Indirect Tensile Stiffness Modulus Tests Research Articles

Effect of Chemical Composition on Rheological Properties of Asphalt Binders Modified with Rap Binders and Rejuvenator

Conventional rejuvenating agents such as virgin binders, polymers and so on, poses environmental, technical, and economic challenges. The objective of this study is to investigate the interaction between chemical components and rheological behavior of hot mix asphalt modified with RAP binder and diesel engine waste oil (DEWO) as rejuvenator. 7.2% DEWO was added to the RAP binder to achieve the modified binder (MB), and the effects of the rejuvenator through the MB were evaluated at varying percentages (0 to 100% by weight of the virgin binder) using Dynamic Shear Rheometer (DSR) under short and long-term aging at high and intermediate temperatures, as well as low temperatures using Bending Beam Rheometer (BBR). Saturates, aromatics, resins, and asphaltenes (SARA)-separation, Indirect tensile stiffness modulus test (ITSM), and fatigue life test were also employed to investigate the interaction between chemical components and rheological properties of binder. Results indicated that incorporating 50% modified RAP binder significantly enhanced the performance of the asphalt mixtures, it was also discovered that 100% of RAP content meets standard specifications when modified with oil rejuvenators. This research suggests that large quantities of diesel engine waste oil can be diverted from landfills and employed as useful resource in asphalt production.

Investigating the Influence of Mineral Fillers at Australian Asphalt Mixtures

Abstract It is commonly known that mineral fillers significantly affect the asphalt mixture's performance. Superior flexible pavement performance can be ensured by gaining a deeper understanding of the function of filler. This research investigates the influence of three different fillers: granite dust, cement, and hydrated lime, at Australian asphalt mixtures. The testing program includes Marshall testing, moisture damage resistance, indirect tensile strength (ITS), and indirect tensile stiffness modulus (ITSM) tests of asphalt mixtures. Analysis of variance (ANOVA) was used to statistically assess the results obtained, besides damage analysis. The results indicate that using natural granite dust yields the highest resistance to moisture, while cement produces the highest stability, ITS, and ITSM. Unexpectedly, using hydrated lime filler decreases the stability/stiffness and moisture resistance of asphalt mixtures. ANOVA tests indicate that the type of filler affects ITS, TSR, and ITSM results (i.e., the p-value <0.05). The damage analysis shows that the design life of the asphalt mixture made with cement filler is higher than that of mixtures made with natural granite dust and hydrated lime fillers respectively. The findings indicate the important role of nontraditional fillers at the performance of Australian asphalt mixtures.

Effect of wet-dry history on performances of dense asphalt mixture: Experimental investigation and predicting model

Asphalt pavement experiences various wet-dry histories in the service stage. However, the influence of wet-dry history on asphalt mixture is unknown. Therefore, to clarify the performance degradation mechanism and predict the performance of asphalt mixture under the action of wet-dry history, the creep-recovery test, indirect tensile stiffness modulus test and indirect tensile strength test were conducted at different temperatures. The finite element method was adopted to analyze the moisture diffusing profile inside the specimen after wet-dry cycles. A moisture damage model considering the soaking time and repeated characteristics was developed to predict the damaged properties. Results show that wet-dry cycles cause a slight mass loss of asphalt mixture. Wet-dry cycling action leads to the increment in high-temperature deformation, and reductions in stiffness modulus and tensile strength. The increase of high-temperature deformation is primarily caused by viscoplastic component. Even if the soaking time is short, high moisture damage occurs while the wet-dry cycle is sufficient. Numerical simulations show that the moisture concentration profiles inside asphalt mixture vary under different wet-dry histories, leading to variations in the damage zone. The degree of damage is also closely related to the acting time of moisture. The critical immersion time of the dense asphalt mixture (about 43 hours) was determined in this study. When the immersion period is shorter than the critical immersion time, the strength loss is greater than the modulus. On the contrary, the degree of modulus damage is higher than that of strength. Considering the actual rainfall climate in China, the strength damage of the on-site asphalt mixture in the field predominates. The proposed model could reflect the weakening trends of modulus and strength. It has good universal applicability in predicting the damaged Marshall stability, modulus, and strength at different temperatures.

