Stiffness Of Asphalt Mixtures Research Articles

Ocena doświadczalna mieszanek mineralno-asfaltowych po częściowym zastąpieniu wypełniacza popiołami dennymi z elektrowni węglowej

The purpose of this study is to evaluate the performance of hot mix asphalt (HMA) prepared with coal bottom ash (CBA) as an alternative mineral filler. In this study, the effect of CBA on rutting, stiffness and fatigue resistance was experimentally evaluated. Combinations of conventional filler (stone dust) with different percentages of CBA (at 1.5%, 3%, and 4.5% by volume) were adopted. The HMA samples were prepared and tested using the Marshall mix design method. Following the Asphalt Institute MS-2 and the Pakistani National Highway Authority (NHA) General Specifications, sixty samples of HMA were compacted; stability tests at varying bitumen contents (3.5%, 4.0%, 4.5%, 5.0%, and 5.5%) were used to determine the optimum bitumen content (OBC) in the mixture for each percentage of CBA in the filler. For 0%, 1.5%, 3%, and 4.5% CBA, the optimum bitumen contents of 4.27%, 4.47%, 4.53%, and 5.0% were obtained, respectively. They were used throughout the study. Three samples with the optimum binder content were made for each of the four analysed CBA proportions. The wheel tracker test was run on 12 OBC samples, and the dynamic modulus test was run on 12 OBC samples. The Marshall stability and flow test results showed that the samples prepared with 3% CBA as filler and an OBC of 4.53% satisfied the NHA requirements for flexible pavement. It was noted that CBA greatly improves the rutting resistance and stiffness of asphalt mixtures. It also improved the fatigue life. Therefore, adding up to 3% CBA by volume to stone dust used as filler in asphalt concrete can minimize the need for stone dust and provide a suitable method of CBA disposal.

Investigating changes in the stiffness of asphalt mixtures caused by laboratory ageing and varying asphalt binder content

The research focuses on evaluating the changes in stiffness of the AC11 50/70 asphalt mixtures with different bitumen content. These changes are induced by the action of thermo-oxidative ageing in both short and long term process. The short-term aging simulates the process of asphalt mixture production, transport and laying. Long-term aging simulates the serviceability process that pavement must withstand during 10 to 15 years of service life. Asphalt mix stiffness measurements were made using the IT-CY method according to EN 12697-26 for 3 different temperatures of 10, 20 and 30°C. To investigate the effect of asphalt binder content on stiffness, measurements were performed on 3 types of mixes with 4.9, 5.4 and 5.9% asphalt binder in the mix. Research in this area has revealed that both the binder content and the thickness of the asphalt film have a relatively significant effect on the change in the stiffness of the asphalt mixture. The changes in stiffness for the asphalt mixture with a binder content of 4.9% were only minimal in terms of the degree of aging. At 10°C, even a minor decrease in stiffness was observed for this mix. The asphalt mixture with 5.9% binder had a very significant increase in stiffness in terms of the degree of ageing.

Regulating asphalt pavement temperature using microencapsulated phase change materials (PCMs)

The use of phase change materials (PCMs) to regulate pavement temperatures has been previously studied, with the most successful studies using porous aggregates to stabilize the PCMs. However, this technique can lead to issues with PCM leakage and low PCM content. A less studied method is the use of PCM microcapsules, which also presents challenges since most microcapsules are not strong nor stable enough to survive the high temperatures and compressive forces experienced during asphalt mixture production and placement. This work presents a study of the properties of a new commercial microcapsule type with robust walls and high thermal stability, that are expected to overcome the aforementioned issues. Results from differential scanning calorimetry and thermogravimetric analysis confirmed the microcapsules exhibited high latent heats (200 J/g) and are thermally stable below 400 °C. Additionally, approximately 90% of the capsules remained unbroken after being milled at 140 °C for 20 min, suggesting they are capable of withstanding the mixing and compaction stages of asphalt pavement construction. When PCM microcapsules were added to HMA, thermal cycling experiments showed that specimens containing 10 and 20 vol% PCM exhibited temperature lags of 5 to 10 °C from the control mixture, as they approached the PCM melting/freezing temperature. These results confirm the ability of microencapsulated PCMs to regulate asphalt pavement temperature. However, results from measurements conducted at 40 °C and 1 Hz showed a 75% reduction of the dynamic modulus in specimens containing PCM microcapsules, which could indicate that the addition of these materials also affect asphalt mixture stiffness.

