Martin Arraigada

Numerical and Experimental Analysis for the Interlayer Behavior of Double-Layered Asphalt Pavement Specimens

Bonding characteristics between pavement layers have an important influence on responses of pavement structures. This paper deals with this subject by analyzing the interlayer behavior of double-layered asphalt DLA specimens taken from an in-service motor- way using a coaxial shear test CAST and a layer-parallel direct shear LPDS test. To analyze and model the influence of the interlayer condition, finite-element simulations of CAST DLA specimens were conducted. In the models, both idealized fully bonded and no- bonding assumptions were used to characterize the interlayer behavior of DLA specimens. Experimental results presented for CAST and LPDS tests demonstrate that there is a strong influence of temperature in the interlayer bonding mechanism. At lower temperatures, there is an increase on the bonding strength produced by the binder stiffening and aggregate interlocking. Further, it was observed that comparisons of CAST experimental and numerical results indicate that the interlayer can be close to the fully bonded condition at low temperatures below 20°C while the interlayer, at higher temperatures, behaves between fully bonded and no-bonding idealized conditions. DOI: 10.1061/ASCEMT.1943-5533.0000003 CE Database subject headings: Asphalt pavements; Finite element method; Numerical analysis; Experimentation. Author keywords: Interlayer; Double-layered asphalt; CAST; LPDS; Finite element.

Determination of Road Deflections from Traffic Induced Accelerations

ABSTRACT Vertical elastic pavement deflections from moving vehicles provide valuable information for assessing the structural behaviour of a road under real loads. Various types of sensors can be installed in a road for deflection monitoring. This paper explores the use of accelerometers. It discusses the problems involving the calculation of deflections from measured acceleration by double integration due to the amplification of measurement errors in the acceleration signal. It proposes a simple algorithm to correct integration errors and obtain deflections from acceleration measurements. It also presents a laboratory testing method to evaluate the performance of two accelerometers for their suitability in road applications. In addition, using a selected accelerometer, pavement deflections at a wheel tracking test site are calculated and discussed.

INNOVATIVE ASPHALT RESEARCH USING ACCELERATED PAVEMENT TESTING

Accelerated pavement testing is one key for innovations in the field of road pavement structures and materials due to its power of assessing mechanical performance in close to reality situations. This paper discusses two types of mobile load simulators for applying unidirectional wheel loads at comparatively high frequencies, the MMLS3, a one third scale device, and the MLS10, a full-scale device. Through examples it is demonstrated that these devices are suitable for testing complex systems, such as mechanical resistance of light reflectors on pavements, traffic resistance of bituminous plug expansion joints for bridges, performance of grid reinforced pavements as well as water resistance of porous asphalt against traffic induced pumping effects. Moreover, an example of MLS10 ultimate bearing capacity tests on a real test section is shown focusing on the discussion of strain gauge, acceleration, rut depth and falling weight deflectometer (FWD) measurement results.

Cracking and interlayer bonding performance of reinforced asphalt pavements

Abstract Reinforcement of asphalt pavements has become a valuable constructive method for preventing reflective cracking and prolonging service life of roads. Although the overall advantages of these reinforcements seem beyond doubt, there is still lack of information about the actual benefit of different systems on the prolongation of the road’s lifespan. Further, it is not clear how they affect the bonding between layers along the pavement’s lifetime. This paper investigates the effect of three types of reinforcement systems on the performance of two layered asphalt pavements, mainly considering: (1) Reflective crack propagation. (2) Shear bonding strength. To that end, model and real pavements were constructed in the laboratory and the field using selected reinforcement systems. Designs with various mesh opening sizes and different bond coatings were considered. Afterwards, the pavements were loaded with a down-scaled (MMLS3) and a full-scale (MLS10) traffic load simulator and their performance was compared to pavements without any type of reinforcement. These devices simulate the effect of traffic-similar loading in a compressed period of time. During the loading phase, the crack formation and propagation was monitored through visual inspections and indirectly by measuring the deformation of the pavements with sensors. The interlayer bonding strength was evaluated by coring the pavements and testing the specimens with a Layer Parallel Direct Shear apparatus. Results showed that two reinforcement systems were generally successful in delaying reflective crack propagation. Only one of the systems presented at least similar or even worse performance than the same pavement without reinforcement. On the other hand, it was found that the bonding properties depend on the reinforcement system type, but that in most cases interlayer bond strength was according to the standard requirements.

Use of APT for Validating the Efficiency of Reinforcement Grids in Asphalt Pavements

Reinforcement of flexible asphalt pavements with interlayer systems containing grids is increasingly used to extend service life of roads. Typically, reinforcements are placed between layers. They can be utilized to prevent the propagation of reflective cracking, prolonging the service life of asphalt pavements. Many research and practical experiences have shown the advantages of using reinforcements to increase the life-span of a pavement. However, only few tests were done using Accelerated Paving Testing (APT), where the application of loads is carried out with controlled passing of truck tires. Further, there is still insufficient research carried out to predict the actual effect on the extension of the pavement’s life-span. This information is critical for pavement design purposes and to improve the design standards. This research focuses on the effect of different reinforcement systems on the life-span extension of two-layered slabs and an asphalt pavement, using scaled and full scale APT with the Model Mobile Load Simulator MMLS3 and the Mobile Load Simulator MLS10 respectively. Laboratory and full-scale results with MMLS3 and MLS10 show that the different grids used in the test will extend the life-span of the tested pavements up to two times. The full-scale tests show, that the effect of the construction of a reinforcement system combining a grid with a stress absorbing membrane (SAMI) with the grid, increases the rutting of the pavement.

