CAPSA 2015 – Peer reviewed published paper © Copyright – CAPSA2015

A Synthesis of Applications of the MLS as an Innovative System for Evaluating Performance of

Asphalt Materials in Pavement EngineeringFred Hugo

University of Stellenbosch

Wynand JvdM SteynUniversity of Pretoria

Abstract— The purpose of this paper is to provide a succinct synthesis of innovative applications of the Mobile Load Simulator (MLS) test system applicable to bituminous pavements. The extensive volume of reported applications of the system during the past fifteen years serves as a reference base validating it as an innovative testing system. A synthesis of facets of analyses and findings from the wide range of selected case studies applicable to bituminous pavements was done. These include MLS applications in laboratories and in the field. Also MMLS3 applications in conjunction with other full-scale trafficking equipment such as, the Accelerated Loading Facility (ALF), Heavy Vehicle Simulator (HVS) and WesTrack and NCAT vehicular test tracks.

The MLS system comprises the one-third scale MMLS3 and the full-scale MLS10 and MLS66 in conjunction with various supplementary devices such as the Portable Seismic Pavement Analyser (PSPA), a heating and cooling system, a wet trafficking system, surface profilometer, contact surface stress measurement with foil pressure cells and a system for extracting specimens from compacted slabs for testing mix properties.

Applications include evaluation of permanent deformation and susceptibility to moisture damage of bituminous road paving mixtures, fatigue evaluation, testing of composite pavement systems including reinforced asphalt and cement treated material layers and other aspects of pavement engineering systems and products.

Keywords accelerated pavement testing; pavement performance; optimising structural design; asphalt design and performance

I. INTRODUCTION

The paper provide a succinct synthesis of nine categories of innovative applications of the Mobile Load Simulator (MLS) test system applicable to bituminous pavements. The system comprises the one third scale Model MLS (MMLS3), and the full-scale MLS10 and MLS66 using different wheel load configurations for trafficking. These can be applied in conjunction with various supplementary devices and testing protocols such as the heating and cooling systems, wet traffic testing, surface profiling, a roller compactor, the Portable Seismic Pavement Analyser (PSPA), contact surface stress measurement with foil pressure cells and a system for

extracting specimens from compacted slabs for testing mix properties.

Findings that will be discussed relate to material characteristics, design evaluation, bituminous surface treatments, reinforced pavements, fatigue, airport pavements and comparative Accelerated Pavement Testing (APT) between different trafficking systems. The results have been published in journals and conference proceedings. These have, among other, served to validate the guidelines for specifying and testing of rutting of asphalt materials under different environmental and trafficking conditions.

The paper synthesizes the innovative methods in which this test system (that is being standardized through a SANS method currently) has been applied internationally to solve pavement-related research and design issues, both within and outside of the original design intent of the system. This supports the notion that it is providing the pavement engineer with a complimentary tool that supplements the range of tests, knowledge and experience applied in pavement engineering.

II. SYNTHESIS OF APPLICATIONS OF THE INNOVATIVE MLS SYSTEM ELEMENTS

A. BackgroundThe MLS system was developed in the early 1990s as a

means to test asphalt mixes for rutting performance in the laboratory of the Institute for Transport Technology (ITT) at the Stellenbosch University (SU). A first major development of the system was the MMLS3 in 1997 and the next was the prototype full-scale MLS10 in 2005. This was followed by the full-scale MLS66 in 2009.

Twenty four MMLS3s have been produced and distributed globally and are being applied in a variety of manners. Four full-scale units are being used in China and Europe. Full details relating to the MMLS3 have been incorporated in the SANS 3001 –PD1 2015 test method 3001(3001) that is currently in the process of publication by SABS. Figures 1, 2 and 3 depict the different MMLS3 units. The full-scale units have been applied in a variety of applications that provide insight into the innovative modes in which they were applied. Publication

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relating to these applications are available in the public domain and will be discussed in the respective categories hereinafter.

The MMLS3 comprises four single wheel bogies (or carriages) and can apply a selection of 1 800 to 7 200 load applications in an hour. Trafficking can be done in a fixed linear longitudinal manner or with lateral random distribution of the machine to simulate traffic wander. The tyre inflation pressure of the 300 mm diameter tyres is normally set at 700 kPa, but it can be increased to 850 kPa, which may result in a reduced tyre life. Contact stresses of the MMLS3 were measured with the Stress In Motion (SIM) device of the CSIR [1]. This correlated with data collected at Reno in Nevada [2]. More comprehensive details of the MLS system can be found on the repository website: www.academic.sun.ac.za/mls at Stellenbosch University that is currently being upgraded.

Fig. 1. MMLS3 linked to the air heating unit alongside an artificial dam and water spray unit in the fore-ground for wet trafficking

Fig. 2. MMLS3 in temperature control chamber on the scaled pavement in U Mass with the heating/cooling unit in the rear

Fig. 3. PSPA measurements & MMLS3 trafficking on NCAT test track [4]

The prototype of the full-scale MLS system (f-s MLS) (MLS10) was developed and commissioned in 2006 to participate in a World Bank sponsored project to evaluate the design and construction system of highways in Mozambique. It was subsequently refurbished and acquired in 2008 by EMPA in Switzerland). This was followed by two MLS66 models supplied to China and another MLS10 supplied to BASt in Germany. Currently, a MLS66 is under construction for delivery to a highway research entity and university in Nanjing. It can apply 1 800 to 6 000 axle load applications per hour with load settings between 8 kN and 75 kN on the trafficking bogies. Some technical details of the f-s MLS system can be found in referenced web sites as well as related references in the respective case studies.

