Assessing recycled/secondary materials as pavement bases

The use of recycled or secondary materials in pavement construction is gaining popularity owing to the added advantages over conventional materials, which include the conservation of natural resources, conservation of energy, preservation of the environment and reduction in life-cycle costs. In this research, two types of recycled materials, namely reclaimed asphalt pavement and cement-stabilised quarry fines, were utilised as pavement base materials for a highway extension project in Arlington, Texas, USA. Prior to the construction of test sections, a series of laboratory studies including strength, compressibility, swell/shrink and resilient modulus tests were performed on the selected base materials to verify their suitability as base materials for pavement construction. Pavement test sections were instrumented with horizontal inclinometers and pressure cells to monitor the long-term performance of these new base materials. Pavement surface profiling surveys were also conducted at regular intervals to monitor for any accumulated roughness of the pavement surfaces. Analysis of results obtained from both laboratory and field monitoring studies demonstrates that these secondary materials can be effectively used as pavement bases. The sustainability issues of this project are also discussed in detail

Repeated Load Tests on Geocell Reinforced Sand Subgrades

In this research, results from a series of large scale dynamic model tests on geocell reinforced and unreinforced homogeneous sand beds are presented. The placement density of sand in all the tests was maintained at 70%. The loading was applied through a circular steel plate which replicates the load application from a passenger car. A single axle wheel load of 40 kN was assumed on the pavement surface of which 7 kN was calculated to be applied on the subgrade layer. The influence of the width and height of the geocell reinforcement on the cyclic behavior of the loading system was studied and the performance improvement in terms of traffic benefit ratios and cumulative plastic deformations/rutting was determined. A traffic benefit ratio was observed to be as high as 45 for the case of geocell size h/D=1, b/D=4 at 10% plate settlement. The cumulative permanent deformations were reduced by 8 fold for the same case against the unreinforced case at 5% plate settlement

Experimental Evaluation of Geojute Reinforced Sand Beds under Repetitive Loading

In this research, a series of large scale dynamic model tests were carried out on geojute and jute-geocell reinforced sand subgrade in controlled laboratory condition. The tests are conducted on geojute and jute-geocell (made from waste jute bags) reinforced and unreinforced sand subgrade under repeated loading to simulate traffic conditions. The placement density of sand in all the tests was maintained at 70% (stiffer subgrade) and 30% (weaker subgrade). A constant area of geojute and jute-geocell reinforcement was maintained throughout the test series. Cyclic behavior was investigated through varying the density, number of geojute layers and geojute arrangement. The influence of the width and height of the jute-geocell reinforcement on the cyclic behavior of the loading system was studied and performance improvement in terms of traffic benefit ratios and cumulative plastic deformation was determined. The loading was applied through a circular steel plate which replicates the load application from a passenger car replicating a single axle wheel load. A single axle wheel load was applied through a sophisticated double acting linear dynamic actuator which is attached to a 3.5m high reaction frame

Development of Fly Ash Stabilized Recycled Base Material (FRB) for Indian Highways

Reclaimed asphalt pavement (RAP) materials in pavement base courses has proven to be a viable alternative not only to conserve the natural resources but also to reduce the environmental pollution and landfilling. Since RAP is ineffective to be used as a pavement base material, they are often blended with virgin aggregates (VA) or stabilized with cementitious materials. This study, an attempt has been made to develop a fly ash stabilized recycled base material (FRB) by utilizing RAP and class F fly ash. To develop a potential design base mix, RAP:VA mixes stabilized with alkali activated fly ash was considered. The alkali activation is proposed to increase the reactivity of the fly ash to further enhance the strength of the mixes as the presence of aged bitumen coat over the RAP aggregates may affect the long-term strength and durability of the design mixes. Hence, the present study also verifies the durability of the mixes by subjecting the specimens to aggressive wet-dry cycles to quantify the weight loss. The permanency of the stabilizer/activator is also verified through leachate studies. The comprehensive experimental test results indicated that the RAP:VA mixes are durable and found suitable for the base course applications. Based on the experimental data, design charts were proposed to design a pavement system with recycled materials

Evaluation of Rutting Behaviour of Geocell Reinforced Sand Subgrades Under Repeated Loading

This paper summarizes the results from a series of large scale cyclic model load tests on geocell reinforced and unreinforced homogeneous sand subgrades. The sand subgrades are prepared at 70 % relative density thru pluviation technic in a large steel tank measuring 1 m3. A cyclic load of 0.7 and 7 kN was applied on a circular steel plate of 150 mm diameter to replicate a portion of load transfer from an equivalent single axle wheel load (ESAL) on the sand subgrade. The cyclic load was applied through a double acting dynamic hydraulic 100 kN actuator. A series of tests were conducted to study the effects of width and height of a geocell reinforcement on the cyclic behavior of sand subgrades. The performance improvement is quantified in terms of traffic benefit ratios (TBR), cumulative plastic deformations (CPD), modulus of subgrade reaction (ks), resilient modulus (Mr) and rut depth reduction (RDR) for different number of cycles and plate settlements. The configuration of the geocell that provides highest performance in terms of TBR, CPD, and RDR, is considered to be the optimum size of the geocell. It is observed that the optimum geometry of the geocell is capable of reducing the rut depth of about 75 % at 100 cycles and provide about a TBR of 23 at 10 % of settlement ratio

