Performance of alkali-activated binder-treated jute

International Journal of Geotechnical Engineering

ISSN: 1938-6362 (Print) 1939-7879 (Online) Journal homepage: http://www.tandfonline.com/loi/yjge20

Performance of alkali-activated binder-treated jute geotextile as reinforcement for subgrade stabilization Shashank Gupta, Anasua GuhaRay, Arkamitra Kar & V. P. Komaravolu To cite this article: Shashank Gupta, Anasua GuhaRay, Arkamitra Kar & V. P. Komaravolu (2018): Performance of alkali-activated binder-treated jute geotextile as reinforcement for subgrade stabilization, International Journal of Geotechnical Engineering, DOI: 10.1080/19386362.2018.1464272 To link to this article: https://doi.org/10.1080/19386362.2018.1464272

Published online: 23 Apr 2018.

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International Journal of Geotechnical Engineering, 2018 https://doi.org/10.1080/19386362.2018.1464272

Performance of alkali-activated binder-treated jute geotextile as reinforcement for subgrade stabilization Shashank Gupta , Anasua GuhaRay , Arkamitra Kar

and V. P. Komaravolu

Department of Civil Engineering, BITS-Pilani Hyderabad Campus, Secunderabad, India

ABSTRACT

Geotextiles are widely used for reinforcing soil, improving drainage, controlling soil erosion and embankment construction. Existing research recommends the improvement of soil in an economic and eco-friendly manner using jute geotextiles. However, jute fibres have the tendency to degrade in the acidic and alkaline environment of the soil. Jute geotextile treated with antimicrobial chemicals are used as a substitute for manmade geosynthetics, as it improves the life expectancy of jute. But these chemicals are expensive and are a potential source of leaching. The present study aims to develop a fly ash-based treatment procedure that is economic, ecologically safe as well as significantly improves the engineering and strength properties of jute as a geotextile. There is an increasing interest in the application of alkaliactivated binders (AAB) in engineering practices. It is produced by the reaction between an aluminosilicate precursor (primarily Class F fly ash and/or slag) and alkali activator solution. AAB-treated jute geotextile shows that the load-bearing capacity increases by 27% approximately. The vertical permeability of sand does not vary significantly with the inclusion of AAB-treated jute. The tensile strength of jute also exhibits a marked improvement following the treatment. Thus, the technique proposed in this study has the potential for implementation in practical applications.

Introduction Over the last few decades, geotextiles have gained a lot of popularity in engineering applications due to their ability to filter, reinforce, drain and separate soil. Presently, geotextiles in the form of manmade synthetics are used extensively due to outstanding mechanical properties (Bouazza, Freund, and Nahlawi 2006; Restall et al. 2002; Shtykov, Blazhko, and Ponomarev 2017). However, these synthetic geotextiles remains underground for a very long period of time and become a nuisance to the environment. Therefore, the mechanical properties and performance properties of natural geotextiles such as jute, coir and flax are being explored by many researchers (Lekha 2004; Rawal and Anandjiwala 2007; Sanyal 2017; Subaida, Chandrakaran, and Sankar 2009). Existing research reported the application of jute geotextile (JGT) in several civil construction. Datta (2007) summarized various case studies, in which jute geotextile was used to control soil erosion, improve subgrade for road construction and protect the river and canal banks. However, the application of JGT was limited as it degrades rapidly under the soil. Depending on the placement and type of soil, JGT bio-degrade within a year (Sanyal 2017). Hence, various chemical treatment processes were developed to improve the durability and mechanical properties of JGT. Treatment with chemicals like sodium hydroxide and hydrogen peroxide reduced the hemicellulose and lignin content of jute; hence, the breaking tenacity was improved and the regain of moisture by the fibres was slightly reduced (Saha et al. 2010;

CONTACT Anasua GuhaRay

[email protected]

© 2018 Informa UK Limited, trading as Taylor & Francis Group

ARTICLE HISTORY

Received 27 February 2018 Accepted 9 April 2018 KEYWORDS

Jute geotextile; alkaliactivated binder; shear strength; bearing capacity; sustainability