A novel foaming additive derived from waste polyethylene terephthalate (PET) for low-carbon warm mix asphalt

Plastic pollution is growing relentlessly due to the careless disposal of waste plastic products. This study focuses on converting waste plastic bottles into a foaming additive for the production of eco-friendly warm mix asphalt (WMA) for paving purposes. The additive, namely PET-TETA, was synthesized from waste polyethylene terephthalate (PET) via an aminolysis process. Its chemical and physical properties were characterized by the scanning electron microscope (SEM), X-ray diffractometer (XRD), and thermogravimetry-differential thermal analyzer (TG-DTA) tests. The WMA mixtures were prepared using PET-TETA and a commercial foaming additive, and their properties were studied and compared to a conventional hot mix asphalt mixture. The performances of the asphalt mixtures were characterized through the indirect tensile stiffness modulus, moisture susceptibility, and immersion Hamburg wheel-tracking tests. The findings revealed that PET-TETA was a semicrystalline material containing approximately 26 % hydration water, which could be released gradually during the preparation of asphalt pavements. The performance of the WMA mixture utilizing PET-TETA was comparable to the other two asphalt mixtures, and it exhibited higher strengths and better resistance to stripping. Therefore, it is promising to apply PET-TETA as a sustainable and effective WMA additive for paving purposes, providing a solution to the issue of waste plastic disposal.

Repurposing agricultural waste: The effectiveness of peanut husk ash in improving asphalt mixture properties

Using agricultural waste in asphalt pavements presents a promising solution for addressing environmental concerns related to waste disposal and resource conservation while enhancing pavement performance. This study aimed to scrutinize the impact of incorporating peanut husk ash (PA) as a modifier for asphalt binder on hot mix asphalt (HMA) characteristics. The base asphalt binder, which had a penetration grade of 60/80, was initially mixed with PA at various concentrations through the utilization of a high-shear mixing apparatus. The resultant modified asphalt binder was then utilized to prepare asphalt mixtures. Various performance evaluations were performed, comprising Marshall, indirect tensile fatigue (ITF), repeated load axial (RLA), and indirect tensile stiffness modulus (ITSM) tests. The incorporation of PA improved the adhesion force between the aggregates and asphalt, resulting in enhanced resistance to applied loads, reversibility, and stiffness modulus. The use of PA also increased the resistance of the mixtures to rutting and reduced their thermal susceptibility. Additionally, adding PA to asphalt mixtures in concentrations up to 8% has the effect of increasing their resistance to fatigue and avoided the occurrence of vertical cracks resulting from horizontal tensile stresses. This study concluded that a substantial enhancement in the mechanical behavior of HMA may be achieved through the incorporation of PA, as compared to a conventional mixture.

Laboratory evaluation of oak ash waste for use in hot mix asphalt modification

In this study, the effect of Oak Ash (OA), a biomass waste, on the mechanical properties of hot mix asphalt (HMA) was investigated and its usability in road engineering was evaluated. For this purpose, firstly, various physical and chemical properties of B70/100 penetration class pure asphalt, OA and crushed limestone aggregate were determined. Then, the optimum asphalt content (OAC) of the mixture was determined according to the Marshall mix design method using aggregate and pure asphalt. Based on this determined content, pure and OA added (1%, 2%, 4% and 6% by weight of asphalt) modified hot mix specimens were prepared. Pure and OA added modified mixture specimens were subjected to Marshall stability, indirect tensile strength (ITS), moisture damage, indirect tensile stiffness modulus (ITSM), static-dynamic creep and calorie tests. According to the results obtained, it has been determined that the OA additive has an improving effect on all mechanical properties of the mixtures, especially on the permanent deformation resistance at high temperatures. It is considered that the use of this additive at a rate of 2% in the hot mixture can increase the resistance of the pavement against deterioration and reduce the maintenance and repair costs of the road.