Encouraging Sustainable Use of RAP Materials for Pavement Construction in Oman: A Review

The Sultanate of Oman has experienced rapid development over the last thirty years and has constructed environmentally friendly and sustainable infrastructure while it continues to find economical alternative resources to achieve the goals of the Oman 2040 vision. The primary concerns are preserving natural resources and reducing the impact of carbon dioxide (CO₂) emissions on the environment. This review aims to encourage the sustainable use of reclaimed asphalt pavement (RAP) materials in pavement construction and focuses primarily on employing RAP materials in new pavement projects. Currently, new construction projects utilise a significant percentage of demolished asphalt pavement to save costs and natural resources. The key issue that arises when mixing RAP into new asphalt mixtures is the effects on the mixtures’ resistance to permanent disfigurements, such as fatigue cracks, that influence asphalt mixture performance. Numerous studies have assessed the impact of using RAP in asphalt mixtures and found that RAP increases the stiffness of asphalt mixtures, and thus improves rutting resistance at high temperatures. Nevertheless, the findings for thermal and fatigue cracking were found to be contradictory. This review will address the primary concerns regarding the use of RAP in asphalt pavements, and aims to encourage highway agencies and academic researchers in the Gulf countries to develop frameworks for the practical usage of RAP in the construction of sustainable pavement systems.

Stiffness Modulus of Aged Asphalt Mixtures

Asphalt mixtures have a dominant position in road construction in most countries. The choice of asphalt mixture type and surface depends mainly on the traffic loading and climatic conditions. The stiffness of asphalt mixture is one of important parameters that determines how road pavement performs and what pavement response to traffic loading. The stiffness modulus of the asphalt mixture changes during its service life, it tends to increase. During this process the mixtures in pavement age and degrade. Aging of asphalt mixtures has a significant effect on changes in the properties of individual mixtures. Presented research was focused on monitoring the change in the stiffness modulus of two asphalt mixtures AC11 50/70 and AC11 PMB 45/80-75 by the effect of aging. The asphalt mixtures have been exposed to the effects of short-term and long-term ageing by the conditioning of loose mixture method. After aging of the asphalt mixtures, the stiffness modulus of compacted asphalt mixture samples was measured. The stiffness modulus was determined using the IT-CY method at temperature of 10 °C, 20 °C and 30 °C and showed an increase after exposure of the mixture to short-term and long-term aging.

Evaluation of the rejuvenation of asphalt by means of oil-saturated porous aggregates

Road degradation is an increasing problem for assets managers. Roads deteriorate mainly due to the combination of different factors, such as temperature, climate and traffic loads. This causes the asphalt to age and, consequently, the bituminous mixtures become more fragile and microcracks begin to appear. To eliminate these degradation effects, the most widely used performed actions are based on the renovation of the pavement to achieve an asphalt surface under acceptable conditions of use. In order to reduce the application of corrective measures when the asphalt pavement is already facing significant defects, it is important to perform regular preventive maintenance that minimise the renovation works of the pavement and improves the asphalt durability. This paper shows a method for the continuous rejuvenation of asphalt, by analysing the evolution of asphalt mixture stiffness and the resistance to cracking on asphalt mixtures with rejuvenator added after having been submitted to a laboratory ageing protocol (short and long-term ageing). The rejuvenator was added to the mixtures following either of these two procedures: first, directly added to the mixture and the second, saturated in porous aggregates, what the authors call encapsulated. Results from this study demonstrate the effectiveness of the second method (encapsulated rejuvenator) as an original solution to achieve long-term performance mixtures with reduced cracking.

