A Study on Flexible Pavement Performance with Reinforced Flyash Subbase.pdf

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94 International Journal of Earth Sciences and EngineeringISSN 0974-5904, Volume 04, No 06 SPL, October 2011, pp 94-99

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A Study on Flexible Pavement Performance with Reinforced Flyash Subbase

D S V Prasad Professor&Principal,Department of Civil Engineering/BVC Engineering College, Odalarevu,AP – 533210, Email:[email protected]. Anjan Kumar

Professor&Principal, Department of Civil Engg./BVC College of Engineering, Rajahmundry,AP, Email:[email protected]

G V R Prasada Raju Professor&DirectorAcadamic Planning, Department of Civil Engineering/J N T University, Kakinada, AP, Email:[email protected]

Research Scholar, JNT University, Kakinada, Email: [email protected]

ABSTRACT : Evaluation Studies on flexible pavement system were carried out by using the different reinforcementmaterials in the flyash subbase courses laid on expansive soil subgrades. Cyclic Load tests were carried out in the field

by placing a circular metal plate on model flexible pavements. It is observed that the maximum load carrying capacityassociated with less value of rebound deflection is obtained for Geogrid reinforced stretch followed bybitumen coatedchicken mesh, bitumen coated bamboo mesh stretch and waste plastics reinforced stretch in the flexible pavementsystem laid on expansive subgrades.

KEY WORDS : Expansive soil; Flexible Pavement; Reinforcement; Heave; Cyclic Plate Load Tests .

INTRODUCTION

Civil and environmental engineering includes the analysis,design, construction and maintenance of structures andsystems. All are built on, in, or with soil or rock. The

properties and behavior of these materials have major influences on the success, economy, and safety of thework. Geo-engineers play a vital role in these projects andare also concerned with virtually all aspects of environmental control, including waste disposal. Manyhighway agencies, private organizations and researchersare doing extensive studies on waste materials andresearch projects concerning the feasibility and

environmental suitability.Commonly, gravel is considered to be suitable for roadconstruction (MOST-1998). However, in the latest MORTspecifications, several types of gravel are found to beunsuitable for road construction in view of higher finer fraction and excessive plasticity properties. In India thereare about 82 thermal power plants, which are currently

producing about 100 million tons of flyash per annumDhar (2001). In order to utilize flyash in bulk quantities,ways and means are being explored all over the world touse it for construction of embankments and roadsHausmann (1990), Veerendra Singh et al.,(1996) andMurthy (1998).

Reinforced earth technique has been gaining popularity inthe field of civil engineering due to its highly versatile andflexible nature. It has been used in the construction of retaining walls, embankments, earth dams, foundation

beds for heavy structures on soft grounds, viaduct bridgesand other applications Henry Vidal (1968), Hausmannn(1990), Rao (1995). The practice of reinforced earthtechnique became easy and simple with geosynthetics. Inspite of its wide use in various engineering practices, itsapplication in the construction of pavements is very muchlimited Prasada Raju (2001).

Reinforcement of soils with natural and synthetic fibres is potentially an effective technique for increasing soilstrength. The growing interest in utilizing waste materialsin civil engineering applications has opened the possibilityof constructing reinforced soil structure withunconventional backfills, such as waste plastics and wastetire shreds. The results of direct shear tests performed onsand specimens by Gray and Osashi (1983), indicatedincreased shear strength and ductility, and reduced post

peak strength loss due to the inclusion of discrete fibers.The study also indicated that shear strength is directly

proportional to fiber area ratio and length of fiber up tocertain limit. These results were supported by number of researchers using consolidated drained triaxial tests likeGray and Al-Refeai (1986), Gray and Maher (1989),Ranjan et al., (1996), Michaowski and Cermak (2003),Temel and Omer (2003), Prabakar et al.,(2004) PraveenKumar et al.,(2005), Sivakumar Babu et al.,(2008), Jadhaoand Nagarnaik (2008).The addition of fibers increasesthe CBR,ultimate strength, stiffness and resistance toliquefaction, shear modulus and damping of reinforced thesand by Lindh and Eriksson(1991); Temel and Omer (2005).The results of compaction tests for a silty, clay soilspecimen reinforced with fibers indicate that increasingthe volume of fibers in the soil generally causes a modest

increase in the maximum dry unit weight, and a slightdecrease in the optimum moisture content by Fletcher andHumphries (1991) and Al-Wahab and Al-Qurna (1995).Rao and Dutta (1997) reported that sand-waste plasticmixtures improve the bearing capacity of granular trenchand consequently the bearing capacity ratios. In the recent

past, use of Reinforced flyash layer as subbase course inflexible pavement construction has been tried efficientlyin laboratory in improving the performance of the flexible

pavement (Chandrasekhar et al., (2001), Bin-shafique etal.,(2004)and Pandian and Leelavathamma, (2005).



