Asphalt-aggregate Bond Research Articles

Nano-scale analysis of moisture diffusion in asphalt-aggregate interface using molecular simulations

Presence of moisture can weaken the asphalt-aggregate bond and result in aggregate stripping and moisture damage in asphalt mixture. This study investigates how the moisture affects the asphalt-aggregate bond and simulates moisture distribution of nano-scale in asphalt-aggregate interface. Effects of aggregate type (basalt, dolomite and limestone minerals), humidity and hydraulic pressure on moisture diffusion in asphalt-aggregate interface are studied. Diffusion coefficient (D), radial distribution function (RDF), contact angle (CA), free volume (FV) are calculated through molecular dynamic simulations. Polarizability of moisture in the asphalt-aggregate interface was measured using density function theory (DFT). Nano-scale moisture migration model in the asphalt-aggregate interface is built for the first time. The results show that D depends more on the hydraulic pressure than humidity and aggregate type which represents the significance of hydraulic pressure on the moisture diffusion. In addition, the aggregate type has significant effects on RDF, CA and FV. DFT results indicate that polarizability of moisture changes for different types of aggregate and hydraulic pressure values. In the asphalt-water-aggregate interface, the asphalt competitively interacts with moisture and ions from minerals through intermolecular forces.

Assessment of the density and moisture content of asphalt mixtures of road pavements

Distresses on asphalt pavements are associated to the traffic and moisture both in asphalt and granular layers. The traffic on road pavements is responsible by the occurrence of cracks that promote the pavement failure. The quality of the asphalt mixes, measured by its density, is an important factor to ensure the integrity of the pavements. The water in pavement surface decreases the driving comfort and reduces the asphalt-aggregate bond leading to the degradation of the asphalt materials. Thus, this paper uses Ground Penetrating Radar (GPR) tests to assess density and moisture content on asphalt mix slabs. Six asphalt mixes were produced in laboratory with the same aggregate gradation and asphalt type, varying the binder content (4.0, 5.0 and 6.0%) and the air-void content (from 3.7% up to 16.9%). For the assessment of the moisture content, each mix was tested with 5, 10, 20 and 40% of the air-void volume filled with water. The effect of the water on GPR results was performed after the sprinkling of the water and 24h after the water application. Results show that the density of the asphalt mixes can be well predicted by the Complex Refractive Index Model while the presence of water is not easy to identify due to the connectivity of the air-voids inside the asphalt mixes.

Atomistic modelling of moisture sensitivity: a damage mechanisms study of asphalt concrete interfaces

Moisture-induced damage mechanisms are characterised by adhesive bond strength reduction at the aggregate–asphalt interfaces. This research examined the physicochemical phenomena that occur at the asphalt–aggregate interfaces, as well as the nanoscale effect of water molecules on the asphalt–aggregate bond using atomistic simulations. The moisture sensitivity behaviour of model asphalt, water molecules, and mineral aggregates of various components was evaluated. Steered molecular dynamics was used to study the interfacial atomic separation under dry and wet conditions. The effect of water on the bond strength between asphalt and aggregate was described through surface free energy studies. It was found that the adhesion and stripping behaviours between asphalt and aggregate were more strongly influenced by the aggregate chemistry and properties than those of the asphalt. The adhesion of different asphalt–aggregate pairs and their susceptibility to water were also validated by available experimental results and pavement engineering observations. This work provides an insight into the orientation and interaction of asphalt molecules in the wet interfaces.

Moisture damage resistance of hot-mix asphalt made with paper industry wastes as filler

Certain paper industry wastes display high recycling potential. In this investigation, the feasibility of using green liquor dregs and biomass fly ash from the paper industry as filler in hot-mix asphalt (HMA) for road pavement construction is analysed. Particularly, the moisture damage resistance (i.e., water sensitivity) of an AC 22 base B50/70 G has been studied using the Indirect Tensile Strength Test at the Marshall mix design optimum asphalt content. The most important filler properties have been determined to study water resistance: filler water content, grain size distribution using light scattering analysis techniques, morphology using a scanning electron microscope (SEM), chemical and mineralogical composition using X-ray fluorescence (XRF) and X-ray diffraction (XRD) techniques, detrimental fines content using the methylene blue test and the stiffening effect of the filler in the mastic by determining the ring and ball (R&B) softening temperature and the bitumen penetration grade. Additionally, the Rolling Bottle method and Boiling Water tests have been conducted to analyse the asphalt-aggregate bond. A control filler (i.e., commercial limestone filler) was used to compare the results. Also the mechanical properties (stiffness and resistance to the permanent deformation) of the mixtures were studied. As a result, it can be concluded that dregs have poor water resistance. Additionally, fly ash displayed inadequate water resistance for HMA.

