Moisture Damage In Asphalt Mixtures Research Articles

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.

Evaluation of Moisture Sorption and Diffusion Characteristics of Asphalt Mastics Using Manual and Automated Gravimetric Sorption Techniques

One of the most important factors influencing the durability of asphalt mixtures is moisture-induced damage resulting from the presence and the transport of moisture in pavements. Moisture-induced damage is an extremely complicated phenomenon that is not completely understood but believed to be governed by the interaction of moisture with asphalt mix components (mastic and aggregates). The objective of this study was, therefore, to characterize the sorption and diffusion characteristics of asphalt mastic using gravimetric vapor sorption techniques. Moisture transport, in the hygroscopic region, in asphalt mastics was studied using both static and dynamic gravimetric vapor sorption techniques to determine equilibrium moisture uptake and diffusion coefficients as a function of aggregate and filler types. For the 25-mm diameter thin asphalt mastic films and the testing conditions (23°C and 85% relative humidity) considered, the kinetics of moisture uptake obtained were characteristic of Fickian diffusion with a concentration-dependent diffusion coefficient. Equilibrium moisture uptake and diffusion coefficient estimated from the static measurements were comparable and of the same order of magnitude as those from dynamic sorption techniques. Both measurement techniques ranked the mixes similarly, which suggest either method could be used to characterize moisture transport in asphalt mastics. Equilibrium moisture uptake was relatively higher in mixtures containing granite aggregates compared with limestone aggregate. In contrast, the diffusion coefficient of limestone aggregate mastics was higher than granite. Thus, an inversely proportional relationship exists between moisture uptake and diffusivity of the asphalt mastics studied. The results suggest moisture transport is a function of aggregate type and that both equilibrium moisture uptake and diffusion coefficient are useful in studying moisture susceptibility in asphalt mixtures. The effect of mineral filler type on diffusion coefficient was minimal in the mastics containing granite aggregate but relatively high in mastic samples containing limestone aggregates. Diffusion coefficient was found to increase with sample thickness, which was unexpected because diffusion coefficient (in an isotropic material) is considered an intrinsic property that is independent of sample size. The results suggested anisotropic diffusivity can occur in asphalt mastics and could be attributed to factors, including mineralogy, microstructure, air voids, and the tendency of the aggregates to settle at the bottom of asphalt mastic with time. In addition to characterizing moisture transport in asphalt mastics, the results presented in this paper will be useful as inputs for numerical simulation of moisture damage in asphalt mixtures.

Influence of using polymeric aggregate treatment on moisture damage in hot mix asphalt

Moisture damage in hot mix asphalt (HMA) occurs due to a loss of adhesion and or cohesion, resulting in the reduced strength or stiffness of the HMA and the development of various forms of pavement distress. One of the convenient approaches to decreasing moisture sensitivity in HMA is coating the aggregate surface with a suitable agent. In this research, the effects of two types of polyethylene (PE), namely high density polyethylene (HDPE) and low density polyethylene (LDPE), on moisture damage of asphalt mixtures were evaluated. Two types of aggregates representing a considerable range in mineralogy (granite and limestone) were evaluated during the course of this study. To assess the impact of PE on moisture damage of HMA, control mixtures (without PE) and mixtures containing PE in dry and wet conditions were tested using indirect tensile strength (ITS) and indirect tensile stiffness modulus (ITSM) tests. The results showed that the ratio of wet/dry values of ITS and ITSM for mixtures containing limestone was higher than those of the samples with granite aggregate. The results of the laboratory tests indicate that PE increases the wettability of asphalt binder over the aggregate and the adhesion between the asphalt binder and aggregate, especially in the mixtures containing acidic (granite) aggregate prone to moisture damage. The aggregates treated with HDPE showed better resistance against moisture damage in both aggregates that were used in this study.

Moisture damage in asphalt mixtures using the modified SATS test and image analysis

This study investigated damage in asphalt due to moisture by using the modified saturation ageing tensile stiffness (SATS) test along with image analysis. Specimens made from both granite and limestone aggregate with a 40/60 penetration grade bitumen were tested in the modified SATS test. The samples were scanned within an X-ray CT facility before the SATS testing, after the initial saturation and at the completion of the SATS test. Bitumen was extracted from tested specimens and scanned separately in a high resolution Nanotom (high resolution X-ray CT). The extracted bitumen was tested in a DSR for shear rheological properties. The specimens made from granite (acidic) and limestone (basic) aggregate were found to have similar permeability and this was found to be high for specimens having high design air void content. Specimens made from basic aggregate had higher stiffness than the specimens made from acidic aggregate. The master curves of the aged binder are different from those of the virgin binder (bitumen). Also the microstructure of binder observed was different for aged and virgin binder.

