lable at ScienceDirect

Geotextiles and Geomembranes xxx (2014) 1e3

Contents lists avai

Geotextiles and Geomembranes

journal homepage: www.elsevier .com/locate/geotexmem

A simple method to assess the wettability of nonwoven geotextiles

Abdelmalek Bouazza*

Department of Civil Engineering, Building 60, Monash University, Melbourne, Vic 3800, Australia

a r t i c l e i n f o

Article history:Received 12 January 2014Received in revised form6 April 2014Accepted 7 April 2014Available online xxx

Keywords:Capillary riseNonwoven geotextilesPolyester

* Tel.: þ61 3 9905 4956; fax: þ61 3 9905 4944.E-mail address: Malek.Bouazza@monash.edu.

http://dx.doi.org/10.1016/j.geotexmem.2014.04.0040266-1144/� 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: BouazGeomembranes (2014), http://dx.doi.org/10

a b s t r a c t

This paper presents a simple test method and analysis based on capillary rise in porous media to assessthe wettability of nonwoven geotextiles. The apparent opening pore size and porosity of the nonwovengeotextiles and their fibres’ surface condition were found to play a significant role in the extent of thewater capillary rise in the geotextiles. Prediction of the maximum capillary rise using a theoreticalcapillary radius compared well with the measured test results. The methodology presented in this papershould help assess wetting of geotextiles in short period of time and less extensive laboratory testing.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction phenomenon can be simulated experimentally by bringing one side

Pre-treatment and finishing of geotextiles are commonly con-ducted by various processes to change the surface condition of thegeotextile fibres to improve their wettability. Ease of wettability isvery important in applications where geotextiles are embedded insoils under unsaturated conditions since they can influencesignificantly the movement of water and give rise to a redistribu-tion of the water content profile (Bouazza, 2004; Iryo and Rowe,2004, 2005; Bouazza et al., 2006b; Nahlawi et al., 2007; Bathurstet al., 2009; Zornberg et al., 2010; Bouazza et al., 2013).

Various methods are currently being used to modify or changethe fibres surface properties. Such methods include chemical wetoxidation (Zhao et al., 2006) or plasma treatment (Zhao et al., 2006;Jeon and Bouazza, 2007; Jeon et al., 2008; Singh and Bouazza, 2013).Chemical wet oxidation is commonly applied by geotextile manu-facturers to alter the surface condition of the geotextile fibres inorder to change their wettability and adhesion properties. Wetta-bility of geotextile polymers is usually attained by adding to thefabric surface a surfactant solution to make them hydrophilic. Thispaper presents a simple testmethod and analysis based on capillaryrise in porous media to assess the wettability of geotextiles.

2. Capillary rise background

Capillary rise describes the upward movement or penetration ofwater, under no applied pressure, in a porous medium. This

za, A., A simple method to.1016/j.geotexmem.2014.04.0

of the porous material of interest in contact with a liquid in a ver-tical direction and observing the capillary rise of the liquid withtime. Poiseuille’s law apply for this type of flow regime. The lawexpresses the balance between capillary, gravity and viscous forcesdriving the flow in an upward direction. Inertia effect is neglectedsince it is only relevant during the first microseconds of water risethrough the largest pores (Siebold et al., 2000). In this case, the rateof liquid penetration is given by:

dHdt

¼ R2DP8hH

(1)

where H is the height reached by the liquid at time t, R is theequivalent pore radius assuming that the nonwoven structure ofthe geotextile is modelled as a series of parallel capillaries (Chenet al., 2009), h is the dynamic viscosity of the liquid, DP is the dif-ference between the Laplace or capillary pressure and the pressuredue to gravity and is given by:

DP ¼ 2T cos qR

� rwgH (2)

where T and rw are: the surface tension and density of the liquid,respectively. q is the advancing contact angle of the liquid on thesolid and g the acceleration due to gravity.

Rearranging Equations (1) and (2) gives the Poiseuille equationapplied to a rise of a liquid in vertical capillaries.

dHdt

¼ R2

8hH

�2T cos q

R� rwgH

�(3)

assess the wettability of nonwoven geotextiles, Geotextiles and04

Table 1Geotextile characteristics.