The Effect of Wetfix and Nanohydrated Lime Additives on Bitumen Aging and the Cohesion and Adhesion Failure Mechanisms of Hot Asphalt Mixtures

Aging due to sunlight and the passage of time is an effective element in the occurrence of moisture damage in hot asphalt mixtures. Still, the effects of this parameter are scarcely considered in the experiments examining the moisture damage potential. Accordingly, this study investigated the effect of aging on the performance of hot asphalt mixtures and examined the improvement of moisture damage performance by using antistripping additives via mechanism and functional tests. Two types of aggregates (limestone and granite) with different degrees of moisture sensitivity, two types of bitumen (PG64-16 and PG58-22) with different performances, and two additives (Wetfix liquid additive and nanohydrated lime) as bitumen modifiers were used. Bitumen samples and asphalt mixtures were subjected to short- and long-term aging. The pull-off test was performed to explore the aging effect on different failure mechanisms (cohesion and adhesion), and the indirect tensile stiffness modulus (ITSM) test was conducted to study the asphalt mixture’s performance against moisture damage. The results specify that aging, in terms of hot asphalt mixture hardening in dry and wet conditions, decreased the MSR (resilient modulus wet to resilient modulus dry ratio), and this decline was greater in long-term aging. The pull-off test results exhibited that aging, especially in the long term, decreased the asphalt mixture’s adhesive strength in dry and wet conditions; this decline in adhesion was greater in the wet than in the dry state, and this difference decreased the wet-to-dry adhesion strength ratio (the pull-off ratio). The additives relatively improved the yield modulus of the asphalt mixture, but their effect was greater in the wet state. A comparison of the pull-off test results in cohesion and adhesion failure demonstrated that Wetfix was more effective in improving bitumen–aggregate adhesion, whereas nanohydrated lime was more effective in enhancing bitumen adhesion. The resilient modulus (Mr) ratio in wet-to-dry conditions indicated that nanohydrated lime had better effects on the overall performance of the aged asphalt mixture against moisture damage. To investigate the effect of additives on the performance of asphalt mixtures, a t-test was performed in all modes of control, short-term aging, and long-term aging. The findings showed the effect of Wetfix and nanohydrated lime on increasing the modulus of elasticity of the samples.

Stiffness of cold-recycled mixtures under variable deformation conditions in the IT-CY test

Stiffness modulus belongs to the most important properties describing the cold-recycled mixtures (CRM) in terms of their usability in road pavement structures. Previous research proved that this property is strongly dependent on the scheme and conditions of the test (temperature and time of loading) and the time that has passed since the compaction of the specimen or pavement layer. It is a result of the influence of two different types of bonds – hydraulic bonds from cement and bituminous bonds from bituminous emulsion or foamed bitumen. Research presented in this paper showed that the target horizontal deformation values selected during the stiffness modulus test have a strong impact on the obtained results as well. In this paper the popular Indirect Tensile Stiffness Modulus (ITSM) test on cylindrical specimen (IT-CY scheme) was used to show the dependence of the stiffness modulus values on the selected target horizontal deformation level. Research was conducted on four different CRM mixtures and three reference materials. The research proved that even for a narrow deformation range the CRMs do not present linear viscoelastic behavior and display very high effort of material even for typical test conditions. In consequence, they are very prone to failure. Research also proved that CRM mixtures present different rheological behavior than cement concrete or asphalt concrete, and more attention should be given to establishing proper test conditions. Based on the research, it was determined that the recommended target horizontal deformation in IT-CY test of CRM should be reduced to 3 µm.

Stiffness and Creep Properties of HRS-BC Powered by Palm Shell Gasification in Dryer Unit

Roads are infrastructure that is very important in supporting people’s daily lives. With the high growth rate of traffic, the traffic load will cause damage to the road pavement in the form of deformation (rutting) and fatigue. The performance of an HRS-BC asphalt mixture was investigated to determine the asphalt’s resistance to damage. HRS-BC asphalt mixture specimens were produced by a palm shell AMP and by a diesel AMP. The performance of the HRS-BC asphalt mixture was tested in the laboratory with indirect tensile stiffness modulus (ITSM) and dynamic creep test. The results showed that the HRS-BC asphalt mixture sample produced by the palm shell AMP had better stiffness than the HRS-BC asphalt mixture produced by the diesel AMP. Both the samples of the HRS-BC asphalt mixture produced by the palm shell AMP and by the diesel AMP were not deformed when given a standard load of 100 kPa and 3,600 load repetitions.