Influence of the physical state of water in the diffusion process in asphalt binders

Moisture damage in asphalt mixtures is a complex phenomenon that involves mechanical, chemical, physical and thermodynamic processes. This damage contributes significantly to the premature deterioration of asphalt pavements, which leads to extra cost in highway maintenance and vehicle operations. One key mechanism of how moisture reaches the asphalt-aggregate interface is by its permeation or diffusion through the asphalt binder or mastic. For the asphalt-water system studied, the Fourier Transform Infrared (FTIR) – Attenuated Total Reflectance (ATR) spectrometry was used. Water shows strong absorption in the infrared region and the FTIR-ATR technique has the ability to monitor both the kinetics of moisture ingress as well as any chemical changes occurring during the test. This paper has the literature review and some results obtained in the comparison between water diffusion in the liquid state with the moisture (or vapor) state, both at room temperature.KEYWORDS: Asphalt Mixtures, Moisture Damage, Diffusion, Spectroscopy

Laboratory evaluation of resistance to moisture damage in asphalt mixtures

Moisture damage in asphalt mixtures refers to loss in strength and durability due to the presence of water. Egypt road network is showing severe deterioration such as raveling and stripping because the bond between aggregates and asphalt film is broken due to water intrusion. To minimize moisture damage, asphalt mixes are investigated to evaluate the effect of air voids, degree of saturation, media of attack and the conditioning period. Two medias of attack are considered and two anti-stripping additives are used (hydrated lime and Portland cement). The retained Marshall stability and tensile strength ratio are calculated to determine the resistance to moisture damage. The results showed that both lime and cement could increase Marshall stability, resilient modulus, tensile strength and resistance to moisture damage of mixtures especially at higher condition periods. Use of hydrated lime had better results than Portland cement.

Application of Sessile Drop Method to Determine Surface Free Energy of Asphalt and Aggregate

Abstract Surface free energy is an important parameter to determine the work of adhesion between the asphalt binder and the aggregate, which is related to the moisture damage of asphalt mixture. In this study, the sessile drop technique was performed to obtain the contact angle between asphalt/aggregate and different probe liquids. The surface free energies of asphalt and aggregate were characterized on the basis of the Owens-Wendt’s theory. It was found that the sessile drop technique is a convenient way to determine the static contact angle. A test procedure was developed to offer a clear method to prepare the sample and measure the contact angle. The surface free energy of aggregate determined in this study was found to be smaller than that measured in other techniques because of equilibrium spreading pressure. The work of adhesion calculated from surface free energy can be utilized to choose the best combination of asphalt and aggregate, which can work as a reference in the selection of materials. Meanwhile, it was found that for the same aggregate, the pull-off strength and the work of adhesion of each asphalt-aggregate have the same trend of ranking.

Influence of using nonmaterial to reduce the moisture susceptibility of hot mix asphalt

Moisture damage in an asphalt mixture can be defined as the loss of strength, stiffness and durability due to the presence of moisture leading to adhesive failure at the binder–aggregate interface and/or cohesive failure within the binder or binder–filler mastic. In order to improve adhesion and reduce moisture sensitivity in asphalt mixtures, two different approaches have become apparent. One approach suggests that the aggregate surface be coated by a suitable agent that will reverse the predominant electrical charges at the surface and thus reduce the surface energy of the aggregate. In this study, the effects of nanomaterial, namely Zycosoil, on the moisture damage of asphalt mixtures were studied. Two types of aggregates that represent a considerable range in mineralogy, limestone and granite, were evaluated during the course of this study. To assess the impact of Zycosoil on moisture damage of hot mix Asphalt, control mixes (without Zycosoil) and mixes containing Zycosoil in dry and wet conditions were tested using indirect tensile-strength (ITS) and indirect tensile fatigue (ITF) tests. The results showed that limestone has less moisture damage potential compared to granite. The ratio of wet/dry values of ITST and ITFT for mixes containing Zycosoil was higher than the control mix for two types of aggregate. However, in mixtures made of granite aggregate, using Zycosoil is more effective. As the density of silanol groups is more in its surface, these groups are hydrophilic, and Zycosoil migrates to the polar water-loving surface, reacts with the silanol groups and forms siloxane bond, the strongest bond in nature, and creates a molecular level hydrophobic zone.