Geotextile Fibre type rf(kg/m3)

AOS*(mm)

tGT(mm)

MA

(g/m2)n (%) Df

(mm)

GT1 Continuousfilament

1300 90 2.6 220 93.50 25

GT2 Continuousfilament

1300 80 3.5 325 92.85 25

Note: rf ¼ density of the fibres, MA ¼ average mass per unit area, tGT ¼ averagegeotextile thickness, n ¼ geotextile porosity ¼ 1�MA=rf tGT , AOS ¼ apparentopening size as provided by the manufacturer (MARV values), Df ¼ diameter of thegeotextile fibres.

A. Bouazza / Geotextiles and Geomembranes xxx (2014) 1e32

When the maximal height (Hmax) of capillary rise is reached, thecapillary pressure and the pressure due to gravity become equal(i.e. DP ¼ 0). Thus at equilibrium:

Hmax ¼ 2 T cos qR rw g

(4)

The above equation is also referred to as the Jurin’s law.

3. Material and test method

Two nonwoven needle-punched polyester geotextiles (GT1,GT2) provided by the same manufacturer were used in the presentinvestigation. Their average basic characteristics are presented inTable 1. The test program included geotextile samples supplied intheir original state (i.e. hydrophobic) and samples which weretreated during the manufacturing process by wet oxidation using aproprietary detergent aqueous solution (i.e. treated to increasetheir hydrophilicity). No difference between the characteristics ofthe treated and untreated geotextiles was observed.

The capillary rise method adopted in this study followed themethod presented by Lafleur et al. (2000). It was conducted on aninitially dry geotextile specimen, which was allowed to equilibratein a vertical position along its in-plane direction. The capillary risewas measured by submerging one end of a dry geotextile strip

0

20

40

60

80

100

0 500 1000 1500 2000 2500 3000

Capi

llary

rise

(mm

)

Time (mns)

GT1-Treated

GT2-Treated

GT1 & GT2-Untreated

Fig. 1. Capillary rise versus time in treated and untreated geotextiles.

Table 2Maximum height of capillary rise predictions.

Geotextile n (%) rf (mm) R-theoretical(mm)

GT1 93.50 12.50 179.80GT2 92.85 12.50 162.30

Please cite this article in press as: Bouazza, A., A simple method toGeomembranes (2014), http://dx.doi.org/10.1016/j.geotexmem.2014.04.0

(500mm long� 100mmwide) in awater bath, while the other endwas raised vertically above the water bath and connected to awooden frame. The geotextile specimen was confined inside aPerspex cylinder to minimize evaporation of water from the geo-textile at room temperature (20 �C). 20 mm of the geotextilespecimen was kept submerged in water and was left to equilibratefor a time period of 72 h as suggested by Lafleur et al. (2000). Tapwater used in the experiments was dyed using blue dye in order tohelp visual identification of the height of the capillary rise withinthe tested geotextile.

The hydrophobicity/hydrophilicity of the geotextile sampleswas cross-checked using the contact angle (q) apparatus OCAH 230(Dataphysics Instruments, Filderstadt, Germany). The OCAH-230consists of a computer controlled liquid drop dispensing syringepump; a syringe pump is an infusion pump which can dispenseaccurate flow rates. In order to generate drops of pure water so-lution, a syringe with a flat tip stainless steel needle is fitted to thesyringe pump. The needle is placed above the water liquid surfacesuch as that the water drop generated could just touch the surfaceof the geotextile. An image software is then used to analyse thedroplet images.

Kutilek and Nielsen (1994) reported that the magnitude of thecontact angle can be used to distinguish three classes of wetting ofsolids. In particular, Kutilek and Nielsen (1994) indicated thefollowing: 1) for q ¼ 0� the surface is completely wet and the solidcan be considered as being fully hydrophilic. 2) The solid is said tobe partly hydrophilic when partial wetting of the surface occurs;i.e. 0 < q < 90� and finally 3) a non-wetting surface exhibitsq � 90� and in this case the solid is considered to be hydrophobic.Contact angle measurements conducted on the geotextile samplesconfirmed that the supplied untreated geotextiles were hydro-phobic (contact angle ¼ 153�), whereas the contact angles of thetreated geotextiles were equal to 0� indicating that they werehydrophilic.

