Comparison of short term and long term performances for polymer stabilized sand and clay

Comparison of short term and long term performances for polymer stabilized sand and clay Q4 ww sciencedirect com 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32[.]

JTTE115_proof ■ February 2017 ■ 1/11 j o u r n a l o f t r a f fi c a n d t r a n s p o r t a t i o n e n g i n e e r i n g ( e n g l i s h e d i t i o n ) ; x ( x ) : e1 Available online at www.sciencedirect.com 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 ScienceDirect journal homepage: www.elsevier.com/locate/jtte Original Research Paper Comparison of short-term and long-term performances for polymer-stabilized sand and clay Q4 Sepehr Rezaeimalek a,*, Abdolreza Nasouri a, Jie Huang a, Sazzad Bin-Shafique a, Simon T Gilazghi b a Department of Civil and Environmental Engineering, The University of Texas at San Antonio, San Antonio, TX 78249, USA b Texas Department of Transportation, Austin, TX 78701, USA highlights
An MDI-based liquid polymer was used to stabilize poorly-graded sand and sulfate-rich clay
The short-term and long-term performances of the stabilized specimens were evaluated
The specimens showcased high durability after undergoing different weathering conditions
The polymer-stabilized sulfate-rich clay specimens showcased minimal swelling potential article info abstract Article history: A series of tests were carried out on sulfate rich, high-plasticity clay and poorly-graded Available online xxx natural sand to study the effectiveness of a methylene diphenyl diisocyanate based liquid polymer soil stabilizer in improving the unconfined compressive strength (UCS) of freshly stabilized soils and aged sand specimens The aged specimens were prepared by Keywords: exposing the specimens to ultraviolet radiation, freeze-thaw, and wet-dry weathering Soil stabilization The polymer soil stabilizer also mitigated the swelling of the expansive clay For clay, the Liquid polymer observations indicated that the sequence of adding water and liquid polymer had great Sand influence on the gained UCS of stabilized specimens However, this was shown to be of Expansive clay little importance for sand Furthermore, sand samples showed incremental gains in UCS Unconfined compressive strength when they were submerged in water This increase was significant for up to days of soaking in water after days of ambient air curing Conversely, the clay samples lost a large fraction of their UCS when soaked in water; however, their remaining strength was still considerable The stabilized specimens showed acceptable endurance under weathering action, although sample yellowing due to ultraviolet radiation was evident on * Corresponding author Tel.: ỵ1 210 458 7905 E-mail addresses: sepehr.rezaeimalek@utsa.edu (S Rezaeimalek), jie.huang@utsa.edu (J Huang) Peer review under responsibility of Periodical Offices of Chang'an University http://dx.doi.org/10.1016/j.jtte.2017.01.003 2095-7564/© 2017 Periodical Offices of Chang'an University Publishing services by Elsevier B.V on behalf of Owner This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Please cite this article in press as: Rezaeimalek, S., et al., Comparison of short-term and long-term performances for polymerstabilized sand and clay, Journal of Traffic and Transportation Engineering (English Edition) (2017), http://dx.doi.org/10.1016/ j.jtte.2017.01.003 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 JTTE115_proof ■ February 2017 ■ 2/11 2 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 J Traffic Transp Eng (Engl Ed.) 2017; x (x): 1e11 the surface of the specimens Except for moisture susceptibility of the clay specimens, the results of this study suggested the liquid stabilizer could be successfully utilized to provide acceptable strength, durability and mitigated swelling © 2017 Periodical Offices of Chang'an University Publishing services by Elsevier B.V on behalf of Owner This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/) Introduction Although cementitious materials such as cement and lime have been widely used as soil stabilizers for many decades, the geotechnical engineering community has never stopped searching for alternative stabilizers for circumstances where traditional cementitious stabilizers are not applicable or favorable When cement is used to stabilize soils, shrinkage, caused by hydration of the cement as well as drying, is a commonly observed phenomenon, which significantly reduces the strength and increases the permeability (George, 1973; Nakayama and Handy, 1965; Sebesta and Scullion, 2004) In addition, the stabilized soils, although having a high strength, are rather brittle, especially under dynamic loading (Acar and El-Tahir, 1986; Schnaid et al., 2001) The cracking and brittleness of cement stabilized soils have greatly influenced the long-term performance of stabilized soils for many applications In addition to the cracking and brittleness, when used for clay, the cementitious stabilizer can cause significant swelling if excessive sulfate is present (Celik and Nalbantoglu, 2013; Hunter, 1988; Mitchell, 1986; Mitchell and