A Study of the Effect of Addition of Nano SiO2 and Polyamide Fiber toward Swelling Potential Expansive Clay

Expansive clay with great swelling potential requires improvement or stabilization of the soil. It can be successfully done by mechanical and chemical stabilization techniques. This study aims to determine the effect of adding Polyamide (PA) fibre as the material for mechanical stabilization and nano SiO2 as the material for chemical stabilization. The expansive clay used in this study deployed a sample of clay containing mineral montmorillonite with the USCS classification in the high plasticity (CH) category. The mixed materials used include PA fibre with variations of 0.5%, 0.75% and 1% by weight of dry soil and nano SiO2 with variations of 1%, 2% and 3% by dry soil weight. To prove the effectiveness of using nano SiO2, this study compares the treatment with the use of micro SiO2 materials under the same comparison variations. This result indicates that the expansive clay that has been stabilized using PA fibre and nano SiO2 is capable of preventing the swelling potential.


Introduction
Expansive clay soil is easily found in Indonesia and is a type of clay that swells or shrinks if there is a change of water contained inside the soil.The swelling and shrinkage may cause cracks to infrastructures, such as those frequently found in buildings, and bumpy roads.Such a negative effect of soil structures results in high repair costs.
Expansive clay soil is easily found in Indonesia and is a type of clay that swells or shrinks if there is a change of water contained inside the soil.The swelling and shrinkage may cause cracks to infrastructures, such as those frequently found in buildings, and bumpy roads.Such a negative effect of soil structures results in high repair costs.As infrastructure needs continue to increase rapidly, it is inevitable to build infrastructure on problematic or expansive clay soil.For this reason, several actions are needed to change the original properties of expansive clay soil, to suit construction needs.All actions to change the original properties of the soil to suit construction needs are actions that can be categorized as soil stabilization.The classification of soil stabilization can be divided into soil improvement and soil strengthening.

Research Purposes
This research aims to develop a method for stabilizing expansive soil using polyamide artificial fibres and SiO2 nanomaterials.The result of this expansive soil stabilization is mainly to reduce the potential swelling.To reach the objectives, the use of nano SiO2 and micro SiO2 materials is compared as a way to promote the urgency of using nano materials.

Research Significance
An important reason for using SiO2 nano material in this research is that this material is waste from Geothermal Power Plants, where Indonesia is a country that has the largest geothermal resource potential in the world.The amount of geothermal sludge waste in Indonesia reaches 165 tons per year.Sludge waste from Geothermal Power Plants contains silica which can be used as a cement mixer.Meanwhile, liquid waste (brine) which contains in the form of silica (SiO2), kalium (K), magnesium (Mg), has the potential to be processed into nano silica (nano SiO2) which can be utilized into a product with high economic value.
SiO2 nano material will fill the voids or spaces between expansive clay particles, thereby reducing the possibility of water particles entering the expansive soil.with reduced water content, it will reduce the expansion of expansive clay soil.Likewise, by inserting SiO2 nano material into the cavities or spaces between expansive clay particles, it will increase the shear strength.[2].Another use of nano material is nano alumina Al2O3 [3], [4] nano copper.[4] On the other hand, Nylon/polyamide fibres have been used for stabilization of expansive soils, [5] but still works best with 1 mm diameter fibre.In this research, the polyamide fibre used is a bar shape type with a diameter of 27 Pm, which is closer to the dimensions of clay particles of 20 Pm.Swelling and shrinkage of expansive soil that has been reinforced with nylon is more controlled due to interlocking between fibers and friction between soil and fibers.[5].Another use of artificial fiber that has previously been researched for stabilizing expansive soil is polypropylene fiber.[6][7]- [14].The use of polyamide fibre was chosen after considering that polyamide fibre has a tensile strength of 90 MPa which is greater than polypropylene which has 70 MPa.

Soil
The expansive clay used in this research was taken from Desa Parungmulya, Ciampel District, Karawang Regency, West Java ( 6 ⁰ 22'39,5"S; dan 107⁰17'58,8"E).In accordance with the Geological Map from the Geological Map Result of Remote Sensing Image Interpretation, Karawang Sheet, West Java, the Tms2 rock type was obtained, namely Tertiary rocks, Miocene series, Subang formation.The landscape is dominated by mudstone, calcareous clay and fine-coarse lithological alternations.This mudstone has shrinkage properties which have the high potential to damage infrastructure.Table 1 shows the physical properties of the expansive clay (samples) used in this research.The liquid limit value of 110.13% and plastic limit of 44.20% indicates that the soil contains the mineral montmorillonite [15].To determine the mineral content of the soil used in this research, X-Ray Diffraction (XRD) testing will then be carried out.It can also be seen that the soil according to the USCS classification is classified as CH (high plasticity).
Table 1.Physical Properties of the Expansive Clay.

