Geotextiles in pavement Overlay Applications: A Case Study

Transcription

1 ECHNICAL ARTICLE Geotextiles in pavement Overlay Applications: A Case Study Dr. A. K. Rakshit, Manisha A. Hira and Suresh Sambari The SynthetIc & Art Silk Mills' Research Association. Sasmira Marg. Worti, Mumboi The earlier papers (March and April 2007 issues af MMTI) published by the authors have stressed on the possibilities of application of geotextiles in pavement overlay applications to improve service life of roads. It has been identified that geotextiles can be used in the subgrade, at the pavement overlay or at the surface overlay to increase the service life of roads. This paper presents a report on the actual pavement overlay geotextile material designed and developed by SASMIRA and field trial of the same at a prominent location in Mumbai. 1. INTRODUCTION Today Infrastructural development holds a key thrust In India. The use gootextiles is gaining popularity, particularly for road repairs and road rehabilitation. It has been identified that geotexliles are used commonly at the subgrade soil level primarily for filtration and reinforcement functions. Apart from this gootextiles can be incorporated in the pavement overlay of roads and also as a surface overlay. SASM IRA R&D has been focussed on development of speciality textile products Indigenously. Accordingly, the development of SUitable gootextiles for pavement overlay applications was taken up. The details of the development, specifications of the developed product and field trials of the same have been descnbed in the subsequent sections. 2. MATERIALS & METHODS Two varieties of fabrics were developed VIZ. woven and nonwovens. The starting (raw) material and process sequence for the same is as below: 2.1 Woven Geotextiles The woven material was prepared from Polypropylene tape yarn. The yarn used in warp direction was of Denier and that In weft was Denier. Respective strength values were Warp = 5.02 kgf Weft = 6.70 kgf These yarns were woven to obtain pavement overlay fabric with specifications as below' Woven Tape x Tape yarn, with mass 135 glm' Grab Strength of 1000 N Grab elongation 15% Wide width tensile strength 60 Nlm Wide Width elongation 15% 2.2 Nonwoven Fabric The nonwovens geotextile had been developed for the Intended application using following raw matenal: Polymer Fibre fineness Fibre length Polypropylene 3.6 D 80 mm II. ~n-m.kle Texti~ in lnella Moly 2007

2 Melting point The Input fibres were processed on needle punching fo~ lowed by calendanng to obtain a nonwovens geetextlle with following specifications Mass Thickness Tensile strength Elongation at break Asaphalt retention Melting POint (greater than) Both the developed fabrics were subjected to laboratory evaluations. 2.3 Laboratory Evaluation 160"C 150 g/sq.m 1.1 mm 350 N/mm 50% 0.9 Iitre/sq.m 150 degree C The developed fabncs were evaluated for various physical, mechanical and hydraulic properties to ascertain their SUitability for the application. The following tests were performed Weight (Mass): Test procedure (ASTM ) apart A CRE tester evaluates the strength of these samples at a speed of 300 mmlmln. Tear Strength testing: ThiS test method determines the tear propagation characteristics of the fabnc and strength requrred In doing so. The test was carried out as per ASTM Bursting Strength testing: The fabric bursting test was executed as per ASTM This test helps to establish the strength of fabric under high pressure. Puncxure strength testing: The test was carried out as per ASTM 0 Aperture opening size 4833 to evaluate ItS resistance to pucture. test: This test estimate the permeability characteristics of the fabrics was executed as per ASTM Water Permittivity test: This IS yet another test to evaluate the water permlttrvity of the geetextile fabncs. It was carried out as per ASTM RESULTS & DISCUSSION The developed pavement overlay samples for laboratory evaluation have been coded as follows Ten samples each 250 mm X 250 mm are taken from the Nonwoven pavement overlay sample S1 fabnc, weighed (nearest to 0.01%) and then mean and standard deviation calculated. Thickness Test procedure (ASTM ) Thickness is measured by thickness testing instrument. The Instrument must be capable to measure a maximum thickness of at least 10mm to an accuracy of at least +/ 0.002mm Also the Instrument shall permit gradual application of pressure to a specific force of 2+/- 0.2 kpa for geotextiles. Tensile strength: Geetextlle tensile testing, especially geegnds, demands test Ing of Wide width samples to ascertain therr stress / strain properties. The following are the test methods followed for these tests Wide width tensile testing: This test was executed as per ASTM The Wide width samples stnps of 50 mm x 200 mm were evaluated for their strength charactenstics on CRE tester. Grab Tensile Strength: Grab tensile strength IS a Uniaxial test where the specimen IS wider than the test clamps. ThiS test IS carried out as per ASTM The tensile strength added by the unclamped portion of the specimen is pnmarily Influenced by geetextlle construction. A 100 mm x 200 mm specimen IS placed centrally in a set of parallel 25 mm x 50 mm clamps such that the clamps are spaced 75 mm Woven pavement overlay sample. S2 The subsequent section uses this terminology for discussion of the results 3.1 Laboratory evaluation: 1. Physical parameters: The physical parameter like fabric weight and thickness were evaluated for both the developed samples as per ASTM & ASTM A summary of the same is shown In Table 1. Table 1. Physical Properties of developed Pavement Sample Fabric type Weight Thickness code (g/sq.m) (mm) 51 Non woven Woven To reach the desrred functional properties in the pavement overlay fabrics, It was essential to develop relatively light weight, thin fabncs with desrrable strength and elongation and AOS. Accordingly, both the fabrics samples are in the light weight range of functional textile g/ sq.m and the woven variety of the fabrics being woven from tape yarns is thinner as compared to nonwovens fabrics. 2. Wide width tensile strength The wide Width tensile test evaluations were carried out as per ASTM Table 2 shows properties of tensile May 2007 Man.made Textiles in Indi.a II