B. Distribution of the MLS System and Development of a Test Protocol for the MMLS3MMLS3 users have applied the device in a number of

ways. As a result, applications cover a wide range of variables that impact on performance of pavements. Findings have been published in a range of journals and conference proceedings. This has served to validate the guidelines for specifying and testing of rutting of asphalt materials under different environmental and trafficking conditions.

At a meeting during the Association of Asphalt Pavement Technologists (AAPT) in Baton Rouge in 2004, the MMLS3 Users Group adopted a test protocol for using the MMLS3 as a tool for evaluating rutting performance of hot mix asphalt. It was primarily based on the performance under trafficking that had been correlated with the full-scale performance of Hot Mix Asphalt (HMA) [5, 6, 7].

It was apparent that apart from mix composition, performance was dependent on a variety of factors such as de-bonding between layers under the rolling wheels, temperature within the mix and failure mechanisms. The latter was dependent on the structure of the underlying support and the extent of lateral constraint of the mix.

The South African Road Pavement Forum (RPF) passed a motion in November 2007 setting up a task team to draft a protocol for applying the MMLS3 as a tool to evaluate

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permanent deformation and susceptibility to moisture damage of bituminous road paving mixtures. In November 2008 a Draft Protocol (DPG1 2008) was approved for use and distribution by the RPF. A decision followed to prepare a civil engineering test method for inclusion as a South African National Standard for inclusion in the SANS. It is currently available for review as SANS 3001-PD1:2013 [8].

Individuals and entities related to the pavement industry (consultants, contractors, asphalt suppliers, highway and airport agencies and authorities) are using the Draft Protocol

In South Africa there are currently two commercial laboratories and a research laboratory at Stellenbosch University using the MMLS3. The MLS Users Group is globally distributed and comprises both MMLS3 and f-s MLS owners and users. (www.mlsglobalusers.com) is being linked with the web based repository for MLS research related publications at Stellenbosch University which is currently being upgraded.

DEVELOPMENT OF THE MMLS3 SYSTEM

As mentioned, the application of the MMLS3 system started with the evaluation of asphalt, but has since expanded to cover a broad spectrum of pavement engineering issues. As a trafficking tool it is not restricted to establishing empirical norms for specific applications or conditions. The focus has shifted towards generating fundamental findings that can be applied for the selection of appropriate materials, processes and conditions in a cost-effective manner. This is apparent from the References. Selected references were categorized and summarized in Table I.

TABLE I. PEER REVIEWED MLS PUBLICATIONS SORTED IN APPLICATION CATEGORIES*

Design & Evaluation

of Bituminous

Surface Treatments

Pavement Design

Evaluation& Perfor-

mance

Com-parative

APT between Traffick-

ing Systems

Effect of Moisture

& Related Damage on

Perfor-mance

Rutting Perfor-

mance & Material Charac-teristics

[9] [13]* [18]* [22] * [8][10] [14] [19] [4 * [24][11] [15]* 20] * [23] [25][12] [16] * [6] * [7] * [26]

[17] [21]] * [27]Reinforcing Airport

Applications[3] * Fatigue,

Abrasion, Cracking & Debonding

[28][5] *[46]

[29] [32]* Contact Stresses

[37] Dimensional Analysis

*[30] [33] * [1] [38] [41][31] [34] [2] [[39]* [42]

[35] [36] [[40]Construction

[43]*[44]*[45]

*Related to more than one category

C. SELECTIVE SYNTHESIS OF MLS APPLICATIONS AND CASE STUDIESThe extensive bibliography (Table I) that has for the most

been peer-reviewed covers international literature and dates back to the 1999 APT conference in Reno Nevada and two earlier studies providing fundamental evaluation of the system.. It served as the basis for the criteria included in the test Protocol and provided guidelines for other applications. A synthesis of the information contained in the bibliography was done to provide insight into the knowledge that has been accumulated, with applications relating to highway authorities, contractors, designers and researchers.

The synthesis covers nine categories that have been identified both specifically and generically. Case details will not be presented except where considered necessary for clarification with reference to the source. A list of keywords for the category is first provided, followed by a summary of main findings.

1) Rutting performance and related material characteristics

Keywords:

Cold-mix asphalt patching, binder interlayer; Mechanistic Empirical Pavement Design Guide (MEPDG); North Carolina DOT Superpave® asphalt mix evaluation; MMLS3; Heavy Wheel Traffic Deflectometer (HWTD) and Asphalt Pavement Analyser (APA) tests

Limitations of application of materials such as emulsion cold-mix asphalt patching material could be defined and placed into context in terms of performance [24].

The benefit of incorporating a binder interlayer into an HMA pavement structure was established [25].

Response and performance of in situ NC Superpave® asphalt pavements was evaluated successfully by MMLS3 and appropriate ancillary laboratory tests and related algorithms similar to those in NCHRP 1-37A Mechanistic-Empirical Pavement Design Guide (MEPDG) [26].

