Durability Of Asphalt Mixtures Research Articles

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.

The mechanisms of hydrated lime modification of asphalt mixtures: a state-of-the-art review

Although already known for a long time, hydrated lime (HL) attracted a strong interest as an asphalt additive during the 1970s in the USA, when moisture damage and frost became some of the most pressing pavement failure modes of the time. Given its extensive use in the past 40 years, HL is known to be more than a moisture damage additive: it is an “active filler” that also reduces the chemical ageing of the bitumen and stiffens the mastic more than a normal mineral filler above room temperature. These properties impact durability, and HL is now seen as an additive that increases asphalt mixture durability. This article is a literature review on the fundamentals of the effect of HL on asphalt mixtures. The reasons for it being so effective lie in the strong interactions between both the aggregate and the bitumen and a combination of four mechanisms, two on the aggregate and two on the bitumen. HL modifies the surface properties of the aggregate, allowing for the development of surface composition and roughness more favourable to bitumen adhesion. Then, HL can treat the existing clayey particles adhering to the aggregate surface, inhibiting their detrimental effect on the mixture. Also, HL reacts chemically with the acids of the bitumen, which in turn slows down the age hardening kinetics and neutralises the effect of the “bad” adhesion promoters originally present inside the bitumen, enhancing the moisture resistance of the mixture. Finally, the high porosity of HL explains its stiffening effect above room temperature.

Optimising the moisture durability SATS conditioning parameters for universal asphalt mixture application

The saturation ageing tensile stiffness (SATS) procedure is the first laboratory asphalt mixture durability protocol to combine moisture damage and oxidative ageing during the conditioning of asphalt mixtures prior to mechanical testing. However, the application of the SATS procedure has tended to be predominantly targeted at base materials with relatively ‘hard’ binders and overall high stiffness modulus requirements and is considered potentially too severe for more standard asphalt mixtures. This research study focused on understanding the effect of changes to the SATS conditioning parameters on the relative moisture damage assessment performance of asphalt mixtures, particularly ‘softer’ binder, high binder content and, finally, low air void content mixtures. Using four different aggregate types, together with ‘hard’ 10/20 pen and ‘softer’ 40/60 pen bitumen, the parameters of pressure, temperature and duration were altered, either one at a time or in combination, to arrive at a suitable combination for testing more commonly used 40/60 pen material. The optimum combination of parameters to allow the SATS procedure to be used for a wide range of typically used asphalt mixtures was found to be 0.5 MPa pressure, 85°C temperature and 24 h duration. The revised SATS durability conditioning protocol was still able to successfully discriminate between ‘poor’ moisture susceptible aggregate and ‘good’ material.

Fatigue Tests of Bituminous Mixtures with Inclusion of Initial Cracks

The method of testing asphalt mixtures, including initial cracks appearing in pavements, is presented in this paper. The main aim of the study was a determination of the durability of asphalt mixtures, in regard to crack sizes. For this purpose, the four-point bending test was performed according to the technical standard PN-EN 12697-24. The test was conducted with selected asphalt mixtures under the controlled strain, and with the application of different crack sizes. Specimens with cracks were analyzed. Moreover, a model based on finite-element method (FEM) calculations was worked out, which allowed for the verification of conditions of the asphalt mixtures’ response to strains and the assessment of the state of stresses and strains at the crack tip. The wide range of studied conditions helped to determine the fatigue criterion for the “cracked” beam in the fatigue tests. The presented fatigue condition is very useful in the estimation of fatigue durability of asphalt mixtures. The results of analyses clearly showed the influence of cracks on the decrease in stiffness modulus. This effect has a nonlinear behaviour in the case of larger cracks. The proposed FEM model of beam, including cracks, is very useful in studies of stresses and tensile strains concentrated at the crack tip.

Surface Energy Characteristics and Impact of Natural Minerals on Aggregate–Bitumen Bond Strengths and Asphalt Mixture Durability

The surface free energy of a solid is a material property that influences its interaction with other solids, liquids, and gases. Mineral aggregates are mixed with bitumen in the production of asphalt mixtures, and the interaction of aggregates with bitumen, water, or chemical modifiers affects the overall performance of the mixtures and, in turn, the pavement structure. A comprehensive characterization of the minerals that make up these aggregates can be used to explain the interactions between the aggregates and components used to bind the aggregates including bitumen, water, and chemical additives. This paper combines several techniques to quantify and describe or catalog mineral properties. These properties primarily include surface free energy, specific surface area, and surface carbon content of some of the most common minerals found in aggregates. The paper presents data that exemplify how this information can be used to characterize the moisture-induced stripping potential for bitumen–mineral combinations. Results indicate that a simple energy ratio calculated on the basis of adhesive bond energies from surface free energy measurements of the minerals and the bitumen can predict performance in asphalt mixtures and that a few minerals can form thermodynamically stable bonds with some bitumens that are inherently resistant to stripping.