Dermatas, 1992; Puppala et al., 1999, 2005; Wang et al., 2004) The clay with excessive sulfate content is usually called sulfate-rich clay It has been found that under pH conditions created by the cementitious materials, sulfate reacts with calcium ions to form ettringite (Ca6[Al(OH)6]2(SO4)3$26H2O) and thaumasite (Ca6[Si(OH)6]2(SO4) (CO3)2$24H2O), which are highly expansive The swelling could be as high as 200% (Faure, 1991; Harris et al., 2004; Little et al., 2010) Such a phenomenon is commonly referred to as sulfate-induced heave by geotechnical engineers The advent of unconventional, non-cementitious materials such as foams, emulsions of petroleum, enzymes, acids, and industrial waste materials have shown promising results in stabilizing problematic soils While these materials are different in nature and chemical composition, they can be used to reduce permeability, mitigate soil liquefaction, and increase soil strength by filling the voids and providing bonding between the particles (Ajalloeian et al., 2013; Ajayi et al., 1991; Al-Khanbashi and Abdalla, 2006; Anagnostopoulos et al., 2013; Mohammad and Vipulanandan, 2013; Moustafa et al., 1981; Naeini et al., 2012; Ohama, 1995; Rauch et al., 2002; Santoni et al., 2002; Zandieh and Yasrobi, 2007) Among these unorthodox stabilizers, liquid polymers have gained attention due to their relative ease of use and promising outcomes However, there is a lack of systematic studies on the stabilization methods of polymers for different soils, such as mixing or curing methods As a result, the reported studies showed different outcomes even for the same soil For instance, varying the polymer content of the specimens did not result in a consistent outcome in terms of resultant UCS (Rauch et al., 2002), and more saliently, in another case, adding polymer to soil samples decreased the strength of the specimens compared to untreated soil (Santoni et al., 2002) This inconsistency hindered the wide applications of polymers as a soil stabilizer for many situations Considering the dilemma, this study focuses on investigating the mixing and curing methods as well as the short-term and long-term performances for sand and sulfate-rich clay The scope of the study includes the following: Determination of suitable mixing and curing methods, and duration for a liquid polymer that was used to stabilize sand and sulfate-rich clay Determining the short-term behavior of the two stabilized soils An unconfined compressive stress (UC) test was carried out for such purpose, and the clay samples were tested for their swelling potential Long-term performance of the stabilized soils was studied For this purpose, clay specimens were subjected to soaking in water for prolonged time before their UCS and swelling potential were measured In contrast, sand specimens Fig e Soils used in the tests (a) Sulfate-rich high plasticity clay (b) Poorly graded sand Please cite this article in press as: Rezaeimalek, S., et al., Comparison of short-term and long-term performances for polymerstabilized sand and clay, Journal of Traffic and Transportation Engineering (English Edition) (2017), http://dx.doi.org/10.1016/ j.jtte.2017.01.003 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 JTTE115_proof ■ February 2017 ■ 3/11 J Traffic Transp Eng (Engl Ed.) 2017; x (x): 1e11 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 were subjected to three aging conditions, i.e., wet-dry cycles, freeze-thaw cycles, and accelerated UV-B weathering The aged sand samples were tested for their UCS Materials 2.1 Sand The selected sand was a light brown natural river sand as shown in Fig 1(a), for which the D60 is 0.45 mm, D30 is 0.3 mm, to form a mixture of diisocyanates and amines resulting in an inert, insoluble polyuria and emission of carbon dioxide as shown by Eqs (1) and (2) The resultant polyuria coating the soil particle surface has two effects, (1) acting as “glue” to bond soil particles together and (2) acting as a barrier to mitigate moisture infiltration The reported properties of the polymer are presented in Table The applications for such a product include a wide range of areas in ground improvement, such as soil stabilization, permeation grouting and sinkhole remediation The measured unit weight of the polymer in the laboratory environment (temperature 20  C ±  C) was 11.39 kN/m3 (1) and D10 is 0.2 mm The gradation curve of the sand is shown in Fig According to the Unified Soil Classification System (USCS), the sand is classified as poorly graded sand (SP) with Cc ¼ 1.1 and Cu ¼ 2.5 The soil has maximum and minimum densities of 18.64 kN/m3 and 15.22 kN/m3, respectively, determined by the ASTM D4253 and ASTM D425 test methods (2) 2.4 2.2 A yellowish clay soil was employed throughout this study To determine the percentage of fines (i.e., silts and clays) of the soil, wet sieve analysis following ASTM C325-07 was performed and the results indicated a fine content of 94% The results of the Atterberg limits test on the soil showed a liquid limit (LL) of 53 and a plasticity index (PI) of 23, which classifies the soil as high plasticity clay (CH) under USCS protocol The