95 A Study on Flexible Pavement Performance with Reinforced Flyash Subbase

International Journal of Earth Sciences and EngineeringISSN 0974-5904, Volume 04, No 06 SPL, October 2011, pp 94-99

In the present investigation, it is attempted to observe the performance of flyash subbase reinforced with differentmaterials, viz: Geogrid, Bitumen Coated Chicken Mesh,Bitumen Coated Bamboo Mesh and Waste Plastics inflexible pavement system. Cyclic load tests were carriedout by placing a circular metal plate directly on theflexible pavement laid on expansive subgrades. Keeping

in view the high cost of geogrid, other materials like bitumen coated chicken mesh ,bamboo mesh and waste plastic strips were also tried for their use as reinforcingmaterials. From the present study it is observed that themaximum load carrying capacity associated with lessvalue of rebound deflection are observed for Geogridreinforcement stretch followed by Bitumen CoatedChicken Mesh , Bitumen Coated Bamboo stretch andWaste Plastics.

2. EXPERIMENTAL STUDY

2.1 Materials Used

The following materials are used in this study.

Soi l: Expansive soil collected from Godi lanka near Amalapuram was used for this investigation as a subgradematerial. The soil properties are W L=75%, W P=35%,WS=12%, I.S. Classification=CH (Clay of highcompressibility), OMC=23%, MDD=15.69 kN/m 3,Differential free swell = 150 %, SoakedCBR=2.0%.Permeability = 1.5 × 10 -7 cm/sec.

Gravel : Gravel collected from Dwarapudi, near Rajahmundry was used as subbase course. The soil

properties are W L=38%, W P = 20 %, OMC=13 %,MDD=18.05 kN/m 3, Soaked CBR=8.0%, Permeability =1.2 × 10 -1 cm/sec.

Flyash : The flyash collected from Vijayawada thermal power station, Vijayawada was used as a subbase coursein this work. The properties of flyash are MDD=13.24kN/m 3, OMC=24%, Soaked CBR=4.0%, Permeability(cm/sec) = 0.5 × 10 -6.Geogrid : Netlon CE 121 Geogrid with a peak tensilestrength of 7.68kN/m and aperture size of 8mm × 6mmwas used.

Chicken Mesh: Chicken Mesh with a peak tensilestrength of 8.85kN/m and an aperture size of 2mm × 2mmcoated with 80/100 grade bitumen was used.

Bamboo Mesh : Bamboo Mesh of thickness 1mm with a peak tensile strength of 26.32kN/m coated with 80/100

grade bitumen was used.Waste Plastics Strips : Waste plastic strips having a size of 12 mm × 6 mm and a thickness of 0.5 mm is used in thisstudy Figure. 1)

Road Metal : Road metal of size varying between 45-63mm was used for the base course.

Figure. 1. Waste Plastic Strips

3. FIELD EXPERIMENTATION

In this study five alternative test tracks (Geogridreinforced subbase, Bitumen Coated Chicken Meshreinforced subbase (BCCM), Bitumen Coated BambooMesh reinforced subbase (BCBM), Waste Plastics

reinforced subbase (WP) and untreated subbase) were prepared on expansive soil subgrade with flyash subbasematerials separately, and the details of which are

presented in the following sections.

3.1 Preparation of Test Stretches

Tests track each of size 3m long and 1.5m wide wasexcavated to an average depth of 0.8m as shown in Figure.2. Out of which 0.5m was for laying subgrade, 0.15m wasfor laying subbase and 0.15m for laying base course. Theexpansive soil was spread in the field, allowed for dryingsufficiently and then pulverized to small pieces withwooden rammers. In the prepared test pit, the pulverizedexpansive soil was mixed with water at OMC and was laid

in the excavated pit in 10 layers, each layer of 0.05 mcompacted thickness, amount to a total thickness of 0.5 mas shown in the Figure. 3. On the prepared subgradeflyash subbase material mixed with water content at OMClaid in 2 layers, each of 0.075m compacted thickness to atotal thickness of 0.15m was laid. The reinforcementmaterials viz. Geogrid, Bitumen Coated Chicken Mesh(BCCM), Bitumen Coated Bamboo Mesh (BCBM) waskept above the first compacted layer of each pit as shownin the Figure. 4. For the Waste Plastic reinforced stretch,the reinforcement materials (optimum percentage basedon laboratory Shear and CBR) was mixed uniformlythroughout the subbase material. On the prepared subbasetwo layers of WBM-II each of 0.075m compacted

thickness to a total thickness of 0.15m using crushed stoneaggregate of size 45mm to 63mm with murrum as bindingmaterial was laid. The compaction was done with the helpof hand operated roller. A critical view of field stretchesused for finding the best alternative reinforcementmaterial in the flexible pavement system is shown in theFigure. 5