4. Results and discussion

Capillary rise tests on the untreated polyester geotextile showedthat no capillary rise occurred and thus the geotextile followed anon-wetting behaviour type (Fig. 1). This is typical of hydrophobicgeotextile fibres which in most cases do not have affinity to waterwhen they are initially dry. Similar observations were reported byHenry and Patton (1998) who indicated that polyester geotextilesshowed no water rise. It is to be noted that Bouazza et al. (2006a)observed a slight capillary rise in similar nonwoven geotextileswhen wrapped in plastic films. However, this was due to the lowercontact angle of the plastic film only and not to the behaviour of thematerial. The treated geotextiles resulted in significant wettingbehaviour along the in-plane direction and considerable capillaryrise height (Fig. 1). The wet-oxidation of the geotextiles using adetergent aqueous solution seems to have been effective onincreasing their water uptake ability or their hyrophilicity. Geo-textiles can resist wetting because of their hydrophobic CH groupsand low free surface energy when they undergo wetting. Whenthey are treated with coatings and finishing agents (i.e. chemicaltreatment), hydrophilic groups (OeH) are formed instead of hy-drophobic (CeH) bonds on the polymer surface (Zhao et al., 2006;

R-experimental(mm)

Hmax-predicted(mm)

Hmax-experimental(mm)

199.30 83.10 75.00166.10 92.10 90.00

assess the wettability of nonwoven geotextiles, Geotextiles and04

A. Bouazza / Geotextiles and Geomembranes xxx (2014) 1e3 3

Nahlawi, 2009). This will result in a reduction of the hydrophobicityof the polymeric materials where the oxidation reactions occur onthe polymeric surface in the presence of oxygen.

Fig. 1 indicates also that the capillary rise is function of theopening size of the pores or porosity of the geotextiles and probablytheir thickness. The upwardmovement of water occurs faster in theless porous material (GT2) than in the more porous material (GT1).Interconnection between the pores seems also to play an importantrole on the capillary rise, Based on the AOS values, one can assumethat smaller pores are more prone to occur in GT2 than in GT1.Water will tend to rise faster through the smaller pores and slowdown when it encounters the larger pores. Hence, the largercapillary rise observed in GT2. Thickness can also have an influenceon the water rise since it can provide the additional pores in-terconnections (in the thickness direction) needed to allow waterto move further up such as in the case of GT2 in addition to thepresence of more small pores.

Chen et al. (2009) reported a methodology proposed by White(1982) to calculate the mean capillary radius R for nonwoven ma-terials based on the fibre radius (rf) and the porosity (n) of thematerial:

R ¼ n1� n

rf (5)

Combining Equations (4) and (5) give:

Hmax ¼ ð1� nÞn rf

2 T cos qrw g

(6)

Equation (6) is used herein to predict the maximum height ofcapillary rise (Hmax) of water (T ¼ 73.10 mN/m; r ¼ 998 kg/m3 at20 �C) attained in GT1 and GT2 when the contact angle is equal tozero for the water on the fibres (i.e. cos q ¼ 1). The predictions areshown in Table 2.

Table 2 indicates that the theoretical radius proposed by Chenet al. (2009) correlates well with the equivalent capillary radiusobtained experimentally based on Equation (4) (underestimation<10%), similar observation was reported by Chen et al. (2009) fornonwoven textile fabrics. More importantly, its use gives areasonable prediction of Hmax with an overestimation of theexperimental values varying between 1 and 11%. Thus a good es-timate of Hmax can be achieved using Equation (6). The above re-sults also confirm the observation made in Fig. 1 that a geotextilewith smaller opening size lead to higher capillary rise.

5. Conclusions

A simple method based on the examination of the capillary risein a one-dimensional geotextile layer along its in-plane directionwas proposed to assess the wettability of nonwoven geotextiles.The apparent opening size pore size and porosity of the nonwovengeotextiles and their fibres’ surface condition were found to play asignificant role in the extent of the water rise in the treated

Please cite this article in press as: Bouazza, A., A simple method toGeomembranes (2014), http://dx.doi.org/10.1016/j.geotexmem.2014.04.0

nonwoven polyester geotextile. The application of the Poiseuilleequationwas found to be representative of the liquid penetration inthe geotextiles. Furthermore, the prediction of the maximumcapillary rise (Hmax) using a theoretical capillary radius comparedwell with the measured test results. The methodology presented inthis paper should help assess wetting of geotextiles in short periodof time and less extensive laboratory testing.