Preliminaries Test
This study used the mixture variations of 1%; 2% and 3% for SiO2 nanomaterial and 0.5%; 0.75% and 1% for polyamide fibre.The preliminaries test carried out was Standard Proctor Test, the expansive clay was compacted in a cylinder with a volume of 1/30 ft 3 (943.3cm 3 ).The diameter of the mold is 4 in (101.6 mm).About 2500 grams of expansive clay was mixed with water with different water contents and then compacted using a tamper with a weight of 5.5 lb (2.5 kg), a fall height of 12 in (30.48 cm).
The soil compaction was carried out in 3 layers with 25 impacts per layer.The experiment can be repeated 5 times with different water contents.To ensure the equal distribution of fibre and nano SiO2, mixing was carried out in oven dry conditions.Then, water was added according to the standard proctor test results and compacted in a mold.In this research, initial tests were also carried out, including Atterberg limit, specific gravity and sieve analysis, the results were as shown in table 1 above.The next initial test carried out was XRD.The results are shown in figure 4 and table 5 below.From the quantitative analysis of the XRD test above, obtained :

Test Conducted and Quantities Determined
The samples, under various mixtures, installed in consolidation ring apparatus (60 mm in diameter and 20 mm in thickness).Place the specimens in the following order: pore stone, pore paper, specimen, pore paper, pore stone and pressure plate on the consolidation ring.Then place the ring containing the specimen into the specimen tub (consolidation cell) located in the consolidometer.Testing the percentage of swelling uses a consolidation test equipment (consolidometer) with a constant load of 1,0 kPa, according to ASTM 4546-14.The swelling percentage test begins by reading the dial gauge which is shown as zero position, the load is changed to 1 kPa, and immediately flooded with water while noting the changes in the dial value that occur at T=0.1; 0.2; 0.5; 1; 2;4;8;15;30;60;120;240;480;1440;2880;4320;5760;7200;8640;10080 minutes (ASTM 4546-14).Then, if the dial is still rising, continue swelling until it reaches maximum swelling.This last condition is defined as the maximum percentage of swelling that occurs.

Experimental Work
The first test to be conducted was by mixing expansive clay with polyamide fibre.The mixture ratios used in the test are sequentially 0%; 0.5%; 0.75% and 1% of dry soil weight.When making samples, the fiber distribution is maximized.The test results can be seen in Figure 5 with the following detail: Swelling potentials for the mixtures of 0%; 0.5%; 0.75% and 1% are respectively 29.73%; 17.22%; 19.94% and 24.00%.It can be seen that the best ratio of polyamide fibre to obtain the lowest swelling potential is at ratio of 0.75%.The second test carried out was mixing expansive clay with SiO2 nano material.The mixture ratio used is 0%; 1%; 2% and 3% of dry soil weight.To obtain maximum distribution of SiO2 nanomaterial, mixing is carried out in dry conditions, then water is added according to the OMC value.The test results can be seen in Figure 6 below.Swelling potential for the mixture is 0%; 1%; 2% and 3% are respectively; 29.73%; 10.83%; 10.78% and 10.03%.It can be seen here that the best ratio of SiO2 nanomaterial to obtain the lowest swelling potential is a ratio of 3%.To determine the effectiveness of using SiO2 nano material, this research also carried out swelling potential testing using a mixture of SiO2 micro material.The third test carried out was by mixing expansive clay with SiO2 micro material.The mixture ratio used is the same as the ratio used for nano SiO2.The test results can be seen in Figure 7 with the following detail: Swelling potentials for the mixtures of 0%; 1%; 2% and 3% are respectively 29.73%; 29.44%; 28.33% and 27.89%.It can be concluded that the best ratio of SiO2 micro material to obtain the lowest swelling potential is at ratio of 3%.The fourth test carried out was with the best mixture of the three previous tests.The variation of the mixture used is expansive clay + 0.75% polyamide fibre + 3% nano SiO2.The comparison results can be seen in Figure 8.It informs that the variation mixture of 3% nano SiO2 + 0.75% polyamide fibre shows the lowest swelling potential, only 6.78%.It is dramatically more significant than the mixture of 3% micro SiO2 of 27.89%, or a mixture of 0.75% polyamide fibre of 17.22%, or a mixture of 3% nano SiO2 of 10.03%.Then the expansive soil that had been mixed with 3% nano SiO2 + 0.75% polyamide fiber was tested with XRD and Scanning Electronic Microscope (SEM) to determine the mineral composition.The results can be shown in the Figure 9 and Table 6 below.

Result and Discussion
From a series of experiments that have been carried out, the following conclusions were obtained : a. SiO2 nanomaterials and polyamide fibers can be used to stabilize expansive clay.In particular, the determined swelling potential of expansive clay soils can be decreased by the addition of SiO2 nanomaterials and polyamide fibers.b.The best percentage for adding SiO2 nanomaterial is 3% and adding polyamide fiber is 0.75%.
Each produces a potential swelling of 10.03% and 17.22%.The combination of adding these two materials produces a potential swelling of 6.78%.This can significantly reduce the potential swelling of expansive clay in this test by 29.73%.c.Polyamide fibers are indicated to reduce swelling potential due to (i) interlocking between fibers and (ii) friction between fibers and soil.Nano SiO2 is indicated to reduce swelling potential

Figure 1 shows
Figure 1 shows Polyamide fibre which was chosen as a soil-reinforcement material because it has a greater tensile strength, around 90.0 MPa compared to polypropylene fibre which has a tensile strength of 55.0 -70.0 MPa.2.3.Nano SiO2Nano materials have been widely used by previous researchers as stabilizing materials for expansive clay [2]-[4].This research uses SiO2 nano material with the consideration that this material is the result of waste processing from Geothermal Power Plants which are often found in Indonesia.Meanwhile, this waste material has not yet been utilized optimally.

Figure 3 .
Figure 3. sample preparation for swelling potential testing.(a) all materials have been prepared properly, (b) a mixture of all materials in dry conditions (c) soil samples.

Figure 4 .
Figure 4. X-Ray Diffraction Test Result of Expansive Clay Sample.

Figure 9 .
Figure 9. X-Ray Diffraction Test Result of Expansive Clay Sample after adding nano SiO2 3%.

Table 2 .
Technical Specification of Polyamide Fiber.

Table 4 .
Standard Proctor Test results.

Table 5 .
Quantity Analysis of XRD Test of Expansive Clay Sample.