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The Huet-Sayegh (HS) and 2S2P1D rheological models represent very well the linear viscoelastic behaviour of asphalt concrete and binder while using less parameters than other models. However, the f...

In order to prevent distresses in asphalt pavement, the analysis of pavement structure should be as close as possible to its real behavior. However, in actual standard for designing asphalt pavement, viscoelastic behavior of asphalt mixtures and effects of moving vehicles are still not considered. In this paper, the authors aim at applying an analytical approach for analyzing the linear viscoelastic behavior of asphalt pavements comprised of conventional and high modulus asphalt concrete caused by a moving loading. It is shown that the effects of moving load give rise to an increase in tensile stress at the pavement surface and at the bottom of asphalt layers, which can be a reason for premature cracks in flexible pavement. The results also show that the use of high modulus asphalt concrete layers gives rise to a significant reduction of tensile stress and strain at the pavement surface as well as at the bottom of asphalt layer.

Permanent deformation of pavements has become a persistent issue to be solved in Vietnam because of hot climatic conditions and high traffic volume. In order to deal with the problem, many attempts have been made by local authorities, researchers and practitioners, e.g. modification of the mixture gradation, improving bitumen rheology and high-quality control of manufacturing and construction of asphalt concrete (AC). SBS-modified bitumen or polymer modified bitumen (PMB) has been applied in Vietnam for many years and very good results in preventing rutting distress have been gained. However, in very high trafficked road and slow-speed area like intersection, PMB did not perform very well. Recently, high modulus asphalt concrete (HMAC) has been considered in the country as an alternative for PMB asphalt concrete. Since the thickness of flexible pavement structures in Vietnam is normally very small, ranging from 12 to 15 cm for asphalt layers while HMAC is stiffer than conventional AC, there are still concerns about the fatigue life of pavement structures comprised of HMAC. The aim of this study is to characterize the linear viscoelastic (LVE) behavior of HMAC and conventional AC and to analyze the LVE behavior of pavement composed of HMAC or (and) AC to evaluate its possible use in Vietnam. The results show that the use of HMAC will decrease the values of stress and strain at the bottom of the second asphalt layer, which increases the resistance to bottom-up fatigue cracking of the pavement.

Along with the rapid increase in the number of road vehicles, a large amount of waste tires have been created, causing negative effects to the environment. Many attempts have been made to effectively reduce this type of solid waste including the reuse of recycled rubber powder from waste tires as an additive for improving the performance of asphalt mixtures. In this work, the authors aim to study the effects of crumb rubber (CR) on the mechanical properties, especially the rutting resistance, of CR modified asphalt concrete (AC) and stone mastic asphalt (SMA) by varying two factors-namely, the content of additive and the curing time. The dimension of used CR ranges from 0 to 2.36 mm, which is not too coarse for promoting the CR–bitumen interaction and not too fine for facilitating the production of CR. The content of CR was increased gradually from 0 to 3% to examine the effects of CR content on the engineering properties and determine the optimal content in the mixture. It was observed that the optimal content is 1.5–2%, while the optimal curing time that contributes to the maximal increase in the mechanical characteristics of both mixtures could not be determined. In the range of 0–5 h of curing time, the longer the asphalt mixture is maintained at a high temperature, the better the performance of mixture will be. Ageing was found to have influence on the performance of asphalt mixtures; however, its effects are not as important as those of CR modification. Keywords: Crumb rubber, Dry process, Asphalt concrete, SMA, Curing time

Despite of hot climatic conditions and high traffic volume, flexible pavement still covers more than 90% of the road system in Vietnam due to its advantages over rigid pavement, e.g. smoothness for vehicles and ease of construction and repair. Consequently, permanent deformation become a persistent problem to be solved in the country. Attempts have been made to improve the resistance to rutting of asphalt mixtures including the modification of the mixture gradation, bitumen rheology improvement and tight quality control in manufacturing and construction of asphalt concrete (AC). High modulus asphalt concrete (HMAC) has long-time been found good material for preventing rutting distress and improving fatigue life of asphalt pavement. Because the thickness of pavement structures in Vietnam is normally very small (12–15 cm of asphalt) while HMAC is 2–3 times stiffer than conventional AC, there is still concern about the fatigue life of pavement structures comprised of HMAC. The aim of this study is to analyse the maximal tensile stress and strain occurring in thin asphalt pavement structures comprised of one or two layers of HMAC and (or) conventional AC and predict their fatigue lives. It was shown that using HMAC properly will increase the bottom-up fatigue life of the pavement. Thus, it is possible to use HMAC in thin asphalt pavement structures like those in Vietnam for preventing rutting distress without concerns about cracking.

In this paper, the fatigue behaviour of several asphalt mixtures that are widely used in Vietnam such as the dense graded asphalt concrete (AC) produced with 60/70 pen bitumen and high rutting resistance asphalt mixtures (HRRA) are investigated using the cyclic indirect tensile (IDT) testing device equipped at Ho Chi Minh City University of Technology and Education (HCMUTE). Several level of stress magnitudes were applied to determine the characteristic fatigue line (CFL) of mixtures. The results show that the widely used power law of CFL is applicable for all investigated mixtures. Although the stiffness of the HRRA is twice that of conventional AC, its resistance to fatigue is much higher. The effect of strain magnitude on the stiffness of mixtures or the nonlinearity effect was also recognized. It was observed that the impact of binder type on the nonlinearity effect is insignificant compared to that due to the volumetric design of mixture.

Asphalt concrete is a composite material comprising aggregate, sand, mineral filler and bitumen as a binder. Although good compaction is performed during the construction, there is still relatively large discontinuity inside the material, and this will favour the appearance of micro-cracks, which decreases the performance of the material. Structural cracking resulted from repeated loading, or fatigue cracking, is a common failure mode of asphalt pavement structure, reducing the serviceability of the pavement. Owing to the present of micro-cracking, the fatigue cracking of asphalt pavement is generally modelled by using damage theory. In this paper, the authors aim to illustrate the application of an isotropic non-local elastic damage model in predicting the fatigue life of a pavement structure. A scalar D, called damage variable, is used to define the damage state at a point of the material, and the evolution of this variable at a point depends on the historic damage state as well as the present strain tensor at that point. The model parameters are determined on the basis of fatigue test results—namely, 4-point bending test. Numerical examples are presented to illustrate the ability of using damage theory to predict the damage evolution of a pavement structure as well as its service life.

Semi-flexible material is a composite pavement surfacing that uses both asphalt concrete (AC) with a unique structure and Portland cement concrete (PCC) in the same layers. The AC introduced in this kind of pavement is initially designed with the air-void content in the range of 25–35%, while the grout of Portland cement is the mixture of Portland cement, silica fume, silica sand, water and a suitable amount of plasticity additive. The process of producing and pouring cement grout into AC layers is conducted when AC layers are totally cool down, which is estimated at least 24 h after finishing the last rolling. Semi-flexible material is believed to have a better rutting resistance compared to that of the conventional AC, this is resulted from the appearance of cement grout. Furthermore, joints are not required in this kind of pavement. As the results, the significant advantages of the material are the combinations of those of AC and PCC. In this paper, the authors intend to access the rutting and indirect tensile strength of this material. The applications of semi-flexible material in the pavements of airport, airfield, port, warehouse and other high traffic areas are feasible.