Effect of Curing Time on the Performance of Fly Ash Geopolymer-Stabilized RAP Bases

The long-term integrity of fly ash (FA) geopolymer-stabilized high-percentage reclaimed asphalt pavement (RAP) in the pavement base layer was investigated in this research. The FA geopolymer-stabilized RAP and virgin aggregate (VA) mixes were studied as an economical and durable alternative to 100% VA bases, with an emphasis on the influence of curing time. The maturity age of FA is usually set as 28 days, similar to traditional portland cement. However, due to partial pozzolanic reactions, though geopolymerized, the dilution of partial FA particles does not fully play its role at 28 days of curing time. Hence, this is not a realistic reference time for predicting the service life of FA geopolymer-stabilized aggregate blends. Therefore, a detailed experimental investigation was undertaken to evaluate the ultimate strength, durability, and microstructural characteristics of four distinct FA geopolymer-stabilized RAP:VA blends for a long-term ambient curing time up to 270 days. In this study, the long-term cured specimens showed significant improvement in mechanical strength and stiffness, yielding lower permanent deformations. It was noticed that only about 12% and 40% average unconfined compressive strength (UCS) could be achieved in 7- and 28-day cured specimens, respectively, with reference to their ultimate strength at 270 days. Hence, to examine the microstructural characteristics of powdered FA geopolymer blends, X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), and Fourier transform-infrared spectroscopy (FT-IR) studies were performed. The test results revealed that the consumption of reactive metal ions was continued for an extended period under a controlled curing regime, which resulted in improved mechanical strength and durability of the solidified product

Elasto-Plastic Behavior of Jute-Geocell-Reinforced Sand Subgrade

In this research, a series of large-scale repeated plate load tests were carried out on jute-geocell-reinforced sand subgrades for low-volume road applications. The jute material obtained from waste gunny bags was used to prepare geocells and planar geojute to test under repeated load low-volume traffic conditions. Sand subgrades were prepared in a steel test tank of size 1 m×1 m×1 m at its 30% to replicate a weak subgrade. The elasto-plastic behavior of the jute-geocell-reinforced beds was investigated by varying the height and width of the geocell mattress, infill material (sand and aggregate), and infill density. The performance improvement in terms of traffic benefit ratio, TBR, and cumulative plastic deformation (CPD) were determined. The load was applied through a circular steel plate, which replicates a passenger car's single axle wheel, through a sophisticated double-acting linear dynamic actuator that is attached to a 3.5 m high reaction frame. Results show that the CPDs were higher for weaker subgrades than the stiffer ones. The traffic benefit ratios were observed to be as high as 56 with jute-geocell subgrades with aggregate infill. It was observed that the performance of jute geocell is inferior when used with sand infil

Mechanical response of full-scale geosynthetic-reinforced asphalt overlays subjected to repeated loads

This study aims at evaluating the influence of geosynthetic reinforcements on the structural improvement of asphalt overlays placed on distressed pavement layers using repeated load tests. Full-scale instrumented pavement models were constructed in an indoor steel tank measuring 1000 mm in length, 1000 mm in width and 1000 mm in depth. Full-scale instrumented pavement models consisted of a 650-mm-thick weak subgrade, 250-mm-thick base, 90-mm-thick distressed asphalt layer, binder tack coat, geosynthetic reinforcement (except in control sections), and 50-mm-thick hot mix asphalt overlay. Sensors used in the instrumentation program included earth pressure cells and linear variable displacement transformers installed on the subgrade and surface layers, respectively. Four different geosynthetic types, including woven geo-jute mat (GJ), polypropylene geogrid (PP), polyester geogrid (PET), and fiberglass geogrid composite (FGC) were adopted as asphalt reinforcements. A servo-hydraulic actuator was used to replicate a live traffic wheel load by applying an equivalent single axle contact pressure of 550 kPa at a frequency of 1 Hz. Repeated load tests were terminated after 100,000 load cycles and the behaviour of geosynthetic-reinforced full-scale models was compared with that of unreinforced model. Performance indicators, including Traffic Benefit Ratio (TBR) and Rut Depth Reductions (RDR), were estimated and repeated load test results indicated an increase in the structural performance of geosynthetic-reinforced full-scale models in relation to that of unreinforced model. Among the geosynthetic-reinforced models considered in this study, the FGC-reinforced model showed a comparatively better performance with a maximum TBR of 20 at a permanent deflection of 5 mm and the highest RDR of 56% after 100,000 load cycles, respectively. Maximum reductions of 56% in surface deflection and of 30% in vertical pressure on the subgrade were also observed after 100,000 load cycles in the FGC-reinforced model. © 2021 Elsevier Lt