Durability Phenomena of Bitumen and Bituminous Pavement Materials

The durability of asphaltic mixtures, in addition to traffic loading, is greatly influenced by the extremes environmental parameters. For instance, at higher temperatures, bitumen becomes soft, thereby reducing the stiffness of asphalt mixtures and making them vulnerable to rutting. On the other hand, at lower temperatures, the stiffness of bitumen is increased, reducing the flexibility of asphaltic concrete and rendering it prone to fatigue failure. Therefore, this evaluation is an extensive research study on the durability of binder and asphalt mixture with their phenomena. Besides that, this paper intends to delve into the various testing methods and measures adopted to evaluate aging and slowing it down. It also presents a critical review of these methods and proposes a future course of action to better address aging issues. According to the evaluation, the behavior of bitumen on the basis of its source varies; when it is mixed with bitumen modifiers, aggregates, and other filler materials, its behavior becomes even more complex. Hence the understanding of the phenomenon of aging is important and the significance cannot be overemphasized. Extensive research work has been done over the last seven decades to evolve the understanding of short- and long-term aging and to improve the durability of asphaltic mixtures. Generally, the aging of bitumen under the influence of both environment and traffic is irreversible as well as inevitable. Apart from entailing hefty maintenance budgets, it remains a challenge to the researchers to slow down aging.

Comparison of Performance Properties and Prediction of Regular and Gamma-Irradiated Granular Waste Polyethylene Terephthalate Modified Asphalt Mixtures

The utilization of waste polyethylene terephthalate (WPET) as aggregate substitutes in pavement has been extensively promoted because of its environmental advantages. However, previous studies have shown that a high percentage of WPET reduces the performance of the pavement. To increase the durability of pavement and mitigate the environmental issues caused by WPET, WPET is treated with gamma-irradiation as a component in asphalt mixtures. The study objectives were to investigate the feasibility of using WPET granules as a sustainable aggregate on asphalt mixture stiffness and rutting and predict the asphalt mixture performance containing irradiated WPET via an RSM-ANN-framework. To achieve the objectives, stiffness and rutting tests were conducted to evaluate the WPET modified mixtures’ performance. The result indicated that samples containing 40% irradiated WPET provided a better performance compared to mixtures containing 20% non-irradiated WPET, increasing the stiffness by 27% and 21% at 25 °C and 40 °C, respectively, and rutting resistance by 11% at 45 °C. Furthermore, both predictive models developed demonstrated excellent reliability. The ANN exhibited superior performance than the RSM. The utilization of WPET as aggregate in asphalt mixtures represents a way to addressing related recycling issues while also improving performance. With gamma-irradiation treatment, the utilization of WPET can be increased with improved asphalt mixture performance.

Dynamic modulus master curve construction of asphalt mixtures: Error analysis in different models and field scenarios

Asphalt mixture stiffness is a key property in any pavement long-life performance analysis; it is used to predict a material’s strain response for any given applied stress. To accurately describe experimental data, different mathematical models have been reported in literature, which allow for extrapolation to ranges not evaluated in laboratory tests. However, a precision analysis comparing each of them is necessary. This study evaluated 50 data points from five temperatures, ten loading frequencies, and 48 different asphalt mixtures to construct dynamic modulus master curves. Sigmoidal, Christensen-Anderson-Marasteanu (CAM), and Havriliak-Negami (HN) models were calibrated with three different target error functions, in addition to 2 Springs, 2 Parabolic creep elements, and 1 Dashpot (2S2P1D) to analyze their relative and absolute errors. In the first part, the mechanical analogs (2S2P1D and HN) achieved the best results. In the second part, the error added by the Williams-Landel-Ferry (WLF) and polynomial function, which describe the time–temperature shift factors used to construct the dynamic modulus master curves, was calculated; this suggested that the polynomial function better fits the master curves’ shift factors. In the third part, three Enhanced Integrated Climate Models (EICM) with different pavement depths and temperatures throughout the year together with the influence of vehicle speed and a depth equation were used to meet a reduced frequency interval that represents practical field conditions. Therefore, by filtering the errors found in part one using the field-representative reduced frequency interval, the fitting models (based on regression adjustments) can reach lower error levels closer to those of the mechanical analog models although still greater than those of the 2S2P1D model. In summary, it is possible to obtain a reliable pavement stiffness prediction using a less robust model as long as the dynamic modulus tested database is wide enough to express the desired reduced frequency range. Nevertheless, the use of a mechanical approach model such as 2S2P1D better describes the dynamic modulus experimental results, which leads to a more reliable prediction in addition to enabling characterization of the rheological behavior of asphalt materials.