Acknowledgements

Dr. Hani Nahlawi conducted the capillary rise tests and contactangle measurements. His help is gratefully acknowledged.

References

Bathurst, R.J., Siemens, G.A., Ho, A.F., 2009. Experimental investigation of infiltrationponding in one-dimensional sand-geotextile columns. Geosynth. Int. 16 (3),158e172.

Bouazza, A., 2004. Effect of wetting on gas transmissivity of a nonwoven geotextile.Geotext. Geomemb. 22 (6), 531e541.

Bouazza, A., Freund, M., Nahlawi, H., 2006a. Water retention of nonwoven polyestergeotextiles. Polym. Test. 25 (8), 1038e1043.

Bouazza, A., Zornberg, J., McCartney, J.S., Singh, R.M., 2013. Unsaturated geotechnicsapplied to geoenvironmental engineering problems involving geosynthetics.Eng. Geol. 165, 143e153.

Bouazza, A., Zornberg, J., McCartney, J., Nahlawi, H., 2006b. Significance of unsat-urated behaviour of geotextiles in earthen structures. Aust. Geomech. J. 41 (3),133e142.

Chen, X., Vroman, P., Lewandoski, M., Perwuelz, A., Zhang, Y., 2009. Study of theinfluence of fibre diameter and fibre blending on liquid absorption insidenonwoven structures. Text. Res. J. 79 (15), 1364e1370.

Henry, K.S., Patton, S., 1998. Measurement of the contact angle of water on geo-textile fibres. Geotech. Test. J. 21 (1), 11e17.

Iryo, T., Rowe, R.K., 2004. Numerical study of infiltration into a soilegeotextilecolumn. Geosynth. Int. 11 (5), 377e389.

Iryo, T., Rowe, R.K., 2005. Infiltration into an embankment reinforced by nonwovengeotextiles. Can. Geotech. J. 42 (4), 1145e1159.

Jeon, H.Y., Kim, S.H., Youk, J.H., Bouazza, A., 2008. Effects of surface modification onperformance of nonwoven geotextiles. Mol. Cryst. Liq. Cryst. 484 (1), 561e572.

Jeon, H.Y., Bouazza, A., 2007. Strength properties of plasma treated nonwovengeotextiles. Geosynth. Int. 14 (4), 244e247.

Kutilek, M., Nielsen, D.R., 1994. Soil Hydrology. Verlag, Germany, p. 370.Lafleur, J., Lebeau, M., Faure, Y.-H., Savard, Y., Kehila, Y., 2000. Influence of matric

suction on the drainage performance of polyester geotextiles. In: Proceedings ofthe 53rd Canadian Geotechnical Conference: Geotechnical Engineering for theUrban Infrastructures, October, Montreal, Canada, pp. 1115e1122.

Nahlawi, H., 2009. Experimental and Numerical Investigation of the UnsaturatedHydraulic Behaviour of Geotextiles. PhD Thesis. Monash University, Melbourne,Australia.

Nahlawi, H., Bouazza, A., Kodikara, J., 2007. Characterisation of geotextiles waterretention using a modified capillary pressure cell. Geotext. Geomemb. 25 (3),186e193.

Siebold, A., Nardin, M., Schultz, J., Walliser, A., Oppliger, M., 2000. Effect of dynamiccontact angle on capillary rise phenomena. Coll. Surf. 161, 81e87.

Singh, R.M., Bouazza, A., 2013. Thermal conductivity of geosynthetics. Geotext.Geomemb. 39, 1e8.

White, L.R., 1982. Capillary rise in powders. J. Coll. Interf. Sci. 90 (2), 536e538.Zhao, Y., Tang, S., Myung, S.W., Lu, N., Choi, H.S., 2006. Effect of washing on surface

energy of polystyrene plate treated by RF atmospheric pressure plasma. Polym.Test. 25 (3), 327e332.

Zornberg, J.G., Bouazza, A., McCartney, J.S., 2010. Geosynthetic capillary barriers:current state of knowledge. Geosynth. Int. 17 (5), 273e300.

assess the wettability of nonwoven geotextiles, Geotextiles and04