soil had negligible sulfate content (i.e., less than 100 ppm) To prepare sulfate-rich clay with a sulfate concentration of 20,000 ppm (2%) by weight, the soil was oven-dried and then sodium sulfate was added After thorough mixing, the prepared sulfate-rich clay was set in an outdoor environment for weeks to reach chemical equilibrium The utilized clay soil is illustrated in Fig 1(b) 2.3 Mixture preparation and specimen casting Sulfate-rich clay Liquid polymer The polymer used as a soil stabilizer in this study, which relies on chemical reactions to polymerize and bond soil particles together, has wide ranging engineering applications The chemical structure and properties of the polymer are discussed in this section Polymer M is a single component, moisture activated, hydrophobic polyurethane prepolymer commercially known as AP Soil 600™ manufactured by Alchemy Polymers, LLC This polymer belongs to the generic family of Methylene Diphenyl Diisocyanate (usually addressed as MDI) and its chemical structure is shown in Fig The NitrogeneCarboneOxygen (N]C]O) group of the polymer precursor reacts chemically with the OxygeneHydrogen (eOeH) groups of added water As suggested by previous studies (Harris et al., 2004; Rauch Q1 et al., 2002; Santoni et al., 2002), the mixing method has a great influence on the outcome when a polymer is used as a soil stabilizer The following section describes the specimen preparation procedure for sand and clay specimens using Polymer M The specimens were initially prepared using 10% water and 10% polymer by weight for all the soils Considering that the polymerization of Polymer M is triggered by moisture as indicated by Eqs (1) and (2), the Polymer M stabilized sand and clay specimens were prepared by two methods For Method-1, the dry soil was first mixed with polymer and then water was added In contrast, for Method-2, dry soil was first mixed with water and then polymer was added Once mixed thoroughly, the sand-polymer mixture was compacted into a cylindrical mold of 50 mm by 175 mm (D  H) It was only filled up to 125 mm high (aspect ratio: 2.5:1), which left 50 mm of extended space This mixture was then poured into the molds in sequential layers of equal thickness, and each layer was individually blown to ensure an acceptable level of compaction The relative density of the samples throughout the study was 77% A thin layer of petroleum jelly was applied to the interior walls of the molds To facilitate the extraction of the samples from the molds, eliminate skin friction, and the boundary effect between the samples and the molds, each mold half was sealed with plastic wrap After compaction, the mold was capped to prevent moisture loss The caps and the molds were removed 24 h after specimen preparation These samples were then subjected to curing in two different media: laboratory room environment (20  C ±  C) and submerged in water Please cite this article in press as: Rezaeimalek, S., et al., Comparison of short-term and long-term performances for polymerstabilized sand and clay, Journal of Traffic and Transportation Engineering (English Edition) (2017), http://dx.doi.org/10.1016/ j.jtte.2017.01.003 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 JTTE115_proof ■ February 2017 ■ 4/11 4 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 J Traffic Transp Eng (Engl Ed.) 2017; x (x): 1e11 thereafter, the strength and swelling potential were measured as indications of long-term performance In contrast, the sand was subjected to three scenarios of aging, that is, UV radiation, wet-dry cycles, and freeze-thaw cycles The aged sand samples were tested for their UCS, which was then compared with that of the un-aged samples Fig summarizes the study outline 3.2 The prepared specimens were cured in three different environments, i.e., in ambient air, in 100% humidity, and in water to find the appropriate curing environment Upon the selection of the appropriate curing environment, the specimens were cured for different durations to determine the suitable curing duration Fig e Gradation curve for sand 3.3 Fig e Chemical composition of methylene diphenyl diisocyanate Table e Properties of the polymer Physical properties Reference/standard Viscosity 25  C Tensile strength (cured) Shrinkage Compressive strength with fine sand ASTM D3574 ASTM D1042/D756 ASTM D575/D695 Value 25e35 Centipoise MPa None 12.5 MPa Similar to sand, Polymer M stabilized sulfate-rich clay specimens were also prepared following Method-1 and Method-2 The clay specimens were compacted to their maximum dry unit weight at the optimum moisture content based on the standard proctor test for 10% polymer (by weight) All the prepared specimens were subjected to curing before they were tested or set in an aging environment Methods 3.1 Testing outline Specimen curing The primary objective of this study is to evaluate the effectiveness of a liquid polymer soil stabilizer on improving the short-term and long-term performances of sulfate-rich clay and poorly-graded sand, by studying the strength improvement for both sand and clay as well as the swelling mitigation for clays that are stabilized