Effects of the Asphalt Penetration Grade and the Mineralogical Composition on the Asphalt-aggregate Bond

This investigation analyzes the loss of bonding between the asphalt binder and the aggregate particles produced by water in hot-mix asphalt pavements. Three asphalt penetration grades were used: B35/50, B50/70, and B160/220. Four different types of aggregates were chosen due to their different expected stripping performances: hornfels, feldspathic schist, gabbro, and dolomitic calcite. To research the loss of adhesion, two laboratory test methods were compared: the rolling bottle method and the boiling water test. The results indicate that a higher asphalt-aggregate bond correlates to a lower asphalt penetration grade. To achieve significant asphalt-aggregate bond improvement, the difference between asphalt penetration grades must be noticeable.

Adhesion of Recycled Concrete Aggregates, Demolition Debris, and Asphalt

In this investigation, rolling bottle tests and boiling water tests were conducted to evaluate the effect of different fillers and treatments on the adhesion between recycled concrete aggregates (RCA) and asphalt. The test results when 100% RCA loose mixtures were evaluated indicated that the filler that achieves the best asphalt aggregate bond was grey Portland cement. Curing the mixture in an oven for 4 h at mix temperature before compacting and coating RCA with bitumen emulsion are treatments that achieved satisfactory adhesion results as well.

Measuring the Effect of Moisture on Asphalt–Aggregate Bond with the Bitumen Bond Strength Test

Understanding moisture damage mechanisms in asphalt pavements and evaluating the right combination of materials that are resistant to moisture damage are important. Moisture damage is the loss of strength or stiffness in asphalt mixtures caused by a combination of mechanical loading and moisture. Many test methods have been developed to evaluate loss of adhesion and cohesion in binders. However, a simple procedure to address moisture damage in the asphalt–aggregate interface is not available. The feasibility of the newly developed bitumen bond strength (BBS) test for moisture damage characterization was investigated. An experimental matrix that included various binders, modifications, and aggregates to account for the chemical and physical conditions in the aggregate–asphalt interface was completed. A statistical analysis was performed to verify reproducibility of the BBS test. The results indicated that the bond strength of asphalt–aggregate systems was highly dependent on modification and moisture exposure time. Polymers were found to improve the adhesion between asphalt and aggregate as well as the cohesion within the binder. Results from this study indicated that the BBS test was repeatable and reproducible. To further validate the effectiveness of the BBS test, a comparison of the BBS test results and the modified dynamic shear rheometer strain sweep test was conducted. The comparison showed that the BBS test could rank materials similarly to a more sophisticated and time-consuming test.

The mechanisms of moisture damage in asphalt pavement by applying chemistry aspects

Moisture damage occurring within asphalt pavement causes the pavement to undergo several types of distress, such as stripping, potholes, and others. The durability or integrity related to moisture damage plays an important role in other types of damage or distress, such as rutting and fatigue. The development of a Dynamic Shear Rheometer (DSR) moisture damage test is the result of an effort to estimate the moisture damage in a simple, practical testing setup. As a conceptual supporting step, in turn, this paper provides fundamental, general mechanisms to explain the asphalt-aggregate bond behaviors during wet conditions in a DSR moisture damage test. Shear-thickening and thixotropy are introduced to explain the asphalt-aggregate interface behaviors under wet conditions, in view of a colloidal system. Moreover, the self-assembly concept is introduced with regard to a supramolecular system. Both systems can be associatively applicable because of their conceptual similarities. The analysis of data recorded during wet conditions supports and explains qualitatively the reversible structure of the asphalt-aggregate interface.