Performance of zeolite synthesized from sewage sludge ash as a warm mix asphalt additive

The disposal of sewage sludge ash (SSA) is a growing problem with both environmental and economic ramifications. This study aims to synthesize zeolite from SSA as a foaming-based warm mix asphalt (WMA) additive, and comprehensively characterize its performance. The SSA-derived zeolite was first characterized using X-ray Diffractometer (XRD), Scanning Electron Microscope (SEM), and Thermogravimetry-Differential Thermal Analyzer (TG-DTA) tests. Then, WMA mixtures with the SSA-derived zeolite and a commercial zeolite additive, and a conventional hot mix asphalt (HMA) mixture were produced in the laboratory for a wide range of engineering performance tests, including the indirect tensile stiffness modulus test, indirect tensile fatigue test, moisture susceptibility test, and Hamburg wheel-tracking test. The experimental results indicated that the SSA-derived zeolite was pure zeolite A which can release approximately 20% crystal water gradually from 70 oC to 200 oC. The overall performance of the WMA mixture with SSA-derived zeolite was better than that of the WMA mixture with commercial additive, and comparable to that of the HMA mixture except for rutting resistance, which is marginally lower but still satisfactory. Cost-benefit analysis was conducted in the end, which demonstrated that SSA-derived zeolite is eco-efficient. This study concluded that it is feasible to use the SSA-derived zeolite as an effective and sustainable WMA additive.

Effect of palm oil capsules on the self-healing properties of aged and unaged asphalt mixtures gained by resting period and microwave heating

Palm oil was used as a new rejuvenating agent for manufacturing calcium alginate capsules to study the self-healing properties of aged and unaged asphalt mixtures. To optimize the palm oil capsule for use in the asphalt mixture, nine types of calcium alginate capsules with various oil-to-water (O/W = 5, 10, and 15 %w) and calcium chloride-to-water percentages (CaCl2/W = 2, 4, and 6 %w) were prepared, and compressive strength, thermal sensitivity, size measurement, density measurement, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) tests were performed on them. Asphalt mixtures with various percentages of optimum capsules (0, 0.35, and 0.7% by total weight of the mixture) were prepared in unaged and long-term-aged conditions, and the effect of capsules on the stiffness modulus of aged and unaged asphalt mixtures was investigated by the indirect tensile stiffness modulus (ITSM) test. Via the semicircular bending (SCB) test, self-healing with a resting period and microwave healing were used to investigate the self-healing properties of aged and unaged asphalt mixtures with and without capsules. To reduce heating time and energy consumption, the effect of incorporating steel wool fibers (SWF) on the microwave heating of palm oil capsule-containing asphalt mixtures was investigated. The results showed that the use of palm oil capsules significantly increased the self-healing capability of the aged and unaged asphalt mixtures. The microwave healing method promoted the healing speed and healing level of the capsule-containing aged and unaged asphalt mixtures. Moreover, with the use of SWF in microwave healing, a healing level similar to that of SWF-less asphalt specimens was obtained in a shorter heating time.

The Influence of Mixing Conditions on the Macro-Scale Homogeneity of Asphalt Mixtures Blended with Reclaimed Asphalt Pavement (RAP).

