Response of Sandy Soil Stabilized by Polymer Additives

Traditional sandy soil stabilizers such as lime cement, fly ash and bituminous materials, etc., usually require long curing time. Hence now a day, polymer stabilizer is used more extensively because of its stable chemical property and shorter curing time. For the developing organization, it is important to judge the performance of stabilized soil during its developing stages only. This paper aims to highlight a quick and easy test to evaluate the mechanical performance of such polymer based stabilized soil. For this study, three different kinds of polymer stabilizers at developing stage were evaluated against a market ready product. The analysis of the test result include a comparison of the strength, moisture loss rate and strain energy under different curing time, polymer type, polymer additive amount and test conditions. This study shows that the strength of the stabilized sandy soil is significantly increased both under wet and dry conditions by using the polymer additives. With the procedure mentioned in the paper it was easier to identify the relative merits and demerits of each product.


Introduction
In the desert areas, large amount of soil is lifted by wind, the road is covered by the soil as shown in Figure 1, therefore, soil stabilization is important for road capacity. Soil stabilization is the alteration of one or more soil properties, by mechanical or chemical means, in order to maximize the suitability of soil for a given construction purpose by improving in-situ soil properties. Soils may be stabilized to increase engineering properties like strength and durability; or to diminish erosion and dust generation. The stabilized product should not only enhance desired soil properties, but they should also create a soil material/soil system which can sustain for the design life of the project, under designated load application. In the field application, the polymer dilution is sprayed normally into the loose soil. After polymer dilution penetrates into the soil, compaction of the "wet" soil is carried out. The stabilized soil gains strength after water evaporates from its soil mix. Traditional stabilization of soil relies on cement, lime, fly ash, and bituminous [1][2][3] material. As the scientists and researchers are developing new engineering materials, many non-traditional materials are available for soil stabilization, for examples polymer emulsion, acids, enzymes and tree resin emulsions [4][5][6][7]. As compared to the traditional stabilizers, these stabilizers have the following advantages: b) They produce less swelling and heaving [8,9]; c) Produce less pollution; and d) They save natural resources.
Apart from above mentioned benefits another advantage is that the liquid concentrate can be diluted with water and thus it is easy to achieve target additive amount by controlling dilution ratio. In many countries, large percentages of roads and parking lots are unpaved. The vehicles and wind together with the loose soil create dust that are known for adverse environmental and human health impact. Apart from increasing the strength of the soil these stabilizers can also be used as a way for controlling dust. For the ease of transportation and storage these Polymer emulsions can also be prepared in the form of powder. Before field application it is important for the industries to understand the mechanical properties of stabilized soil primarily during development phase of the product. Thus, the main objective of this paper is to highlight a quick and easy way to evaluate the mechanical performance of such stabilized soil before actual field application. Such assessment will quickly provide them a guide to modify their product if at all needed.
For a comparison study, three in development products from the same company namely a) L13126; b) L13140; c) L13142 and one a market ready "Product A" is chosen, all as anonymous reference products. Overall, they constitute three polymer emulsions and one polymer powder type as described later in the paper. Goals within the scope of this paper include the following:

Materials Used
Four different kinds of stabilizers were used in this study, three polymer emulsion type namely: L13126, L13142 and Product A and one powder polymer type namely: L13140. Table 1

Specimens Preparation
In order to perform compression tests, cylindrical specimens of 100 mm diameter and 150 mm height were prepared. The optimum moisture content of the sandy soil without stabilizer was measured by the modified proctor method (ASTM D1557). Figure  The compacted sample was then placed in the curing room at 200C and 40 percent relative humidity. In order to simulate the field condition, air-dried curing process was used. Each sample was weighed after 3 days, 7 days, 14 days, 21 days, and 28 days to get the moisture loss rate.

Unconfined Compression Test
The sandy soil samples stabilized with the different type and number of additives were tested by using unconfined compression (UC) setup under soaked and un soaked conditions. In the soaked UC test, the dry sample was placed in the 25 mm deep water bath for 15 minutes and after removing it from the water it was drained for 5 minutes. Then the soaked samples, as shown in Figure 4, were tested. The soaked UC test reflects the influence of moisture on the strength reduction of the stabilized soil in the field condition.