Wang et al. 2009). In another technique, the chemical structure of jute was altered by acetylation of jute at higher temperatures or in presence of catalysts due to the replacement of the hydroxyl groups of cellulose by the ester group. This chemical change in jute increased the hydrophobicity of jute, thereby, reduced its water intake and significantly improved its durability. However, the H-bonding was weakened by replacement of hydroxyl groups and hence the thermal stability and breaking strength of jute fibre were reduced (Andersson and Tillman 1989; Teli and Valia 2013). Saha et al. (2012) reported that the resistance of jute to biological degradation was improved when it was treated with a mixture of plant oils in presence of sodium hydroxide and formaldehyde. It was inferred from the study that a transesterification reaction took place as the hydroxyl group was replaced by oleic and stearic acid. Sanyal and Chakraborty (1994) concluded that bitumen-treated JGT was used for bank protection and it had been observed that the treated JGT retained appreciable tensile strength even after 1.5 years. Chattopadhyay and Chakravarty (2009) performed the consolidation tests on silty sand reinforced with bitumen-treated JGT. It was observed that the drainage properties of soil improved due to the inclusion of a layer of treated geotextile. On a separate note, a noticeable improvement in the durability and 80% higher tensile strength were observed when jute fabric was treated with N-vinyl pyrrolidone and ethyl hexyl acrylate in presence of plasticizers and an initiator (Uddin, Khan, and Ali

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Table 1. Properties of jute geotextile. Properties Thickness Mass density Tensile strength Aperture

Table 2. Amount of AAB required treating per m2 of JGT. Values 0.69 mm 260.17 gm/m2 10.6 kN/m 1.22 × 1.63 mm

(1997)). Basu et al. (2009) performed CBR tests on the road constructed with jute-polypropylene (PP) composite and observed that the CBR value of geotextile-reinforced road was 76.7% more than the unreinforced section of road after 18 months of construction. The subgrade reinforced with jute-PP composite also had less rutting compared to the unreinforced portion. The past research work shows that the existing chemical treatment methods require either expensive chemicals or sophisticated procedure that is impractical to implement in the field construction. Thus, the present study aims to develop a fly ashbased treatment procedure that is easy to execute as well as significantly improves the performance of jute as a geotextile. The treatment solution used in the present study is alkali-activated binder (AAB) that is produced by the reaction between an aluminosilicate precursor and alkali activator solution. The precursors are usually Class F fly ash and/or slag and the alkali activator solution is a mixture of sodium silicate and sodium hydroxide (Kar et al. 2014). The properties of alkali-activated binders are similar to cement, however, the reaction mechanism is different for both of them. The strength gain in cement and AAB are due to hydration and silica polymerization, respectively (Provis and Van Deventer 2009). Fly ash is the major waste product of thermal power plants and it is generally disposed of in the landfills. Moreover, many challenges and limitations were faced for reclamation and revegetation of these landfills (Haynes 2009). Therefore, the utilization of fly ash for treatment could avoid its disposal as solid waste as well as can improve the properties of jute as a geotextile. The present study primarily aims to determine the change in chemical and strength properties of jute due to AAB coating and associate them with the performance of treated jute geotextile in the soil. The amount of water is varied to prepare the AAB solutions having different water to solid ratios (w/s) of 0.35, 0.40 and 0.45 and the optimum is proposed. The tensile and shear strength and bearing capacity of soil reinforced with AAB-treated jute are carried out. A numerical study is also performed to validate the experimental results. The study expects to improve the strength and durability characteristics of JGT by environmental friendly and economically viable treatment procedure.

Materials Jute and treatment mix Commercially available jute (Corchorus olitorius) hessian cloth is used for this study. The jute brought is available in a roll of 0.91 m (1 yd) width and 30 m length. The properties of jute geotextile are provided in Table 1. The sodium hydroxide pellets and sodium silicate solution are obtained from Hychem chemicals. The purity of sodium hydroxide pellets is 99%. The sodium silicate solution is composed of 55.9% water, 29.4% SiO2 and 14.7% Na2O.

Water/Sol- AAB applied Fly ash id ratio (kg/m2) (kg/m2) 0.35 3.44 2.18 0.40 3.07 1.87 0.45 2.75 1.62

