SUITABILITY OF GEOGRID REINFORCED - RUBBER WASTE IN PAVEMENTS

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1 Abstract S. Thenmozhi et. al. / International Journal of Engineering Science and Technology SUITABILITY OF GEOGRID REINFORCED - RUBBER WASTE IN PAVEMENTS S. THENMOZHI 1 Research Scholar, Department of Civil Engineering, College of Engineering, Anna University Chennai,Tamil Nadu, 6, India. V.K. STALIN 2 Professor & Head, Division of Soil Mechanics and Foundation Engineering, Department of Civil Engineering, College of Engineering, Anna University Chennai, Chennai,Tamil Nadu, 6, India. In order to evaluate the performance of soil and rubber waste mix as subgrade material, static and repeated load tests were conducted on soil and rubber waste in four different layer forms as well intermixed combination. Rubber chips of 3-4 mm were used. It is found that load carrying capacity of the soil + + soil layer and soil + inter mix are found to be better than the other combinations such as soil + soil + or soil + +, both in reinforced and unreinforced case. The soil++soil or soil+ inter mix can be effectively used in order to reduce the plastic deformation that the subgrade clay undergoes and also to enhance the recoverable elastic strain. The placement of geogrid reinforcement at the interfaces of soil and layer improved not only the load carrying capacity but also very much the recoverable elastic strain. Key Words: Clay soil, Rubber Waste, Geogrid, Pavement Introduction One of the problems associated with socio-economic development of a country is waste disposal. In engineering and transportation sector one of the wastes generated is scrap tire and it poses serious environmental problem. Majority of them end up in the already congested landfill or becoming mosquito breeding places. Worst when it is burnt. Recent statistics in India indicated more than 1% increase in number of registered vehicle within ten years. Some of the applications of rubber waste in geotechnical area are lightweight fill for embankments and retaining walls, leachate drainage material and alternative daily cover at municipal solid waste landfills, insulating layer beneath roads and behind retaining walls, agriculture - soil aeration and detoxification, golf course green liners, and mats. Laboratory investigations showed that strength and compressibility of shredded tire can be engineered to the requirements. Tatlisoz et al. (1997) evaluated the mechanical properties and behavior of waste tire chips and their mixtures with fine- and coarse-grained soils. Results of the tests showed that tire chips and soil-tire chip mixtures behave like soils, but are more compressible and also require more deformation to mobilize their ultimate shear strength. Drescher et al. (1999) investigated the deformation behavior of shredded tires, under repeated and constant loads. They found that under repeated loads, the shredded tire chips undergo less plastic strain per cycle with successive load cycles, ranging from 8% strain for first cycle to.3% strain for 8 th cycle. They concluded that by assuming a constant rate of creep for the period of 6-63 days after completion of load, settlements in the shredded tire layer of a representative embankment fill can be predicted. Young et al. (23) determined the physical and chemical properties of tire shreds for use in engineering construction as a replacement for aggregates in embankments or as backfill. As the size of tire shreds increases, physical properties such as specific gravity remains at , hydraulic conductivity increased from.2 to.8 cm/s, angle of friction ranges from to 32, cohesion from 349 to 394 N/m 2, shear strength and compacted density and compressibility increased. Cetina et al. (26) investigated the geotechnical properties of pure fine and coarse grained tire-chips and their mixtures (1, 2, 3, 4 and %) with a cohesive clayey soil by performing grain size and Atterberg limits analysis, permeability and direct shear and compaction tests. The results indicate that the mixtures up to ISSN:

2 2% coarse grained and 3% fine grained tire- chips can be used above ground water tables where low weight, low permeability and high strength are needed in fills such as highway embankments, bridge abutments and behind retaining structures especially built on weak foundation soils with low bearing capacity and high settlement problems. Sungmin Yoon et al. () evaluated the feasibility of using tire shred sand mixtures as a fill material in embankment construction and studied effect of Tire shred sand mixtures, on the other hand, were found to be effective in inhibiting exothermic reactions. When compared with pure tire shreds, tire shred sand mixtures were found to be less compressible and possessed higher shear strength. This paper focuses on the utilization of shredded tire as lightweight geo-material in subgrade for pavement construction. 2. Materials 2.1. Natural soil Natural clay collected from Vijaya Nagar, Velachery, Chennai at 1. m depth. The physical properties of soil are summarized in table 1. The soil is classified as CH type Rubber Tire Waste () Table 1 Physical Properties of Soil Properties Values Specific gravity 2.6 Gravel % trace Sand % 3 Silt % 14 Clay % 33 Liquid limit % 4 Plastic limit % 18 Plasticity index % 36 Free swell index % 6 Maximum dry density, kn / m 3 17 Optimum moisture content, % 16. Classification CH As per ASTM D 627, the particles less than about 12mm in size, termed granulated or ground rubber, particles from 12mm to mm in size are grouped as tire chips and particles greater than mm ( to 3 mm) are grouped with tire shreds obtained by shredding on waste rubber tires. George Foose et al (1996), used size of between 3 mm to 1 mm and reported that angle of internal friction varies from 19 to 3.Yang et al (22), Youwai et al (24) and Shobana (28) used tire maximum size 4.7 mm to 14 mm and reported friction angle value of 23 to 32 and cohesion intercept of 7 kn/m 2 to 9 kn/m 2. In the present study, tire waste chips of maximum size 4mm was used whose unit weight is found as 6.3 kn/m 3. The cohesion intercept and angle of internal friction found as 9. kn/m 2 and 26 respectively. The properties of rubber tire waste is shown in table Geogrid (GG) Table 2. Properties of Tire Chips Properties Values Particle size, mm 3 to 4 Thickness, cm.7 Maximum density, kn/m Minimum density, kn/m Cohesion Intercept, kn/m 2 9. Friction Angle, degree 26 The low strength geogrid is selected because soil-tire chip mixtures should require lighter reinforcement because of their high strength and thus low cost geosynthetics is employed. Properties of geogrid used is summarized in table 3. ISSN:

3 Table 3 Physical Properties of Geogrid Properties Values Type CE121 Aperture shape Diamond Aperture size (mm) 8 6 Mesh thickness, mm 3.1 Weight (g/ m 2 ) 737 Tensile strength (kn/m) 7.68 Extension at maximum load (%) 2.2 Extension at peak load 3.2% Load at 1% extension (kn/m) Methods Rubber waste was used in soil in two different modes. In mode 1, four different layer combination of soil and rubber waste were used such as, soil + soil +, soil + + soil, + soil + soil and soil + + (Figure1). In mode 2, soil and completely inter mixed and compacted to maximum dry density. To study the load-deformation behavior of soil and soil + rubber tire waste mixtures, load tests were conducted on constrained samples of soil, rubber and soil + rubber tire waste mixture in a cylindrical tank of.3 cm and 18 cm height both in unreinforced and reinforced case. Soil, rubber tire waste and layered soil + rubber tire waste mixtures were compacted to its maximum dry density and optimum moisture content (if applicable). The steel loading plate, which is 8 mm in diameter and 7 mm in thickness, was placed such that the centroid of samples and the plate coincides with each other to prevent eccentric loading acting on the soil. A surcharge plate providing pressure of 1.46 kn/m 2 is placed. The load was applied on the circular plate through a proving ring by reaction method. SOIL SOIL SOIL Soil alone Rubber Waste alone Fig.1. Various Combinations of Soil + Rubber Tire Waste Mixture Repeated load tests were also conducted with a cyclic load of.8 times the observed maximum load (peak load could not be observed) was applied for soil and rubber and soil-rubber mixture of selected combination from the static load test. The strain rate was designed to simulate rapid straining, such as the dumping of overburden fill above a rubber waste layer or that caused by construction equipment or traffic vehicles. The range of loads applied in tests was governed by the range of vertical stresses acting on sample in sub grade fills. Samples were subjected to as many as or 6 cycles of load until the slope of the load- ISSN:

4 deformation curve get constant. After reaching safe stress, the sample was allowed to rebound completely before applying the next loading cycle. The value of total, elastic and plastic strain was noted and the variation of static strain with percentage of rubber waste and accumulated strain with number of cycles was also plotted. 4. Results and discussions 4.1. Load-Deformation Characteristics of Soil + Rubber Waste (Unreinforced) Figure 2 shows a comparison of load-deformation characteristics of soil, rubber waste and four different combinations of soil + layers along with inter mixes soil + materials. Load-deformation of soil alone and alone are the two extremes and other combinations very much lie well within the same irrespective of deformation level. Among the combinations, S + + S layer and intermixes soil + seemed to have similar behaviour compared to other layer combinations, especially when deformations are less than %. Load carrying capacity was calculated and shown in table.4.for both at % and 2% deformation level. At % deformation, the peak load for S + S + and S + intermix gave.46 kn and.4 kn respectively and where as at 2% deformation, S+S+ resulted in.44 kn and S + intermix gained a peak of.68 kn. This only suggests that apart from the recoverable strain that will be gained in the soil by using rubber tire waste material, the placement combinations are also very important in using as an admixture for the improvement of subgrade soil. Either at low strain level or larger strain level, intermixing is expected to perform better than keeping in layers. In case of difficulty arises in mixing, if is to be placed in layers, than soil, cover can be placed on the top so that the load is transferred uniformly and efficiently over through soil layer as a member. Fig. 2. Load-Deformation Curve for Soil + Layer 4.2. Load Carrying Capacity of Soil + Rubber Tire Waste (Geogrid Reinforced) From figure 3, it can be observed that in all the cases, with the presence of geogrid reinforcement, the peak load corresponding to any deformation increases. At % deformation the reinforced S+S+ layer has shown a peak load of.3 kn and.46 kn for unreinforced case. The peak load at % and 3% for reinforced (GG) + S(GG) + S is.8 kn and.61 kn respectively and the same have come down to.26 kn and.3 kn in case of unreinforced and there is not much difference between the reinforced and unreinforced + Soil + Soil layer. Unlike the perivious case, where was below the soil mass, the stiffness of reinforcement is coming to effect on load sharing mechanism only when the load is transferred from soil to underlying. Refering figure 3, for S (GG) + (GG) + combination, it is seen that there is no difference between reinforced and unreinforced case on load carrying capacity for any level of deformation. In case of reinforced Soil + (GG) mix the peak load observed is.9 kn and unreinforced case is.68 kn with a percentage difference of 24.4%. These results only implied that providing reinforcement could not alter the load carrying capacity substantially unlike the case where sandwiched between soil layers. ISSN:

5 Fig. 3. Load-Deformation Curve of Soil + Rubber (GG) for Different Combinations Table 4 gives the details of peak load corresponding to % and 2% deformations. The geogrid reinforced S (GG) + (GG) +S and Soil + (GG) are giving a promising results and the stiffness of geogrid is very much pronounced. Provision of geogrid could not effectively act as reinforcement even when it is placed in layers for the cases of + S + S and S + +. Both at % and 2% deformation load, the load carrying capacity of reinforced soil + layer always higher compared with unreinforced soil + layer. Table 4. Load-Deformation Behaviour of Soil+Rubber Waste with and without Geogrid Reinforcement Peak load in kn Deformation of % Deformation of 2% Description Un reinforced Un Reinforced Reinforced reinforced Soil alone Rubber alone S +S S ++S S+S S S + inter mix Cyclic Response of Soil + Layers (Unreinforced) The static stress under which repeated load test conducted was kpa for soil and 9 kpa for rubber tire waste, which is approximately 8% of the peak load corresponding to the deformation of %. In the first cycle, the soil alone showed (Figure. 4. &.) a plastic strain of 14.4% and alone showed 3.% strain and consecutive number of cycles, the soil responded a recovering strain level of. to 2% till the end of the cycles and whereas for alone, the recovery was the same as in the first case and in the process total accumulated strain for soil is more than 17% and for, it is hardly 3% only. Figure 6 & 7 Show the stress-strain characteristics, under repeated load condition, for S++S and S+S+ layer respectively. While elastic recovery is low for S+S+S layers and the same is relatively high for S++S layers. The unrecovered strain is % to 1% for S++S combination, where as it is 7% to 12% for S+S+. This may be due to the fact that only after the compression of soil layer the load is transferred to the underlying layer. ISSN:

6 STRESS IN KN/m STRAIN % Fig. 4. Stress-Strain Response of Soil under Repeated Load Strain (%) Fig.. Stress-strain Response of rubber alone under repeated load Figure 8 shows the repeated load test on Soil+ intermix. Total strain is between 9% to 13% and recoverable strain did not show the expected value. It is varying between.8% to.9% only. Even though Soil+ mix provided a better strength equal to that of soil compared with other soil+ layer combinations the recoverable elastic strain is high. This may be because the operating stress and corresponding deformation level is low for the to undergo its fullest compression in turn to regain its original size, as is happening with the individual layer system. Table.. shows the compression of total strain and recoverable elastic strain for varying number of cycles, for soil and layer. In different combinations while soil alone is having the total strain of 2% and elastic strain of.8%. The has total strain of 18.6% and recoverable strain of 13.8%. ISSN:

7 Soil Soil Fig. 6. Stress-Strain Response of Soil Layer + Rubber Waste Layer + Soil Layer under Repeated Load Soil Soil Fig. 7. Stress-strain Response of soil layer + soil layer + rubber waste layer under repeated load The total strain in the combination of layers of S++S and S+S+ is varying from 9% to 16% and the elastic strain is the least for S+S+ layer and Soil+ mix (.7% to.9%) (Table.6). Corresponding to fifth cycle, the same is between.4% to 7% for S+ S+ and S+ +S. From the variation of recoverable strain, it may be inferred that considering the load carrying capacity and as well as the enhancement of recoverable elastic strain, preference of layer may be S++S > S++ > Soil+ intermixing. It can also be observed from the table.6. that introducing 33% of rubber waste to soil results in more elastic strain which is relatively comparable to that of pure rubber waste. For example, considering fifth cycle, the elastic strain of soil increases from 4% to 42.89% of total strain. But the elastic strain of pure rubber waste is arrived as 74.2% of its total strain and hence introduction of 33% rubber waste content is more effective when considering both load carrying capacity and rebound nature. Earlier Andrew et al. (1999) investigated the deformation behavior of shredded tires alone under repeated load and found that shredded tire chips undergo less plastic strain per cycle with successive load cycles, ranging from 8% strain for first cycle to.3% strain for 8 th cycle. Tatlisoz and Edil (1997) conducted three loading and unloading cycles on sand, silty sand and clay-tire chip mixtures and found % static strain in ISSN:

8 the first loading cycle and of 2-3% in subsequent cycles for all soil-tire chip mixtures, but arrived a static strain of 26% for tire chips only Soil+ intermix Fig.8. Stress-strain Response of soil + rubber inter mix under repeated load Table.. Total and Elastic Strain for soil and layer Description Soil alone alone No of Cycles Total Strain (%) Elastic Strain (%) Table.6. Variation of Total and Elastic Strain For 33% of Soil-Rubber Mixtures Description S +S + S + +S S + inter mix No. of Total Strain (%) Elastic Strain (%) Cycles Unreinforced Reinforced Unreinforced Reinforced ISSN:

9 4.4. Behaviour of Geogrid Reinforced Rubber Tire Waste on Soil Layers under Repeated Load. Figure. 9, 1 and 11 shows the results of a typical repeated loading test on S+S +, S + +S and Soil + inter mix with geogrid. This stress-strain curve behaves as same as to that of without geogrid except that increase in static strain in all cycles of loading because the applied stress was more than that of mixtures alone. Referring table.6 it can also be observed that the presence of geogrid showed moderated to high influence in change of elastic or accumulated strain (when considering as percentage of static strain) Geogrid Soil(GG) Soil(GG) Fig.9. Stress-strain Response of soil layer (GG) + soil layer (GG) + rubber tire waste layer with geogrid reinforcement under repeated load Geogrid Soil(GG) (GG) Soil Fig.1. Stress-Strain Response of Soil Layer (GG) + Rubber Tire Waste Layer (GG) + Soil Layer with Geogrid Reinforcement under Repeated Load The percentage increase of recoverable strain in reinforced Soil+ layer is higher compared to unreinforced case. Comparing static load bahaviour with repeated load, eventhough soil++soil and soil+ inter mix did not show so much of recoverable strain, but considering the overall behavior, this two combination is expected to behave much better than other two combinations especially at larger number of cycles of loading. The variation of accumulated strain (expressed as percentage of its total strain) with number of cycles is shown in figure. 12. It can be understood from the figure that the plastic strain of soil decreases with increase in percentage of rubber waste and also introduction of 33% rubber waste reduces the plastic strain of soil by ISSN:

10 more than 1% and thereafter decrease in plastic strain is marginal. Hence introduction of 33% rubber waste content is more effective in both the cases with and without geogrid. Futher comparing table 6, it may observed that the provision of geogrid reinforcement improved the recoverable elastic strain considerably compared to unreinforced case. Thus it may be concluded that the geogrid reinforced Soil+ either intermixed one and Soil++Soil layer form, can perform as a better material compared to soil itself Soil+ (GG)inter Geogrid mix Fig. 11. Stress-strain Response of soil + rubber (GG) inter mix with geogrid reinforcement under repeated load Fig.12. Accumulated Strain with Number of Cycles for Soil-Rubber Waste Mixtures with and without Geogrid Reinforcement. Conclusions Static and repeated load was conducted on soil with in layer combinations with and without geogrid reinforcement. The same tests were also conducted on soil + completely mixed conditions. Based on the analysis of results following general conclusions may be drawn. 1. Among the four different soil + in layer form load carrying capacity of soil + + soil is found to be higher than other combinations such as + soil + soil and Soil + + and soil + soil + layers. ISSN:

11 2. inter mixed with soil showed strength equal to that of soil itself, whereas in layer combinations none of the four combinations showed load carrying capacity equal to the soil itself. This could be because of larger amount of elastic compression of, no resistance offered by the soil + layers, especially when deformations are less than %. 3. Compared to unreinforced case, the reinforced soil + layer showed higher load only at 2% deformation and at % deformation effect of reinforcement is not seen, and this is the trend even in other soil + layer combinations. 4. Total strain for soil++soil, soil+soil+ was between 9% and 12% corresponding to five numbers of cycles and the recoverable strain was varying between 2% and 7%. In Soil+ mix produced total strain of 13.8%, still the recovery was close to.9% only. Reason for less percentage of recoverable strain for soil+ inter mix may be due to the operating stress level and also very fewer number of repeated load cycles selected in this study. It is postulated that at larger number of repeated load cycles the soil+ mix may show a better recoverable strain.. Reinforced Soil+ layers produced the total strain of 22% to26% corresponding to five numbers of cycles whereas reinforced soil+ inter mix produced % strain. The recoverable elastic strain varied between 9% to a maximum of 14% and for soil+ inter mix it is 2.4%. These values are 2 to 2. times higher than that of unreinforced case under the same repeated load conditions. These results only imply that reinforced soil++soil layer or soil+ intermix could always behave as a good foundation material below the pavement under the repeated load conditions. As the pavement is subjected to repetitive loading, it is suggested that geogrid reinforced soil + + soil (or) soil + intermixed can be used as subgrade component to enhance the elastic property of subgrade and to reduce the plastic deformation. 6. References [1] Cetina H.; Fenerb M.; and Gunaydinb O.; (26). Geotechnical properties of tire-cohesive clayey soil mixtures as a fill material, Engineering Geology, vol. 88 (11), pp [2] Drescher.A., Newcomb.D., and Heimdhal.T.(1999). Deformability of shredded tires, Final report of Department of Transportation. [3] Gary J. Foose.; Craig H.Bensonand Peter J.;Boosscher (1996). Sand Reinforced with Shredded Waste Tires Journal of Geotechnical enginnering, vol. 122 (9), pp [4] Shobana.K.G (28). Enhancement of Soil Suitability Using Rubber and Plastic Wastes. A post graduate thesis submitted to faculty of civil engineering, Anna University Chennai. [] Sungmin Yoon.; Monica Prezzi.; Nayyar Zia Siddiki.; Bumjoo Kim ().Construction of test embankment using a sand tire shred mixture as fill material, Waste Management, vol. 26, pp [6] Tatlisoz.N.; Benson, C. H., and Edil. T.B. (1997). Effect of fines on mechanical properties of soil-tire chip mixtures. ASTM International, vol.12 (), pp [7] Yang, S.;Lohnes.R.A.; and Kjartanson.B. H.; (22). Mechanical properties of shredded tires. Geotechnical Testing Journal, Vol (1), 22, pp [8] Young, M. H.; Sellasie, K.; Zeroka, D.; and Sabni. G.; (23). Physical and chemical properties of recycled tire shreds for use in construction. Geotechnical Engineering, vol. 129 (1), pp [9] Youwai,S.; Bergado, D. T.; and Supawiwat. N.; (24). Interaction between hexagonalwire reinforcement and rubber tire chips with and without sand mixture. Geotechnical Testing Journal, vol. 27(3), pp ISSN: