Investigating the effect of filler types on thermodynamic parameters and their relationship with moisture sensitivity of asphalt mixes

Filler plays a significant role in mastic cohesion and adhesion between aggregate–asphalt binder in asphalt mixes. In the majority of research on investigating moisture damage based on thermodynamic concepts, little attention has been given to the role of filler. In the present study, 20 different combinations of asphalt mixes made with 4 filler types (stone powder, hydrated lime, calcium carbonate and portland cement), with two types of asphalt binder (60–70 and 85–100), and two types of aggregate (limestone and granite) were used. Then thermodynamic parameters (with and without considering the effect of filler) were calculated and the relationship between these parameters and test results of moisture sensitivity of asphalt mixes was investigated using statistical analyses. Results obtained by thermodynamic parameters show that only stone powder filler caused an increase in free energy of adhesion between base asphalt binder and aggregates, and other fillers reduced free energy of adhesion. The maximum amount of debonding energy in samples made by asphalt binder 60–70, was related to mastics containing calcium carbonate and hydrated lime fillers, and in asphalt binder 85–100, mastics containing portland cement and calcium carbonate had the maximum amount of debonding energy. However, the minimum amount of debonding energy was related to the mastic containing stone powder. In addition, the results of moisture sensitivity mechanical tests show that samples containing calcium carbonate and hydrated lime fillers had the maximum amount of tensile strength ratio. Finally, the amount of adjusted coefficient of correlation between debonding energy and modified Lottman test results increased from 0.553 in 4 base compounds (without filler) to 0.701 in 16 compounds with filler. The difference in correlation coefficients show the necessity to use the effect of filler on calculating thermodynamic parameters in investigating moisture sensitivity of various asphalt mixes.     

Effects of long-term aging on moisture sensitivity of foamed WMA mixtures containing moist aggregates

Long-term aging of an asphalt mixture is complicated, but can be simulated in the laboratory. The objective of this study was to investigate the influence of long-term aging on moisture susceptibility of foamed warm mix asphalt (WMA) mixtures containing moist aggregate. Weight loss, indirect tensile strength (ITS) of dry and conditioned specimens, and deformation (flow) were measured for all mixtures. The experimental design included two aggregate moisture contents (0 and ~0.5% by weight of the dry mass of the aggregate); two lime contents (1 and 2% lime by weight of dry aggregate) and one liquid anti-stripping agent (ASA); one foaming WMA additive (Asphamin) and two foaming water contents (2 and 3%); and two aggregate sources. A common long-term aging procedure was used in this study. A total of 64 mixtures were evaluated and 256 specimens were made and tested in this study. The test results indicated that long-term aging improved the moisture resistance of WMA mixtures regardless of the ASA and moisture conditioning. In addition, aggregate source significantly affected the moisture resistance regardless of the foaming technology, ASA, and aggregate moisture content. The mixture with various hydrated lime contents exhibited similar moisture resistance under dry and wet conditions. The liquid ASA used in the WMA mixture showed a weaker resistance to the moisture damage in comparison with hydrated lime.     

Effect of warm mix additives on the interfacial bonding characteristics of asphalt binders

The quality of the interfacial bonding between asphalt binder and aggregates plays a significant role in determining the durability of asphalt mixtures. Warm mix asphalt (WMA) modifiers have been used extensively in the last decade primarily to reduce production and compaction temperatures as well as to improve workability of asphalt mixtures. This study aimed to provide better understanding of the effects of these WMA modifiers on the interfacial bonding between asphalt binders and aggregates. The evaluation focused on measuring surface energy of binders in unaged and aged states and aggregates and then calculating energy parameters that describe the potential of a given asphalt-aggregate combination to resist fatigue cracking and moisture damage. Results show that the combination of asphalt-WMA additive, as well as the content applied of WMA additive has a significant impact on the fatigue cracking and moisture damage resistance. The results suggest that it is poor practice to use a given type and percentage of WMA modifier without regard for binder type. Instead, test methods are recommended to evaluate the compatibility of asphalt binder, WMA additive type/content, and aggregates for improved performance at different conditions.     