Asphalt Pavement Temperature Prediction Models: A Review

The performance of bituminous materials is mainly affected by the prevailing maximum and minimum temperatures, and their mechanical properties can vary significantly with the magnitude of the temperature changes. The given effect can be observed from changes occurring in the bitumen or asphalt mixture stiffness and the materials’ serviceable life. Furthermore, when asphalt pavement layer are used, the temperature changes can be credited to climatic factors such as air temperature, solar radiation and wind. Thus in relevance to the discussed issue, the contents of this paper displays a comprehensive review of the collected existing 38 prediction models and broadly classifies them into their corresponding numerical, analytical and statistical models. These models further present different formulas based on the climate, environment, and methods of data collection and analyses. Corresponding to which, most models provide reasonable predictions for both minimum and maximum pavement temperatures. Some models can even predict the temperature of asphalt pavement layers on an hourly or daily basis using the provided statistical method. The analytical models can provide straight-forward solutions, but assumptions on boundary conditions should be simplified. Critical climatic and pavement factors influencing the accuracy of predicting temperature were examined. This paper recommends future studies involving coupled heat transfer model for the pavement and the environment, particularly consider to be made on the impact of surface water and temperature of pavements in urban areas.

Contact mechanics based solution to predict modulus of asphalt materials with high porosities

Asphalt mixtures with high porosities (known as porous asphalt (PA) mixes) are becoming a popular choice among road authorities as it provides better skid resistance while also reducing tire-pavement noises. Towards the design and manufacture of PA mix pavement, the evaluation of the mechanical properties of PA mixes is of great importance. To predict the mechanical properties of PA mixes, micromechanical models have been considered as an effective tool. In most research studies, continuum-based micromechanical models, i.e. the Self-consistent model, the Mori-Tanaka model, etc. are widely used to predict the stiffness of asphalt mixtures. However, the limitation of these models is that they cannot describe the characteristics of individual particles and thus they cannot provide accurate predictions. On the other hand, the discrete-based micromechanical model (DBMM) which simulates a granular material as an assembly of bonded particles seems to be a promising alternative. Limited research studies have focused on studying the utilization and the applicability of this model for asphalt mixes. Therefore, this paper aims to propose a framework to use DBMM and to evaluate its performance in estimating a PA mix’s stiffness. Based on the obtained results, both the merits and limitations of this model were highlighted.

Understanding the Stiffness of Porous Asphalt Mixture through Micromechanics

Micromechanics, which can be used to relate the properties of a composite to the properties of individual constituents, is considered a good approach to understanding the fundamental mechanisms behind the behavior of asphalt materials. Compared with the semi-empirical and numerical micromechanical models, analytical micromechanical models do not need calibration factors. In addition, they can provide analytical solutions on the basis of a series of assumptions. Using these models, researchers have separated the effects of different stiffening mechanisms (i.e., the volume-filling reinforcement, the physicochemical reinforcement, and the particle-contact reinforcement) for mastic. However, similar research work has not been conducted for asphalt mixtures and, moreover, the characteristics of the particle-contact reinforcement have not been deeply analyzed by researchers. Therefore, this paper aims to understand the stiffness of asphalt mixture through micromechanics. The focus of this study was on porous asphalt mixture where particle-contact reinforcement plays an important role in its behavior. The stiffening effects of different mechanisms were separated using analytical micromechanical models. The effects of temperature/frequency and the properties of the matrix phase on the stiffening effect of the particle-contact reinforcement were analyzed.

