31.5-63.8) % for other percentages. This may be attributed to that fly ash class F does not react with the soil but will fill the voids and increase the density of the mixture. However, specimens collapsed when tested under absorbed condition.

Table 9. Influence of silica fumes on unconfined compressive strength of asphalt stabilized soil.

Mixture type Unconfined compressive strength, dry kPa
20% fluid +0% silica fumes 2909
20% fluid +1% silica fumes 1922
20% fluid +3% silica fumes 1987
20% fluid +5% silica fumes 3177
20% fluid +7% silica fumes 1559
20% fluid +9% silica fumes 1053

Table 10. Illustrate the unconfined compressive strength for soil stabilized with optimum percentage emulsion17% and fly ash. It can be noted that the impact of fly ash class F was negative on the unconfined compressive strength of the mixture. The reduction in the strength was in the range of (100-120) % for various fly ash content. This may be attributed to the fact that fly ash class F has low lime content which is sufficient for the proposed chemical reaction, while the Nano size fly ash requires more asphalt to cover, and this will reduce the compressive strength.

Table 10. Influence of fly ash on unconfined compressive strength of asphalt stabilized soil.

Mixture type Unconfined compressive strength – dry (kPa)
20% fluid +0% fly ash 2909
20% fluid +2% fly ash 16
20% fluid +4% fly ash 22
20% fluid +6% fly ash 18.5
20% fluid +8% fly ash 18
20% fluid +10% fly ash 10

4. Conclusions

Based on the testing program, the following conclusions could be drawn:

(1)   The unconfined compressive strength of the soil stabilized with emulsion asphalt under dry test increases by 13-25 folds with increasing emulsion asphalt content up to an optimum of 17% and then decreases, while in absorbed test all samples failed.

(2)   It can be observed that a typical brittle shear failure could be achieved at the dry test condition. However, the absorbed test exhibits a plastic type of failure.

(3)   The implementation of lime shows that the cohesive strength is increased by a range of (93-517) % for absorbed condition as compared with asphalt stabilized soil, while the unconfined compressive strength was decreased by a range of (50-31)% at dry test conditions.

(4)   When 5% silica fumes was introduced, the compressive strength increased by 9.2% in dry test condition as compared with untreated soil, while it decreases in a range of (31.5-63.8)% for other percentages. However, when fly ash class F was introduced, the reduction in the strength was in the range of (100-120) % for various fly ash content at dry test condition.


References

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