by the polymer To fulfill this objective, a study was carried out in three major steps In the first step, the appropriate mixing method and curing time were determined for the studied soils and polymer In Step 2, the strength improvement of the freshly stabilized sand and clay specimens was assessed and the swelling mitigation for the freshly stabilized clay was studied In Step 3, the long-term performance of the polymer stabilized soils was evaluated In this step, the clay soil was soaked for a prolonged period; Specimen aging The long-term performance of the stabilized sand and sulfaterich clay was evaluated by testing the aged specimens The sand specimens were aged in three different conditions, separately, (1) 2000 h of Ultraviolet (UV) radiation to simulate the effect of long-term sunlight exposure; (2) 24 wet-dry cycles to simulate the effect of rain; and (3) 24 freeze-thaw cycles to simulate the effect of seasonal changes on the performance of the stabilized specimens The stabilized clay specimens were soaked in water for a prolonged time 3.3.1 Prolonged UV exposure Extensive exposure to UV radiation in polymers with aromatic isocyanate will result in a phenomenon known as “yellowing” in which a drastic color change and gradual polymer degradation occurs due to an oxidation reaction at the backbone of the polymer (Rosu et al., 2009) UV radiation from sunlight is divided into wavelength ranges categorized as UV-A, ranging from 315 to 400 nm, UV-B ranging from 280 to 315 nm, and UV-C ranging from 100 to 280 nm (NTP, 1992) Although only 5% of solar radiation accounts for UV-B wavelengths, it is reportedly the contributing element for polymer photodegradation and the consequent negative impact on polymer life span (Andrady et al., 1998) Given the increasing application of polymers for geotechnical/transportation purposes, it is crucial to have an understanding of the durability of the soil-polymer composites, particularly where the composite is on the surface and exposed to sunlight Examples of such applications are the use of polymers on slope surfaces to prevent failure and to mitigate erosion The polymer-stabilized sand specimens were tested for their endurance after prolonged exposure to UV radiation UV-B wavelengths were selected for the strength assessment of the soil-polymer composite To evaluate the performance of polymers in different industries, tests have been defined to monitor the possible degradation of the polymers in the course of time To so, two batches of sand specimens were exposed to accelerated weathering tests following ASTM D4329-13 Cycle A Guidelines The samples were exposed to UV-B radiation for 2000 h The selected exposure duration is beyond what happens in normal exposure to observe the performance of the specimens under worst-case Please cite this article in press as: Rezaeimalek, S., et al., Comparison of short-term and long-term performances for polymerstabilized sand and clay, Journal of Traffic and Transportation Engineering (English Edition) (2017), http://dx.doi.org/10.1016/ j.jtte.2017.01.003 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 JTTE115_proof ■ February 2017 ■ 5/11 J Traffic Transp Eng (Engl Ed.) 2017; x (x): 1e11 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Fig e Outline of study scenarios The exposed samples were then tested for their UCS and the results were compared with un-weathered samples Fig presents the test setup for the accelerated weathering test Considering the stabilized clay has minimal chance of being exposed to UV radiation, the clay was not subjected to UV radiation 3.3.2 Prolonged soaking for clay specimens Although the wet-dry and freeze-thaw cycles had been planned for the clay specimens, they showed susceptibility in water when different curing methods were compared As a result, the clay specimens were only conditioned in water for a prolonged time to assess their strength and volume stability in that environment Wet-dry cycles There is no direct test method to perform wet-dry tests for polymer stabilized soils Consequently, ASTM D559-15, used for wet-dry cycling of soil-cement mixtures, was adopted to perform the test The stabilized sand specimens were subjected to 24 wet-dry cycles In each cycle, the specimens were submerged in water for 24 h and then were dried for 48 h to permit the dissipation of the excess moisture The specimens were then tested for their UCS and compared with nonweathered samples to determine if the cycles had any impact on their strength 3.3.3 3.3.4 Freeze-thaw cycles For a similar reason, ASTM D560-15, used for the freeze-thaw cycling of soil-cement mixtures, was adopted for freeze-thaw cycles of the stabilized sand specimens The samples were set in a 18  C environment for 24 h and then were put in a laboratory environment (i.e., 20  C ±  C) to thaw Consequently, the samples were tested for their UCS and compared with unweathered specimens Fig e Accelerated UV-B weathering test setup 3.4 Testing procedure The UCS of the stabilized soils prepared with various curing and mixing methods was assessed for short-term and longterm performances For the evaluation