Experimental Measurement and Numerical Simulation of Water Vapor Diffusion through Asphalt Pavement Materials

Moisture damage in asphalt mixtures is defined as the gradual loss of structural integrity caused by the presence of moisture. A simple experimental procedure was developed in this study to measure water vapor diffusion coefficients in coarse aggregates, fine aggregate mixture (blend of the fine portion of the aggregates with the asphalt binder), and hot-mix asphalt. The procedure is based on periodic weight measurements of specimen-container ensembles subjected to a controlled temperature and relative humidity environment. Fick’s first law was used to estimate the diffusion coefficients of the materials. The results show that the proposed experimental method is an economic and efficient tool to quantify water vapor diffusion coefficients. Determining these material properties is fundamental to develop numerical models to study the deleterious effects of moisture vapor on the mechanical performance of asphalt mixtures. In order to exemplify the significance of the experimental measurements, a numerical simulation of transient moisture diffusion within the cross section microstructure of an asphalt mixture was conducted. The results of the simulations suggest that diffusion coefficients are fundamental for tracking the potential of a mixture to develop moisture-related degradation processes. Furthermore, it was observed that under the same environmental conditions, moisture damage in an asphalt mixture is highly influenced by the moisture diffusion coefficient of its constitutive phases.

Estimation of resistance to moisture destruction in asphalt mixtures

Moisture damage in asphalt mixtures refers to loss in strength and durability due to the presence of water. The level and the extent of moisture damage, also called moisture susceptibility, depend on environmental, construction, and pavement design factors; internal structure distribution and the quality and type of materials used in the asphalt mixture. In order to assess the moisture destruction, the current study bears out an analytical approach based on surface energy. Two types of bitumen represent very different chemical extremes (AC-10 and AC-20) and the three aggregates represent a considerable range in mineralogy (limestone, siliceous gravel, and granite) were evaluated during the course of this study. Repeated compressive test was conducted on samples in dry and wet conditions under controlled temperature and moisture destruction was monitored as a change in dynamic modulus with load cycles. Further, mixtures including the two types of bitumen with or without hydrated lime were evaluated to determine quantity improvement of hydrated lime on moisture destruction. The result show that AC-20 have less moisture induced damages compared to AC-10 and dynamic modulus values for mixes with AC-20 were higher than the one with AC-10 for all the aggregate types. Hydrated lime increased the dynamic modulus values and wet/dry ratio stiffness. Addition of lime for river gravel samples showed significant difference between two types of bitumen but no major differences were found in crashed granite.

Evaluation of Moisture Damage Mechanisms and Effects of Hydrated Lime in Asphalt Mixtures through Measurements of Mixture Component Properties and Performance Testing

This study presents an approach to help understand moisture damage mechanisms and to evaluate the effects of hydrated lime as moisture damage resisting agents. To this end, various performance testing of hot mix asphalt (HMA) samples induced by moisture damage and several fundamental property measurements (stiffness, strength, toughness, and bonding energy) of mixture components were conducted. Testing data and analyses demonstrated that hydrated lime contributed to moisture damage resistance due to synergistic effects of mastic stiffening, toughening, and advanced bonding characteristics at mastic-aggregate interfaces. However, a well-controlled lime treatment is required to maximize distribution and dispersion of lime particles on aggregate surfaces. In addition to the clear effects of hydrated lime, mineral filler in the HMA samples showed its effects on damage resistance in an early stage of moisture damage due to substantial stiffening-toughening effects from filler addition. Properties and damage characteristics of mixture components measured in this study were related to macroscopic performance behavior of asphalt concrete samples, which infers that the approach herein based on the mixture components can be effectively used to evaluate (or predict) moisture damage of asphalt mixtures and pavements with much less effort.

Moisture susceptibility of asphalt mixtures, Part 2: characterisation and modelling

Moisture damage in asphalt pavements is the degradation of the mechanical properties of the asphalt composite due to the action of water. In a companion paper the mechanisms of moisture damage were discussed. It was established that in order to characterise moisture damage in asphalt mixtures, it is important to comprehensively describe and model the effect of thermodynamic, chemical, physical, and mechanical processes. This paper discusses existing tests and analytical methods that can be used to assess and quantify moisture damage potential in asphalt mixtures. These methods range from visual qualification of asphalt binder stripped from the aggregate, to analytical-based models that include multiple material properties derived using fracture mechanics, continuum mechanics, thermodynamics, and/or micromechanics. In addition, this paper presents a new approach for classifying moisture damage, which emphasises recent analytical developments. Finally, advances in the mathematical modelling of moisture damage are summarised and future research efforts in this area are identified.