The homogeneity of asphalt mixtures blended with reclaimed asphalt pavement (RAP) is affected by many factors. Due to the complicated compositions of recycled asphalt mixtures, the inhomogeneity issue might cause insufficient mechanical properties of asphalt mixtures, even though a design method was appropriately adopted. Therefore, it is of great significance to study the influence of mixing conditions on the homogeneity of asphalt mixtures blended with RAP materials. This study focused on the macro-scale homogeneity of produced asphalt mixtures. Specifically, asphalt mixtures incorporated with 40% RAP content were produced in a laboratory using different mixing times and mixing temperatures. A multi-direction indirect tensile stiffness modulus (ITSM) test was proposed to quantify the homogeneity of produced samples. In addition, the digital image processing (DIP) method was used to identify the distribution of aggregates and RAP binder. The results indicated that the influence of mixing time on the macro-homogeneity of asphalt mixtures indicated that a longer mixing time was favorable for the material dispersion. The influence of mixing temperature mainly rested on two perspectives. One was that the temperature variation induced the change of binder viscosity. The other was that the temperature influences the diffusion process between RAP binder and new bitumen, which further affected the mechanical performance of produced asphalt mixtures.

Evaluation of measured and predicted resilient modulus of rubberized Stone Mastic Asphalt (SMA) modified with truck tire rubber powder

Rubberized asphalt is known for its elastic deformation recovery and good resilience in response to loads owing to the elastic characteristics of tire rubber powder. There are several methods for the prediction of the stiffness modulus of asphalt mixtures. However, there are limited studies on predicting the stiffness modulus incorporating both wet and dry rubberization methods based on the available methods of Asphalt Institute (AI) and IDOT (Illinois department of transportation). In this research, Stone Mastic Asphalt (SMA) mixtures were modified with truck tire rubber powder (TRP) with two different processes: SMA-WP (SMA mixtures modified in the wet process) and SMA-DP (SMA mixtures modified in the dry process). In both methods, 3%, 6%, and 9% of TRP were used for modification, and the performance of the control and modified mixtures was evaluated under indirect tensile strength (ITS) and indirect tensile stiffness modulus (ITSM) tests. Finally, the results of ITSM were compared to predicted resilient modulus based on the Asphalt Institute (AI) and Illinois Department of Transportation (IDOT). The experiments revealed that SMA-DP mixes have higher ITS than SMA-WP. At the same time, both methods showed a decrease in ITS as TRP content increases. Furthermore, the SMA-WP samples showed a lower phase angle than SMA-DP samples, indicating higher elasticity for the mixtures. In addition, SMA-WP showed lower horizontal deformation than SMA-DP, which helps reduce rutting on the surface layer. Finally, the prediction results showed that the IDOT method could not predict the Stiffness Modulus, while the AI method was more accurate and can be used for prediction.

A Novel Emulsion-Based Mixture (EBM) Containing Ground Granulated Blast-Furnace Slag and Waste Alkaline Ca(OH)2 Solution

Emulsion-based mixtures (EBM) attract less interest to use as a structural layer due to the weak mechanical performance, although it has environmental, economic, energy-saving benefits. Ground granulated blast-furnace slag (GGBS) activated by waste alkaline Ca(OH)2 solution is used in the present investigation to replace the conventional limestone filler in a new Emulsion-based mixture (EBM). The mechanical properties by means of indirect tensile stiffness modulus test of the EBM with the activated GGBS are examined and compared with those of EBM contained traditional limestone filler. The results indicate that the activated GGBS by waste alkaline Ca(OH)2 solution can enhance the ITSM in both early and mature ages. The hydration products can improve the bond strength inside the new EBM.

Investigating the Effective Laboratory Parameters on the Stiffness Modulus and Fatigue Cracking of Warm Mix Asphalt

Lack of attention to the effect of laboratory conditions on the results of asphalt mixture tests, especially these of the warm mix asphalt (WMA), makes the analysis of results misleading. Thus herein, after examining the research on WMA and factors affecting test results in laboratory conditions, the effect of three parameters including short-term aging (asphalt binder storage in the oven), curing time (from construction to placement in the test chamber), and thermal equilibrium time (from placement in the test chamber to the test onset) were investigated on the characteristics of WMA at mid-temperature. To simultaneously examine these three factors, 36 modes were developed to evaluate their effect on the stiffness modulus and fatigue cracking, using the indirect tensile stiffness modulus test (ITSM) and indirect tensile fatigue test (ITFT), respectively. Results of the experiments showed that increasing the time of asphalt binder placement in the oven for 2–6 h significantly increased the stiffness modulus of the mixture, which reduced the fatigue life of the WMA. With increasing the curing time and improving the adhesion between asphalt binder and aggregates, the stiffness modulus and fatigue life of the specimens increased; however, by increasing the thermal equilibrium time, the stiffness modulus and fatigue life of the specimens decreased due to asphalt binder viscoelastic behavior and temperature sensitivity. Results of statistical analyses revealed that short-term aging, curing time, and thermal equilibrium time in laboratory conditions were effective on the stiffness modulus and fatigue life of WMA at a 95% confidence level.

