Modelling of the variation of granular base materials resilient modulus with material characteristics and humidity conditions

This study aims to quantify the susceptibility of granular materials used in pavements to changes in moisture content and propose a correlation model to incorporate this susceptibility into seasonal analyses.The fines content and the percentage of fractured coarse aggregates were identified as direct indicators of the resilient modulus susceptibility to changes in water content.The results showed that the percentage of fractured coarse aggregates particles(FR)has a more significant impact on the resilient modulus(Er)of crushed granular materials used in pavement construction than the combined indicator of the fines content and sample volumetrics(nf).Crushed granular materials with a higher percentage of fractured coarse aggregates are relatively insensitive to changes in the degree of saturation,but become more sensitive as the fine fraction porosity decreases.An adjusted model was proposed based on the existing formulation,but considers a complex parameter to describe and adjust the sensitivity of base granular materials to variations in moisture content with respect to fabrication charac-teristics,fines content and volumetric properties.The model shows that the variation of Er values is below10%for fully crushed granular materials.However,it reaches approximately±12%for materials with 75%of crushed coarse aggregates andþ40%and-25%for materials with FR=50%.This model could help select good ag-gregates characteristics and adjust grain-size distribution for environments where significant moisture content variations can occur in the pavement system,such as in the Province of Quebec(Canada).As it is based on pa-rameters that can be easily determined or estimated,it also represents a valuable tool for detailed design and analysis that can consider material characteristics.

Resilient modulus prediction of soft low-plasticity Piedmont residual soil using dynamic cone penetrometer

Dynamic cone penetrometer（DCP） has been used for decades to estimate the shear strength and stiffness properties of the subgrade soils. There are several empirical correlations in the literature to predict the resilient modulus values at only a specific stress state from DCP data, corresponding to the predefined thicknesses of pavement layers（a 50 mm asphalt wearing course, a 100 mm asphalt binder course and a200 mm aggregate base course）. In this study, field-measured DCP data were utilized to estimate the resilient modulus of low-plasticity subgrade Piedmont residual soil. Piedmont residual soils are in-place weathered soils from igneous and metamorphic rocks, as opposed to transported or compacted soils.Hence the existing empirical correlations might not be applicable for these soils. An experimental program was conducted incorporating field DCP and laboratory resilient modulus tests on "undisturbed" soil specimens. The DCP tests were carried out at various locations in four test sections to evaluate subgrade stiffness variation laterally and with depth. Laboratory resilient modulus test results were analyzed in the context of the mechanistic-empirical pavement design guide（MEPDG） recommended universal constitutive model. A new approach for predicting the resilient modulus from DCP by estimating MEPDG constitutive model coefficients（k;,k;and k;） was developed through statistical analyses. The new model is capable of not only taking into account the in situ soil condition on the basis of field measurements,but also representing the resilient modulus at any stress state which addresses a limitation with existing empirical DCP models and its applicability for a specific case. Validation of the model is demonstrated by using data that were not used for model development, as well as data reported in the literature.

Preliminary Investigation on Establishing a New Resilient Modulus Test Approach for Reduced Size Asphalt Mixture Samples Smaller Than 100 mm Diameter

The performance evaluation of existing flexible pavements has become a priority issue for many highway maintenances engineers.To make appropriate rehabilitation and management decisions,the engineers most often rely on efficient methods for the determination of the strength of pavement layers.Resilient modulus is a very important parameter to be identified and used in pavement design.The resilient moduli of asphalt mixtures are typically measured using the indirect tension test procedure in compliance with the ASTM D4123 standard that is superseded by ASTM D7369.The standard requirement is that the prepared specimens for the tests should have a minimum height of the sample over its diameter ratio of 0.4.Generally,specimens used in the tests are either a nominal 100 mm or 150 mm in diameter with a minimum thickness over diameter ratio of 0.4.However,100 mm diameter core specimens taken from site wearing courses with thicknesses ranging from 40 mm to 50 mm most often do not fulfil the minimum ratio of 0.4 after they are trimmed for testing.Since there was no any option,part of the binder courses had to be trimmed to make up for the minimum ratio requirement.This tends to result in inaccurate assessment of the resilient modulus values of the samples.As such,a new procedure was explored to test specimens smaller than 100 mm in diameter.This may minimize the material volume requirement from the field and also for the fabrication of smaller samples in the laboratory.Based on the available thickness of wearing course or overlay,the appropriate sizes were determined.For a two-layer system a 56.3 mm diameter was deemed necessary while a 37.5 mm diameter was observed to be appropriate for a three-layer system.Such an approach for resilient modulus test using miniature specimens of 56.3 mm and 37.5 mm in diameter has a great potential for practical relevance for the industry.

Impact of Freeze-Thaw Cycles on Compressive Characteristics of Asphalt Mixture in Cold Regions

Low average temperature, large temperature difference and continual freeze-thaw （F-T） cycles have significant impacts on mechanical property of asphalt pavement. F-T cycles test was applied to illustrate the mixtures＇ compressive characteristics. Exponential model was applied to analyze the variation of compressive characteristics with F-T cycles; Loss ratio model and Logistic model were used to present the deterioration trend with the increase of F-T cycles. ANOVA was applied to show the significant impact of F-T cycles and asphalt- aggregate ratio. The experiment results show that the compressive strength and resilient modulus decline with increasing F-T cycles; the degradation is sharp during the initial F-T cycles, after 8 F-T cycles it turns to gentle. ANOVA results show that F-T cycles, and asphalt-aggregate ratio have significant influence on the compressive characteristics. Exponential model, Loss ratio model and Logistic model are significantly fitting the test data from statistics view. These models well reflect the compressive characteristics of asphalt mixture degradation trend with increasing F-T cycles.

Laboratory Evaluation of Fiber-Modified Asphalt Mixtures Incorporating Steel Slag Aggregates

Vigorous and continued efforts by researchers and engineers have contributed towards maintaining environmental sustainability through the utilization of waste materials in civil engineering applications as an alternative to natural sources.In this study,granite aggregates in asphaltic mixes were replaced by electric arc furnace(EAF)steel slag aggregates with different proportions to identify the best combination in terms of superior performance.Asphalt mixtures showing the best performance were further reinforced with polyvinyl alcohol(PVA),acrylic,and polyester fibers at the dosages of 0.05%,0.15%,and 0.3%by weight of the aggregates.The performance tests of this study were resilient modulus,moisture susceptibility,and indirect tensile fatigue cracking test.The findings of this study revealed that the asphalt mixtures containing coarse steel slag aggregate exhibited the best performance in comparison with the other substitutions.Moreover,the reinforced asphalt mixtures with synthetic fibers at the content of 0.05%exhibited an almost comparable performance to the unreinforced asphalt mixtures.Modifying the asphalt mixtures with PVA,acrylic,and polyester fibers at the proportion of 0.15%have improved the fatigue cracking resistance by 41.13%,29.87%,and 18.97%,respectively.Also,the fiber-modified asphalt mixtures with PVA,acrylic,and polyester have enhanced the fatigue cracking resistance by about 57%,44%,and 39%,respectively.The results of the resilient modulus demonstrated that as the fiber content increase,the resilient modulus of the reinforced asphalt mixtures decreases.Therefore,introducing synthetic fibers at the content of 0.3%has slightly decreased the resilient modulus in comparison with unreinforced mixtures.On the other hand,the results of the mechanisticempirical pavement design showed that the reinforced asphalt mixes with a high content of synthetic fibers have shown lower service life than the control mixes due to the low resilient modulus.On the contrary,based on the laboratory results,the asphalt mixes incorporating PVA,acrylic,and polyester fibers at the proportion of 0.15%have shown the potential to reduce the thickness of the asphalt layer by about 14.9%,11.80%,and 8.70%,respectively.

A geomechanics classification for the rating of railroad subgrade performance

The type of subgrade of a railroad foundation is vital to the overall performance of the track structure.With the train speed and tonnage increase,as well as environmental changes,the evaluation and influence of subgrade are even more paramount in the railroad track structure performance.A geomechanics classification for subgrade is proposed coupling the stiffness(resilient modulus)and permanent deformation behaviour evaluated by means of repeated triaxial loading tests.This classification covers from fine-to coarse-grained soils,grouped by UIC and ASTM.For this achievement,we first summarize the main models for estimating resilient modulus and permanent deformation,including the evaluation of their robustness and their sensitivity to mechanical and environmental parameters.This is followed by the procedure required to arrive at the geomechanical classification and rating,as well as a discussion of the influence of environmental factors.This work is the first attempt to obtain a new geomechanical classification that can be a useful tool in the evaluation and modelling of the foundation of railway structures.

Soil Subgrade’s Characterization and Classification of Thies (Senegal, West Africa) on a Radius of 2.5 Kilometers along Five Roads

This article explains the results of a study conducted on the characterizations of subgrade soils in the region of Thies. The road platforms are mainly composed of a background soil, which is generally overlapped by a surface layer that plays two roles. Firstly, it protects the soil structure, ensures the leveling, and facilitates the movement of vehicles. Secondly, it brings harmony in the mechanistic characteristics of the materials that compose the soil while improving the long-term life force. The methodology consisted in taking samples of subgrade soil along the roads all over the region of Thies in a 5 km diameter span. The identification tests allowed the Thies-Tivaoune, Thies-Khombole and Thies-Noto axes are characterized by tight sands, poorly graded size. While Thies Pout-axis is characteristic of severe solid particle size and spread well graded and serious to spread and well graded particle size. Finally the Thies-Montrolland axis is characterized by severe to very tight particle size and graduated to spread and serious and well graded particle size. The specific gravity values found Proctor test shows the presence of sand, sandy laterite and laterite. In the target area, polished soils of the A-3 type according to the AASHTO classification system are the most represented with 60%, followed by the A-2-6 type 25%, and the A-2-4 type with 9%, which are typical of gravel, clay, and silty sands. Soils of the A-1-b type (2%) typical of roc fragments, sands and clay are also represented. Polished sands of the A-3 type have a better efficiency on road infrastructures than other types of soil listed above. Finally, we’ve also noted the presence of soils of the A-2-7 and A-4 types with the low percentage of 2%. Subgrade soils of class S4 are the most represented with 58%, followed by those of class S5 with 42%. Samples of the Thies-Montrolland road have a claylike plasticity (CL or CH group), while those of the Thies-Pout road belong to the ML or OL and CL or OL groups with a tendency mostly directed to the CL or OL group. All these results confirm the very nature of soils on the two roads and put the light on the presence of lateritic materials with certain plasticity.

Performance of Recycled Ceramic Waste as Aggregatesin Asphalt Mixtures

Ceramic waste materials are abundantly available in Malaysia from the production of ceramic tiles.In general,ceramic materials seem to possess low thermal conductivity characteristics that could reduce pavement temperatures when used as aggregates in asphalt mixtures.A study was undertaken to look into the performance of crushed ceramics incorporated in asphalt mixtures to replace the conventional granite aggregates from sizes 5.0 mm down including the 75 micron filler.The replacement was done proportionally with 0%,20%,40%,60%,80%and 100%ceramic aggregates by weight of granite.Several mix designs with various percentages of ceramic aggregates were formulated to determine the marshal properties such as stability,flow,and resilient modulus.In addition,the potential of ceramic aggregates in reducing the asphalt pavement temperatures was also studied.The outcome of the study showed that the ceramic aggregates in the asphalt mixtures were able to improve the performance of the mixture up to 20%which means there is a great potential for the use of it in road construction.Besides that,the rate of heating(RoH)compacted samples subjected to various temperatures dropped significantly as compared with the control granite specimens.The fatigue performance of the compacted and temperature conditioned ceramic asphalt mixtures displayed an interesting trend in terms of strain resistance at elevated temperatures.

Effect of Water Content and Grains Size Distribution on the Characteristic Resilient Young’s Modulus (<i>E_c</i>) Obtained Using Anisotropic Boyce Model on Gravelly Lateritic Soils from Tropical Africa (Burkina Faso and Senegal)

This research was carried out to determine the rheological parameters of lateritic soils in order to contribute to the improvement of the technical documents used for pavement design in tropical Africa. The study is based on the loading repeated of cyclic triaxial tests (LRT) performed at University Gustave Eiffel (formerly Institut Français des Sciences et Technologies des Transports de l’Aménagement et des Réseaux (IFSTTAR)) in Nantes with the application of the European standard EN 13286-7: 2004 [1]. The tests were performed at constant confinement stress and using the stepwise method to determine the resilient axial () and radial () deformation as a function of the axial and radial stresses. Four gravel lateritic soils from different sites selected in Burkina Faso and Senegal were the subject of this research for the triaxial tests. These materials have a maximum diameter of 20 mm and a percentage of fines less than 20%. The LRT tests were carried out on samples compacted at three moisture contents (wopm - 2%, wopm and wopm + 2%) and at 95% and 100% of optimal dry density (γdopm). Test results showed that the characteristic resilient Young’s modulus (Ec) of gravelly laterites soils depends on the compacted water content and the variation of the grains size distribution (sand (ø < 2 mm), motor (ø < 0.5 mm) and fines content (ø < 0.063 mm) obtained after (LRT). Materials with a high percent of fines (>20%), mortar and sand (Sindia and Lam-Lam) are more sensitive to variations in water content. The presence of water combined with the excess of fines leads to a decrease in modulus around 25% for Lam-Lam and 20.2% for Sindia. Materials containing a low percent of fines, mortar and sand (Badnogo and Dedougou) behave differently. And the resilient modulus increases about 225.67% for Badnogo and 312.24% for Dedougou with the rise of the water content for approximately unchanged the percentage of fines, mortar and sand. Granularity therefore has an indirect influence on the resilient modulus of the lateritic soils by controlling the effects of water on the entire system. Results of statistical analysis and coefficients of correlation (0.659 to 0.865) showed that the anisotropic Boyce’s model is suitable to predict the volumetric () and deviatoric strain () with stress path (Δq/Δp) of the lateritic soils. The predicted Er resilient Young’s modulus from anisotropic Boyce’s model varies according to the evolution of the bulk stress (). A correlation around 0.9 is obtained from the power law model.

Assessing the Resilient Behavior of Recycled Mix-granulate with Repeated Load CBR Testing

A new characterization technique,a repeated load CBR test,was used to evaluate the resilient properties recycled mix-granulate unbound base material. This is a mixture of crushed concrete and crushed masonry,so recycled demolition waste,this is used on a wide scale in the Netherlands as road base material. The repeated load CBR test,done with standard CBR testing facility,was conducted to estimate the resilient modulus. For comparison and assessment purposes the tests were carried out with the same material conditions (composition,grading,moisture and compaction degree) as have been applied in earlier triaxial testing in the Road and Railway Engineering Laboratory,Delft University of Technology. The results indicate that the repeated load CBR test yields a good estimate of the stress dependent equivalent modulus for the sample material as bulk,which can be used in mechanistic pavement analysis in the absence of triaxial test results.

Rutting prediction models for flexible pavement structures: A review of historical and recent developments

Rutting is the major distress mode in flexible pavements occurring due to the repeated movement of traffic loading. Deformation in the pavements comprise of both recoverable(elastic) and irrecoverable(plastic) part. Overall deformation occurring in the flexible pavement system due to continuous vehicular movement is contributed from all the components of pavement. A number of empirical models have been proposed by several researchers for analysis and prediction of accumulated rutting in different components of pavement. The accumulated permanent strain has been expressed as the function of the number of load applications and deviator stress applications in most of the models proposed;however, factors such as stress state, moisture content, material type and environmental conditions also impose a significant influence on the permanent deformation characteristics of pavement materials under cyclic loading. In this article, a comprehensive review has been carried out covering every aspect of deformation related to distress occurring in pavements. Important rut models, modeling approaches and modern concepts in the rutting analysis of pavement structures have been presented. In addition to review, fallacy existing in the current design practices related to adaptation of stiffness parameters and negligence of shear strength aspect of subgrade soil has been also presented with the support of literatures.

Performances of hydrated cement treated crushed rock base for Western Australian roads

The resilient modulus （RM） of hydrated cement treated crushed rock base （HCTCRB） affected by amount of hydration periods, compaction and dryback processes was presented using repeated load triaxial tests. The related trends of RM corresponding to the different hydration periods still cannot be concluded. Instead, It is found that the moisture content plays more major influence on the RM performance. Higher additional water during compaction of HCTCRB, even at its optimum moisture content and induced higher dry density, led to the inferior RM performance compared to the sample without water addition. The RM of damper samples can be improved through dryback process and superior to that of the sample without water addition at the same moisture content. However, the samples withut water addition during compaction deliver the comparable RM values even its dry density is lower than the other two types. These results indicate the significant influence of moisture content to the performances of HCTCRB with regardless of the dry density. Finally, the experimental results of HCT- CRB and parent material are evaluated with the K-O model and the model recommended by Austroads. These two models provide the excellent fit of the tested results with high degree of determination.

Evaluation of asphalt mixture behavior incorporating warm mix additives and reclaimed asphalt pavement

Incorporation of warm mix asphalt （WMA） and reclaimed asphalt pavement （RAP） has benefited the asphalt industry in many ways such as reducing the demand for virgin materials, lowering energy requirement during the asphalt production and construction, in addition to reducing greenhouse-gas emissions. This study evaluated the effects of Evotherm and RH-WMA and RAP on mixtures＇ behavior in terms of the compaction energy index （CEI）, indirect tensile strength （ITS） and resilient modulus. The results showed that warm mix additives reduced the CEI, ITS and resilient modulus; while RAP increased the corresponding values. Statistical analysis showed that mixtures incorporating Evotherm and RAP had significant effects on CEI, while the effects of RH-WMA on the corresponding value were found to be statistically insignificant. General Linear Model showed that Evotherm, RAP and RH-WMA exhibited no significant effects on the ITS and resilient modulus. The one-way analysis of variance showed that Evotherm influenced mixture behavior significantly, while RAP and RH-WMA effects were found to be statistically insignificant. Regression equations with high accuracy levels were proposed to predict CEI, ITS and resilient modulus with respect to modification of mixture variables such as mix constituents （Evotherm, RH-WMA, and RAP） and compaction temperature.

Characterization of subgrade soil mixed with recycled asphalt pavement

Due to awareness to greener environment, use of recycled asphalt material has become popular in asphalt pavement industry. The use of recycled asphalt pavement （RAP） ma- terials in subgrade soil can be an additional scope of utilizing RAP. This study investigates the effect of RAP on the resilient modulus （MR） of subgrade soils mixed with RAP materials. Note that MR is the principal material input parameter for designing asphalt pavement using the recent mechanistic-empirical pavement design software. As a first step of the current study, different percentages of RAP and moisture were thoroughly mixed with subgrade soils. Then, the MR of these RAP mixed soils were determined using the AASHTO T 307 （1999） at different stress levels in the laboratory. Results show that the MR of RAP mixed soil increases with the applied deviatoric and bulk stresses, however, it is less sensitive to applied confining pressure. Use of RAP materials has made the soils stiff enough not to respond to the confining pressure. As expected, the MR value reaches a maximum at the optimum moisture content and increases linearly with RAP content. The MR values and characteristics of the RAP mixed subgrade soils, as determined by the current study, can be used for subgrade design and stabilization using RAP for better pavement design.

Gement improved highly weathered phyllite for highway subgrades:A case study in Shaanxi province

In a cost-saving move, the soft rocks composed of highly-weathered phyllites available on- site were used to fill the subgrade in the eastern Ankang section of the expressway of Shiyan to Tianshui, China. Cement admixture was used to improve the performance of the weathered phyllites. In order to determine the best mix ratio, values corresponding to compaction performance, unconfined compressive strength, and the California bearing ratio （CBR） were analyzed for variable cement content weight percentages （3%, 4%, 5%, and 6%） using test subgrade plots in the field. Field measurements of resilience modulus and deflection confirmed that the strength of the subgrade increased as the cement ratio increased. In order to further evaluate the cement/phyllite mixture, the performance of the 3% cement ratio sample was evaluated under saturated conditions （with various levels of moisture addition and soaking time） using both the wetting deformation and resilient modulus values. Results suggest that moisture added and soaking time are key factors that affect the seepage depth, water content, and resilient modulus. The recommend values for the cement addition and for the water content are given out. This study can aid in pre- vention of highway damage by improving the foundation capacity and lengthening the lifecycle of the highway in phyllite distributed region at home and abroad.

Prediction of performance and evaluation of flexible pavement rehabilitation strategies

Five test sections with different additives and strategies were established to rehabilitate a State-maintained highway more effectively in Rhode Island （RI）： control, calcium chloride, asphalt emulsion, Portland cement and geogrid. Resilient moduli of subgrade soils and subbase materials before and after full depth rehabilitation were employed as input pa- rameters to predict the performance of pavement structures using AASHTOWare Pave- ment ME Design （Pavement ME） software in terms of rutting, cracking and roughness. It was attempted to use Level i input （which includes traffic full spectrum data, climate data and structural layer properties） for Pavement ME. Traffic data was obtained from a Weigh- in-Motion （WIM} instrument and Providence station was used for collecting climatic data. Volumetric properties, dynamic modulus and creep compliance were used as input pa- rameters for 19 mm （0.75 in.} warm mix asphalt （WMA） base and 12.S mm （0.5 in.） WMA surface layer. The results indicated that all test sections observed AC top-down （longitu- dinal） cracking except Portland cement section which passed for all criteria. The order in terms of performance （best to worst） for all test sections by Pavement ME was Portland cement, calcium chloride, control, geogrid, and asphalt emulsion. It was also observed that all test sections passed for both bottom up and top down fatigue cracking by increasing thickness of either of the two top asphalt layers. Test sections with five different base/ subbase materials were evaluated in last two years through visual condition survey and measurements of deflection and roughness to confirm the prediction, but there was no serious distress and roughness. Thus these experiments allowed selecting the best reha- bilitation/reconstruction techniques for the particular and/or similar highway, and a framework was formulated to select an optimal technique and/or strategy for future rehabilitation/reconstruction projects. Finally, guidelines for long-term evaluation were developed to verify short-term prediction and performance.