Probabilistic Analysis of Fracture in Asphalt Mixtures Caused by Moisture Damage

Moisture damage in asphalt mixtures is a complex phenomenon involving thermodynamic, chemical, physical, and mechanical processes that contribute to pavement deterioration. The empirical nature of the majority of test methods and the inherent variability of the results are the two primary challenges impeding the reliable characterization and assessment of moisture damage. This paper addresses these two challenges by offering a framework that (a) is based on probabilistic analysis that accounts for the uncertainty of the deterioration process and the inherent variability associated with the experimental data, (b) is based on a fracture mechanics damage model for viscoelastic materials that has successfully been applied to the characterization of moisture damage in asphalt mixtures, and (c) combines the fundamental material properties of the asphalt mixture that can be obtained from reliable tests (e.g., surface energy measurements of the material components and dynamic shear test and relaxation modulus data from the dynamic mechanical analyzer). This framework was applied to analysis of the fine matrices of four asphalt mixtures containing different aggregate materials and fillers. The results are compared with the results obtained by assessment of moisture susceptibility for the full asphalt mixtures by the saturation aging tensile stiffness test.

Moisture Susceptibility of Asphalt Mixtures with Known Field Performance

Moisture damage in asphalt mixtures refers to loss in strength and durability due to the presence of water. The level and the extent of moisture damage, also called moisture susceptibility, depend on environmental, construction, and pavement design factors; internal structure distribution; and the quality and type of materials used in the asphalt mixture. This study evaluates the moisture susceptibility of asphalt mixtures with known field performance using dynamic analysis and a crack growth model to characterize the asphalt mixtures and corresponding asphalt mastics. The model parameters were obtained from surface energy measurements, uniaxial dynamic testing for the asphalt mixtures, and dynamic shear testing for the asphalt mastics. Results showed good differentiation between the moisture-conditioned (wet) and unconditioned (dry) specimen behavior and provided a good correlation with the reported field performance of the asphalt mixtures.

Effects of various additives on the moisture damage sensitivity of asphalt mixtures

Effects of four additives, namely two fatty amine (Wetfix I, Lilamin VP 75P), one catalyst (Chemcrete) and a polymer (rubber), on the moisture damage of asphalt mixtures were studied. Rheological characteristics of the binders were measured using conventional methods both original and thin-film oven aged. Mechanical characteristics of the mixtures were evaluated with Marshall, indirect tensile and Lottman treatment tests. The additives used in this study reduced the level of damage due to moisture in asphalt mixtures. Minimum acceptable indirect tensile strength ratio (0.70) is achieved when Chemcrete and 0.2% of Wetfix I, and 0.4–0.6% of Lilamin VP 75P are used in asphalt mixtures. Indirect tensile strength ratio may decrease due to the relatively higher strength obtained in dry specimens with respect to the conditioned ones. Indirect tensile strength ratios of asphalt paving specimens were found to be less than the Marshall Stability ratios.

Mechanistic Analysis of Asphalt Pavements, Using Superpave Shear Tester and Hamburg Wheel-Tracking Device

A comparative evaluation of permanent deformation and moisture damage of asphalt mixtures using the Superpave shear tester and the Hamburg wheel-tracking device (HWTD) is presented. The damage analysis of simulated asphalt pavements is also included. The selected materials were a PG 64-22 asphalt binder and a sandstone aggregate with and without an antistripping additive. The repeated shear at constant height (RSCH) and HWTD tests were performed for the evaluation of permanent deformation. The results showed that the Superpave mixtures were less susceptible to permanent deformation than the Marshall mixture. The results of the HWTD tests performed at 40°C were consistent with those of the RSCH tests. Two permanent deformation models were compared to relate plastic strain accumulation with the number of load repetitions. The one selected for use in the Strategic Highway Research Program A-005 contract is generally better than the other model. For moisture susceptibility evaluation of these mixtures, the results of the AASHTO T283 tests were consistent with those of the HWTD tests at 40°C. The creep compliances calculated from the frequency sweep at constant height tests were applied to the KENLAYER program for pavement damage analysis. On the basis of the data analyses in this study, the simulated asphalt pavements are considered more of a material and mix design problem than a structural problem. The use of creep compliances of the above mixtures could not successfully predict the pavement performance in comparison with results of the RSCH and HWTD tests.