Investigation into engineering properties and strength mechanism of grouted macadam composite materials

To further understand engineering properties of grouted macadam composite materials (GMCM) used as a surfacing layer in pavement, the mechanical properties and durability characteristics of GMCM were evaluated, and the relevant strength mechanisms were investigated at the micro level. Results indicate that GMCM has better high-temperature stability, fatigue performance and moisture stability than that of conventional asphalt mix, while it shows an acceptable decrease in low-temperature crack resistance due to the relative brittleness of hardened cement paste. The hardened cement paste also generates a spatial network crystalline lattice in asphalt mix skeleton to form a three-dimensional integral coagulation-crystalloid structure. This facilitates the asphalt mix skeleton and hardened cement paste to bear loads in unison and increase durability of the GMCM. Further, the fibre-like hydrated products of fresh cement slurry on the bitumen film surface increase the interfacial strength between bitumen and hardened cement paste due to toughening and bridging effects, which plays an important role to enhance mechanical properties and durability of GMCM. Finally, GMCM strength is from the internal friction of asphalt mix skeleton, the network structure of hardened cement paste and the adhesion between porous asphalt mix and hardened cement paste. It is concluded that GMCM can better meet the requirements of mechanical properties and durability characteristics than the conventional asphalt mix.     

Laboratory investigation of utilizing high percentage of RAP in rubberized asphalt mixture

The utilization of crumb rubber and reclaimed asphalt pavement (RAP) has proven to be economical, environmentally sound and effective in increasing the performance properties of the asphalt mixtures. The objective of this research was to investigate the laboratory engineering behavior characteristics of the rubberized asphalt binders and mixtures made with PG 64-22 and a softer binder (PG 52-28) containing a high percentage of RAP (30%). Some of the testing used for this research included viscosity, dynamic shear rheometer (DSR), bending beam rheometer (BBR), indirect tensile strength (ITS), resilient modulus, and fatigue life evaluations. The experimental design included the use of two aggregate and RAP sources, two virgin binder grades (PG 64-22 and PG 52-28), two types of crumb rubber (ambient and cryogenic), and four rubber contents (0%, 5%, 10%, and 15%). The results indicated that: (1) the crumb rubber improved the aging resistance of the aged binder and prolonged the fatigue life of the mixtures containing 0% RAP, in addition, results indicated a decrease of ITS and resilient modulus values was found as the rubber content increased, regardless of rubber type; (2) the utilization of softer binder decreased the influence of aged binder and decreased the resilient modulus values of the mixtures. In most cases, regardless of rubber types, the rubberized mixtures containing 30% RAP made with PG 52-28 binder did not show a significant increase in fatigue life with those made with PG 64-22 binder.     

Using the surface free energy method to evaluate the effects of liquid antistrip additives on moisture sensitivity in hot mix asphalt

The objectives of this research are to evaluate the susceptibility of aggregates and asphalt binder with and without liquid antistrip (LAA) additives to moisture damage based on the properties that affect the adhesion bond between the aggregate and asphalt binder and the cohesion strength of the asphalt binder using the surface free energy (SFE) concept and laboratory testing. The percentage of the aggregate surface area that was exposed to water (P) due to each cycle was used as a screening parameter for evaluating the compatibility of the asphalt binder and aggregates in terms of the resistance to moisture damage. The results show that adding LAA causes the total SFE of the asphalt binder to increase, which results in a decrease in stripping between the aggregate and asphalt binder in the presence of water. Similar results were obtained from a dynamic modulus test. From the data obtained, we conclude that LAA caused a reduction of the magnitude of P that improves its resistance to moisture damage.     

Light-coloured grey asphalt pavements: from theory to practice

This paper presents the technological development and application of hydrated lime in treating the surface of asphalt concrete to develop light-coloured, grey asphalt pavements. When appropriately applied on the surface of fresh asphalt concrete, hydrated lime makes the surface grey, significantly increases its albedo and effectively reduces the pavement's temperature caused by hot weather. Two application case studies are presented, focusing on how to ensure hydrated lime's long-term effectiveness on the surface of asphalt pavements and take into account the effect of the subsequent reduced temperature on the resilient modulus of asphalt concrete in the design of long-life flexible pavements. The increased asphalt concrete modulus, owing to lowered temperature, can reduce the design thickness of the asphalt concrete without sacrificing pavement performance. This also has a positive influence on reduced pavement heat island effects. It is concluded that the appropriate use of hydrated lime on asphalt pavement surfaces is an effective and economical method to produce light-coloured, grey asphalt pavements.     