of the short-term performance of both soils, the UCS of specimens made with the two different mixing methods and cured in a laboratory environment was acquired In addition, the clay specimens were tested for their swelling potential For the long-term performance, the sand and clay specimens were first aged in the afore-mentioned environments After the conditioning, the sand specimens were subjected to UCS tests, whereas the Fig e UCS test setup Please cite this article in press as: Rezaeimalek, S., et al., Comparison of short-term and long-term performances for polymerstabilized sand and clay, Journal of Traffic and Transportation Engineering (English Edition) (2017), http://dx.doi.org/10.1016/ j.jtte.2017.01.003 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 JTTE115_proof ■ February 2017 ■ 6/11 6 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 J Traffic Transp Eng (Engl Ed.) 2017; x (x): 1e11 clay specimens were subjected to UC and swelling potential tests 3.4.1 Unconfined compression strength test assembly and a typical soil specimen for the free swell test are illustrated in Fig Specimens were carefully prepared at their maximum dry unit weights The overburden stress due to the weight of porous stones on top of the soil was kPa The vertical swell was measured at certain time intervals The UC test was carried out following ASTM D2166/D2166M13 A digital Pneumatic Universal Testing Machine (UTM) was employed to provide the compressionestrain curve for the specimens Fig illustrates a UCS test specimen Results 3.4.2 4.1 Mixing methods evaluation Free swelling test A free swelling test was used to evaluate the swelling potential of the polymer stabilized sulfate-rich clay and it was performed following ASTM D4546-14 guidelines The entire The two mixing methods (Method-1 and Method-2) employed in this study showed insignificant differences in terms of Fig e Free swelling test setup (Gilazghi et al., 2016) Fig e Visual differences between different specimens (a) Method-1 for sand (b) Method-2 for sand (c) Method-1 for clay (d) Method-2 for clay Please cite this article in press as: Rezaeimalek, S., et al., Comparison of short-term and long-term performances for polymerstabilized sand and clay, Journal of Traffic and Transportation Engineering (English Edition) (2017), http://dx.doi.org/10.1016/ j.jtte.2017.01.003 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 JTTE115_proof ■ February 2017 ■ 7/11 J Traffic Transp Eng (Engl Ed.) 2017; x (x): 1e11 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 appearance and UCS in the sand specimens (Fig 8(a) and (b)) Conversely, for clay, the resultant samples from the mixing methods were significantly different from each other both in appearance and their gained UCS The specimens prepared following Method-2 (Figs 8(d) and 9(b)) appeared clear with a shiny, smooth, yellowish surface suggesting the proper coating of the surface with polymer However, the specimens made using Method-1 (Figs 8(c) and 9(a)) had a dark brown surface with numerous voids, whereas the polymer coating was generally missing from the surface In terms of UCS, the sand specimens made with Method-1 and Method-2 were similar as shown in Fig 10(a), whereas in the case of clay, the UCS of the specimens made with Method2 were significantly higher than that of mixing Method-1 as shown in Fig 10(b) Basically, the observed performance of the specimens stabilized by employing mixing Method-1 did not differ significantly with that of the unstabilized control specimen, suggesting the ineffectiveness of the method The maximum UCS gained for Method-1 as well as the unstabilized control specimens of clay was approximately 400 kPa, while the specimens made with Method-2 sustained up to 1400 kPa (Fig 10(b)) Therefore, the results suggest following mixing Method-2 for clay soil Because the use of Method-1 and Method-2 made no difference for sand, Method-2 was adopted for convenience While sand and clay specimens behaved similarly under the maximum compressive pressure, the strain at failure for the clay samples (8%) was higher than that of the sand (6.5%) 4.2 Curing method and duration evaluation To study the curing procedure and their overall gained strength, sand and clay specimens were soaked in water for various durations and different scenarios The reason for evaluating water soaking was the triggering role of water in the polymerization process as previously discussed in Eqs (1) and (2) When clay samples were soaked in water they only kept a fraction of their strength after 48 h Alternatively, when the specimens were cured in a humid environment for a total of days, similar to what was suggested by Gilazghi et al (2016) instead of being soaked, significant improvements were observed in their performance under the UC test Conversely, the humid environment did not result in any salient improvements on sand specimens A comparison of all of the above-mentioned cases is illustrated in Fig 11 The term “Soaked” refers to days of curing in air followed by days of curing in water, while “Unsoaked” means the specimens were only cured in air and no water curing was