New Parameter to Evaluate Moisture Damage of Asphalt-Aggregate Bond in Using Dynamic Shear Rheometer

Most of the techniques used today to evaluate practically moisture damage in asphalt pavements are involved in compacted asphalt mixtures. These tests generally simulate field conditions, and provide a performance-related parameter of moisture effects by applying mechanical techniques. No test of the compacted mixtures, however, can isolate the fundamental and rheological properties of the asphalt-aggregate bond, which hinder proper understanding and quantification of the moisture damage phenomenon. To avoid these complications and improve the evaluation of asphalt-aggregate interfacial properties in moist situations, this study proposes a new experimental method. In this method, dynamic shear rheometer was used to measure asphalt-aggregate interfacial properties. A degree of moisture damage relating to the interfacial properties was then quantified using linear viscoelastic concepts to propose a meaningful parameter, called wet to dry yield shear stress ratio. Moreover, possible factors such as film thicknesses, conditioning times, and chemical effects were studied in terms of the W/D YSS ratio.

A Study on the Increase in the Durability of Asphalt Paving Mixtures

A novel approach of increasing the durability of the asphalt-paving mixtures was attempted in this study by pretreatment of the aggregate surface with styrene butadiene rubber (SBR) latex as an antistripping additive (ASA). The boiling water test showed that the pretreatment method could increase the asphalt–aggregate bond strength effectively. This result was confirmed by the indirect tensile test and the stiffness index measurement of the asphalt-paving mixtures. Even though the conventional method of direct addition of ASA to the asphalt could also improve the asphalt–aggregate bond strength compared to the asphalt paving mixtures without ASA, the performance was poorer than the pretreatment method because of its inherent disadvantages of losing the effectiveness of ASA in hot asphalt. Increase of pretreatment drying time, drying temperature, and ASA concentrations could improve the asphalt–aggregate bond strength confirmed by the boiling water test. Increase in pH of the contacting water showed a detrimental effect on the asphalt paving mixtures by dissociation of the acidic functionalities of the asphalt to disrupt the asphalt–aggregate bond.

Chemical model to explain asphalt binder and asphalt–aggregate interface behaviors

The behavior of asphalt mixtures is very complicated due to structural configuration and interfacial friction of aggregates as well as chemical and rheological reactions of the asphalt binder itself or with the aggregates. Furthermore, this complex response is more complicated under various loads, temperatures, and other environmental factors. To control the complex responses and reduce the complex factors, a DSR moisture damage test using small rock disks was developed. This paper focuses on the more fundamental concepts to explain asphalt and asphalt–aggregate bond behavior exhibited under the newly-developed DSR moisture damage test. The traditional model of asphalt structure is based on the theory of colloid and surface chemistry. Although this traditional model can explain many physical phenomena of asphalt structure, it cannot explain all the asphalt behaviors, such as steric hardening. Therefore, more general, but fundamental concepts may be required to attain insight of the material. As one of the possible concepts, a self-assembly concept in supramolecular chemistry is proposed and phenomena and results of the DSR moisture damage test are explained by the concept.

Effect of Chemical Additives on the Binding Strength of Arabian Asphalts

Premature deterioration of asphalt highway pavements in Saudi Arabia have considerably reduced their service lives, sacrificed rider comfort, and increased maintenance costs. The physicochemical phenomena as well as the long-range effect of the interstitial asphalt on the asphalt-aggregate bond plays a vital role in determining the stripping properties of aggregates. Chemical additives, known as antistripping agents, were mixed with asphalts to study their enhanced bonding capabilities with aggregates. Three antistripping agents that are locally available were used in this study. The results indicated that the adsorption of Riyadh asphalt on Riyadh aggregates is greatly increased with all three antistripping agents. Taif aggregates have also shown a substantial increase in their adsorption behavior due to the presence of antistripping agents. Similarly, the amounts of Restaurant asphalt remaining adsorbed after aggregates were coated with antistripping agents were found to be significantly higher than uncoated aggregate samples. The antistripping agents were found to promote stronger bonding, resulting in less asphalt desorption by water. This study provided important information regarding the effect of antistripping agents on the adsorption and desorption behavior of Arabian asphalts and asphalt-aggregate systems. The overall results were interpreted with regard to their usefulness in finding solutions to pavement damage problems in Saudi Arabia.