A comparative study to evaluate field performance of asphalt mixes in Texas with three trafficking tests (MMLS3, HWTD and APA) in the laboratory. Nine sections comprising mixture combinations similar to those used in the studies were constructed on IH-20 in Marshall, Texas during November, 2000. Each section received the same traffic volume. Three years after construction, rut depths were measured. The MMLS3 and HWTD were able to distinguish the relative performance of better and poorer mixes in terms of rutting as observed in the field. However, the sensitivity of classification differed. The research done by TxDOT to establish the best Superpave® shear test protocol concluded the MMLS3 to be the most sensitive of the devices evaluated. It was the only

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device able to separate the four mixtures tested into four significant performance groups [27].

MLS66 testing was conducted on a semi-rigid base asphalt pavement of a highway on Chongming Island, Shanghai, China. The goal was to investigate performance of the asphalt pavement with the fine sand subgrade that is abundant in Chongming, terminal of the G40 highway. Performance of the pavement structure was evaluated under high-frequency heavy trafficking while being subject to high-temperature and ambient environmental impact. This included monitoring of strains, temperature, modulus, rutting deformation, pavement depth and water level. Generally good agreement was reached between measured and calculated strains with back-calculation resilient modulus considering modulus reduction of asphalt layers because of temperature. Findings regarding spatial distribution, time-history, change of three-dimensional dynamic strain response and relationships between influencing factors and strains, served as validation for use of the sand [28].

Typical examples of rutting performance under MMLS3 trafficking are shown in Fig. 4. These were measured in a rutting study on Chongming Island in Shanghai [3].

Fig. 4. MMLS3 rutting profiles of SMA13 and AC-20 mixes in a rutting case study on Chongming Island in Shanghai China [3]

2) Impact of moisture and related damage on performanceKeywords:

Wet field MMLS3 trafficking with lateral wander; stripping distress; fatigue testing to evaluate MMLS3 moisture damage; variance in effect of wet testing of Swiss cores.

Wet field MMLS3 trafficking of a highway pavement in Texas provided physical evidence of stripping distress. It was also confirmed through a 62 per cent reduction in the Young’s modulus (SASW measured) of the asphalt concrete surfacing of the pavement after 1.45 million MMLS3 load applications. After dry trafficking of the same pavement with 1.0 million load applications the rut depth was only 1.8 ± 0.2 mm and a nominal increase of 25 per cent increase in Young’s modulus (SASW measured) [22].

Extensive field testing with the MMLS3 on selected sections at the NCAT test track provided evidence of increased distress of the asphalt due to wet MMLS3 trafficking with lateral wander. Cores extracted after a wet MMLS3 test fractured during trafficking. This did not happen under the full-scale truck trafficking [4]

MMLS3 tests on 48 cores from different regions and pavements in Switzerland provided evidence of variance in the effect of wet testing. In some cases there was in fact an improvement in the performance. It was apparent that testing would reduce the risk of unexpected distress [23].

The use of fatigue testing to evaluate moisture damage due to wet trafficking whether under conventional vehicular or MMLS3 trafficking was an important spin-off finding from the MMLS3 testing in Texas. Reduction in tensile strength as measured by the Semi-Circular-Bending test (SCB) was also identified as a quantification of distress due to wet trafficking Of equal importance was the finding that, the AASHTO T283 specification does not necessarily guarantee that the asphalt will not be damaged by water or stripping. Likewise, failure to meet the specification (TSR<0.8) may not necessarily mean that the asphalt will be damaged by water or stripping [7].

3) Fatigue, abrasion, cracking and debondingKeywords:

Effect of excessive permanent strain on fatigue behaviour; quantification of fine particle PM10 emissions due to abrasion and re-suspension from road pavements; similarity of fatigue performance under ALF and MMLS3 trafficking.

Testing of a model pavement structure indicated the effect of wheel load on fatigue behaviour of a pavement in terms of strain history response, cracking and reduction of modulus. It was shown that rutting related, excessive permanent strain due to movement of particles under wheel path, can affect fatigue performance of HMA pavement [37].

Specific quantification of fine particle PM10 emissions due to abrasion and re-suspension from road pavements is difficult to obtain from field studies since a large variety of potential sources affect local PM concentrations. It is thus difficult to quantitatively attribute measured PM10 to individual sources. In a Swiss study emission rates were derived from two road simulators of different size on two types of road pavements (asphalt concrete, porous asphalt). The experimental set-up allowed for separate characterisation of emission due to fresh in-situ abrasion and re-suspension of previously deposited dust. Direct abrasion from the road surface was found to be of minor importance for intact pavements. In contrast, damaged pavement surfaces can cause significant fine partial emissions [38].

The fatigue performance of a pavement under trafficking with the FHWA ALF was compared to that of a scaled pavement under MMLS3 trafficking at North Carolina State University (NCSU) in terms of the trend of measured stress wave results and cumulative crack length per pavement length relative to the respective number of wheel applications. The physical characteristics of the performance of the two pavements were similar. The phase velocity (and therefore asphalt mix stiffness) decreased as the number of loading cycles increased in both the MMLS3 and ALF pavements. Fig. 5 shows that prior to the appearance of visible surface cracks, after 125 000 load applications, the phase velocities had already significantly reduced. The reduction in phase velocity

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indicates that the structural degradation in the model pavement test is similar in character, although at a somewhat slower initial rate, than observed for the ALF results [3, 39].