NaOH (kg/m2) 0.058 0.049 0.043

Sodium silicate (kg/m2) 0.706 0.606 0.526

Water (kg/m2) 0.498 0.537 0.5611

The JGT is treated with a coating of AAB produced by the reaction of fly ash using an activating solution containing sodium silicate, sodium hydroxide and water. The mass ratio of fly ash to sodium hydroxide to sodium silicate is 400:10.57:129.43 (Kar 2013). The amount of water is varied to prepare the solutions having different water to solid ratios (w/s) of 0.35, 0.40 and 0.45. The w/s ratio for AAB mix proportion is selected in order to achieve the optimum combination of desirable workability and load-bearing capacity (Rangan 2008). The activator solution is prepared by mixing sodium silicate, sodium hydroxide and water till a clear blend was obtained. The addition of sodium hydroxide to sodium silicate is exothermic. Hence, the activator solution is prepared at least 24 h before using it to react with the fly ash in order to dissipate any residual heat that can hasten the alkali activation of fly ash and lead to a flash set. If the alkali-activated fly ash hardens too soon, it will be impossible to use it to coat the JGT. After the 24-h wait period, the prepared activator solution is then mixed with fly ash. The quantities of raw materials required for the treatment of a unit area of JGT are provided in Table 2. The rheological properties of alkali-activated fly ash resemble those of hydrated Portland cement. Hence, setting and hardening start as soon as the alkali solution is added to fly ash. Therefore, the mix is applied while it is still workable in order to avoid the wastage due to hardening. The treatment mix is then applied using a paintbrush such that the treatment coating covers the complete surface area of jute geotextile. The JGT covered with the AAB coating is then stored at 40 °C in a humidity-controlled environment for 24 h. This is followed by a further 6 days of curing the AAB coated JGT at ambient temperature to make it suitable for practical application in ground improvement. This 7-day period enables the AAB to harden and gain sufficient strength to withstand externally applied loads. Figure 1 shows the untreated and 0.40 w/s AAB-treated jute. Sand Locally available river sand, collected from Godavari River basin, Telangana, India is used in the present study. The sand is classified as poorly graded sand (SP) according to Unified Soil Classification System. The maximum and minimum dry densities are measured conforming IS 2720: 1983 Part 14 (1983). A constant relative density of 40% is maintained throughout the experimental procedure to stimulate medium dense sand condition. The properties of the cohesionless soil used are presented in Table 3.

Experimental methodology Chemical characterization X-ray diffraction (XRD) X-ray Diffraction analyses are performed using a RIGAKU Ultime IV diffractometer to identify the minerals present in the

INTERNATIONAL JOURNAL OF GEOTECHNICAL ENGINEERING

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Figure 1. Untreated and treated jute geotextile.

Table 3. Properties of sand. Properties Coefficient of uniformity (Cu) Coefficient of curvature (Cc) Classification Internal angle of friction (φ) Maximum void ratio Minimum void ratio

Values 2.5 0.9 SP 26.1° 0.637 0.411

untreated and treated jute geotextile. The powdered samples are examined through CuKα rays generated at 40 mA and 40 kV. The operating 2θ range is from 0o to 100o with a step of 0.02o 2θ and integrated at the rate of 2 s per step. Fourier-transform infra-red (FTIR) spectroscopy Fourier-transform infrared (FTIR) spectroscopy of the untreated and treated fibres are collected using a JASCO FTIR 4200 set-up. The geotextile samples are shredded to powder-like fineness. The powder is then dried in an oven at 105 °C for 1 h to remove any residual moisture and then mixed with dried KBr powder to prepare pellets. The spectral range is specified as 4000–400 cm−1 for all the samples. The FTIR spectra for untreated and treated jute samples are performed to study the change in the formation of chemical bonds following the treatment by analysing the transmittance spectra. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) The SEM-EDS study is conducted using the JSM-7600F, a thermal Field Emission Scanning Electron Microscope (FE-SEM), provided by JEOL Ltd. The jute geotextiles used in the study are mostly composed of cellulose, hemicellulose. In case of treated jute geotextiles, there is the additional presence of fly ash. Hence, the possibility of the presence of elements having atomic numbers higher than that of iron is rare in this case. However, if the raw materials of treatment solution or jute are collected from an unknown source, a thorough investigation has to be carried out. In that case, 20 kV might be used as excitation voltage. However, the high excitation voltage would cause an electron cloud, hence the obtained image would be blurred. The commonly used range for alkali-activated binder is 5–15 kV (Kar 2013). Hence, the

excitation voltage for this study is kept as 10 kV. The images of different magnification are captured, at three different locations for each sample. At each location, three different regions are chosen at random and further in each of these regions, five different points are studied. The EDS spectra are provided by INCA software system. For the adequate working of EDS analyzer, the probe current and working distance are maintained at 65.4–67.0 μA and 8–15 mm, respectively. Prior to analysis, the geotextiles fibres are dried at 105 °C for 24 h to remove all the internal moisture. To make the fibres electrically conductive, a 15-nm layer of platinum is coated on the jute fibres in argon gas atmosphere. Thermogravimetric analysis (TGA) Differential thermogravimetric analysis (TGA) is carried out through a SHIMADZU/DTG-60 set-up to evaluate the thermal stability of untreated and treated jute. The geotextile samples weighing between 4 and 10 mg are kept on a platinum pan in a nitrogen-rich environment. The samples are heated gradually from 30 to 950 °C, which is in agreement with the decomposing range of jute (Yang et al. 2007). The rate of temperature increment is kept as 10 °C/min. to assure uniform heating. Geotechnical characterization Permeability Permeability is a very important parameter for predicting the drainage conditions of the subsoil. Material with very less permeability will possess the disadvantage of building up of excess pore water pressure. The vertical permeability of reinforced sand is determined by the falling head permeability test (ASTM D2434-8 (2006), 2006; IS 2720-1986 Part 17, 1986). A steel cylindrical mould of diameter 100 mm and depth 115 mm is used to enclose the soil. The reinforcement layer is placed at the depth of 50 mm from top such that it perfectly covers the horizontal surface area. The porous stone is placed at the top of the cylindrical mould for uniform distribution of water over the horizontal cross-section of the mould. The known weight of sand is filled by layer such that the relative density of 40% is maintained. The tests are repeated 20 times for 3 samples of each type of reinforcement to abate the error and the mean values are considered as the final vertical permeability of the reinforced soil.