96 D S V Prasad, M. Anjan Kumar, G V R Prasada Raju and V. Kondayya


Figure. 2 Excavated Model Pavement Stretch

Figure. 3 Prepared Expansive Soil Subgrade

Figure. 4 Placing of Reinforcement Material in theSubbase Course

Figure. 5 Prepared Model Flexible Pavement Stretch

3.2 Cyclic Load Testing Cyclic Plate load tests were carried out for different teststretches with different reinforcement materials viz.Geogrid, Chicken Mesh, Bamboo mesh, Waste plastics,

and unreinforced flyash stretch under normal tyre pressures using circular steel plate of diameter 0.3m. Aloading frame was arranged centrally over the test track asshown in the Figure. 6 The loading frame was loaded withthe help of sand bags. A steel base plate of 0.3m diameter was placed centrally over the test pit. Hydraulic Jack of capacity 100kN was placed over the plate attached to theloading frame with a loading cylinder. Three dial gaugeswith a least count of 0.01mm were placed on the metalflats to measure the settlements. A load of 5kPa wasapplied as a seating load with the help of hydraulic jack and released. The load was applied in incrementscorresponding to tyre pressures of 500, 560, 630,700 and1000 kPa and each pressure increment was appliedcyclically until there is insignificant increase in thesettlement of the plate. These tests were carried out on the

prepared expansive soil subgrade with four differentreinforcement materials.

Figure: 6 Experimental Set Up for Cyclic Plate Load Teston the Test Tack

3.3 Heave MeasurementsCement concrete panels of size 0.3 m x 0.3 m x 0.05mwere placed centrally in all the stretches for heavemeasurements. The reduced levels of the top of panelswere fixed using leveling instrument with 1 mm accuracyand heave measurements were taken during wet and dryseasons for all the stretches.

4. LABORATORY EXPERIMENTATION

4.1 Direct Shear and C B R Tests

The direct shear and CBR tests were conducted as per IS:2720 (part XIII, 1986) and IS: 2720 (part-XVI, 1979), inthe laboratory, by using different percentages of waste

plastics mixed with flyash materials uniformly with dry

weight of soil and compacted to maximum dry densityand optimum moisture content of flyash material with aview to find the optimum percentage of waste plastics.

5. DISCUSSION ON TEST RESULTSDirect shear tests and CBR tests were conducted by usingdifferent percentages of waste plastics were mixed withflyash material for finding the optimum percentage.Cyclic load tests are conducted on the flyash subbases,reinforced with optimum percentage of waste plastics.





5.1 Direct Shear and C B R Test ResultsFrom the test results it is observed that flyash reinforcedwith waste plastics has given comparatively higher valuesof shear strength parameters in comparison with untreatedflyash. From the direct shear test results ,it is observedthat for flyash reinforced with waste plastics, the cohesion

and angle of internal friction values are increased from7.85 to 18.64 kN/m 2 and 33 0 to 40 0 respectively with 0.4% of waste plastics and there after decreased. It is alsoobserved that flyash reinforced with waste plastic strips,soaked CBR values are increased from 4.0 to 10.81 for 0.40 % of waste plastics as shown in Figure. 7

Figure. 7 Strength Parameters for Flyash Reinforced withDifferent Percentages of Waste Plastic Strips

From the results of direct shear and California BearingRatio tests, the optimum percentage of waste plastics for flyash materials is 0.3 %.

5.2 Load Test Results The cyclic load test results for the different alternativesare presented in the following section.

5.2.1 Pressure – deformation behaviour on expansivesoil subgradesAt saturation state, the total and elastic deformationsobserved at a load of 1000 kPa is equal to 12.42 mm, 4.49mm for untreated stretch, 11.43 mm, 3.27 mm for waste

plastics reinforced stretch, 9.83 mm, 2.94 mm for bitumencoated bamboo mesh stretch, 7.69 mm, 2.49 mm for

bitumen coated chicken mesh, 6.93 mm, 2.12 mm for geogrid reinforced stretch respectively. The total and

elastic deformation are decreased by 44 %, 54 %; 38 %,46 %; 21 %, 36 % and 8 %, 29% for geogrid reinforcedstretch, reinforced bitumen coated chicken mesh stretch,reinforced bitumen coated bamboo mesh stretch and waste

plastics reinforced stretch respectively as shown in theFigures. 8&9. Higher deformations are recorded at higher load intensities as expected. It can be observed from theresults, that the load carrying capacity has substantiallyincreased for all the types of reinforcement materials atsaturated states.

