Experimental Study on Geocell-Reinforced Recycled Asphalt Pavement (RAP) Bases under Static and Cyclic Loading
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Asphalt pavement
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Utilization of 100% recycled asphalt pavement (RAP) material in the base layer of road construction can provide a cost-effective and sustainable solution. However, excessive permanent deformation of RAP reduces its applicability for such projects. In this study, the effectiveness of geocell reinforced RAP base (GRRB) layers for the flexible pavement sections constructed over the expansive subgrade is investigated. Furthermore, the mechanism involved in the improvement of material stiffness because of the development of additional confining stress in the reinforced base layer is also presented in this paper. During the initial monitoring period, the average vertical compressive stresses over the pavement subgrade for the reinforced sections were observed to be significantly lower in comparison with the corresponding unreinforced sections. The preliminary results indicate that GRRB layers can significantly improve the performance of the pavement by controlling the subgrade deformation.
Expansive
Asphalt pavement
Subbase
Base course
Base (topology)
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Asphalt pavement
Resilience
Infill
Asphalt concrete
Fatigue cracking
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When flexible pavements reach the end of their service life, they are often rehabilitated by removing existing hot mix asphalt (HMA) surfaces and replacing the removed portion with new HMA or concrete. A large amount of recycled asphalt pavement (RAP) materials are created every year during the rehabilitation and reconstruction of existing flexible pavements. Due to the existence of asphalt, 100% RAP typically has low stiffness and high creep and permanent deformation potentials under traffic loading, which are the concerns in the use of RAP as a base course. The use of RAP for pavement construction by itself is a sustainable option, and more sustainability can be obtained by increasing the life of such pavements. Geocell, a three-dimensional geosynthetic product, has been proposed by the authors to stabilize RAP bases. A series of medium-scale static plate loading tests and large-scale cyclic plate loading tests were conducted on unstabilized and geocell-stabilized RAP bases to investigate their stiffness and creep and permanent deformations. The test results showed that geocell significantly reduced the creep and permanent deformations of the RAP bases and increased the resilient deformation and stiffness of the RAP bases. Therefore, 100% RAP can be used as a base course material with geocell confinement as a sustainable roadway construction technology.
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Asphalt pavement
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In the present study, the feasibility of coarse reclaimed asphalt pavement (RAP) for dry lean concrete (DLC) and pavement quality concrete (PQC) mixes is assessed through laboratory and field investigation. Two kinds of RAP aggregates, namely RAP1 and RAP2 obtained from two differently aged pavements (10 and 20 years) were used for the present investigation. The properties of aggregates and concrete mixes were investigated in the laboratory and based on the results, 100% replacement of natural aggregates by RAP1 in the DLC layer and 65% replacement by RAP2 in the PQC layer was carried out. Additionally, one control slab was constructed. It was found that for achieving the suggested strength, RAP1-inclusive DLC mixes required at least 50% extra cement quantity. Similarly, incorporations of RAP2 was found to reduce the compressive strength of the PQC mix; however, the percentage reduction in flexural strength was comparatively lower. Structural evaluation through falling weight deflectometer provided with similar findings. Incorporation of RAP2 was found to increase the porosity of the slab but found to have a beneficial effect in terms of lower temperature differential. The combined stresses on the pavement slab were found to be either comparable or slightly lower in RAP-inclusive pavement as compared with the control slab.
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The research project encompassed evaluating the performance of New Jersey Department of Transportation (NJDOT) specified aggregates at the respective NJDOT gradation ranges (high end, middle, and low end) and providing guidance as how to modify the gradation ranges to provide better performance in the field. Currently, the NJDOT specifies the use of granular materials by gradation only. However, it is well known that the gradation of granular materials has a dramatic impact on its performance. Therefore, base and subbase materials were sampled from three regions in the state and evaluated under the following performance tests: permeability (falling and constant head conditions), triaxial shear strength, cyclic triaxial loading, California Bearing Ratio (CBR) and resilient modulus. Testing was also conducted on recycled asphalt pavement (RAP) and recycled concrete (RCA) to evaluate their potential use as base and subbase materials. Materials were tested at their respective natural gradations and at manufactured gradations which represented the NJDOT high, middle, and low areas of the gradation specification in order to provide guidance as how to better refine the current NJDOT gradation specification. Testing concluded that the gradation has an impact on each material and source tested. On average, permeability increased with increasing coarse fraction and decreasing percent fines. The triaxial strength increased as coarse fraction increased; however, the permanent deformation measured from the cyclic triaxial test indicated that at the gap-graded high end of the gradation band, instability was prevalent for the rounded subbase aggregates. This is most likely due to rounded aggregate particles not interlocking during loading (The gradation of this type of material is very similar to the non-stabilized open graded base layer that the NJDOT has used in the past). The resilient modulus testing followed a similar trend. Overall, the closer the aggregate gradation was to the middle/high side of the NJDOT gradation specification, the better the performance. The testing of the RAP, RCA, and their blends with the base material, showed that as the % RAP increased in the blend, both the CBR value and permeability decreased. RAP also caused larger permanent deformations during the cyclic triaxial testing. The inclusion of RCA provided the largest CBR, largest resilient modulus, and lowest permanent deformation values. However, as the % RCA increased, the blend’s permeability decreased.
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Subbase
California bearing ratio
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The objective of this study is to understand the importance of using RAP for the construction of bituminous pavements. From this study and from previous research papers it can be concluded that using RAP is advantageous as RAP mixes can yield results equal or even higher than virgin mixes. If calculated and implemented appropriately RAP mixes have a constructive effect on various parameters like Marshall Stability, moisture resistance and density. This paper presents the importance of using RAP mixes.
Asphalt pavement
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Asphalt pavement
Base (topology)
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The term Reclaimed Asphalt Pavement (RAP) is used to designate a material obtained from the removal of pavement materials. RAP is used across the US in multiple applications, largely on asphalt pavement layers. RAP can be described as a uniform granular non-plastic material, with a very low percentage of fines. It is formed by aggregate coated with a thin layer of asphalt. It is often used mixed with other granular materials. The addition of RAP to aggregates decreases the maximum dry unit weight of the mixture and decreases the optimum water content. It also increases the Resilient Modulus of the blend but decreases permeability. RAP can be used safely, as it does not pose any environmental concerns. The most important disadvantage of RAP is that it displays significant creep. It seems that this is caused by the presence of the asphaltic layer coating the aggregate. Creep increases with pressure and with temperature and decreases with the degree of compaction. Creep can be mitigated by either blending RAP with aggregate or by stabilization with chemical compounds. Fly ash and cement have shown to decrease, albeit not eliminate, the amount of creep. Mechanical stabilizing agents such as geotextiles may also be used.
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