Road Pavement Material Characterization and Rehabilitation: Selected Papers from the 2009 GeoHunan International Conference

Hydrated Cement Treated Crushed Rock Base (HCTCRB) is widely used as a base course material for Western Australian roads. HCTCRB has been designed and used based on an empirical approach and practical experience, respectively, but those are not capable of explaining behavior of HCTCRB. Presently, a mechanistic approach is considered more reliable in pavement design and analysis. Mechanistic methods also provide effective tools in better understanding of pavement performance. The study provides laboratory testing and the corresponding analysis so as to assess the mechanical characteristics of HCTCRB. Conventional triaxial tests and repeated load triaxial tests (RLT tests) were performed. Factors, which would affect the performance of HCTCRB such as hydration periods and the amount of added water, were also investigated.

The aging of domestic typical paving asphalt was evaluated by the rolling thin-film oven test (RTFOT), the modified German rotating flask test (MGRF) and the stirred air flow test (SAFT) in order to find out a binder aging system that be applied to both the modified and unmodified binders. The experimental condition was changed, and the properties of the asphalt after aging were tested. Tests included penetration, viscosity, softening point, ductility, group composition and infrared spectrum analysis. The kinetics of aging of asphalt was investigated, and the merits and shortcomings of the indices in evaluating the anti-aging capability of asphalt binders were investigated. The experimental results showed that SAFT and MGRF could be used as alternatives to RTFOT even though further research on these aging methods is needed.

This paper presents the results of laboratory testing to determine the complex modulus of asphalt treated mixtures. Laboratory tests were performed on two different asphalt treated mixtures from Qingyuan. Testing was performed at six temperatures and five frequencies. It was found, as expected, that the dynamic modulus increased with an increase in frequency and a decrease in temperature. Data from the tests were processed through a nonlinear regression curve fit to generate master curves of dynamic modulus vs. frequency. The model used to fit dynamic modulus master curves provided a good fit for the experimental data.

Porous cement concrete's excellent skid resistance, sound transmission ability and water permeability make it a good choice of material for highway construction. However, there are many differences in the manufacturing technology used for porous concrete and ordinary concrete. The main differences are constituent materials, workability test, mix proportioning, and indoor molding craft. Based on an analysis of the structural pattern of porous concrete applied in highway pavement, target porosity is viewed as the most important structural index, and all manufacturing phases must focus on this factor. In this paper the constituent materials and reinforcement measures, the methods for testing, evaluating and adjusting porous concrete workability, and indoor molding craft are introduced. A mix proportioning design with the aim of target porosity is suggested for the first time and the rational range of values for mix parameters are given for further research. Performances of several highway porous concrete pavements are also listed.

To study methodology of determining mixing and compaction temperature for modified asphalt mixture, the Superpave gyratory compaction tests are adopted to study the volumetric parameters of several modified asphalt mixtures. First, the rational compaction temperature is obtained based on the optimal compaction effect, and according to the relationship of viscosity with temperature and shear rate considerations, a shear rate of 60(1·s^–1) is proposed to measure the viscosity of modified asphalt. At this shear rate, the viscosity of modified asphalt at different temperatures can be obtained and the viscosity-temperature curve can be achieved. As a result, the mixing and compaction temperature for modified asphalt can be determined to deliver 0.17±0.02Pa·s and 0.28±0.03Pa·s for HMA mixing and compaction, respectively. The difference between temperatures obtained with the methodology and temperatures at which optimal compaction effect can be obtained is less than 5°C. The proposed temperatures are also kept in good accordance with paving practice.

The high pressure-gel permeation chromatographic (HP-GPC) testing was adopted to determine the molecular size distribution (MSD) of asphalt binders. The percentages of large, medium and small molecular sizes of asphalt binders are able to help the researcher and engineer determine the aging characteristics of asphalt binder. The objective of this research was to investigate the aging behavior of the rubberized asphalt binders as well as the virgin binder and the binder using 3% Styrene-butadiene-styrene (SBS) polymer after a long-term aging through the laboratory HP-GPC testing approach. The experimental design included the uses of three binder sources, three binder grades and three aging levels, i. e., virgin, rolling thin film oven and pressure aging vessel that included three testing temperatures (85, 100 and 110°C) and three aging durations (15, 20, and 40 hours). The results indicated that the HP-GPC approach can effectively describe the aging status of asphalt binders; the use of crumb rubber could improve the aging resistance of the asphalt binder; in addition, the PG 64-22 binder mixed with 10% crumb rubber generally showed the similar aging properties as of PG 76-22 using 3% SBS polymer after a long-term aging process in this study.

Permanent deformation (rutting) is one of the major distresses in hot-mix asphalt (HMA) pavements. Load and temperature have important effects on the rutting characteristics of HMA. The present study evaluated the rut-resistance of HMA under different loads and temperatures through the Asphalt Pavement Analyzer (APA) and the Flat Rubber Wheeled Loaded Wheel Tester (FLWT). The mixtures selected in this study included Sup-25, Sup-19, Sup-13 and SMA-13 mixtures with different aggregates (limestone and basalt) and asphalt binders (conventional and modified asphalt binder). For Superpave 13-mm mixtures, three different asphalt contents were used to produce the specimens. The rut resistance properties of mixtures were tested under two APA load levels (445N load, 0.7MPa hose pressure and 890N load, 0.81MPa hose pressure) and temperatures (60 and 70°C) through APA and FLWT. The result from this study indicated that load and temperature have significant effect on the rutting characteristics of HMA, and the rut-resistance of HMA can be improved by mixture design.

The present study presents an investigation into different factors affecting the resilient modulus of hot mix asphalt. So, a fractional factorial analysis of experiment was carried out considering five factors, each at two different levels. These factors were the maximum nominal aggregate size, specimen diameter and thickness, and the load pulse form and duration. During the course of analysis, two types of hot mix asphalts with different maximum aggregate sizes were taken into consideration. Marshall compaction method was used to prepare the specimens. Furthermore, for measuring the resilient modulus, sinusoidal and triangular load pulse forms were applied. Finally, we examined the different factors interrelations, which affect the resilient modulus. Analysis of the factorial experimental design showed that the maximum nominal aggregate size is the most important factor affecting the resilient modulus, followed by the load duration, and the specimen geometry represented by the thickness and diameter.

It is well known that fatigue cracking generally is a process of crack initiation and crack propagation. However, the crack propagation, in most cases, has not been fully considered in pavement analysis and design. One of the reasons is lack of a simple and rapid test for determining fracture properties of hot-mix asphalt (HMA) mixes. In this paper, an Overlay Tester-based test procedure was developed to determine fracture properties (A and n) of HMA mixes. The three main features of this Overlay Tester-based procedure are 1) its simplicity: neither a hole in the center nor a notch at the bottom of the specimen is required, since a crack is always automatically initiated in the first cycle. Also, no LVDT (Linear Variable Differential Transformer) is required to mount on the specimen; 2) its rapidity (short testing time): in contrast to other fracture types of tests (i.e. indirect tension or repeated direct tension test) which generally take long testing time, the proposed procedure only take about 20 minutes; and 3) its specific specimen size (150 mm long by 75 mm wide by 38 mm high): this size of specimen can be easily cut from samples compacted by the Superpave gyratory compactor or from field cores.

The characteristics of the roadbed material are critical to the overall performance of the pavement. The paper presents examples with discussion of the form of distress experienced within the pavement layers, based on observations made during the profiling exercise of an investigation into the causes of the premature failure of a pavement. The field investigation entailed a detailed inspection and recording of the profile exposed in test pits, with particular attention being paid to areas with cracks, noting their positions and extent within the pavement layers. The focus of the paper is on the observed orientation of crack propagation within the pavement layers. It is shown that the crack propagation is not always in the vertical plane. This has implications in dealing with crack sealing procedures. The causes of the observed distress were attributed to the behavior of the roadbed as it experienced fluctuating moisture conditions.

As the uses of geosynthetic reinforced structures continue to increase, the possibility of their failure also continues to grow. In recent years, more failures of geosynthetic reinforced slopes initiated by intense rainfall have been reported. These incidents were likely the effect of water being absorbed by the unsaturated fill and thereby reducing its strength. This paper reports the results of a forensic study and proposes a practical approach to evaluate the probable errors in analysis that are responsible for such failures. The results of this study are consistent with those observed in the field. The rational procedures found in this research offer a logical and practical way to examine the stability of reinforced slopes upon wetting.

Forensic studies are conducted in Texas when premature pavement failures occur. The purpose of these studies is threefold; firstly to identify the cause of the pavement problem, secondly to identify what actions the DOT should take immediately to minimize its impact and thirdly to identify changes to materials/design/construction practices or specifications which will eliminate this problem in the future. While conducting forensic studies TxDOT makes extensive use of non-destructive testing equipment. For flexible pavements air coupled high speed Ground Penetrating Radar (GPR) is a critical tool. The device can, at highway speeds, detect defects in both surface and base layers. GPR testing is followed by deflection testing and validation coring. Basic and advanced laboratory testing are also frequently required to fully diagnose problems. In this paper the nondestructive tools found most useful will also be described together with examples of recent forensic studies. The main focus of this paper will be to address the third issue described above that of avoiding problems in the future. In many instances forensic studies identify areas where future research studies are required. Examples will be given where the forensic study initiated a research project which provided products aimed at eliminating the problem. Examples of this include recently completed studies on minimizing the impact of sulfate heave and improving the crack resistance of asphalt overlays.

Pavement preservation treatment selection is a complex process which involves many factors ranging from pavement engineering to economic analysis. To determine the most preferable treatment is very challenging to many pavement engineers, especially for someone with limited experience. Most states or local agencies utilize either decision trees or decision tables to assist with the treatment selection. However, there are some disadvantages of using these decision trees or decision tables. This paper proposes to incorporate the expert system concept into the pavement treatment selection process. The California Department of Transportation (Caltrans) decision tables for treatment selection have been converted to a prototype expert system which includes a user interface, an inference engine, and a knowledge base. The prototype system allows one to evaluate various treatment alternatives. The best alternative based on user provided roadway conditions and weighting scores can then be selected by the expert system. The system can help inexperienced engineers to make a better choice; it can also help streamline the decision making process for seasoned pavement engineers.

Crack sealants prevent moisture and debris intrusion into pavements. The length of time that crack sealants are effective is important to highway agencies. Many highway agencies utilize a magnesium chloride solution to prevent snow and ice accumulation on roadway surfaces. It has been reported that this de-icing solution leaves a residue inside unfilled cracks in asphalt pavements, potentially affecting the performance of crack sealants. The purpose of this study was to assess the effect of magnesium chloride application on the performance of two types of crack sealants at two elevations in Colorado, United States. The experiment was designed to evaluate the association between crack fill remaining over a three year period and two different crack sealants, with and without exposure to magnesium chloride. Using factorial ANOVA, a statistically significant difference (p < 0.05) between the two crack fill products was observed at both elevations; however, the effect of magnesium chloride was only observed for the crack sealants at the higher elevation.

Aiming at existing void between initial lining and surrounding rock or initial and secondary lining, with ground-penetrating radar nondestructive testing technology and polymer grouting technology, the article has attempted to study the polymer grouting technology of tunnel maintenance. Taking an under construction highway tunnel as a test section, the tunnel lining has been tested with ground-penetrating radar, and the disease scope of the tunnel has been determined, the detected void region has been treated with polymer grouting, the grouting effect has been verified with ground-penetrating radar, the polymer grouting technology applying in treating with the disease of tunnel lining has been studied, and the tunnel polymer grouting repair technology has been initially formed. The field testing result shows that using polymer grouting technology, the tunnel damage can be treated, and a new idea for tunnel quick maintenance can be provided.

Differential settlement of the subgrade is the main problem encountered in the reconstruction of ole road to expressway. Numerical analysis indicated that the treatment to new nature ground is the key to decreasing the differential settlement. Dynamic compaction is an effective method of improving ground. In order to optimize its construction parameters, dynamic-compaction-induced dynamic pore pressure and dynamic soil stress and the dissipation of excess pore pressure after tamping were measured and analyzed. For the soil subgrade tested, the maximum tamping number shouldn't exceed 4 and the dynamic compactions of the next time should be carried out two days after the previous.

To minimize the differential deformation between the widening subgrade and the existing one, geosynthetic-reinforced and pile-supported (GRPS) embankment was chosen as a typical geotechnical composite system in Shanghai A11 expressway-widening engineering. Due to the complexity of this problem, 3D finite element analysis was conducted to investigate the mechanical behavior and effect of GRPS embankment in subgrade-widening engineering over soft soil. Analysis results indicate that, GRPS embankment can reduce differential settlement and enhance the stability significantly, spacing of outer piles can be larger than that of the inner piles, and the installation of piles under the existing embankment slope combined with excavation of old filling is very necessary when the height of embankment is not less than 3 meters.

The purpose of this paper is to analyze the different foundation treatments effect on road deformation numerically according to a widening practice. Results show that the plastic drainage board used in the new foundation enhances the old road deformation greatly during widening, while the new foundation with composite foundation produce less settlement of the new and old embankment after construction and disturbance to the existing road. At the same time, the distribution of the horizontal displacement in foundation provides the theory base to use the stress isolation wall to treat the new foundation. The wall depth depends on the depth of the horizontal displacement concentration zones.

This work evaluates the resistance to fatigue cracking of hot asphalt mixtures made with aggregates from construction and demolition debris. The mixtures were fabricated with 50% recycled aggregates to be used as road bases and binder courses in roads with low traffic volumes. For each mixture studied the fatigue law constants in deformation were obtained as well as the dynamic modulus. These results were compared to those obtained in hot asphalt mixtures elaborated with only virgin aggregates from quarries.

This study considers the use of artificial neural networks (ANNs) to predict the unconfined compressive strength (UCS) of soil-stabilizer mix. Radial basis function (RBF) as one of the most widely used ANN architectures is utilized to construct comprehensive models to relate the UCS of stabilized soil to the properties of natural soil and type and quantity of stabilizing additives. A comprehensive set of data obtained from previously published stabilization test results was used for model development. A subsequent parametric study was carried out and the trends of the results have been confirmed via previous laboratory studies. The RBF based estimates are compared with the experimental and numerical results of other researchers and found to be more accurate.

In this research, Firming agent (FA) and a small amount of hydrated lime were used to stabilize soil. Five types of soil, 0.2L/m³ of FA, and several low dosages of hydrated lime were selected. Total 15 different soil mixes were studied. The unconfined compressive strength (UCS) of each stabilized soil was tested at the age of 7, 14, 28, and 90 days. Test results show that FA and a low dosage of hydrated lime could effectively stabilize clay soil, but are not suitable for silt. A highly significant linear correlation exists between the UCS of stabilized soil and the cation exchange capacity (CEC) of the soil. The greater the CEC, the higher the strength is. Among the three factors of plasticity index (PI), clay particle content, and CEC, the CEC is themost direct and reliable indicator that reflects whether the soil is suitable for being stabilized with FA and hydrated lime. Minimum criterion of CEC of soil was approximately calculated as 10m mol/kg. If PI is used as a criterion, stabilization results can be ideal when the PI is about 15~ 22.

Foamed bitumen bound base course materials were manufactured in the laboratory by mixing reclaimed asphalt pavement (RAP) with new crushed limestone and treated with foamed bitumen. Gyratory compacted specimens were also subjected to repeated loading under triaxial conditions which provided an approximate simulation of the traffic loadings experienced in actual pavements. A pilot-scale foamed bitumen stabilized pavement base course was also constructed. The Nottingham Pavement Test Facility was used to more realistically traffic the various trial pavement sections using a loaded wheel. It was found that the deformation resistance of foamed bitumen bound mixtures was dependant primarily on percentage of RAP in the mixes and penetration grade of bitumen generating the foam. The addition of small amounts of cement significantly enhances the deformation resistance of foamed mixes.

In many areas of Alaska, clean, durable aggregates normally utilized for base course either require long hauls from outside, or are difficult to obtain within the project limits. Asphalt treatment is the most commonly used type of stabilization for the available lower quality materials to increase their strength thus extending their life and saving money to the state in the long run. This paper presents the resilient modulus characterization of hot asphalt treated base (HATB) course material in northern region of Alaska. Experimental studies were conducted to evaluate the resilient modulus of HATBs through repeated load triaxial tests. Effect of different stabilization levels (i.e. asphalt content) on the performance of HATB materials was investigated and a model was developed to reflect the influence of confining pressure and deviator stress on HATBs.

The sand-gravel materials have a nonlinear behavior, the resilient modulus can describe the behavior effectively, and the resilient modulus model can be attained through enlarged bearing plate test. By analyzing the limitations of traditional bearing plate test with measuring the rebound deformation property of sand-gravel material, the experimental apparatus was ameliorated. Based on the test data of enlarged bearing plate test, the fitting result shows that the L-H model can effectively display nonlinear rebound deformation behavior of sand-gravel material, and the regression coefficient has relation with gradation of sand-gravel and clay, water content, compactness. Two important parameters of influencing resilient modulus of sand-gravel material, gradation of sand-gravel and clay and water content, are analyzed. Corresponding engineering suggestions are put forward.

In this paper, laboratory tests of recycled aggregate concrete(RAC) were carried out to investigate the influence of net water-binder ratio, sand percentage substitution recycled fine aggregate for natural sand on compressive strength and flexural strength of RAC. The results indicate that relatively high strength and good fluidity of RAC can be obtained by application of suitable chemical admixture addition of fly ash and silica fume, optimization of sand percentage. The application of recycled fine aggregate (RFA) for pavement construction cannot meet the requirements in specification.

The debate around the implementation of cold recycling methods for road rehabilitation would be purely academic if it weren't for the wherewithal to efficiently perform the task. Creative machine designers with technological foresight have made the debate a real one. The development of recycling equipment has preceded the initiatives of Civil Engineering practitioners to recycle existing pavement materials effectively. Modern recyclers offer minimal energy consumption and wastage with optimal enhancement to performance properties of the mix. The development of accurate mix design and pavement design procedures for told recycled materials by researchers and practitioners has followed the availability of recycling tools. Figure 1 bears testimony to the trend of investment of contractors globally in one brand of cold recycler capable of cementitious, emulsion or foamed bitumen stabilization.