Pavement Reinforcement Research Articles

GEOGRID REINFORCEMENT OF ASPHALT PAVEMENTS

Geogrid materials applied within asphalt layers defer or prevent the occurrence of reflective cracking. The contribution of this work significantly adds to extending pavement serviceability and improving benefit/cost analysis. Since 1970s many studies have demonstrated the benefits of geogrid reinforcement in asphalt pavements, but this knowledge did not translate to their extensive usage in the actual construction practice. Among potential reasons are higher initial costs, lack of in-depth understanding of working mechanism within adjacent asphalt layers and lack of commonly standard design procedures. This paper presents a recent study, which investigated the effect of geogrid reinforcement on asphalt mixture specimens. Two types of laboratory experiments were conducted, namely monotonic (strength and fracture) testing and cyclic (fatigue and modulus) testing. The results demonstrated a significant strengthening contribution of geogrid, which was observed regarding fracture energy results and terminal deflections in the fatigue testing. This paper also presents a short example connecting pavement deflections with the allowable axle loading (also known as fatigue life) to demonstrate the practical implications of geogrid reinforcement. The undertaken analysis shows the reduction of pavement deflections due to the geogrid application, which potentially leads to a significant extension of pavement fatigue life. Paper concludes with several recommendations for further work in the area of geogrid reinforcement.

Effect of geogrid reinforcement on flexible pavements

Effectiveness of geogrids in flexible pavement reinforcement was investigated throughout laboratory testing and finite-element analysis (FEA). The laboratory testing involved routine material characterization, resilient modulus testing, and five pavement prototype sections. These sections consisted of a 5 cm asphalt concrete (AC) layer, 15 cm granular base layer, and a 30 cm clay subgrade. The base layer was reinforced with a single layer of uniaxial geogrid placed at four different positions within the base layer. The pavement sections were loaded with a static plate-loading equipment and the results were compared with the control section (CS), which had no reinforcement. Results from this study showed that geogrids can be used to reduce tensile stresses in flexible pavement systems. The optimum position of the geogrid reinforcement to reduce tensile strains was found to be directly underneath the AC layer then within 33–50% of the granular base layer height as measured from the bottom of the base layer.

Cracking and interlayer bonding performance of reinforced asphalt pavements

Reinforcement of asphalt pavements has become a valuable constructive method for preventing reflective cracking and prolonging service life of roads. Although the overall advantages of these reinforcements seem beyond doubt, there is still lack of information about the actual benefit of different systems on the prolongation of the road’s lifespan. Further, it is not clear how they affect the bonding between layers along the pavement’s lifetime. This paper investigates the effect of three types of reinforcement systems on the performance of two layered asphalt pavements, mainly considering: (1) Reflective crack propagation. (2) Shear bonding strength. To that end, model and real pavements were constructed in the laboratory and the field using selected reinforcement systems. Designs with various mesh opening sizes and different bond coatings were considered. Afterwards, the pavements were loaded with a down-scaled (MMLS3) and a full-scale (MLS10) traffic load simulator and their performance was compared to pavements without any type of reinforcement. These devices simulate the effect of traffic-similar loading in a compressed period of time. During the loading phase, the crack formation and propagation was monitored through visual inspections and indirectly by measuring the deformation of the pavements with sensors. The interlayer bonding strength was evaluated by coring the pavements and testing the specimens with a Layer Parallel Direct Shear apparatus. Results showed that two reinforcement systems were generally successful in delaying reflective crack propagation. Only one of the systems presented at least similar or even worse performance than the same pavement without reinforcement. On the other hand, it was found that the bonding properties depend on the reinforcement system type, but that in most cases interlayer bond strength was according to the standard requirements.

Nonlinear Deformation Analysis of Geocell Reinforcement in Pavements

Geocell reinforcement has found a large applicability in the area of pavement engineering, and its deformation characteristics play an important role in the analysis and design of pavements. In the present work, a simple analytical approach that idealizes geocell reinforcement as a beam subjected to vertical symmetrical loads and foundation soil as nonlinear Winkler springs are proposed. A detailed parametric study indicated the influence of the weight of infill material, applied loads, the modulus of subgrade reaction, flexural rigidity of reinforcement, interface resistance, and the ultimate bearing resistance of foundation soil on deformation characteristics of reinforcement. Charts that are useful in the analysis and design of pavements reinforced with geocell are presented.