Figure. 8 Pressure-Total deformation Curves for DifferentPavement Stretches laid on Expansive Soil subgrade

Figure. 9 Pressure - Elastic deformation curves for Different PavementStretches Laid on Expansive Soil Subgrade .

5.2.2 In-Situ Heave MeasurementsThe in-situ Heave measurements with respect to time weretaken on the different pavement stretches laid onexpansive soil subgrade. The observed in-situ heavevalues were plotted with respect to time in days, as shownin Figure. 10. The heave measurements are taken for different time intervals for all the alternatives of modelflexible pavements in the field laid on expansive soilsubgrade. The observed maximum values of heave for model pavement stretches laid on expansive soil subgradefor flyash subbases are equal to 34.4 mm; 32.80 mm;31.40 mm; 32.00 mm; 31.80 mm for untreated stretch,waste plastics, bitumen coated bamboo mesh, bitumencoated chicken mesh and geogrid reinforced stretchesrespectively. There is no significant control of heave for flyash subbases reinforced with geogrid, bitumen coatedchicken mesh, and bitumen coated bamboo mesh andwaste plastics. This behavior is evident from the fact thatthere is no heave control mechanism with thereinforcement in pavement system.



98 D S V Prasad, M. Anjan Kumar, G V R Prasada Raju and V. Kondayya


Figure. 10 In-situ Heave-Time Plot for Different Model FlexiblePavements laid on Expansive Soil Subgrade with Flyash Subbase

5.3 Performance of Model Pavement Stretches Laid onExpansive Soil SubgradeThe load carrying capacity of the model flexible pavementsystem is significantly increased by introducingreinforcement materials in flyash subbases, laid on

expansive soil subgrade. The load carrying capacity ismaximum for Geogrid reinforced subbase stretch,followed by Bitumen coated Chicken mesh subbasestretch, Bitumen coated Bamboo mesh stretch and waste

plastic reinforced stretch. Geogrid reinforced stretch hasshown better performance compared to the other reinforced stretches. Geogrid and chicken mesh provide

better interlocking with the soil particles thus ensuringadequate anchorage during loading. Relatively lower

performance of bitumen coated bamboo mesh could beattributed to its smooth surface to mobilize adequatefriction. No significant control of heave is observed whenreinforcement is placed in flexible pavement subbase laidon expansive soil subgrade. In fact, it is intended to

incorporate reinforcement material in the flexible pavement to strengthen it with little emphasis on heavecontrol. Further it can be seen that heaving of theexpansive soil considerably decreases the load carryingcapacity of the pavement system. The improvement in theload carrying capacity could be attributed to improvedload dispersion through reinforced subbase on to thesubgrade. This in-turn, results in lesser intensity of stresses getting transfer to subgrade, thus leading to lesser sub grade distress.

6. CONCLUSIONS

The optimum percentages of waste plastics from the directshear and California bearing ratio tests for flyash materialsis 0.3% . The total and elastic deformation values of theflexible pavement system are decreased by the provisionof the reinforcement viz., Geogrid, bitumen coatedchicken mesh, bitumen coated bamboo mesh and waste

plastics laid on expansive soil subgrades, in comparisonwith the conventional flexible pavement system.

The load carrying capacity of the model flexible pavementsystem is significantly increased by introducingreinforcement material in flyash subbases laid onexpansive soil subgrade.

The improvement of the pavement performance iscognizable for the two reinforcement materials tried viz.geogrid and bitumen coated chicken mesh. Both geogridand bitumen coated chicken mesh provide excellentinterlocking of soil particles, there by resulting in better

performance compared to other material. Relatively poor performance of bitumen coated bamboo mesh could be

attributed to its smooth surface to mobilize adequatefriction.

The total and elastic deformation values of the flexible pavement system are decreased by the provision of thereinforcement viz: Geogrid, Bitumen Coated ChickenMesh,Bitumen Coated Bamboo Mesh and waste plasticsreinforced subbases laid on expansive soil subgrade.

The maximum load carrying capacity followed by lessvalue of rebound deflection is obtained for Geogridreinforced subbase stretch followed by Bitumen CoatedChicken Mesh stretch, Bitumen Coated Bamboo Meshand waste plastics stretch laid on the flexible pavementsystem.

No significant control of heave is observed for the teststretches, reinforced with different materials, tried in thisinvestigation, laid on expansive soil subgrade.

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A Study on Flexible Pavement Performance with Reinforced Flyash Subbase.pdf