3 Table 2. Wide width Tensile Properties of developed Pavement Sample Fabric type Strength Elongation code Warp Weft Warp Weft direction direction direction direction (KN/m) (KN/m) (Of,) (Ofo) S1 Non woven S2 Woven properties of both the samples. Both the samples are found to be acceptable as per the standard pavement overlay samples. It can be seen that as compared to the woven fabncs, the nonwovens fabric IS relatively lower in strength and high In elongation. A standard pavement overlay fabnc has an acceptable level of tensile strength along with higher elongation IS most desirable for the application. This makes both the fabrics suitable for the application. Standard acceptable values for Pavement overlay fabncs Wide width tensile strength Wide width elongation >50% 3. Grab tensile strength 45 kn/m The grab strength of the fabrics was tested as per standard ASTM The fabrics developed have found the resulls as shown In Table 3 It can be seen that both the fabncs have acceptable level of grab strength, i.e 400 N The woven sample S2 has much higher grab strength by virtue of its construction It IS expected to show better overlay performance. Table 3. Grab Tensile Properties of developed Pavement Sample Fabric type Strength code Warp direction Weft direction (N) (N) 51 Non woven Woven , Bursting strength The bursting property of the developed samples has been evaluated as per ASTM As seen In Table 4, both the fabncs are found to be satisfactory as far as the bursting property is concerned. The woven fabric however, has very high bursting strength. Table 4. Bursting strength of developed Pavement Sample code Fabric type Strength (kg/em') 51 Non woven Woven 342 Table 5 It can be seen that both the fabncs have high puncture resistance. However, the high strength woven fabnc is found to have a very high resistance 6, Trapezoid tear strength Tear strength of pavement overlay fabrics IS equally Important as wide width and grab strength of these fabncs. As depicted in Table 6. both the fabncs are found to be acceptable In terms of tear strength, the woven vanety, being high in tensile strength has equally high tear strength too. Table 5. Puncture resistance of developed Pavement Sample code Fabric type Resistance (N) 51 Non woven Woven 5554 Table 6. Tear Strength of developed Pavement Overlay Geotextiles Sample Fabric type Warp direction Weft direction code Max, load (N) Max. load (N) 51 Non woven Woven Apparent opening size (AOS) The permittivity of the pavement overlay fabrics IS adjudged from the Apparent Opening Size of the fabrics. The evaluation of the property was done as per ASTM The results of the same have been shown in Table 7 for both the samples developed, The AOS values for the nonwovens fabncs are found to be acceptable. However. the woven fabrics failed to yield any value for the same due to the varying permittivity level of the fabrics. Table 7. AOS Properties of developed Pavement Overlay Geotextiles Sample code Fabric type AOS (~) 51 Non woven <75 52 Woven - 8. Water permittivity The hydraulic permittivity of the pavement overlay samples was evaluated from their water permitlivlty. The test was carned out as per ASTM The results have been summarised in Table 8 As in case of AOS, the water permittivity could give acceptable value established only for the nonwoven sample. The woven sample failed In this regard. Table 8. Water Permittivity Characteristics of developed Pavement 5. Puncture resistance The puncture resistance of the fabncs was evaluated as per ASTM The results of the same are shown In the Sample code Fabric type Water permltvlty (sec.) 51 Non woven Woven III Man-made Tutiles in India _ May 2007