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head level h 2 in the manometer tube is recorded. By using the equation mentioned above the permeability K t is calculated. The procedure is repeated at least three times interval until the K t value is constant.

Optimal Polymer Adding Amount
Preliminary test was conducted to get a reasonable amount of stabilizer quantity to be investigated, L13126 polymer was taken as an example, various additive amounts of 0L/m 3 (pure water), 1.5L/ m 3 , 7L/m 3 , 14L/m 3 , 19L/m 3 and 24L/m 3 stabilizer quantity were examined. Figure 5 shows a plot of the additive amount versus UCS results after 28 days curing. As shown in Figure 5, the compression strength increases with stabilizer adding amount, it is expected that higher polymer content leads to thicker polymer matrix and more interaction between the soil particles, the compression strength increase almost linearly. It is hereby defined that "incremental strength" means the UCS of stabilized sample deducted by the UCS of samples with pure water. According to the Netherlands specification, the minimum UCS of bounded base layer shall be not less than 2MPa. Therefore, in this investigation, the incremental UCS value of 2 MPa was set as our minimum strength requirement.
As can be seen from the prediction curve of Figure

Wet and Dry Condition Effect
The soaked UCS of the sandy soil samples with pure water were not able to be tested because the samples disaggregated in the water bath. For comparison of moisture sensitivity of the samples, the strength loss rate of different stabilized samples was determined as Figure 7 In general, it can be observed that the strength loss rate decreases with the increase in the stabilizers amount, it indicates the thicker polymer coating will prevent moisture diffusion better. L13140 powder polymer specimens provide better water resistance to moisture deterioration and lose about 20% compression strength, the compression strength loss rate of others stabilizer specimens is about 30%. The specimens without stabilizer begin to disintegrate when they are placed in the water, and then lose load bearing capacity, the polymer can improve the water resistance of sandy soil.

Curing Time and moisture lose effect
The effect of curing time on residual moisture rate is presented in Table 2 68 21 and 28 curing days, as shown in Table 2, the residual moisture rate became a constant, almost all the moisture has evaporated by the 14th day of curing for all the stabilizer specimens with different adding amount, the final value is not zero duo to the moisture loss in the mixture process. Comparing the values of specimens with stabilizer and pure water, the different is slight, it illustrates polymer do not affect the moisture evaporation. The moisture evaporates from the sample that will enhance the bonding between polymer and soil particles, the relation between compression strength and residual moisture rate are shown in Figure 8, duo to residual moisture rate decrease with curing time for all the specimens is similar, for brevity, the residual moisture rate result of pure water sample is taken as an example to compare with the compression strength variation. The sample with polymer stabilizers develop approximately 60% of the 28 days compression strength within the first 7 days of curing, however, the strength growth after 14 days curing period is not significant, the strength growth trend is similar to that of residual moisture rate decrease, this indicates that the gain in strength of the stabilized sample may only be related to the rate of moisture evaporation and not to any chemical reaction as normally observed in cementitious stabilized products.  The moisture in the stabilized sample will influence the soaked UCS loss rate, the effect of curing time on USC loss rate is shown in Figure 9. In general, the USC loss rate decrease with the increase of curing time, the trend is similar to that of strength growth, it illustrates the sample with less moisture inside has a better moisture damage resistance. Samples utilized for permeability test were prepared in the same method as the ones used in the UC test (refer to "Specimens preparation" section). As shown in Figure 10, show highest permeability.

Implication and Discussion
Polymer is an environmental way for dust control and soil stabilization, as important as dust control, the mechanical and hydraulic property are also key points of polymer application, in this paper, mechanical and hydraulic property include three key indexes: UCS, soaked UCS loss rate and permeability, after 28 curing days, the moisture evaporate from the stabilized soil, the specimens become stronger and have a lower UCS loss rate. Unfortunately, there are no significant relation between the three indexes for all the polymers, the highest UCS is product A, the lowest UCS loss rate is L13140, and the lowest permeability is L13142, therefore it is hard to find a polymer with higher UCS, lower UCS loss rate and lower permeability, for the application, field condition, strength requirement and cost should be considered for stabilizer selection.