Fig. 5. Comparative results of phase velocity and cumulative surface crack length related to MMLS3 & ALF wheel load applications [3]

A replication of this study at Virginia Tech in Blacksburg, is reported in the concurrent International Symposium [40]

4) Comparative Performance between APT Trafficking Systems

Keywords:

Comparative permanent deformation rate vs. temperature under HVS and MMLS3 trafficking; comparative maximum shear stresses under HVS and MMLS3 trafficking; reliable MMLS3 pre-diction of rutting performance under full-scale trafficking; compatibility of strains at 30 mm under MMLS3 and MLS10 trafficking; validation of comparative rutting performance under trafficking by MMLS3 and conventional traffic vehicles; validation of MMLS3 estimates of full-scale rutting performance under conventional trucks

Several comparative applications of the MMLS3 in conjunction with different full-scale APT devices/systems have been reported. These case studies provided findings and definitive test conditions to validate the test Protocols that have been formulated with the appropriate criteria [8].

Trends in permanent deformation rate versus temperature under the HVS and the MMLS3 were compatible when the speed and test environment is similar. When the higher speed of the MMLS3 is used, the permanent deformation rate reduces in comparison to the HVS [18]. Good correlation has also been reported between MMLS3 and HVS APT when trafficked at the same speed [19]. It is important to ensure that comparative tests between MMLS3 and full-scale trafficking devices (e.g. APT or conventional vehicular traffic) are done with the same level of accuracy and under compatible conditions [20].

The MMLS3 was used to traffic five pavement sections (including one replicate) at WesTrack to establish and validate its ability to reliably predict rutting performance under full-scale vehicular trafficking. Stress analyses were conducted to

explore the hypothesis of comparable stress distribution, and compare theoretical and measured rutting performance toward validating the performance prediction methodology. Statistical analyses were conducted for field and laboratory results to compare performance of three coarse-graded sections that showed poor performance and one fine-graded section with good performance under both loading conditions. Theoretically calculated rutting ratios based on stress analyses after correcting for differences in loading and environ-mental conditions were compared with actual measured field rutting ratios. The results were credible. It demonstrated that rutting performance under full-scale vehicular loading could be predicted based on MMLS3 results and stress analysis when all influencing factors are taken into account [6, 21, 32, 41, 42].

Strain measurements at a depth of 30 mm under the MMLS3 trafficking, were compatible with strains measured under the full-scale MLS10 at the same depth in the pavement structure by EMPA in Switzerland. This is a significant advance in application of MMLS3 trafficking to evaluate structural performance [3].

Field studies with the MMLS3 and conventional traffic vehicles have provided examples of interlinked testing to provide a platform for validating the findings of reported test findings to be able to use the information to expand the reference base of findings [3, 4, 5, 6, 15, 16]. The projects validated the rut prediction approach developed to compare MMLS3 and full-scale rutting performance and indicated that the MMLS3 may be used to estimate full-scale rutting of the trafficking under specific conditions. Comparative full-scale rutting performance of the track sections evaluated may be quantified and ranked by the MMLS3 performance of these sections.

5) Pavement Design Evaluation and PerformanceKeywords:

Compatible comparative test results of trafficked scaled and full-scale pavements; validation of Protocol adaptations to cater for harsh trafficking conditions; slow heavy traffic, high temperatures

Findings in Mozambique show good comparative compatible tests results of scaled and full-scale pavements in terms of trends in stiffness change as measured with the PSPA, distress mechanisms and surface deformation relative to respective wheel loads and number of load applications [13, 15]. Two unique failure mechanisms were identified in the Mozambique study, namely, horizontal shear within the CTB layer and de-bonding at the interface between asphalt surfacing and CTB [13].

Results of experiments for various applications indicated that the MMLS3, when equipped with ancillary instrumentation and devices, is a valuable tool for investigating the structural responses of a roadway system and for evaluating the effectiveness and durability of roadway pavement products [14]. It was concluded that the results of accelerated trafficking tests using the MMLS3 are comparable with field full-scale accelerated tests due to the nature of similitude in the MMLS3 design.

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In studies of field performance of pavements it was found that the MMLS3 test protocol [8] had correctly been adapted to cater for harsh vehicular trafficking conditions. This was done by prescribing slower trafficking speeds and reduced rutting limits. This was validated with MMLS3 testing of the asphalt mixes with appropriate modified binders to accommodate slow heavy traffic under high temperatures [16].

Epoxy asphalt was considered for surfacing the deck of the new Liaohe Bridge being constructed in Liaoning Province in China ca. 2010, but there was only limited experience with its performance on long-span steel box girder bridge decks. An 8 m long simulated section of the full-scale structure was tested with the MLS66 in a laboratory with the epoxy asphalt and Gußasphalt as alternative options for the pavement deck (Fig. 6). To test the effects of boundary conditions, Spatial Finite Element analyses were used to compare the mechanical characteristics of the pavement deck, diaphragm and stiffening rib between the steel bridge model and a mathematical FE analysis of the simulated bridge structure. The load response was evaluated at three different positions theoretically and compared under APT loading conditions. Values of the deck deformation, the diaphragm principal stress and the deck lateral stress were compared between the tested structure and the real structure under different conditions. Results were found to be very close. The epoxy pavement structure on the deck plate comprised 35 mm SMA, supported by 25 mm resin asphalt concrete epoxy on an epoxy bonded chip layer for waterproofing. This was compared to the alternative design comprising 35 mm SMA, 25 mm Gußasphalt on UK Eliminator waterproofing. The APT started on 1 March 2010 and finished on the 1 June 2010. The test bridge had been loaded 2.9 million applications in total. The test load was varied from 100 kN to 150 kN on each bogie fitted with dual tyres. Temperature was varied in three test stages through seven cycles (ambient; 15 to 25°C, 40°C and 55°C). Trafficking was done without lateral wander. Wet trafficking was applied during one cycle. After 1 900 000 applications, deformation at high temperature caused longitudinal bulges to develop between the dual wheels. Longitudinal cracking developed adjacent to the bulges. The bulges were artificially removed by milling to allow the test to continue. The milled surface was painted to enable visual cracking inspection. Trafficking continued to 2 900 000 and no new cracks developed with the maximum rut depth at 20 mm.