Carbonate binders: Reaction kinetics,strength and microstructure

This study focussed on the synthesis of calcium carbonate binders, in situ, from the reaction between hydrated lime and carbon dioxide (CO₂). The aim was to establish the characteristics of the calcium carbonate binders that are associated with its strength, which was considered as an indicator of binder performance. The role of the parameters that are known to play an important part in the kinetics of hydrated lime carbonation processes, in changing the strength of a binder was examined in detail.The parameters identified were CO₂ gas pressure, exposure time and the initial degree of compaction of raw material. All hydrated lime mixtures were prepared at a constant water/solid ratio of 0.25. The hydrated lime compacts made at a range of compaction water/solid ratio (W/S) of 0.25. The hydrated lime compacts made at a range of compaction pressures (0.65–6.0 MPa) were exposed to different CO₂ gas pressures (ambient to 2 MPa) for different periods of time. The resulting products were tested for the amount of Ca(OH)₂ that had converted to carbonate, and for compressive strength. A microstructural analysis of the products was carried out using scanning electron microscopy.The rate of Ca(OH)₂ conversion to carbonate seemed to be enhanced with increasing gas pressure, but it decreased with increasing compaction of the initial mixture. It was revealed that the crystalline state and the morphology of the carbonate formed, rather than the degree of conversion of calcium hydroxide into carbonate, is highly critical to the strength of the binder. The study concluded that in the development of calcium carbonate binder, it is important to meet the experimental conditions that favour the crystallisation of calcium carbonate.     

苯乙烯-丁二烯嵌段共聚物与废橡胶粉复合改性高黏沥青及混合料性能研究

为了评价高黏改性剂对沥青性能的影响,采用高速剪切法制备了苯乙烯-丁二烯嵌段共聚物(SBS)改性沥青、废橡胶粉改性沥青和两种SBS/橡胶粉复合改性高黏沥青。通过三大指标试验、黏度试验、高温车辙试验和低温小梁弯曲试验,研究了高黏沥青的高低温性能、感温性能及沥青混合料路用性能。结果表明:4种改性沥青的高低温性能随各自改性剂掺量的增加逐渐提高,掺加10%北美岩沥青或2.5%多聚磷酸(PPA)的高黏沥青感温性能更稳定,较大幅度提升了黏度值,高温性能改善明显;掺加2.5%PPA的高黏沥青及其混合料能够更好地抵抗高温条件下的性能衰减,保证了使用效果,更适用于温度较高地区;掺加10%北美岩沥青的高黏沥青及其混合料在低温条件下性能良好,推荐在低温地区使用。     

A preliminary investigation of strength development in Jamaican red mud composites

The 28-day strength of 50 mm cubes of composites formed by the addition of various amounts of hydrated lime, condensed silica fume and limestone to Jamaican red mud is investigated. The aim is to produce a red mud composite suitable for use as a construction material, without employing Portland cement as binder. The identities of compounds formed in the composites are deduced from XRD scans, in combination with DTG and electron micrography where appropriate. The strongest composite found in this preliminary study has compressive strength in the range 15–18 MPa at 28 days, with the strength increasing slowly with age to a maximum so far, in the range 18–22 MPa at 122 days. The strength development is observed to be associated with the formation of stratlingite, and possibly also with the formation of complex carbonates such as hydrogrossular. This composite compares favorably, in terms of compressive strength and durability, with the one other composite reported in the literature, which is formed similarly from red mud with additives, not including Portland cement.     

Characterization of the material from the induction healing porous asphalt concrete trial section

An induction healing approach was developed to increase the service life of porous asphalt wearing course. Steel wool fibers were mixed in the asphalt mixtures, and then induction heating was applied to heat up the localized steel wool fibers in asphalt mixtures when damage is expected. As a result of induction heating, possible cracks and damages inside porous asphalt can be healed. The objective of this paper is to characterize the field obtained material from an induction healing porous asphalt trial section with laboratory experiments. Heating speed of the field cores was first measured with an infrared camera. It was found that these cores with steel wool can be heated with induction energy. Then, the particle loss value, indirect tensile strength, water sensitivity and nano indentation modulus of the field cores were studied. The results indicate that the addition of steel wool improves the particle loss resistance and ductility of the porous asphalt concrete cores. The mortar phase in porous asphalt core with steel wool shows higher indentation modulus than that in the plain core. These findings imply that steel wool can increase the ravelling resistance of porous asphalt concrete. Finally, the fatigue life extension parameter in four point bending test was applied to investigate the healing potential of this porous asphalt mixture with and without induction heating. The fatigue life of the beams can be greatly extended with induction heating. It was also found that the aged beams can heal much more and faster with induction heating than that with natural healing. Based on these findings, it is expected that the durability of porous asphalt pavement will be improved by the reinforcement of steel wool and induction healing.     