performed For sand, Rezaeimalek et al (2016) found that a combination of air and soaking curing yielded the maximum strength, suggesting that a total curing of days including days of air curing followed by days of soaking in water as the minimum curing duration Fig 12 shows that days of water soaking the specimens after days of air curing resulted in the maximum UCS and extending the curing beyond days did not result in salient improvement of UCS for sand specimens Fig e Mixture of sulfate-rich clay with water and polymer (a) Dry soil mixing (Method-1) (b) Wet soil mixing (Method-2) for sulfate-rich clay Fig 10 e UCS results for different mixing methods (a) Sand (b) Clay stabilized with the polymer Please cite this article in press as: Rezaeimalek, S., et al., Comparison of short-term and long-term performances for polymerstabilized sand and clay, Journal of Traffic and Transportation Engineering (English Edition) (2017), http://dx.doi.org/10.1016/ j.jtte.2017.01.003 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 JTTE115_proof ■ February 2017 ■ 8/11 8 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 J Traffic Transp Eng (Engl Ed.) 2017; x (x): 1e11 4.3 Short-term and long-term performances of stabilized sand Fig 11 e Comparison of performance for polymer stabilized specimens Fig 12 e Effect of curing time on UCS of Polymer M stabilized sulfate-rich clay and sand Fig 13 e UC test results for optimal stabilization of sand When the curing procedure and the duration were determined, a number of polymer, water combination ratios were assessed, and then the strongest specimens were selected for further evaluation For sand, the specimens with a polymer to water ratio of 2:1 provided the strongest case The strongest stabilized sand specimens showed 4931 kPa of UCS and strain at the failure was 6.45%, approximately days after completion of curing that allowed the samples to dry at laboratory temperature Fig 13 illustrates the results Consoli et al (2012) showed that for the uniform sand which was approximately similar to the one used for the present study and stabilized using cement, a linear relationship between the cement content and the UCS could be observed Their work indicated a UCS in the order of 500e1000 kPa when 7% cement was used for stabilization If the linear relationship between the cement content and UCS is extrapolated to 15%e20% polymer content which is the amount used for the present study, a UCS in the order of 2142e2857 kPa should be anticipated, which is approximately half of the UCS achieved with Polymer M, suggesting the advantageous outcome of the stabilization process when compared to traditional approaches Fig 14 shows the results of accelerated UV-B radiation Fig 14(a) illustrates the specimens prior to radiation and Fig 14(b) illustrates the specimens after 667 h of radiation Evidently, the stabilized specimens significantly transformed in color from light to dark brown after exposure, although no evidence of cracks or damage was observed This color change confirms the yellowing phenomena Compared to photos taken at 667 h of radiation, the color of the stabilized specimens darkened further However, the color change was applicable only to the surface of the specimens and the interior sections of the samples stayed similar to those prior to radiation as shown in Fig 14(c) When tested for their UCS, the specimens did not show salient strength loss due to UV radiation as a result of polymer degradation The specimens, however, were more brittle than the nonweathered specimens, as shown in Fig 15 The UV-B radiated specimens sustained 4.08% of strain at the peak stress, whereas the non-weathered samples showed 6.45% strain at the peak stress, indicating an increase in brittleness after exposure to radiation Fig 16 summarizes the results of the UC test on sand specimens after freeze-thaw cycles The UCS remained Fig 14 e Polymer M specimens (a) Prior to radiation (b) After 667 h of radiation (c) Tested for UCS after 2000 h of radiation Please cite this article in press as: Rezaeimalek, S., et al., Comparison of short-term and long-term performances for polymerstabilized sand and clay, Journal of Traffic and Transportation Engineering (English Edition) (2017), http://dx.doi.org/10.1016/ j.jtte.2017.01.003 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 JTTE115_proof ■ February 2017 ■ 9/11 J Traffic Transp Eng (Engl Ed.) 2017; x (x): 1e11 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 unchanged However, the specimens became more brittle as the aged specimens failed at a much lower strain compared with unaged specimens Fig 17 summarizes the UC test results after wet-dry cycles The stabilized specimens did not show a significant loss of strength after wet-dry cycles The peak stress sustained by these specimens was 3933 kPa, which was approximately 85% of the peak compressive stress sustained by unweathered specimens and the final UC test curve was close to what was observed for non-weathered specimens strongest in terms of UCS were observed when the water content of the soils was optimum, and the amount of polymer was equal to the volume