The goal was to compare the structural attenuation and the fatigue damage of the deck pavement under different loading stages and axle load cycles. This was evaluated in terms of temperature performance and resistance to water damage due to surface infiltration and skid resistance. Performance of the two pavements was similar except for rutting. The epoxy rutting was 25 per cent less on average. According to the analysis and calculation, the tested designed structure could simulate the constructed model’s deck deformation and stress distribution of the diaphragm. The bridge was completed in July 2011 with an epoxy deck and is performing well [17].

Fig. 6. Liaohe bridge with insertions showing MLS66 lab testing (17)

6) Airport ApplicationsKeywords:

Reasonable results from fundamental analytical analysis of rutting performance compared to aircraft trafficking; MMLS3 effective in identifying good and poor performing mixes for Boston International Airport; successful diagnosis of cause of unexpected early rutting of asphalt runway rehabilitation at Johannesburg International airport.

Performance prediction of rutting of HMA under aircraft traffic at airports in the Middle East from MMLS3 tests using a fundamental analytical procedure yielded reasonable results. As an example, on a Taxiway at Dubai International Airport ruts measured 32 to 34 mm compared to the calculated scaled rut depth of 28.3 mm. In each case the traffic volume was estimated to have been 20 000 aircraft movements. The findings served as a reasonable basis for evaluating performance of the pavement [3, 32].

Accelerated trafficking test with the MMLS3 was found to be effective in identifying good and poor performing mixes for Boston-Logan International Airport. The feasibility of producing a desirable mix, conforming to these limits, with locally available materials was confirmed [33]. Prior calibration with full-scale vehicular APT had enabled quantitative results to be obtained for predicting rutting at high temperature and durability under wet trafficking [4, 34].

Two sections of Runway 03–21R at the OR Tambo Johannesburg International airport rutted early after rehabilitation (3 mm at the threshold and 7 to 8 mm at 700 m along the runway). Protocols for evaluation of rutting performance of the asphalt mixes were based on the 2004 preliminary Baton Rouge protocol with adaptations for airport trafficking. The results of the predicted performance were found to in accordance with the measured values [1].

7) Design & Evaluation of Bituminous Surface Treatments (BST)

Keywords:

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BST performance test; Uniformity Coefficient (UC); aggregate selection for the chips

The new MMLS3 BST performance test method was applied to evaluate the effects of various mix parameters on aggregate retention and bleeding; these parameters include aggregate and emulsion application rates, fines content, and aggregate gradation [9].

The Performance–based Uniformity Coefficient (PUC), which is a gradation-based performance indicator, was found to be an improvement over the previous Uniformity Coefficient (UC) for chip seal construction [10, 11]. The PUC can also aid in aggregate selection for the chip seal and can also ease and clarify engineering communications within the chip seal industry [12].

8) ReinforcingKeywords:

grid effectiveness for restricting development of permanent deformation; Carbon Fibre Reinforcement Polymer (FRP) grid; rutting resistance

MMLS3 test results showed that 3-D grid contributes significantly to rut resistance, of a reinforced slab. This was apparent from the fact that the reinforced slab showed much less rutting than the unreinforced mix. The failure of the unreinforced slabs manifested as shear distress with the asphalt being forced out beneath the MMLS3 wheels. The grids appear to be an effective means of restricting the development of permanent deformation due to shear failure in wearing course mixes [29].

The fatigue resistance of porous asphalt was successfully improved under both dry and wet conditions with the use of a system comprising a Carbon Fibre Reinforcement Polymer (FRP) grid in Switzerland [30].

Geogrid reinforcement effectiveness was found to be related to the difference in geogrids properties. Test results show that the geogrid reinforcement enhances the pavement performance with respect to rutting resistance compared to a non-reinforced system [31].

9) ConstructionKeywords:

Evaluation of effect of compaction density on performance, decisions on acceptance non-compliant paved asphalt material, price reduction factors (PRF), (NCHRP) 1-37A

Wet, dry, laboratory and field tests were utilized to conduct a diagnostic evaluation of rehab constructed pavement in Namibia. Laboratory tests were done on field cores and field MMLS3 tests were conducted on in-service highway sections in Namibia. Evaluation of the effect of compaction density on performance of the mix was done with the MMLS3. Performance was evaluated in terms of expected traffic and environmental conditions. This provided a sound basis for decisions on adjustments to mixes and adjudication of already paved asphalt mix [43].

Research was undertaken for the development of Price Reduction Factors (PRF) for density-deficient asphalt pavements. The results from the material level performance tests and MMLS3 APT on laboratory pavement slabs for fatigue and rutting evaluation served as basis for the calculation of the PRF values. The methodology for pavement performance prediction was implemented by a computer program called AP4 (Asphalt Pavement Performance Prediction Program). The algorithm adopted in AP4 for the damage calculation was based on the incremental damage concept which is very similar to that used in the National Cooperative Highway Research Program (NCHRP) 1-37A Mechanistic-Empirical Pavement Design Guide. This program allows the determination of the service life for fatigue cracking and rutting based on the inputs of air void contents in all the HMA layers. Acceptable price reduction factors were determined from analysis of five density-deficient pavements in North Carolina [44, 45].