Study of the Bearing Capacity of Swiss Standard Pavements Under MLS10 Loading

Accelerated Pavement Testing (APT) is an efficient testing procedure to evaluate the performance of different pavement concepts. With APT, it is possible to determine and measure the structural response and pavement performance under a controlled, accelerated accumulation of load damage that simulate the long-term in-service condition, but in a compressed period of time. The repeatability of the loads applied permits making accurate predictions about the bearing capacity and lifespan of the pavement under study. It also allows making comparative assessments of potential long term performance of any type of pavements. This paper summarizes the results of a series of initial tests carried out on pavements with similar structure but different stiffnesses designed following Swiss standards. Each pavement was loaded with the Mobile Load Simulator MLS10 until reaching its bearing capacity limit. The aim of these tests was to use the results as a benchmark to compare it to other non-standard structures with similar stiffness in terms of dimensioning and/or materials. It was found that the pavements’ life-spans were basically longer to the ones anticipated by the standards. This difference was larger for the pavements with lower stiffness. Further, as expected, the distress mechanisms were similar for all the pavements considered.

Digital image correlation to monitor cracking and induction healing of asphalt roads

The Road Engineering/Sealing Components Laboratory at Empa has been working during the last four years in an innovative experimental approach aiming at developing a new kind of healable asphalt road via induction heating. The last step of this research focused on the analysis of 1.8 m long test slabs damaged by the Model Mobile Load Simulator MMLS3 in order to prove the feasibility of the healing concept at larger scale. It is known that visible cracks could not be completely healed by this technique and therefore, the recovering of the mechanical performance was not significant. In this context, it seems clear that the healing treatment must be applied not later than the initiation of microcracks to avoid their propagation. For this reason, a digital image correlation system has been used successfully to monitor the damage level of a number of test slabs during the loading phase. This system employs two digital cameras which record the deformation process by means of high resolution images. Then, these images are analysed with correlation algorithms in order to calculate the 3D displacements and strain components for every object point. This optical method allowed to visualize the accumulated damage as well as to select the right moment for initiating the healing process. In addition, this method was useful to confirm that the strength is partially recovered after the healing process resulting in an increase of life of the road. Finally, it was shown that the healing procedure by induction heating can be a feasible alternative for maintenance purposes by acting before irreversible damage of the pavement occurs.

Effect of Reinforced Asphalt Pavements on Reflective Crack Propagation and Interlayer Bonding Performance

Reinforcement of asphalt pavements has become a valuable constructive method for preventing reflective cracking and prolonging the service life of asphalt pavements. Although the advantage of reinforcement overall seems beyond doubt, there is still insufficient information about the actual effect on the prolongation of the pavement’s life-span. Further, it is not clear how the different grids affect the bonding performance between layers. This paper investigates the performance of different reinforcement grids on the performance of two layered asphalt pavements, mainly considering: (a) Reflexive crack propagation, (b) Shear bonding strength. The paper compares the performance of different non-reinforced and reinforced pavements, constructed in the laboratory and in the field and trafficked with a down-scaled (Model Mobile Load Simulator MMLS3) and a full-scale traffic load simulator (Mobile Load Simulator MLS10) respectively. Loading the pavements with rolling tires (cyclic loading) could show differences in the durability between the different reinforcement types as well as the improvement in the flexural bonding strength when using reinforcements compared to non-reinforced structures. Grid styles with different mesh opening sizes of 12.5 and 25 mm plus different tack coats or tack films were also considered. The investigation of the interlayer bonding strength was done by means of the layer parallel direct shear tester (LPDS) and 150 mm cores. It was found that the bonding properties do depend on the reinforcement type, but that in most cases the interlayer bond is according to the requirements.

Influence of SAMI on the Performance of Reinforcement Grids

Over the last decades, reinforcement grids have been used to prolong the service life of pavements. Although there is a broad consensus about their overall efficiency, there are still many open questions about the best alternatives regarding the materials to use, the shapes of the grid, their installation method or their position in the pavement among others. One controversial aspect is the use of Stress Absorbing Membranes Interlayers (SAMI) together with the application of a grid. Many manufacturers claim that the SAMI helps sealing any preexisting cracks in the underlying layer, retarding their propagation to the surface. This paper reports about the performance of a reinforcement grid installed with SAMI in a pavement with artificial cracks. One of the parameters analyzed to evaluate the performance, is the propagation of artificial cracks from the base course to the pavement surface. Other important consideration is the rutting development. To that end, the same cracked pavement, reinforced with a fiber grid and SAMI and without any reinforcement is loaded with identical accelerated trafficking, carried out with the traffic simulator MLS10. Results show that, although the grid with SAMI is able to slow down the formation of cracks in the surface, the density of cracks at the end of the tests is as high as if no grid was used. Moreover, resulting rutting in the reinforced pavement is higher than in the pavement without grid, indicating that the use of SAMI has a counterproductive effect on the rutting performance of the reinforcement.