Study of the Stiffness of the Bitumen Emulsion Based Cold Recycling Mixes for Road Base Courses.

The benefits of the use of cold recycling mixtures (CRMs) in pavement rehabilitation are associated with both the reduction of natural resource consumption by replacing them with recycled materials and the reduction of energy consumption during their production and paving. The evolution of the stiffness of CRMs in road construction and the fatigue life of pavements with CRM base layers are still being investigated. In this paper, CRMs with 1% cement content, called bitumen-stabilized materials with bitumen emulsion (BSM-Es), were examined. Mixtures that were differentiated in terms of Reclaimed Asphalt Pavement (RAP) content, as well as the amount and type of bitumen emulsions, were subjected to indirect tensile stiffness modulus (ITSM) tests at 5 °C, 13 °C, and 20 °C. The thermal sensitivities of the BSM-E mixtures were analyzed. BSM-E mixture stiffness modulus levels at various temperatures were determined using a statistical approach. On the basis of the results obtained, a discussion on the mechanistic-empirical design of flexible pavements with BSM-E base layers is presented. The potential benefits of using BSM-E materials in road construction in certain aspects of pavement life are indicated.

Effects of different fillers on pavement deformation of hot mix asphalt in hot climates

Permanent deformation in the form of rutting is one of the major distresses affecting flexible asphalt pavements. This is a serious issue in hot countries and is closely associated with the viscosity of the bitumen binders used. In hot countries, temperatures can exceed 45 °C. Even in the construction of primary roads, bitumen 60/70 (B60/70), which is a relatively low-grade and soft bitumen, continues to be used for Hot Mix Asphalt (HMA) construction. Libyan asphalt concrete pavement roads therefore develop extreme deformations in the form of rutting. This study tests the effects of filler materials on mechanical and volumetric HMA performance with recourse to cellulose fiber (CF) and Ordinary Portland Cement (OPC). CF and OPC were added to a B60/70 HMA mix according to Superpave design specifications. Three percentages of OPC (2%, 4%, and 6%) and three different percentages of CF (0.25%, 0.5%, and 0.75%) were used as filler; there was also a control mix with no filler (0%). Mix performance was assessed with the rutting analyzer and The Indirect Tensile Stiffness Modulus (ITSM). ITSM test were conducted at −5 °C, 10 °C, 25 °C and the rutting analyzer test was conducted at 60 °C to simulate temperatures in the region. The mixes using cellulose fiber performed better than those with OPC. The results suggest potential budgetary savings because roadworks projects can use inexpensive additives instead of more expensive bitumen binders.

Laboratory Evaluation on the Performance Degradation of Styrene-Butadiene-Styrene-Modified Asphalt Mixture Reinforced with Basalt Fiber under Freeze-Thaw Cycles.

This paper aims at the freeze–thaw (F-T) cycles resistance of styrene-butadiene-styrene (SBS) modified asphalt mixture reinforced with basalt fiber in order to explore the performance evaluation and prediction of asphalt mixtures at seasonal frozen regions. Asphalt was firstly modified by the common SBS and then SBS-modified stone mastic asphalt (SMA) specimens with basalt fiber were prepared by using Superpave gyratory compaction (SGC) method. Next, asphalt mixture specimens processed by 0–21 F-T cycles were adopted for the high-temperature compression test, low-temperature splitting test and indirect tensile stiffness modulus test. Meanwhile, a three-dimensional model of F-T damage evolution of the mixtures was also established based on the reliability and damage theory. The test results showed that the loss rates of mechanical strength increased rapidly, and then gradually flattened; however, these indications changed significantly after 15–18 F-T cycles. In addition, the exponential function could reflect the variation trend of the mechanical performances with F-T cycles to a certain degree. The damage evolution and prediction model based on the reliability and damage theory can be established to analyze the internal degradation law better.