A review on the degradability of polymeric composites based on natural fibres

The applications of natural fibre/polymer composites in civil engineering are mostly concentrated on non-load bearing indoor components due to its vulnerability to environmental attack. This paper evaluates the characteristics of several natural fibre composites exposed to moisture, thermal, fire, and ultraviolet degradation through an extensive literature review. The effects of chemical additives such as fibre treatments, fire retardants and Ultraviolet (UV) stabilizers are also addressed. Based on the evaluation conducted, optimum fibre content provides strength in a polymer composite but it also becomes an entry point for moisture attack. Several fibre treatments are also being used to improve fibre/matrix interface, thereby increasing moisture durability. However, the treated fibres were found to behave poorly when exposed to weather. The addition of UV stabilizers and fire retardants are suggested to enhance outdoor and fire performance of natural fibre/polymer composite but compromises its strength. Therefore, from the collected data and various experimental results, it was concluded that an optimum blend ratio of chemical additives must be employed to achieve a balance between strength and durability requirements for natural fibre composites.     

Ground iron blast furnace slag as a matrix for cellulose-cement materials

The use of ground iron blast furnace slag (BFS) as a low-cost alternative to ordinary Portland cement (OPC) binders in fibre-cement products was examined. Both high quality softwood fibres and residual sisal from agricultural waste were chemically pulped and used as reinforcement. Composites based on several different binder formulations consisting of slag chemically activated by mixtures of gypsum and hydrated lime displayed their optimum strength and fracture toughness properties at fibre contents between 8% and 12%, with values in the ranges of 14.7–24.5 MPa and 1.13–2.36 kJ/m², respectively. Corresponding flexural moduli lay in the range 4.3–7.8 GPa and, at 12% fibre content, the composites possessed water absorption values up to 34% by mass and densities in the region of 1.3 g/cm³. A formulation of BFS activated by 10% gypsum and 2% lime presented a good compromise between strength and energy absorption combined with a reasonable price.     

The effects of chemical composition on asphalt microstructure and their association to pavement performance

The primary objective of this paper was to investigate the impact of asphalt chemical composition on the microstructure and performance characteristics of asphalt binder. The methods implemented in this study include adsorption–desorption chromatography analysis and a range of atomic force microscopy (AFM) and chemical force microscopy techniques. It was revealed through the study that certain asphalt chemical parameters have a consistent and measureable effect on the asphalt microstructure that is observed with AFM. Particular microstructures that emerged via chemical doping were then discovered to have unique chemical polarity, which explicitly impact durability and performance of asphalt. In fact, a surprising correlation was found between the saturates chemical parameter and the effects of oxidative aging on asphalt behaviour. The findings from this research directly contribute to the improvement of modelling capability while also creating new prospects for enhancing the performance characteristics and durability of asphalt binder.     

A new look at rubber-modified asphalt binders

The high-temperature rheological characteristics and the low-temperature fracture properties of asphalt binders containing crumb and devulcanized rubber waste have been investigated. Asphalt binders containing crumb rubber of different mesh sizes, with and without surface modification, and a commercially available binder containing devulcanized rubber, were tested and compared with an unmodified asphalt and three commercially available polymer-modified binders. Interfacial modification of asphalt systems containing crumb rubber was found to give binders that were far superior in their low-temperature performance to commercially available products. The data suggest that a crack-pinning or crack-blunting mechanism is responsible for the increase in toughness found in these systems. A commercially available binder containing devulcanized rubber showed reasonably good high-temperature properties; however, its low-temperature fracture performance was disappointing in that it was not significantly better than that of unmodified asphalt binders.     

Investigation into three-layered HMA mixtures

Hot-mix asphalt (HMA) mixtures consist of three phases: aggregate, asphalt binder (mastic) and air voids, of which the first two (aggregate and asphalt binder) provide the structure that withstands various kinds of loading.