Investigating the performance of geosynthetic-reinforced asphaltic pavement under various axle loads using finite-element method

One of the major factors influencing the performance of highway pavements is traffic loading, which is continuously increasing in number, magnitude and contact pressure. Geosynthetic reinforcement of asphalt pavements is a method for improving the bearing capacity of pavements against heavy traffic loads. This study aims to investigate the effectiveness of geosynthetic on the reduction of critical strains of flexible pavements under various axle load levels. Three types of geogrid have been placed in different positions in a typical asphalt pavement structure, and the critical strains, including the compressive vertical strain on top of subgrade, the maximum tensile strain at the bottom and the maximum shear strain of asphaltic layer have been evaluated under different axle loads of 5, 8.2 and 15 ton. The finite-element method has been utilised for modelling and analysis of pavement structure, in which, the asphaltic layer has been characterised as a viscoelastic material using Prony series. Results show that placing the geosynthetic beneath the asphaltic layer results in the reduction of the longitudinal tensile strain of asphaltic layer, while it is not effective on the vertical compressive strain on the subgrade. Furthermore, results show that, in spite of increasing the critical strains with increasing axle load, the effectiveness of geosynthetic reinforcement under different axle loads varied. At higher levels of axle load, the geosynthetic on the subgrade is more effective in reducing the compressive strain on the subgrade. However, the effectiveness of the geosynthetic beneath the asphaltic surface layer decreases with increasing axle load. In addition, the highest improvement in the effectiveness of geosynthetic for reducing the critical strains at higher axle load levels is achieved when it is placed at the position of the desired critical strain. It is also found that the effectiveness of geosynthetic in reducing the critical strains at higher axle loads increases with an increase in the modulus of geosynthetic.

A Numerical Study on the Implications of Subgrade Reinforcement with Geosynthetics in Pavement Design

The main purpose of this paper is to present a numerical study to demonstrate the implications of subgrade reinforcement with geosynthetics in road pavement design. A parametric analysis was carried out with the finite element program ADINA using two-dimensional modeling. This analysis considered different pavement materials and structures, traffic conditions and subgrade soil quality. The pavement reinforcement effect was analyzed in terms of fatigue and rutting design criteria. Overall, the results of numerical modeling confirmed the reinforcement effect and pointed out the most important factors influencing the use of geosynthetics at the subgrade level for this purpose.

Laboratory Fatigue and Toughness Evaluation of Fiber-Reinforced Concrete

Concrete pavement design is currently centered on steel reinforcement: whether in the form of dowel bars, as in jointed plain concrete pavement, or in the form of continuous rebar reinforcement, as in continuously reinforced concrete pavement. The use of steel in concrete pavements presents durability problems because of the corrodibility of steel. This study evaluated the use of polypropylene fibrillated fibers, polypropylene macrofibers, and carbon fibers as primary reinforcement in concrete pavements for the Louisiana Department of Transportation and Development. Results showed that fiber reinforcement can be used to improve both the fatigue and toughness performance of concrete. When post-cracked strength or toughness was the concern, concrete containing more fibers and fibers with a high tensile strength was desirable. Carbon fibers maintained greater load-carrying capacity at lower deflections than did the steel fibers, which produced the greatest ductility. However, toughness and fatigue performance did not correlate for small deflections; this result suggests that polypropylene macrofibers may be adequate for repeated, low-stress loading. This study also found that when repeated low deflections were a concern, such as with pavements, there had to be sufficient fibers across a crack to maintain a tight crack. Conversely, too many fibers prevented adequate consolidation and aggregate interlock and negatively influenced performance. The resultant pavement design, continuously fiber-reinforced concrete pavement, will provide an alternative to jointed plain concrete pavement and continuously reinforced concrete pavement in highway pavement design that is not susceptible to durability problems associated with corrosion of reinforcement.

The Research of the Governance of Instability Retaining Wall

According to retaining walls of joint construction buildings and office building of the mine of three yuan weizi town, outdoor pavement reinforcement of engineering practice, introduced the design parameters and construction process of the high-pressure jet grouting pile, soil nail wall and drilling grouting, the results showed that reinforcement scheme is reasonable and feasible, there is reference to other similar projects.