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Tensile strength The tensile strength of narrow strip of geotextile is determined by an MCS universal testing machine (UTM). The width and the gauge length of a tested sample are considered as 50 mm and 200 mm, respectively. The grab length is kept as 25 mm. The tensile loading is maintained at a deformation rate of 100 mm/ min following the ISO 13934-1:1999 (1999) standards to determine narrow strip tensile strength. Ten specimens of each type of geotextile are tested in the machine direction and the average of tensile strength is reported for each sample. Shear strength A HEICO automatic large-size direct shear apparatus is used to study the interface properties of soil and reinforcement. The experiment is carried out according to the ASTM D5321/ D5321M-17 (2017). The upper shear box of size 300 mm length, 300 mm width and 150 mm depth is filled with sand and the geotextile is fixed at the top of the lower shear box. The set of gears, powered by an electric motor, controls the motion of the lower shear box. The thick rigid plate is placed at the top of the upper shear box to uniformly distribute the normal load. The horizontal and vertical loading capacities of apparatus are 100 and 100 kN, respectively. The shearing stage of the test is conducted under three normal stress levels of 1.25, 1.75 and 2.25 kg/ cm2. The horizontal and vertical displacements are measured by linear variable differential transformers (LVDT) of 100 mm capacities. The shear rate is kept at 1.2617 mm/min. Bearing capacity The relative study of the bearing capacity of sandy soil reinforced with treated and untreated geotextile is carried out in a model plate load set-up. According to ASTM D1195 (2015), the tank dimension should be five times the width of the foundation to depreciate scaling issues. The tests are conducted in a steel tank of size 1.2 m length, 0.91 m width and 0.91 m depth. The loading set-up is fabricated of steel columns and channels that support the hydraulic loading cell of 150 kN capacity. The loading cell transfers the load to the soil through the square steel plate of sides 200 mm and 25 mm thickness. The settlement of the plate is measured by the four LVDTs placed at the radial distance of 100 mm from the centre of the load cell. Figure 2 shows the schematic diagram of the plate load set-up. The sand is filled by layer by sand pouring method and uniformly compacted to a relative density of 40%. Sand was poured from different heights into the tank by means of a funnel and the optimum height of fall corresponding to 40% relative density is determined. The layer of geotextile is placed at a depth of 100 mm. As per IS: 1888 (1982), the strain was maintained at a constant rate of 0.02 mm/min.

Results and discussions Chemical characterization XRD Figure 3 presents the X-ray diffraction patterns of untreated as well as treated jute samples. The peaks at 15.7°, 22.3° and 34.5° (denoted by ‘J’) visible in the raw jute diffractogram are consistent with the findings of Wang et al. (2009). The diffractogram for treated jute indicates the presence of quartz (SiO2), analcime

Figure 2. Schematic diagram of model plate load.

(NaAlSi2O6.H2O), mullite (Al6Si2O13) and hydroxy sodalite (Na6(Si6Al6O24).8H2O) which are recognized by their characteristic peaks. These minerals are characteristic to the hardened AAB paste (Kar 2013). Moreover, the peaks characteristic to jute geotextiles are present in the diffractograms for all the treated jute samples This indicates that jute has not lost its mineralogical characteristics during treatment. These findings show that a hardened paste of AAB has formed a layer over the jute fibres following the treatment of the jute with the AAB coating. This statement is further supported by SEM-EDS results as shown below. On a separate note, with increasing water to cement ratio in treatment solution, the amorphous content was observed to be more dominant. This happens due to the production of the greater quantity of sodium aluminosilicate hydrate matrix in the alkali-activated fly ash as a result of the greater water content. FTIR Figure 4 presents the FTIR spectra for the untreated jute as well as the AAB treated jute. The peaks at 3434, 3463, 3460 and 3467 cm−1 in case of untreated, 0.35 w/s AAB treated, 0.40 w/s AAB treated and 0.45 w/s AAB-treated jute, respectively, represent the O–H stretching vibrations. In case of untreated jute, the peaks at 2988, 2921 and 1381 cm−1 represent the C–H stretching vibrations. C–O–C stretching vibrations are observed at 1035 and 900 cm−1. These observations are consistent with the FTIR spectra for typical cellulose (Wang et al. 2009). The peaks at 1730 and 1428 cm−1 represent the C–O bending and symmetric –CH2 bending vibration (Abderrahim et al. 2015). The bands at 1700 and 1644 cm−1 correspond to the acetyl groups and C=O bonds, characteristic of hemicellulose (Abdulkhani et al. 2013). A lignin peak is located at the 1542 cm−1 band due to C=C in-plane aromatic vibrations (Neto et al. 2013). The disappearance of the transmittance peak from 2988 to 1700 cm−1 and 1490 to 1214 cm−1 indicates that the cellulose backbone and the hemicellulose could have partially been removed due to the AAB treatment. The peaks at 1024, 1034 and 1037.5 cm−1 in 0.35 w/s AAB treated, 0.40 w/s AAB treated and 0.45 w/s AAB-treated jute, respectively, correspond to the primary siloxane unit (Si–O–Si) of the AAB system (Kar 2013). Increase in w/s ratio in the AAB mixes led


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along the longitudinal section of the jute fibres in each case. The surface of the raw jute fibre is covered by impurities like hemicellulose, lignin, pectin (Wang et al. 2009) (Figure 5a). The 0.35 w/s AAB-treated jute fibres show unevenly distributed cavities. This indicates that the fibre surface gets partially covered with a matrix of sodium aluminosilicate hydrate which is characterized by a vitreous network (Kar 2013). Additionally, there is some unreacted residue of fly ash, distinguished by the spherical particles (Figure 5(b)). As the w/s in the treatment mix increase, the extent of coating on the jute fibre increases. With increasing w/s ratio, there is a greater extent of reaction between fly ash and the alkali-activating solution. Hence, an increase in the proportion of the sodium aluminosilicate hydrate matrix and a consequent reduction in the unreacted fly ash residue are visible in Figure 5(c) and (d). EDS shows the weight per cent (Wt %) and atomic per cent (At %) of several elements in various samples. The predominance of C and O are observed in the untreated jute (Table 4). As this technique is unable to detect any element below Be in the periodic table, the presence of H is not seen. There are traces of Na and Si. Al and Fe are completely absent, as expected. In case of the treated jute specimens, the marked presence of Al and Si are noticed due to their abundance in fly ash. Increase in Na content is also noticed due to its substantial presence in the alkali-activating solution. The decrease in C-content in treated jute shows the dominance of AAB characteristics over jute properties to some extent. Since EDS scans the whole volume of the specimen and not just the surface, it cannot be inferred that AAB just adheres to the surface of the jute fibres and leads merely to changes in surface characteristics. The results provide indication towards the possible formation of a jute-AAB composite. These findings are corroborated by the results from tensile strength experiment. Figure 3. X- Ray diffractogram of untreated and treated jute samples (J = Jute, S = Hydoxy sodalite, M = Mullite, Q = Quartz, A = Analcine).

to the chemical shift observed in case of the Si–O–Si peaks. The respective peaks for treated jute samples at 774−1, 777 and 778 cm−1 correspond to the Al–OH stretching vibrations. The peaks at 520 cm−1 in case of 0.35 w/s AAB-treated jute represent Si–O–Al bending vibration. The peaks in treated jute samples at 483–469 cm−1 represent the Si–O in-plane bending vibration. The peak at the 849 cm−1 in 0.45 w/s AAB-treated jute represents the bending vibration of the Si–OH bond (Kar 2013). These peaks represent the aluminosilicate components of the AAB system. The transmittance peak corresponding to untreated jute is also observed to exist in case of treated jute samples. This indicates that the structure of cellulose is not completely damaged following the treatment. Moreover, transmittance peaks at 1644, 1647 and 1644 cm−1 in AAB-treated samples correspond to the acetyl groups and C=O bonds of hemicellulose. This shows that the jute did not lose its individual chemical characteristics completely after treatment. SEM/EDS The scanning electron micrographs at 2000× and 5000× magnifications along with the EDS results are presented in Figure 5(a) through 5(d). Several grooves are visible in the micrographs

TGA The thermogravimetric curves for untreated and treated jute geotextiles are presented in Figure 6. As the temperature increases to 950 °C, various components in the sample start to decompose leading to a loss in weights at certain characteristic temperatures. The TG curve for untreated jute sample indicates an initial loss in weight at 100 °C due to vaporization of the evaporable water. The thermal degradation of the biomass present in the untreated jute takes place in three phases – thermal decompositions of lignin, hemicellulose and cellulose. The weight loss in untreated jute from 270 to 310 °C is a consequence of the hemicellulose decomposition. Following the hemicellulose decomposition, a significant weight loss occurs within the temperature range of 323–392 °C due to cellulose decomposition and the process continues up to 525 °C. Lignin decomposition starts at the temperature range of 155–169 °C. However, lignin is composed of various aromatic branches that impart greater thermal stability than cellulose or hemicellulose. Thus, the decomposition of lignin takes place over a wide temperature range of 150–550 °C. Similar behaviour is observed by previous researchers and it is reported that the decomposition of cellulose, hemicellulose and lignin occurred in the range of 315–400 °C, 220–315 °C and 100–900 °C, respectively (Yang et al. 2007). Another study shows the range of cellulose and lignin decomposition to be 200–400 °C and 150–750 °C, respectively (Nunn et al. 1985).