Durability of asphalt mixture in different corrosion solution

The corrosion to asphalt mixture under different kinds of corrosion solution, such as pH=2 solution, pH=12 solution, pH = 12 solution and 10% Na2SO4 solution, was studied. The performance attenuation of asphalt mixture was analyzed under the normal environment and the freeze-thaw environment, and the analysis was given on the sensitivity of the test results to the evaluation index. The experimental results show that the performance of asphalt mixture is attenuated faster under the acidic solution, alkaline solution and sulfate solution. Corrosion factor Kc, freeze-thaw corrosion factor Kf, and freeze-thaw effect factor Kfc are proposed to evaluate asphalt mixture resistance to corrosion in different kinds of corrosion solution. The values of Kc and Kfc decrease with the increasing of corrosion time. The change rule of Kf show that the rate of corrosion is decreased by the action of freeze-thaw in acidic solution and in alkaline solution, but is increased by the action of freeze-thaw in sulfate solution. The microscopic analysis indicates that acid solution reacts with aggregate of asphalt mixture, alkaline solution reacts with asphalt cement of asphalt mixture, the surface tension of sulfate solution and crystallization of sulfate are the main reasons which weak the performance of asphalt mixture.

Experimental study on effects of flood puddle to durability of asphaltic concrete containing refined butonic asphalt

The purpose of this paper is to grasp effect of flood puddle to durability of asphalt concrete mixture on road pavement. In this regard, an experimental study was carried out by using Modified Immersion test in order to represent the flood phenomenon and Marshall Immersion test as reference. The experimental treated immersion test during 1, 3, 5, and 7 days to the two types of asphalt mixture, i.e. the mixture containing Retona additive and un-containing it. The research adopted three types of durability indexes to describe asphalt mixture durability, i.e. the retaining strength index (RSI), the first durability index (FDI), and the second durability index (SDI). The results show that Modified Immersion test gave good appearance to grasp deterioration of the mixtures durability due to flood puddle during some days. In further, the asphalt concrete mixtures still retained until seven days immersion, where the mixture containing Retona was more durable than the other mixture.

Application of Microcalorimeter to Characterize Adhesion between Asphalt Binders and Aggregates

Adhesion between asphalt binder and aggregate in a dry state as well as in the presence of water is critical to the performance and durability of asphalt mixtures. According to the literature, distress mechanisms in asphalt mixtures such as rutting, fatigue cracking, and moisture-induced damage are correlated to the nature and quality of adhesion between asphalt binder and aggregate. Surface free energy components of aggregates and asphalt binders can be used to compute the work of adhesion between the two materials in a dry condition as well as the thermodynamic potential of water to displace the asphalt binder from the surface of the aggregate. This paper presents a methodology to estimate the surface free energy components of aggregates using the microcalorimeter. The microcalorimeter is a relatively fast and simple alternative tool to estimate surface free energy components of aggregates compared to other techniques such as the gas adsorption method. In addition to surface energy measurement, the application of the microcalorimeter to directly measure the total energy of adhesion between the asphalt binder and the aggregate at mixing temperatures and the hydrophilicity of different aggregates at ambient temperatures is also demonstrated. Both of these properties influence the performance of asphalt mixtures in dry conditions and in the presence of water.

Analytical Formulas for Film Thickness in Compacted Asphalt Mixture

Recently, several researchers have proposed asphalt film thickness as a criterion for ensuring the durability of asphalt mixtures. However, they suggested that the standard film thickness equation, which dates back to the 1940s, needs to be examined by modern technology and improved. A presumable background on which the Asphalt Institute surface area factors are based was recovered and analyzed in detail. A fundamentally sound model for film thickness calculation was developed using a model of asphalt concrete in which the aggregates are spherical but have an arbitrary size distribution. A recent result from statistical geometry is applied to determine the film thickness for any volume fraction of aggregates and any volume fraction of effective asphalt. The analytical formulas are presented, the details of the calculation are summarized, and examples are provided.

Durability of Asphalt Mixtures for Asphalt Facing Type Dam

Durability of Asphalt Mixtures for Asphalt Facing Type Dam