Laboratory characterisation of optimised geocomposites for asphalt pavement reinforcement

ABSTRACT: In order to improve road pavement performance, reinforcement systems can be employed in asphalt layers. In this regard, composite materials obtained by combining bituminous membranes with fibreglass grids represent a promising option because they are able to allow both waterproofing and improved mechanical properties of asphalt pavements. At the same time, the presence of reinforcement at the interface inevitably causes a reduction of interlayer bonding that may negatively influence overall pavement strength. The present research had the twofold objective of evaluating the effectiveness of pavement rehabilitation by using geocomposites and identifying an optimised product. Particularly, the present experimental study intended to characterise three reinforcing materials produced by combining an elastomeric membrane with different reinforcement types and positions. Moreover, the prospective use of a tack coat at the interface was also evaluated. To achieve these aims, interface shear tests and both quasi-static and dynamic flexural tests were carried out on double-layered reinforced samples prepared in the laboratory. An unreinforced reference system was also investigated for comparison purposes. The experimental results showed that improved mechanical properties were achieved in the case of reinforced systems. This research study also provided useful suggestions for the production and utilisation of an optimised geocomposite for asphalt pavement reinforcement.

A Review on Using Crumb Rubber in Reinforcement of Asphalt Pavement

An immense problem affecting environmental pollution is the increase of waste tyre vehicles. In an attempt to decrease the magnitude of this issue, crumb rubber modifier (CRM) obtained from waste tyre rubber has gained interest in asphalt reinforcement. The use of crumb rubber in the reinforcement of asphalt is considered as a smart solution for sustainable development by reusing waste materials, and it is believed that crumb rubber modifier (CRM) could be an alternative polymer material in improving hot mix asphalt performance properties. In this paper, a critical review on the use of crumb rubber in reinforcement of asphalt pavement will be presented and discussed. It will also include a review on the effects of CRM on the stiffness, rutting, and fatigue resistance of road pavement construction.

Long-Term Evaluation of Geosynthetic Reinforcement of Flexible Pavements Constructed over Thick Organic Soil Deposits

Many regions throughout Florida have thick deposits of organic soil. Roadways built over these deposits often exhibit differential settlement, significant rut depths, and extensive cracks in a relatively short period of time. The Florida Department of Transportation constructed an experimental project on a realigned portion of State Road 15 on the southeastern shore of Lake Okeechobee in Palm Beach County to evaluate the effect of geosynthetic reinforcement on pavement performance. This roadway traverses farmlands with deep layers of organic material just beneath the surface and has a history of poor performance. The experimental project included four 500-ft sections with combinations of geogrids and geotextiles placed below the base and above the organic material. A fifth section of similar length was constructed with no geosynthetic reinforcement and served as a control. In addition to geosynthetic reinforcement, the alignment was surcharged before construction. The investigation showed that surcharging alone significantly improved the pavement performance compared with historical pavement condition and rehabilitation records. Geosynthetic reinforcement doubled the equivalent single-axle loads allowed on the unreinforced section. A rigid geogrid or woven geotextile placed below the base appeared to provide a slightly stiffer and better-performing pavement than a flexible geogrid. This paper documents the research program and provides details on the improvement resulting from surcharging and geosynthetic reinforcement.

The Effect of Utilization of Geogrids on Reducing the Required Thickness of Unpaved Roads

The inadequacy of many existing roads due to rapid growth in traffic volume provides a motivation for exploring alternatives to existing methods of constructing and rehabilitating roads. The use of geosynthetics to stabilize and reinforce paved and unpaved roadways offers one such alternative. Many studies were conducted to evaluate the improvements associated with geogrid reinforcement of pavements. It is widely believed that geogrid reinforcement of roadways can extend the pavements service life and/or reduce the pavements structural thickness. This paper examines a method to compare traditional pavement structure designs, absent of geosynthetics, to pavement structure designs incorporating geosynthetics. At first, a specific unpaved road structure design is presented with recommended corresponding traditional road structure components. The road structure is then re-examined incorporating newly developed, reengineered geogrid. Finally, related costs with this particular design are outlined, analyzed and compared. In this case, cost savings achieved by using geogrid are substantial.