III. GENERAL CONCLUSIONS FROM SYNTHESIS OF THE CASE STUDIES

From an evaluation of the findings captured through the synthesis, it was apparent that a wide range and volume of applications had been covered. This included highways, airports and ancillary structures, with different materials and performance criteria. Furthermore, the findings generated lessons learned in relation to the different applications and related findings. In this regard, the authors concluded that the synthesised data provided the opportunity for linking issues and themes to at least four of the CAPSA themes with a supporting theme of innovation in the pavement testing regime.

In the same vein the findings provided valuable guidelines that should be considered if meaningful performance evaluation and prediction is to be achieved from APT applications:

Speed of heavy vehicles has to be considered when trafficking is applied to the asphalt. This necessitates due regard to the geometric layout of the pavement;

Environmental conditions during the life cycles of the pavement have to be taken into account in terms of temperature, wet-dry cycles and aging of the material. This has to be done with due regard to the vertical and horizontal structure of the pavement;

Tyre inflation pressure and related contact stress between tyres and the pavement surface have selected to reflect the traffic that will be using the pavement;

Structural composition of the pavement has to be known in order to account for the influence of the different pavement layers on the performance in terms of differences in response of the materials during trafficking and the life cycle of the pavement;

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Variability in construction quality can influence the response and performance of pavement materials and structure. It has to be included in the analytical evaluation of the analyses;

Possible external contamination must be considered when performance of an asphalt pavement is evaluated;

The effect of lateral wander influences the number of load applications impacting on the structure. This has to be considered when comparison between different trafficking systems is evaluated;

Mechanisms of failure influence performance and therefore have to be considered.

From the overview of the respective case studies, it is concluded that the MLS trafficking systems were appropriate and innovative APT tools for evaluating performance of asphalt pavements. However, it is imperative that the test protocols are formulated with due regard to the various influence factors that have been reported in the related bibliographic references.

IV. CONCLUDING REMARKSThe authors consider the extensive findings from the

synthesis to be sound bases for innovation to consider when embarking on future projects that are likely to render reward in terms of solutions and financial gains. However, they consider it necessary to quote Dr David Grant CBE FREng Vice President, The Royal Academy of Engineering Vice-Chancellor, Cardiff University on the issue of innovation,

“The UK remains home to some of the very best designers and engineers in the world, but an incomplete understanding or application of innovation processes means that many of their good ideas will go no further than the drawing board or the computer screen”.

ACKNOWLEDGMENTSThis presentation represents a collaborative international

effort between MLS users. The findings from the respective case studies have served to establish a basis for improving the successful application of the system. The bibliography that was mined for the synthesis was referenced appropriately and for the most peer reviewed. It must be emphasized that the referenced publications were selected to serve as anecdotes suited to convey a message of innovation in pavement engineering through the use of a test system that have evolved from a novel device to a standardized system. They should not be taken to be the only studies that explored or discussed the issue(s) raised. In the same vein, there may be other studies that have reported on other findings or aspects that should be considered of value for the debate. The final responsibility for the views expressed in the presentation rest solely with the authors.

REFERENCES

[1] M. de Beer, E. Sadzik, “Comparison of Contact Stresses of the Test Tyres used by the 1/3rd Scale Model Mobile Load Simulator (MMLS3) and the Full-Scale Test Tyres of the Heavy Vehicle Simulator (HVS) –

A Summary,” Proceedings of the 26th Southern African Transport Conference (SATC 2007), Pretoria, July. 2007.

[2] M. Sime, S.C. Ashmore, “Tyre Pavement Interface Pressure Patterns, Measurement of Contact Stresses under MMLS3 Tyres at Westrack under Axle Load of 2.1kN,” Federal Highway Administration. 1999.

[3] F. Hugo, T. Zefeng, M. Arraigada, Y.R. Kim, Li Shu-ming, “International Case Studies in Support of Successful Applications of APT in Pavement Engineering,” Paper presented and published in the proceedings of the APT Conference in Sacramento, CA September 2012.

[4] F. Hugo, A de F. Smit, P. Poolman, B. Powell, C. Bacchi, “Distress of hot mix asphalt on the NCAT test track due to accelerated wet trafficking with the MMLS3,” CD-ROM Proceedings Second International APT Conference, Minneapolis, USA. 2004.

[5] A de F. Smit, F. Hugo, D. Rand, B. Powell, “Model Mobile Load Simulator Testing at National Centre for Asphalt Technology Test Track,” Transportation Research Record 1832, Journal of the Transportation Research Board, Washington, D. C. USA, October 2003.

[6] M. Epps, T. Ahmed, D.C. Little, F. Hugo, P. Poolman, M. Mikhail, “Performance prediction with the MMLS3 at WesTrack,” International Conference on Asphalt Pavements, 9th, 2002, Copenhagen, Denmark. 2002.

[7] L.F. Walubita, F. Hugo, M. Epps, A.L. Martin, “Indirect tensile fatigue performance of asphalt after MMLS trafficking under different environmental conditions,” Journal of the SA Institution of Civil Engineering, Johannesburg, South Africa, Vol. 44, Number 3. 2002.

[8] SOUTH AFRICAN NATIONAL STANDARD SANS 3001-PD1:2015 Edition 1.: Determination of permanent deformation and moisture sensitivity in asphalt mixes using a one-third-scale model mobile load simulator (MMLS3) -Draft-July-2014.

[9] J. Lee, Y.R. Kim, E.O. McGraw, “Performance Evaluation of Bituminous Surface Treatment Using the Third-Scale Model Mobile Loading Simulator,” Journal of Transportation Research Board, No. 1958, National Research Council, Washington, D.C., pp. 59-70. 2006a.

[10] J.S. Lee, Y.R. Kim, “Understanding the Effects of Aggregate and Emulsion Application Rates on the Performance of Asphalt Surface Treatments,” Journal of the Transportation Research Board, No. 2044 National Research Council, Washington, D.C., pp. 71–78. 2008.

[11] J.S. Lee, Y.R. Kim, “Performance-Based Uniformity Coefficient of Chip Seal Aggregate,” Journal of Transportation Research Board, No. 2040, National Research Council, Washington, D.C., pp. 53-60., TRB Washington DC, December. 2009.

[12] T.I. Milne, M.F.C van de Ven, K.J. Jenkins, “Performance Evaluation of Sprayed Surfacing Seals: Field and Laboratory Trials,” 1st International Sprayed Sealing Conference ARRB, Australia. 2008.

[13] E.R. de Vos, F. Hugo, P.J. Strauss, J.A. Prozzi, K.W. Fults, H. Tayob, “Comparative Scaled MMLS3 Tests vs. Full-Scale MLS10 Tests in Mozambique,” CD-ROM Proc, 86th Annual TRB Meeting; Washington D.C. 2007

[14] R. Ghassan Chebab, T. Xiaochao, “The use of a multi-set-up, reduced-scale accelerated trafficking simulator for evaluating roadway systems and products,” Intl Journal of Pavement Engineering, Issue 13(6) Nov. 2011.

[15] F. Hugo, E.R. de Vos, H. Tayob, L. Kannemeyer, M. Partl, “Innovative Applications of the MLS10 for Developing Pavement Design Systems,” Third International Conference on APT in Madrid. 2008.

[16] F. Hugo, I. Bowker, J. Liebenberg, D. Rossmann, “Evaluation of Performance of Asphalt Paving Mixes under Harsh Conditions using the MMLS3,” Proc. CAPSA, August 2011.

[17] T. Zefeng, X, Fan, Y. Liu, “Introduction of Full-Scale Accelerated Pavement Tes on Asphalt Pavement Practice,” Chapter 6 North East China University Press (Chinese), First Print, Nov. ISBN 978 -7-5517-0277-5G. 2011.

[18] E. Denneman, W.J.vdM. Steyn, J. Maina, E.S. Sadzik, “Evaluation of Deformation Response of HMA under APT and Wheel Tracking Tests,” Madrid Proceedings of the 3rd International APT Conference, Madrid. 2008.

CAPSA 2015 – Peer reviewed published paper © Copyright – CAPSA2015

[19] L-J. Ebels, K. Jenkins, E. Sadzik, “Investigation into the Correlation of the MMLS3 and HVS Devices,” CD-Rom Proceedings Second International APT Conference, Minneapolis, USA. 2004.

[20] A.L. Epps, T. Ahmed, D. Little, M. Mikhail, “Performance assessment with the MMLS3 at WesTrack,” Proceedings of the Association of Asphalt Pavement Technologists, vol. 70. 2001.

[21] A.L. Epps, L.F. Walubita, F. Hugo, N. Bangera, “Comparing Pavement Response and Rutting Performance for Full-Scale and One-Third Scale Accelerated Pavement Testing,” Journal of Transportation Engineering, ASCE, Vol. 129, No. 4, pp. 451-461. 2003.

[22] F. Hugo, A de F. Smit, A. Epps, “A Case study of model APT in the field,” CD-ROM Proceedings of the International Conference on Accelerated Pavement Testing, Reno, Nevada, 18-20 October 1999.

[23] C. Raab, M.N. Partl, K. Jenkins, F. Hugo, “Determination of Rutting and Water Susceptibility of Selected Pavement Materials Using MMLS3,” Bearing Capacity Conference Trondheim CRA'05, Norway, June 2005.

[24] K.J. Jenkins, S.J. Bredenhann, A.A. Munyagi, “Evaluation of Cold-Mix Asphalt for Patching,” 23rd ARRB Australian Roads Research Board. 2008.

[25] T. Kumar, G. Chehab, S. Stoffels, D. Morian, L. Cernansky, “Effect of Binder Course on HMA Overlay Performance: Case Study I -79,” Proc of the ISAP International Conference on Asphalt Pavements, Quebec, Canada. 2006.

[26] S.J. Lee, Y. Seo, Y.R. Kim, “Validation of Material-Level Performance Models: Using the Third-Scale Model Mobile Loading Simulator,” Journal of Transportation Re-search Board, No. 1949, National Research Council, Washington, D.C., pp. 75-82. 2006.

[27] A de F. Smit, F. Hugo, Y. Yeldirim, “A Discussion of MMLS3 Performance Testing of Laboratory Prepared HMA Slabs and Briquettes Compared with Hamburg and APA Wheel Tracking Tests,” CD-ROM Proceedings Second International APT Conference, Seattle, USA. 2004.