A novel self-healing system: Towards a sustainable porous asphalt

Self-healing asphalt, aimed to produce a sustainable asphalt pavement using green technology, has been studied in the past two decades. Technologies including encapsulated rejuvenator and induction heating have been proposed, demonstrated in the laboratory, and gradually evaluated in field application. This paper looks into the synergy effect of the above two technologies, where induction heating serves as the asphalt damage repair mechanism, requiring just 2 min heating time and encapsulated rejuvenator will replenish (rejuvenate) aged asphalt binder and reinstate bitumen’s healing ability. Moreover, the increased temperature from induction heating could in turn accelerate the diffusion process of rejuvenator into aged bitumen. In this paper, the healing efficiency of the combined healing system was tested in comparison with autonomous asphalt healing system, induction healing system and capsule healing system. Porous asphalt concrete with various healing systems were prepared and a laboratory ageing procedure was followed to simulate the condition when healing was needed (after years of serving). X-ray computed tomography was employed to visualize the material composition and distribution inside of each healing systems. The properties of binder extracted from the porous asphalt samples were examined by dynamic shear rheometer. Indirect tensile strength and indirect tensile stiffness modulus tests were employed to characterize the mechanical properties of the porous asphalt samples with various healing systems. Finally, the cracking resistance of these healing systems was investigated by semi-circular bending test, and the healing efficiency was evaluated using a bending and healing programme. The results indicated that the combined healing system, with synergistic effects of aged binder rejuvenation and crack healing, shows a longer life extension prospect over the other healing systems.

The role of nanomaterials in reducing moisture damage of asphalt mixes

Interest of researchers in using nanomaterials in asphalt mixes is increasing rapidly. In this research, the effects of using various nanomaterials in asphalt mixes were investigated. In addition, the effects of two different types of fillers at their conventional size and their nano-size in asphalt mixes were tested. Four types of nanomaterials, namely nano-CaCO3, nano-hydrated lime, nano-bentonite and nano-silica, and two types of anti-stripping fillers, namely hydrated lime and CaCO3 were selected. Nano-hydrated lime was produced using a planetary ball mill apparatus. In producing nano-hydrated lime, optimum combinations of the main parameters that affect particle size reduction in milling process were determined applying trial and error procedure. Minimum particle size of the produced nano-hydrated lime was determined using Scanning Electron Microscope (SEM) and Dynamic Light Scattering (DLS) tests. From these tests, sizes of 125 and 208 nm were recorded, respectively.With applying Field-Emission Scanning Electron Microscopy (FE-SEM) technique, homogenous distribution of the additives in a 60–70 bitumen binder was verified. Asphalt concrete mixes were prepared using the above additives and a siliceous type aggregate. Moisture damage of different mixes was evaluated applying modified Lottman test at different Freeze-Thaw (F-T) cycles. F-T cycles results indicated that Indirect Tensile Strength (ITS) values were reduced appreciably at the first cycle. In fact, it was shown that 4% nano-hydrated lime exhibited the most resistance against different F-T cycles. In addition, Indirect Tensile Stiffness Modulus (ITSM) test was performed at 25 °C. From these tests, Tensile Strength Ratio (TSR) and Index of Retained Resilient Modulus (IRMr) parameters were determined. Testing results indicated that by adding 20% hydrated lime filler and 4% nano-hydrated lime to the binder, TSR values of mixes increased to some 60%. In the case of using CaCO3 filler and nano-CaCO3, 60% increase in TSR, was achieved when either 5% CaCO3 filler or 4% nano-CaCO3 were used. These results were validated performing resilient modulus test. IRMr of mixes containing 20% hydrated lime filler and 4% nano-hydrated lime increased to 56% and 60%, respectively. IRMr values of asphalt mixes increased to 48% and 54% where 5% CaCO3 filler and 4% nano-CaCO3 were added, respectively.