Review of glass fibre grid use for pavement reinforcement and APT experiments at IFSTTAR

Reinforcement using an interlayer system has been demonstrated for more than four decades as a multi-purpose solution to improve performance, to extend service life and thus to reduce maintenance costs of road pavements. Among a large number of existing interlayer systems, glass fibre grids have shown effective use in pavement reinforcement with a hot mix asphalt overlay. Recently they have received increasing attention from the pavement community. However, as for other types of interlayer systems, the mechanisms underlying the effectiveness and proper installation of this type of reinforcement system are still not fully understood, and the choice of the most appropriate grid (e.g. mesh size, tensile strength) and its optimal location in the pavement system are mainly based on experience. This article presents firstly a literature review on the use of glass fibre grids in pavement reinforcement. Then some results of recent full-scale tests on the accelerated pavement testing facility of the IFSTTAR are presented. They confirm that glass fibre grid properly installed near the bottom of the asphalt layer improves significantly the fatigue life of the reinforced pavement. They also demonstrate the efficiency of glass grid use under only a thin asphalt overlay. Finally, first results obtained using an original instrumentation of glass grid strands by means of strain gages, to understand better the mechanical behaviour of the glass fibre reinforcement in a new pavement structure are described.

Laboratory Testing of Fatigue Crack Growth in Geosynthetically Reinforced Large Scale Asphalt Pavement Samples

While using the geosynthetics for pavement reinforcement the proper role and designed application is often misunderstood by engineers and constructors of such technology in asphalt road structures. The efficiency of reinforcement is erroneously identified with increasing the AC stiffness rather than fatigue life of reinforced pavement system. The original laboratory method is developed here in order to check the influence of selected reinforcing geosynthetic type on a fatigue life of asphalt pavement samples. To simulate real pavement conditions the research laboratory set-up scale was fit to large size samples cut from asphalt pavement layers. Two types of commonly used in Poland geosynthetic materials were tested in order to evaluate the reinforcement efficiency on inhibition of crack propagation. Test results also gave some indications on numerical model simulation parameters.

Toward a Better Understanding of Benefits of Geosynthetics Embedded in Asphalt Pavements

Reflective cracking is a serious issue in asphalt pavements. A common technique for preventive maintenance and rehabilitation is a thin asphalt concrete overlay; however, the application of a reinforcement can be a more suitable solution because such reinforcement can prevent or delay crack propagation. This paper presents research undertaken within a study of asphalt concrete overlays that included geosynthetics. A program of laboratory experiments and detailed analyses was conducted to gain insight into the effect of reinforcement in asphalt pavements by evaluating and quantifying the benefits of geosynthetic interlayers. Two test approaches were used. In the first approach, the specimens were analyzed by means of monotonic tests to investigate the bond at the interface and the contribution of the reinforcement to tensile strength. The results of the direct shear test indicated that the geosynthetic was able to guarantee a good bond at the interface, even at the end of the test. In the second approach, a nonconventional fatigue test was adopted to characterize the reinforced systems’ ability to resist fatigue cracking. X-ray tomography was performed to investigate the void structure of the beams tested under cyclic loadings. The research findings underline the benefits of geosynthetic interlayers embedded in asphalt pavements. The geosynthetics reduce the amplitude of the crack for high displacements and keep the pavement structure intact, even after moderate cracking has occurred in the overlay.

An overview on the use of geosynthetics in pavement structures

Pavement structures commonly fall into two main categories, namely, flexible and rigid pavements. Such structures just as other structures are susceptible to different types of distresses. In order to minimize the deterioration of pavements, geosynthetic reinforcement is one of the techniques adopted to improve their performance. As a result, employment of different geosynthetics to pavement structures is reported by various researchers. This paper aims to present and discuss the findings from some of the studies on utilizing geosynthetics in flexible pavements. Furthermore, three most common usages of geosynthetics, so called, fluid barrier, strain absorbing, and reinforcement agent in pavement structures are investigated in this paper. Key words: Pavement deterioration, geosynthetics, pavement reinforcement, cracks, rutting, durability.