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Figure 4. FTIR spectral pattern of (a) Untreated jute, (b) 0.35 w/s AAB-treated jute, (c) 0.40 w/s AAB-treated jute, (d) 0.45 w/s AAB-treated jute.

The jute geotextiles treated with various types of AAB exhibit combined characteristics of both jute and the hardened AAB pastes. Figure 6 shows that in case of the treated jute samples, there is a significant loss in weight up to 250 °C due to loss of evaporable water from the AAB. This is followed by a constant decrease in weight up to 700 °C due to the decomposition of lignin, hemicellulose and cellulose present in the jute. Moreover, the loss in weight is observed to be negligible after 700 °C. These findings are consistent with the results observed by Al Bakri et al. (2012). These observations indicate that the fabric lost it complete integrity after 700 °C and only the AAB coating has not undergone complete decomposition. Geotechnical characterization Permeability It is observed (Figure 7) that there is a slight decrease in the vertical permeability of sand reinforced with treated geotextile, however, the change is insignificant as the range of permeability for all reinforcement lies in the same order of 10−2 cm/s. The results infer that the inclusion of a layer of treated jute geotextile does not affect the permeability of sand adversely. The permeability results show the presence of voids in jute geotextile, following the treatment that allows the seepage of water. Tensile strength The tensile strength of jute is increased remarkably following the treatment with AAB solution. The tensile strength of untreated and treated jute samples are presented in Figure 8. The tensile

strength of treated jute sample is measured after 28 days following the application of solution as the AAB gained 95% of its compressive strength after 28 days (Kar 2013). It is also assured that the relative humidity for all the samples was kept constant while curing. The tensile strength of jute is increased by 37.7, 35.8 and 34% after treating it with AAB solution of 0.35, 0.40 and 0.45 w/s ratio, respectively. A possible explanation is that, following the treatment, the combined stiffness of jute-AAB composite is higher than the corresponding values for jute and AAB separately. It is also observed that the modulus of elasticity of jute and hardened AAB lies in the range of 20.4–24.2 GPa (Mwaikambo 2009) and 18.7–21.4 GPa (Kar 2013), respectively. Consequently, the treatment of jute with AAB leads to the increased stiffness that further led to improvement in the load-bearing capacity of jute. Shear properties The interface friction angles between sand and geotextile reinforcement are provided in the Figure 9. It is observed that the interface friction between untreated jute and sand was 39.1% higher than the internal angle of friction of sand. However, the treatment of jute significantly reduces the interface friction between sand and geotextile. The interface friction values between jute and sand dropped by 32.5, 38.3 and 45.7%, respectively, following the treatment with AAB solution of 0.35, 0.40, and 0.45 w/s ratios. On the contrary, cohesion developed between geotextile and sand following the treatment. It can be observed from Figure 10, that the cohesion between jute and reinforcement is commensurate to the water to solid ratio of the treatment solution.


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Figure 5 . SEM images of untreated jute at X2000 and X5000 magnification along with EDS analysis (a) Untreated jute, (b) 0.35 w/s AAB-treated jute, (c) 0.40 w/s AABtreated jute, (d) 0.45 w/s AAB-treated jute.

Bearing capacity The load-settlement curves of the only sand and sand reinforced with untreated as well as treated jute geotextile are shown in Figure 11. The inclusion of untreated and treated jute geotextile improves the load-bearing capacity and increases the

displacement corresponding to the ultimate load, however, the improvement is more pronounced in treated jute geotextile. The ultimate load of sand, reinforced with 0.35 w/s AAB-treated jute, is observed to be slightly higher than sand reinforced with other samples. The compressive strength conducted on

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Figure 5 . (Continued).

hardened AAB specimen shows that the lowest water to solid ratio leads to the highest load-bearing capacity (ASTM C39, 2001). The compressive strength of standard AAB concrete cube with w/s 0.40 and 0.45 are 48.3% and 63.9%, respectively, lower than that of corresponding cubes made of 0.35 w/s. The concave

portion followed by the peak in load–displacement graphs of all reinforced sand marks the rupture of geotextile. It can be observed that rupture of treated jute, mainly 0.35 w/s AABtreated jute, takes place at higher displacements compare to untreated jute geotextile. However, the residual load following