Investigation on three-dimensional failure criterion of asphalt mixture considering the effect of stiffness

In order to reveal the effect of complex stress state on the characteristics of strength and stiffness of asphalt mixture, the self-developed double confining pressure triaxial test method was used in this study. The one-time failure and resilient modulus tests in complex stress state were carried out on the SMA-13 and AC-13 asphalt mixtures widely used in China's asphalt pavement, especially in the combined tensile-compressive stress state. The failure principal stress of material and its stress-strain data under the step loading condition were obtained. The calculation model of resilient modulus in complex stress state and the failure criterion I1-J2 in the principal stress space were established. On this basis, based on the generalized Hooke's law, a three-dimensional strain failure criterion model for asphalt mixture considering the effect of stiffness was also established by the conversion method. The research results can provide experimental and theoretical support for the reasonable selection and resistance calculation of material parameters of asphalt mixture in complex stress state.

The Usage of Treated Plastic as Additive to Improve the Asphalt Mixture’s Performance by Using Dry Mix Method

Nowadays, road damage issue become the norm due to increment of traffic load and traffic volume. It shortens the service life of asphalt mixtures and increase the cost of maintenance. One way to reduce the issue is by using polymer additive in asphalt mixture. Treated Plastic is one type of polymer additive made of plastic bag (Polyethylene). The main purpose of this research is to determine the improvement of asphalt mixture’s performance incorporating Treated Plastic (TP) as additive in terms of stability, stiffness, fatigue cracking, stripping and rutting. The mechanical properties of asphalt mixes that include various percentages of TP (0%, 0.25%, 0.5%, 0.75%, 1%, 2% and 3%) were calculated and assessed with laboratory tests. 0.75% by weight of total mix of TP was found to be the optimum amount. The outcomes were analyzed by Marshall Stability and Flow, Resilient Modulus, Tensile Strength Ratio and Hamburg Wheel Tracker test. As the results shown, the addition of TP gave significant improvement to the stability and stiffness of asphalt mixture. 0.75% of TP was selected as the optimum percent content with percent improvement about 100, 73 and 25% for fatigue cracking, rutting and stripping resistance respectively. Hence, 0.75% of TP improved the resistance of rutting and stripping but susceptible to fatigue cracking.

Research into effect of asphalt mixture aging on stiffness

The paper focuses on the research of the stiffness of asphalt mixtures exposed to short-term and long-term aging. Asphalt mixtures are exposed to this type of ageing during their production, laying and compaction and subsequently during service. The research was carried out on test samples of asphalt mixtures AC11 50/70 and AC11 PMB 45/80-75 for wearing course of asphalt pavements. The asphalt samples have been exposed to the effects of short-term and long-term ageing by the conditioning of loose mixture method. Subsequently, the stiffness modulus of asphalt mixtures at temperature 20 °C was determined by the IT-CY method according to EN 12697-26. The obtained results showed higher values of stiffness modulus for the mixture with paving grade bitumen 50/70. The largest difference in the stiffness modulus was recorded for origin asphalt mixtures. Furthermore, an increase in the mixture stiffness due to ageing was observed, more pronounced in the case of the mixture with the polymer modified bitumen PMB 45/80-75. Gradual ageing changes the properties of asphalt mixtures, which are essential for the durability of the road.

Effect of laboratory long-term oven aging on the stiffness of asphalt mixtures

This study evaluates the effect of laboratory long-term oven aging (LTOA) on the stiffness of asphalt mixture using laboratory dynamic modulus test. A large variety of materials was subjected to diverse LTOA conditions including different aging temperatures and durations with loose mixture and compacted samples. Dynamic modulus master curve and dynamic modulus ratio (DMR) data shows that the aging of loose mixture at 95 °C could be an ideal LTOA procedure with the efficiency and capability to characterize the long-term aging in the field. The variety of materials including the use of recycled asphalt pavement, warm mix asphalt technologies and asphalt binder performance grade was also found to have appreciable effect on the LTOA properties.