4 To summarise, it can be said that both the samples are acceptable for the pavement overlay application when com pared to the standard requirement of the applicalion In terms of physical parameters and strength and elongation. The nonwoven fabnc matches the standard requirements of pavement overlay geotextlle, however, the woven fabric has relatively high strength with sufficient elongation for specialised pavement overlay uses. The nonwoven was taken up for overlay tnals on an asphalt road construction site The field tnals of woven geotextiles on airport service road are awaited In near future. 3.2 Field Trials: An asphalt concrete road construction site was Idenlifled with help of B M C at Gandhinagar, Worli, Mumbai A 90 m stretch of road was under construction. A part of road (40 m) was laid conventionally with only asphalt concrete, while other 50 m of the road was reinforced with geotextile. The following was the procedure followed for laying of the geotextlle. The fabnc was to be laid at the top most course I.e Asphalt Concrete (AC). It was proposed to keep the thickness of AC would be of 40 mm. The paving fabric was laid between the Bitumen Macadam (BM) and the AC The surface of BM was cleaned so that it was free of dust and debris and the cracks were filled. The tack coat on the pavement surface was spray. The rate of tack coat was less than m' Spraying was evenly done. Nonwoven was rolled out after the tack coat cracksed, that is, about 10 minutes afterwards. It was laid without any pretension. Immediately the AC was laid on the nonwoven and compacted to the required density Fig. 1 depicts the laying tnal for the pavement overlay fabnco Fig. 1. Field Trial or Pavement Overlay Fabric The laying of geotexlile resulted In comparative sample of roads viz, pavement overlay reinforced road and unrelnforced standard road. These roads were periodically monitored to observe the changes In the surface observation study was executed in terms of: ThiS field 1 The site where the fabric was laid has been marked for identificatlon 2. Comparative observation of the road surface and structure have been carned out every week, 3 the axle load study has been taken every week for evaluating traffic load on the road. 4 Every fortnight photographs of the site and the juxtaposed site without paving fabric have been taken to identify the condition of the road with passage of time, Accordingly, the nonwovens sample was taken up for actual field tnal of pavement overlay. The results of the field trial evaluation have been discussed here The field trial study carned out for a period of one year has yielded the following observations. Table 9 summarises the average axle load observed on the roads under study. Table 9. Average Axle Load on the Roads Vehicle Type Average Nos. Two Wheeler 94 Three Wheeler 10 Four Wheeler 93 Two Axle 8 Multl-axle 0 Other 7 The roads under study were observed for the following surface changes General appearance Water spet Cracks emerging Edge Cracking (dimensions) Crocodile cracks Block cracking Ruts Waviness The general appearance and performance of both roads has been equivalent and satisfactory Since the period of observation has been short and the study is in progress, there has been no surface changes observed for both sections of the roads Photographs have been taken periodically during the observation study. The photograph of the present condition of the paved road with and without geotextile have been depicted in the Fig. 2. May Man-made Texliles in India III

5 4. CONCLUSIONS Fig. 2. Photograph of Present Road condition with and without Geotextile Overlay SASMIRA developed geotextiles both woven and nonwovens were found to be acceptable for pavement overlay application as per the laboratory evaluation. 80th woven and nonwovens can be used for pavement overlay applications. These help to Improve the service life of the roads. Reinforcing strength and permittivity characteristics are the major attributes for the geotextiles used for pavement overlay applications The nonwoven material developed has been put o~ freld trial at a prominent location in Mumbai. It has been found effective over the period of observation.