Due to the nature of high inhomogeneity between aggregate and asphalt binder, significant stress and strain concentration occurs at the interface between the two phases, which causes adverse effect to HMA mixtures and potentially contributes to pavement distresses/failure.

This paper presents a novel idea to mitigate the stress and strain concentration by introducing an intermediate layer between aggregate and asphalt binder in HMA mixture. Microstructural analyses of layered system indicated that the three-layered composite HMA mixture would greatly improve the performance of asphalt mixture. The composite mixture showed more than 10% reduction in internal stress and strain and consequently its performance could be potentially improved. To validate the theoretical analyses, a laboratory experiment was conducted to compare the performance of a conventional mixture to that of a conceptual three-layered composite HMA mixture, which was formed by incorporating a stiff natural asphalt (gilsonite) as the intermediate layer. The results of the limited laboratory experiment confirmed the findings from the theoretical analyses.     

Durability of cementitious binder derived from industrial wastes

The durability of cementitious binder hydrated at 27°C and 50°C under high humidity was examined by alternate wetting and drying, as well as heating and cooling, cycles at temperatures ranging from 27°C to 60°C and by performance in water. The results show that cementitious binder hardened at 50°C possesses higher water resistance and lower porosity than the binder hardened at 27°C. A decrease in the strength of the cementitious binder was observed with an increase in temperature and in the wetting and drying and heating and cooling cycles. The maximum decrease in strength occurred at 60°C. The cementitious binder cured at 27°C showed a much smaller decrease in strength with a rise in temperature and in weathering cycles. The changes in strength of the cementitious binder were monitored by differential thermal analysis and microscopy.     

Estimating the moisture damage of asphalt mixture modified with nano zinc oxide

One of the main distresses of hot mix asphalt (HMA) is moisture damage. The most common method for decreasing this type of distress is using antistrip additives. In this study, the effect of nanoparticles was evaluated as an antistrip agent on the moisture damage of HMA. Two types of aggregates were evaluated in this study with different sensitivities against moisture damage (limestone and granite aggregate) and the asphalt binder with 60/70 penetration grade and nano zinc oxide (ZnO) in two different percentages by weight of the asphalt binder. The tests employed to evaluate the effects of modifying asphalt binder by nanomaterials on the moisture damage of asphalt mixture were surface free energy (SFE) and AASHTO T283. The results showed that the ratio of wet/dry values of indirect tensile strength for the mixtures containing nano ZnO for two types of aggregate were higher than the control mixtures. In addition, the results of the SFE method showed that adding nano ZnO increased the total SFE of the asphalt binder, which led to better coating of the aggregate with asphalt binder. Nano ZnO decreased the acid to base ratio of SFE of asphalt binder, while it led to improving adhesion between the asphalt binder and acidic aggregate that are prone to moisture damage.     

Study on durability of high-modulus asphalt mixture based on TLA and fibre composite modification technology

In order to improve the low-temperature cracking resistance and durability of high-modulus asphalt mixture, this article proposes the use of Trinidad Lake Asphalt (TLA) and polyester fibre complex methods to obtain high-modulus asphalt mixture, based on indoor accelerated load, low bending temperature, freeze-thaw splitting and APA fatigue test to study the influence of TLA content on permanent deformation resistance performance, water stability, low-temperature crack resistance and fatigue resistance of high-modulus asphalt mixtures. Meanwhile, it reveals the mechanism of the TLA and polyester fibre composite modified on high-modulus asphalt mixture and recommends the best solution of high-modulus asphalt complex is 30% TLA + 3‰ polyester fibre.     

Fatigue resistance potential for hot mix asphalt using viscoelastic continuum damage analysis

This paper describes testing and evaluation of the fatigue resistance potential of hot‐mix asphalt mixtures using viscoelastic continuum damage analysis, which is based on dynamic modulus determination, a state‐variable approach and damage calculation. The dynamic modulus test for stiffness characterization and the direct tension test for fatigue resistance characterization were used in the testing procedure. The state‐variable approach can be used for numerical computation of a viscoelastic convolution integral. A Nelder–Mead simplex search was used in this study to determine the damage parameter of a stiffness reduction function. The fatigue resistance was evaluated as a function of loading rate, asphalt binder content, modifier (e.g. usage of hydrated lime), and temperature, and was found experimentally to have a strong dependence on these factors.