[28] J. Wu, Y. Fen, F. Hugo, Y. Wu, “Strain response of a semi-rigid base asphalt pavement based on heavy-load full-scale accelerated pavement testing with fibre Bragg grating sensors,” Road Materials and Pavement Design, DOI: 10.1080/14680629.2014.995211. 2015.

[29] K.J. Jenkins, P. Dennison P, L.J. Ebels, L.S. Mullins, “3-D Polymer Grid Reinforcement of Asphalt for Rut Resistance,” CD Rom Proceedings of the 8th Conference on Asphalt Pavements for Southern Africa (CAPSA'04) 12 – 16 September 2004 ISBN Number: 1-920-01718-6 Sun City. 2004.

[30] H. Kim, K. Sokolov, L.D. Poulikakos, M.N. Partl, “Fatigue Evaluation of Carbon FRP-Reinforced Porous Asphalt Composite System Using a Model Mobile Load Simulator,” Transportation Research Record, Vol.2116, pp.108-117. 2009.

[31] X. Tang., G.R. Chehab., A. Palomino, "Evaluation of geogrids for stabilizing weak pavement subgrade", Intl Journal of Pavement Engineering. 2008.

[32] S. Emery, I. Mihaljevic, “Accelerated Load Testing of Asphalt Mix Designs for Heavy Duty Pavements in Hot Climates,” 23rd ARRB Conference, Adelaide Australia. 2008.

[33] K.J. Jenkins, F.J. Pretorius, F. Hugo, R. Carr, “Asphalt Mix Design for Cape Town International Airport using Scaled APT and other Selected Tests,” Paper presented at the 6th International RILEM Symposium on

Performance Testing and Evaluation of Bituminous Materials, PTEBM’03 April 14-16, Zurich, Switzerland. 2003.

[34] R. Mallick, R. Pelland, E. Dawes, C. Bowker, “Research and Implementation of Research Results for Improving Airfield Pavements at Boston-Logan International Airport,” Paper presented at 85th Annual TRB Meeting, TRB Washington DC, January. 2006.

[35] P. Molenaar, F. Hugo, J. Beukes, G. Catin, “Rehabilitation of RWY 03L-21R at Johannesburg International Airport: the quest for a suitable surfacing mix,” CD Rom Proceedings of the 8th Conference on Asphalt Pavements for Southern Africa (CAPSA'04) 12 – 16 September 2004 ISBN Number: 1-920-01718-6 Sun City, South Africa. 2004.

[36] W.J.vdM. Steyn, "Measurement of MMLS contact stresses on various surfacings," Report number UP/WJVDMS/01/2015, University of Pretoria, Pretoria. 2015.

[37] Bhattacharjee, R.B. Mallick, F. Hugo, F, “Use of MMLS3 scaled accelerated loading for fatigue characterization of Hot Mix Asphalt (HMA) in the laboratory,” CD-ROM Proceedings Second International APT Conference, Minneapolis, USA. 2004.

[38] R. Gehrig, K. Zeyer, N. Bukowiecki, P. Lienemann, L. Poulikakos, “Abrasion and resuspension from road surfaces – an important source of fine particles in the environment,” International Air Quality Conference, March, Istanbul, 4p proc on CD. 2009.

[39] S. Lee, Y.R. Kim, “Fatigue Investigation of Laboratory Asphalt Pavement Using the Third Scale Model Mobile Loading Simulator,” Proceedings of the 5th International RILEM Conference on Cracking in Pavements, France, pp. 29-36. 2004

[40] F. Hugo, Y Huang, X. Xiong, L Wang, , W.J.vdM. Steyn “Lessoned Learned During the First Application of MSP for Extracting Asphalt Slabs in Comparative Testing of Fatigue Performance of Warm Mix RAP Asphalt MMLS3 Trafficking.” Paper submitted to Intl. Symposium on Asphalt Pavements, Pilanesberg, South Africa, August, 2015

[41] S.M. Kim., F. Hugo, J.M. Roesset T.D. White, “Dimensional Analysis of the Mobile Load Simulator on Pavements,” Report 2914-3F, Center for Transportation Research, The University of Texas at Austin, May. 1995.

[42] S.M. Kim, F. Hugo, J.M. Roesset, “Small-Scale Accelerated Pavement Testing,” Journal of Transportation Engineering, ASCE, Vol. 124, No.2, Mar/Apr 1998, pp. 117-122. 1998.

[43] F. Hugo, R. de Witt, A. Helmich, “Application of theMMLS3 as APT tool for evaluating asphalt performance in Namibia,” CD Rom Proceedings of the 8th Conference on Asphalt Pavements for Southern Africa (CAPSA'04) 12 – 16 September. 2004.

[44] Y.R. Kim, S.J. Lee, Y. Seo, O. El-Haggan, “A Mechanistic Approach to Determine Price Reduction Factors for Density-Deficient Asphalt Pavements,” Proc of 2006 Airfield and Highway Pavement Specialty Conference, (Imad L. Al-Qadi, editor) Atlanta, May, pp. 1018-1029. 2006.

[45] Y. Kim, S. Richard, L. Joon, S. Youngguk, “Determination of Price Reduction Factors for Density Deficient Asphalt Pavements,” ASTM Journal of Testing and Evaluation (JTE), Vol 36, Issue 4, ISSN 1945 – 7553, April. 2008