The effect of vehicle speed on the stiffness modulus of conventional asphalt and bioasphalt

Stiffness modulus is the ratio between stress and strain found in a layer. The value of the stiffness modulus is related to the performance of the layer in bearing the load. High modulus of stiffness makes the asphalt mixture stiff and resistant to deformation, while a decrease in the modulus of stiffness will make the pavement layer vulnerable to crack. The purpose of this study was to analysis the characteristic differences between damar asphalt mixture and conventional asphalt mixture in term of the stiffness of asphalt mixtures due to the variations in vehicle speed at the specified temperature. Speed variations are 10, 20, 30, 40, 50 and 60 kph and the temperature reference are 20 and 40°C. Data analysis is performed by comparing the stiffness values of damar asphalt mixtures and conventional asphalt mixture. The results of this study indicate that damar asphalt mixes are more resistant to changes in temperature and vehicle speed than conventional asphalt.

Investigation of Crack Initiation Behavior of Asphalt Mixtures: Fatigue through Dynamic Semicircular Bending Test

Abstract The objective of this study was to investigate the crack initiation behavior of asphalt mixtures and examine the fracture mechanism using dynamic semicircular bending (SCB) test. The scope of the study encompassed estimation of crack initiation parameter (Ni) and fatigue failure of six asphalt mixtures, including, conventional dense-graded (D) and rubber-modified gap-graded (AR) mixtures covering 144 SCB specimens. At 5°C, 15°C, and 25°C, D-mixes produced higher Ni than AR mixtures attributed to higher stiffness of D-mixes. Relative share analysis of Ni was found to be higher for D-mix than AR mixtures. Furthermore, correlation between |E*| and Ni indicated that higher stiffness of the mix resulted in brittle failure, which in turn increased the time for crack initiation to occur. Importantly, the stiffness of asphalt mixtures played a deciding role in contributing to the crack initiation phenomenon of these materials. Overall, the dynamic SCB test developed as part of the study was found to be a promising assessment technique to characterize crack initiation behavior of different types of asphalt mixtures.

Characterization of Asphalt Mixture Moduli under Different Stress States.

Modulus testing methods under various test conditions have a large influence on modulus test results, which hinders the accurate evaluation of the stiffness of asphalt mixtures. In order to decrease the uncertainty in the stiffness characteristics of asphalt mixtures under various stress states, the traditional unconfined compression test, direct tensile test, and the synchronous test method, based on the indirect tension and four-point bending tests, were carried out for different loading frequencies. Results showed that modulus test results were highly sensitive to the shape, size, and stress state of the specimen. Additionally, existing modulus characteristics did not reduce these differences. There is a certain correlation between the elastic modulus ratio and the frequency ratio for asphalt under multiple stress states. The modulus, under multiple stress states, was processed using min–max normalization. Then, the standardization model for tensile and compressive characteristics of asphalt under diverse stress states was established based on the sample preparation, modulus ratio variations, and loading frequency ratio. A method for deriving other moduli from one modulus was realized. It is difficult to evaluate the stiffness performance in diverse stress states for asphalt by only using conventional compressive and tensile tests. However, taking into account the effects of stress states and loading frequencies, standardized models can be used to reduce or even eliminate these effects. The model realizes the unification of different modulus test results, and provides a theoretical, methodological, and technical basis for objectively evaluating moduli.

Using Simulation Technique to overcome the multi-collinearity problem for estimating fuzzy linear regression parameters.

Fatigue cracking is one of the common types of pavement distresses and is an indicator of structural failure; cracks allow moisture infiltration, roughness, may further deteriorate to a pothole. Some causes of pavement deterioration are: traffic loading; environment influences; drainage deficiencies; materials quality problems; construction deficiencies and external contributors. Many researchers have made models that contain many variables like asphalt content, asphalt viscosity, fatigue life, stiffness of asphalt mixture, temperature and other parameters that affect the fatigue life. For this situation, a fuzzy linear regression model was employed and analyzed by using the traditional methods and our proposed method in order to overcome the multi-collinearity problem. The total spread error was used as a criterion to compare the performance of the studied methods. Simulation program was used to obtain the required results.