of voids minus the volume of optimum water content (Exhibit A, Fig 18) The maximum UCS reached was 3422 kPa, with approximately 8.51% of strain at failure for non-sulfated and sulfated cases, respectively A close yet more ductile alternative to this batch was when the volume of the added liquid (polymer and water) was equal to the volume of the voids (Exhibit B) with a polymer to water ratio of 2:1 for the stabilized samples For this latter alternative, the clay samples yielded 2464 kPa 4.4 Short-term and long-term performances of stabilized sulfate-rich clay As for clay, the results suggested a different pattern than sand For freshly cured specimens (short-term results), the Fig 18 e UC test results for optimal stabilization of clay Fig 15 e UC test results after 2000 h of UV radiation Fig 19 e Free swelling test results for unstabilized and polymerized sulfate-rich clay Fig 16 e UC test results after 24 freeze-thaw cycles Fig 17 e UC test results after 24 wet-dry cycles Fig 20 e Short-term and long-term swelling of unstabilized and polymerized sulfate-rich clay Please cite this article in press as: Rezaeimalek, S., et al., Comparison of short-term and long-term performances for polymerstabilized sand and clay, Journal of Traffic and Transportation Engineering (English Edition) (2017), http://dx.doi.org/10.1016/ j.jtte.2017.01.003 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 JTTE115_proof ■ February 2017 ■ 10/11 10 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 J Traffic Transp Eng (Engl Ed.) 2017; x (x): 1e11 of compressive strength with 7.54% of strain at failure Therefore, selecting the optimal case between these two alternatives will depend on the project specifications and other considerations such as economic concerns, since the higher polymer ratio will result in added overall cost In addition, benchmarking the findings of the present study with the one conducted by Horpibulsuk et al (2005) where the performance of cement-clay admixtures was investigated showed that when 8%e33% of cement was used to stabilize soft clay, the axial stress varied between approximately 400 kPae2100 kPa with the strain ranging approximately from 1% to 2.5% Polymer-stabilized clay specimens provided much higher short-term UCS (approximately 62% for Exhibit A and approximately 17% for Exhibit B, respectively) and strain at failure (approximately 240% for Exhibit A and 200% for Exhibit B, respectively) To evaluate the long-term performance of the clay specimens, batches made following Exhibit A and Exhibit B methods were soaked in water for a specific period of time Although the specimens significantly lost their strength due to water susceptibility, the remaining strength was still considerable as shown in Fig 18 Specimens from Exhibit A and B sustained maximum compressive pressures of 1082 and 527 kPa, respectively and their strain at failure were 8.89% and 6.67%, respectively Fig 19 summarizes the results of the swell test for clay samples As shown in Fig 12, the curing of the stabilized clay samples is complete within days Thus, the swelling occurring within days is taken as the short-term swelling The swelling occurring after curing is considered as the long-term swelling Overall, the unstabilized sulfate-rich clay experienced more than 20% of its swelling within the first days of the test With the addition of 10% polymer, the swelling was reduced to a negligible 2%, as shown in Fig 20 Conclusions This study was conducted using a liquid polymer soil stabilizer from the generic family of methylene diphenyl diisocyanate Therefore, the results may be generalized to products from the same generic family
In the case of sulfate-rich high plasticity clay, for salient improvements the mixing method should be followed by thoroughly mixing water with the soil prior to adding the polymer (mixing Method-2) However, this is not the case for sand specimens The difference was insignificant in the resultant UCS of sand specimens made following Method-1 and Method-2
When subjected to UV radiation the tested specimens became more brittle and yellowing was evident on their surface with no salient measured strength loss More variations should be expected for longer periods of exposure However, it should be noted that this length of exposure may not be observed in real field conditions
The stabilized sand specimens showcased acceptable longterm performance after repetitive cycles of freeze-thaw and wet-dry Overall, the aged specimens performed similarly to unweathered samples