Effects of Aggregate Surface and Water on Rheology of Asphalt Films

Most tests used to evaluate moisture damage require compacted asphalt mixtures. The tests generally simulate field material and conditions and provide a performance-related parameter of moisture effects. In mixtures, however, variable asphalt-aggregate-air void structure contributes to the difficulty of isolating the fundamental rheological properties of an asphalt-aggregate bond. To avoid the complications and obtain the properties of the asphalt-aggregate interface, a new experimental design was developed in this study. This test features a dynamic shear rheometer (DSR) as an improved tool for evaluating interface properties. One key feature of the experimental design is the use of rock disks to simulate an asphalt-aggregate interface. The simulated interface is easily wet-conditioned in a water cup installed on the DSR. From various testing protocols, a stress sweep test that defines a linear viscoelastic (LVE) region is adopted to evaluate the interaction and moisture effects of selected specimens. A viscoelastic characteristic produced from stress sweep tests is recommended as the fundamental property of the interaction and can be used to evaluate moisture effects onto the rheological behavior. One of the critical findings is that the LVE complex modulus, G*, measured at relatively small strains or stresses cannot evaluate the moisture effects on the bond of the asphalt-aggregate interface. The LVE G* measured at high shear stresses are instead much more effective at evaluating such moisture effects. Therefore, the results indicate that the role of moisture damage in pavement problems such as rutting or fatigue needs to be evaluated at design stresses covering a nonlinear viscoelastic range. This study focuses on understanding more the basic characteristics of asphalt-aggregate interface than the bulk properties of mixtures.

MOISTURE SUSCEPTIBILITY OF ASPHALT MIXTURE AND EFFECTIVENESS OF ANTISTRIPPING ADDITIVE

A series of laboratory tests was conducted to evaluate the moisture susceptibility of asphalt mixtures, including moisture damage of asphalt-aggregate bond, and the influence of water immersion on the properties of asphalt mixtures. Furthermore, the effectiveness of various anti-stripping additives was investigated through a variety of tests. It was found that both the asphalt and aggregate types have dominating influences on the moisture susceptibility of asphalt mixtures; hydrated lime slurry is an effective anti-stripping additive for improving the moisture susceptibility; and the net adsorption test, Lottman test and immersed wheel tracking test are effective tools to evaluate the moisture susceptibility.

INVESTIGATION OF THE EFFECT OF AGGREGATE PRETREATMENT WITH ANTISTRIPPING AGENTS ON THE ASPHALT-AGGREGATE BOND

ABSTRACT Addition of Chemical antistripping agents (ASA)to asphalt has inherent disadvantages such as reduction of the effectiveness of ASA in hot asphalt and formation of relatively weak bond with the aggregate surface. To circumvent such problems, a novel approach of aggregate pretreatment with ASA was investigated in this study. The aggregate was pretreated with aqueous emulsions/solutions of different organic surface modifiers. The effectiveness of this aggregate pretreatment procedure was evaluated to ascertain the asphalt-aggregate bond strength using the boiling water test. Boiling water test was selected for its rapidity and simplicity. The

PARAFFIN-WAX WATER-HARVESTING SOIL TREATMENT IMPROVED WITH ANTISTRIPPING AGENTS

ABSTRACT The paraffin-wax water-harvesting soil-treatment is being used in arid areas to supply precipitation-runoff water for a variety of agricultural uses. However, because paraffin has only weak van der Waals-type binding forces, it may, under adverse weathering conditions, be easily stripped off the soil by the wedging action of water acting at the wax-soil interface. Addition of 2 to 4% antistripping agent (compounds added to asphalt during highway construction to strengthen the asphalt-aggregate interfacial bond) to the paraffin-wax water-harvesting soil treatment markedly improved the treated soil's resistance to the weathering effects of freeze-thaw cycling and water erosion. Addition of the better of the nine antistrip compounds tested permitted a reduction of the wax application rate to 0.5 kg/m2. Prior stabilization of the soil with cellulose xanthate reduced the required wax/antistrip rate to only 0.25 kg/m2. This is 1/8 the currently recommended application rate of wax for soils exposed to freeze-thaw weathering.