Table 4. EDS elemental analysis. Elements/ Samples C Wt % At % O Wt % At % Na Wt % At % Al Wt % At % Si Wt % At % Ca Wt % At % Fe Wt % At %

Untreated jute 59.05 65.99 40.06 33.6 0.22 0.13 0.0 0.0 0.37 0.18 0.31 0.1 0.0 0.0

0.35 w/s AAB-treated jute 9.55 14.92 47.96 56.29 6.98 5.7 7.49 5.21 25.04 16.74 1 0.47 1.99 0.67

0.40 w/s AAB-treated jute 8.29 13.41 43.36 52.67 6.47 5.47 10.74 7.74 28.09 19.43 1.66 0.8 1.39 0.48

0.45 w/s AAB-treated jute 13.29 19.5 49.72 54.78 22.38 17.16 2.26 1.47 9.84 6.18 0.93 0.41 1.59 0.5

Figure 6. Thermogravimetric curves of untreated and AAB-treated jute fibre.

Figure 7. Permeability of reinforced sand.

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the peak is highest for the sand-reinforced with untreated jute. Moreover, it can also be inferred from the Figure 11, that the inclusion of reinforcement at the depth of 10 cm did not alter the type of failure of bearing capacity as in all the cases the failure was a general shear failure. A non-dimensional quantity, the bearing capacity improvement factor (BCIF) is introduced to quantify the percentage of increase in bearing capacity values. It is defined as

BCIF =

BCrs BCnrs

where BCrs and BCnrs are the bearing capacities of reinforced and unreinforced soil, respectively.

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Figure 8. Tensile strength of untreated and AAB-treated jute fabric.

Figure 9. Interface friction angle between sand and reinforcement.

Figure 10. Cohesion between sand and reinforcement.


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Figure 11. Load-settlement curve of reinforced sand.

Figure 12. Meshing with (a) Soil (b) Soil reinforced with geotextile.

The BCIF for soil reinforced with untreated, 0.35 w/s AAB, 0.40 w/s AAB, and 0.45 w/s AAB-treated jute are 1.09, 1.27, 1.17 and 1.13, respectively. Hence, it can be observed that the BCIF value increases substantially on the addition of a 0.35 w/s AABtreated jute geotextile.

Numerical study The results obtained from the plate load test are simulated in commercially available software PLAXIS 2D 2016. A sand chamber of the same dimensions is modelled for the unreinforced

sand and the sand reinforced with untreated and different treated jute geotextile. To keep the similar boundary conditions as the model plate load, the bottom edge is kept fixed in both horizontal and vertical direction and the vertical side edge is kept fixed in horizontal direction. The vertical edge of the box is kept at the adequate distance from the edge of the footing so that the results are not affected by the side edges. The geostatic stress is kept as the initial condition for the numerical model. The stage construction is used in the modelling, where the displacement is applied step by step at the rate of 1 mm/sec on the footing.

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Figure 13. Deformed mesh for (a) Soil, (b) Soil reinforced with 0.40 w/s AAB-treated jute geotextile.

The vertical reaction load corresponding to each displacement is calculated. Footing In the present study, as the model is axisymmetric, the circular plate is used for the application of load. The base area of the circular plate is kept same as that of the square plate used in the experimental model plate load. Hence, the equivalent circular plate of diameter 225 mm and depth 25 mm has been used in the numerical model (Figure 12(a)-(b)). The plate is considered as rigid and rough. Soil and geotextile The elastic-perfectly plastic Mohr-Coulomb model is used to determine the behaviour of reinforced sand under the load. The model used in this study is consistent with existing literature on foundation design (Potts and Zdravković 2001). Twelve-point integrated, 15 noded triangular elements are used to model the soil. The modulus of elasticity is taken as 23,000 kPa which lies

within the typical range of the modulus of elasticity of sand (Bowles 1988). The Poisson’s ratio of sand was taken as 0.3 for all the simulations. Axial stiffness is the material property used as model input according to the requirement of PLAXIS 2D. The axial stiffness of geotextile is calculated from the load–displacement graph, obtained from the tensile test. The linear portion of the curve is considered to determine the initial axial stiffness of the treated jute geotextile. The values of axial stiffness of untreated, 0.35 w/s AAB treated, 0.40 w/s AAB treated and 0.45 w/s AAB-treated jute sample are 220, 373.3, 280 and 240 kN/m, respectively. Mesh The meshing or discretization in finite element model is a process of breaking the numerical model into smaller discrete pieces. In the present study, very fine global coarseness along with cluster and global refinement are used. The former refinement is used to intensify the number of elements in particular cluster and the latter refinement is used to globally increase the number of elements. To intensify the elements in the boundaries, line


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Figure 14. Comparison of load-settlement curves from numerical and experimental study.

refinement is done for the rigid plate. Additionally, the dense and smaller meshing is done below the plate as the stress–strain behaviour under the plate is of primary importance. The meshing details of the unreinforced and reinforced sand are provided in Figure 13(a) and (b), respectively.