Evaluation of geogrid base reinforcement in flexible pavement using cyclic plate load testing

In this paper, the performance of geogrid base reinforcement in flexible pavements was evaluated using cyclic plate load testing. A 40-kN cyclic load was applied through a 305-mm diameter steel plate. The investigated parameters included geometry, location and tensile modulus of geogrids. The stress distribution, permanent vertical strain and developed porewater pressure in the subgrade, as well as, the strain distribution along geogrids were studied. The test results showed that the inclusion of geogrid can significantly improve the performance of a flexible pavement and that the traffic benefit ratio can be increased up to 15.3 at a rut depth of 19.1 mm. Better performance was observed when geogrid layer was placed at the upper one-third of the base aggregate layer. The results also demonstrated that the geogrid helps in redistributing the applied load to a wider area on top of the subgrade layer, thus resulting in less accumulated permanent deformation in the subgrade.

The behavior of grids and nets in asphalt pavement

In this article, we want to clarify conceptual confusions about grids and nets applying in asphalt pavements structures, define the repairing and -in some cases- damaging effect of grid usage. The biggest question in reinforcement of pavement is the possibility of mixture of grid and net with the asphalt layer below. To observe these attributes we used the method used at bridge lining: slide method. Small and large wheel observations have been made to research track appearances in fortified construction. The lifetime of the construction have been observed by a fatigue method: the standard four point bending method and master curve of the structure. The computer limited number model have been used to prove fatigue results, and with the adequate material model development used at different type of asphalts showed how gross asphalt can be replaced by the nets and grids usage.

Mechanistic–Empirical Design Model Predictions for Base-Reinforced Pavements

A mechanistic–empirical design method for geosynthetic-reinforced bases of flexible pavements is described. This method shares features with a nationally recognized mechanistic–empirical method developed through NCHRP Project 1-37a for conventional, unreinforced flexible pavements. The method developed for reinforced pavements contains material and damage models for the different layers of the pavement cross section, testing methods for identification of material properties, incorporation of reinforcement into a finite element response model, and development of response model modules that account for fundamental mechanisms of reinforcement. Unreinforced mechanistic–empirical models were field calibrated from low-volume road test sections constructed in two pavement test facilities. One facility involved full-scale tests loaded by a heavy vehicle simulator. The second facility involved large-scale laboratory model tests with cyclic load applied to a stationary circular plate resting on the pavement surface. Reinforced models were then compared with test sections from these same two facilities to gauge the suitability of the developed modeling techniques. A sensitivity study was performed to evaluate reinforced models for bracketing combinations of pavement traffic level, sub-grade stiffness, reinforcement type, and reinforcement position. The majority of the models were set up to evaluate the increased number of traffic passes that could be applied when reinforcement was added to the cross section. Several models were created to evaluate the reduction in base course thickness for an equal number of traffic passes for reinforced and unreinforced sections. Pavement section performance was evaluated for permanent surface deformation and asphalt concrete fatigue cracking. This paper focuses on the results of these predictions and the implications for the use of geosynthetic reinforcement in low-volume roads.

Importance of Concrete Temperature Control During Concrete Pavement Construction in Hot Weather Conditions

The development of high concrete temperatures could cause a number of effects that have been shown to be detrimental to long-term concrete performance. High concrete temperatures increase the rate of hydration, thermal stresses, the tendency for drying shrinkage cracking, and permeability and decrease long-term concrete strengths and durability as a result of cracking. Data from the Texas Rigid Pavement database were analyzed to reveal whether there are increased numbers of failures as the air temperature at placement increases. It was shown that this was the case for both major coarse aggregate types: limestone and siliceous river gravel. The results of the analysis emphasize the importance of concrete temperature control during concrete pavement construction in hot weather conditions. Most states specify a maximum concrete temperature at placement to mitigate the detrimental effects of placement during hot weather. The specified limit remains the same irrespective of the type of mineral or chemical admixtures used. To produce specifications that encourage contractor innovation and the use of improved materials, modern specifications should account for these materials to ensure improved concrete performance under all placement conditions. To provide improved performance for sections paved under hot weather conditions, it is proposed that the continuously reinforced concrete pavement reinforcement standards be redesigned to provide steel quantities for specific use during hot weather conditions and that an end-result specification that limits the maximum in-place concrete temperature during hydration be implemented.