The liquid polymer soil stabilizer is potentially highly effective in mitigating soil swelling By adding 10% polymer, the swelling was insignificant For the stabilized sample, the majority of the swelling occurred during its long-term service and only a small fraction occurred during construction, i.e., curing Acknowledgments The authors would like to greatly acknowledge Alchemy Polymers Company, LLC for their financial support Q2 references Acar, Y.B., El-Tahir, A.E., 1986 Low strain dynamic properties of artificially cemented sand Journal of Geotechnical Engineering 112 (11), 1001e1015 Ajalloeian, R., Matinmanesh, H., Abtahi, S., et al., 2013 Effect of polyvinyl acetate grout injection on geotechnical properties of fine sand Geomechanics and Geoengineering (2), 86e96 Ajayi, M.A., Grissom, W.A., Smith, L.S., et al., 1991 Epoxy-resinbased chemical stabilization of a fine, poorly graded soil system Transportation Research Record 1295, 95e108 Al-Khanbashi, A., Abdalla, S., 2006 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triaxial compression Journal of Geotechnical and Geoenvironmental Engineering 127 (10), 404e411 Sebesta, S., Scullion, T., 2004 Effectiveness of Minimizing Reflective Cracking in Cement-treated Bases by Microcracking Research report, FHWA/TX-05/0-4502-1 Texas Transportation Institute, College Station Wang, L., Roy, A., Tittsworth, R., et al., 2004 Mineralogy of soil susceptible to sulfate attack after stabilization Journal of Materials In Civil Engineering 16 (4), 375e382 Zandieh, A.R., Yasrobi, S.S., 2007 Study of factors affecting the compressive strength of sandy soil stabilized with polymer Geotechnical and Geological Engineering 28 (2), 139e145 Sepehr Rezaeimalek is currently a PhD candidate at the Department of Civil and Environmental Engineering of the University of Texas at San Antonio (UTSA) Since joining UTSA in 2013, Mr Rezaeimalek has made significant contributions to the Geotechnical Engineering Research Group by defining and conducting innovative research His area of expertise includes numerical modeling in geotechnical engineering, experimental geotechnics, ground improvement, construction material testing and foundation engineering His primary PhD research subject focuses on assessing the potentials of liquid polymer soil stabilizers on improving the 11 engineering properties and mitigating the swelling potential of various problematic soils Abdolreza Nasouri is a PhD Student majored in civil and environmental engineering at the University of Texas at San Antonio (UTSA) Nasouri obtained his Bachelor of Science Degree in civil engineering from Islamic Azad University Central Tehran Branch (IAUCTB) During his studies at IAUCTB, he was involved in several lab projects which honed his skills in decision making and planning Currently, Nasouri, as a PhD student, has been developing a model for simulating the hot dipping galvanizing process of steel poles employing complex thermal-displacement technique in finite element analysis Simultaneously, he has been working on simulation of fracture growth induced by thermal shocks in wedge opening loading specimens (WOL) These computational capabilities are essential to perform the bridge, high mast illumination pole, and wind turbine reliability analysis Jie Huang, PhD, P.E., is currently an associate professor in geotechnical engineering at the University of Texas at San Antonio (UTSA) He received his PhD in December 2007 and joined UTSA in 2010 Dr Huang research interests cover a board range of topic in geotechnical engineering, including soil improvement, geosynthetics, deep and shallow foundations, earth retaining structures, expansive soils, etc Now he serves as a committee member of two geo-institute technical committees, soil improvement committee and geosynthetics committee Sazzad Bin-Shafique, PhD, P.E., is a professor of geotechnical engineering at the Department of Civil and Environmental Engineering of the University of Texas at San Antonio (UTSA) and an alumni of the University of Wisconsin at Madison His areas of expertise include beneficial use of wastes and industrial by-products, solidification and stabilization of soil and waste, waste geotechnics, remediation geotechnics, leachability testing and groundwater & contaminant transport modeling Simon T Gilazghi was born in 1984 in Eritrea He attended his studies up to undergraduate level in Eritrea, and graduated with a Bachelor of Science Degree in civil engineering from the University of Asmara, Eritrea, in 2008 He attended graduate study at the University of Texas in San Antonio, and graduated with a Master of Science Degree in civil engineering in December 2014dgeotechnical specialty Currently, he is working with the Texas Department of TransportationdBrazoria Countyd as an engineering assistant Please cite this article in press as: Rezaeimalek, S., et al., Comparison of short-term and long-term performances for polymerstabilized sand and clay, Journal of Traffic and Transportation Engineering (English Edition) (2017), http://dx.doi.org/10.1016/ j.jtte.2017.01.003 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 ... (a) Sand (b) Clay stabilized with the polymer Please cite this article in press as: Rezaeimalek, S., et al., Comparison of short- term and long -term performances for polymerstabilized sand and clay, ... 1e11 4.3 Short- term and long -term performances of stabilized sand Fig 11 e Comparison of performance for polymer stabilized specimens Fig 12 e Effect of curing time on UCS of Polymer M stabilized. .. Method-2 for clay Please cite this article in press as: Rezaeimalek, S., et al., Comparison of short- term and long -term performances for polymerstabilized sand and clay, Journal of Traffic and Transportation