Results The comparison of load–settlement curves from experimental and numerical methods is presented in Figure 14. The results obtained from the numerical study show a good resemblance with the results obtained from the experimental study. It is observed that the load–settlement curves are roughly same, irrespective of geotextile that is also observed from the experimental study. Hence, it may be concluded that the numerical study is in good agreement with the experimental study and so verifies the experimental results. The further study can be done on the basis of the present model.

Conclusion The natural geotextile are more suitable than synthetic geotextiles as they don’t leave carbon footprint and costs less. Moreover, the use of fly ash as treatment ingredient serves dual benefit of aiding environment by avoiding the disposal of fly ash and decreasing the cost associated to fly ash disposal. The current techniques of treating jute to improve its strength, durability and performance, require convoluted methods and expensive chemicals. Therefore, the present study devises a new technique of treating jute geotextile with AAB solution of different w/s ratio (0.35–0.45) in order

to improve the strength characteristics of soil. The important findings of the present study can be summarized as follows: • FTIR and TGA show that the characteristic of untreated jute is more or less reserved following the treatment with AAB coating. With increasing w/s ratio, the amorphous characteristic of sodium aluminate silicate hydrate from the alkali-activated fly ash becomes predominant as deduced from XRD results. • SEM/EDS results show the production of a greater quantity of sodium aluminosilicate hydrate at higher w/s ratios. These aluminosilicates contained a greater number of pores which leads to higher permeability. On the contrary, there is the relatively lesser quantity of this aluminosilicate at lower w/s ratio. • Consequently, this leads to lesser porosity and hence lower permeability and higher load-bearing capacity. These findings are later corroborated by permeability test and tensile strength test. • The surface roughness of jute fabric decreases to some extent as a consequence of AAB coating. Hence, the shear strength of treated jute decreases slightly. • The layer of AAB coating becomes gradually softer with increasing w/s ratio, thus reducing the flexibility of jute geotextile. This leads to a lower bearing capacity of jute fabric treated with higher w/s AAB ratio. A w/s ratio of 0.35 is found to be optimum for achieving maximum load-bearing capacity. • The numerical analysis shows a similar trend for bearing capacity; however, the peak load is more clearly defined in the experimental results compared to numerical study.

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Notations

References

The following symbols are used in this paper:

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A Analcime AAB Alkali-activated binder BCIF Bearing capacity improvement factor BCnrs Bearing capacities of unreinforced soil BCrs Bearing capacities of reinforced soil EDS Energy dispersive X-ray Spectroscopy FE-SEM Field Emission Scanning Electron Microscope FTIR Fourier-transform infrared spectroscopy J Jute LVDT Linear variable differential transformer M Mullite PP Polypropylene Q Quartz S Hydroxy sodalite SEM Scanning electron microscopy SP Poorly graded sand TGA Thermogravimetric analysis UTM Universal testing machine w/s Water to solid ratio XRD X-ray diffraction

Acknowledgements The authors are grateful to the Sophisticated Analytical Instruments Facility (SAIF) at IIT Bombay for their immense assistance in generating the images and spectra.

Disclosure statement No potential conflict of interest was reported by the authors.

Notes on contributors Shashank Gupta is a UG Student in the Department of Civil Engineering, BITS-Pilani Hyderabad Campus. His research interests are ground improvement with natural fibers and artificial intelligence. Anasua GuhaRay is an assistant professor in the Department of Civil Engineering, BITS-Pilani Hyderabad Campus. Her research interests are utilisation of waste materials for ground improvement, ground improvement with natural fibers, reliability application in geotechnical engineering, sensitivity analysis, earth retaining structures and dynamic behaviour of soil. Arkamitra Kar is an assistant professor in the Department of Civil Engineering, BITS-Pilani Hyderabad Campus. Her research interests are development of concrete with alkali-activated aluminosilicates, hydration chemistry of cementitious systems, lifecycle assessment of concrete with alkali-activated binder, bacterial inclusions in concrete, durability of concrete with alkali-activated binders. V.P. Komaravolu is a UG student in the Department of Civil Engineering, BITS-Pilani Hyderabad Campus. His research interest is ground improvement with natural fibers.

ORCID Shashank Gupta http://orcid.org/0000-0002-1192-9603 Anasua GuhaRay http://orcid.org/0000-0002-4973-0499 Arkamitra Kar http://orcid.org/0000-0002-7215-7491 V. P. Komaravolu http://orcid.org/0000-0003-4391-2299


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