Francesco Canestrari

ADVANCED TESTING AND CHARACTERIZATION OF INTERLAYER SHEAR RESISTANCE

The performance of multilayered pavement systems depends strongly on interlayer bonding. To guarantee good bonding, tack coats (also called bond coats) are usually applied at various interfaces during pavement construction or overlay. The effectiveness of the tack coat can be assessed with the use of several devices arranged by different laboratories to evaluate interlayer shear resistance. This paper shows how interlayer shear resistance may be evaluated through the Ancona shear testing research and analysis (ASTRA) device. ASTRA results, expressed in units of maximum interlayer shear stress (τpeak) highlight the effects of various influence parameters such as type of interface treatment, curing time, procedure of specimen preparation, temperature, and applied normal load. Moreover, this paper compares the τpeak results obtained by two different shear test devices: the ASTRA tester designed and developed in the Polytechnic University of Marche (Italy) and the layer-parallel direct shear tester created by...

Temperature Effects on The Shear Behaviour of Tack Coat Emulsions Used in Flexible Pavements

In this paper, the authors present the experimental results obtained in the laboratory by using the ASTRA interface shear test for the performance-related characterisation of tack coat emulsions. The test focuses on the failure properties of bituminous multi-layered systems and yields results which may be modelled by means of a straightforward theoretical approach based on the identification of various strength components due to cohesion, pure friction and dilatancy. It was found that the latest version of the testing apparatus may be conveniently used to evaluate temperature-related effects. This was done in a research project in which test conditions were obtained by combining test temperatures and normal stress levels comprised within wide variation ranges.

Adhesive and Cohesive Properties of Asphalt-Aggregate Systems Subjected to Moisture Damage

ABSTRACT The bond strength between asphalt and aggregate plays a fundamental role in evaluating the moisture sensitivity of HMA Mixtures. In this study the effect of water on adhesive and cohesive properties of asphalt-aggregate systems was investigated using a modified version of the PATTI. The device was used to measure the pull-off strength on different asphalt-aggregate combinations and to evaluate the influence of water immersion at two different temperatures. In particular, six asphalt binders were employed in combination with two aggregate types, having different asphalt affinity. The effect of the aggregate surface temperature during specimen preparation was also tested. In the first phase of the study the within-laboratory repeatability of the test procedure was investigated. The results showed the PATTI test is able to evaluate with good precision the pull-off strength and that its repeatability depends on the failure type (adhesive or cohesive). In the second phase of the study a full factorial experiment was employed to verify the reliability of the test for routine use in determining the adhesive and cohesive properties of asphalt-aggregate combinations and the effects of moisture damage. The results showed that, in the dry condition, the test was able to measure the internal cohesion of the asphalt binders. The results also showed the effects of water damage on the pull-off strength and the decisive role of asphalt-aggregate affinity was clearly highlighted. Using wet conditioning of the PATTI samples it was proven that water affects the adhesive bond between asphalt and aggregate much more than the asphalt cohesion. Moreover, the results indicate that aggregate temperature during sample preparation has only a limited effect on the adhesive strength.

Advances in Interlaboratory Testing and Evaluation of Bituminous Materials

A background on RILEM interlaboratory testing is presented with some comments regarding general development and objectives for advanced testing, providing also a general overview on requirements and needs. It is emphasized that development of today is driven by the evaluation of performance based material behavior, moving more and more from semi-empirical to fundamental test methods. Given this background, an updated version of the RILEM methodology for testing of bituminous pavement materials is presented with a short discussion of basic elements. This framework is the basis for this report on the achievements of RILEM technical committee TC 206-ATB on “Advanced Testing and Characterization of Bituminous Materials”. Furthermore, main principles and key elements for planning of interlaboratory tests are summarized containing points that proved also relevant for the interlaboratory tests presented and discussed in the following chapters of this book. This summary is intended as general checklist and practical tool for initiating and conducting future interlaboratory tests. 1.1 Background of RILEM interlaboratory tests

Performance evaluation of a cold-recycled mixture containing high percentage of reclaimed asphalt

Cold recycling of asphalt pavements proved to be an effective maintenance and rehabilitation technology for both environmental and economic reasons. Nevertheless, the use of cold-recycled (CR) asphalt mixtures requires a careful assessment of their mechanical properties, especially when they are designed to replace traditional hot-mix asphalt concrete (AC) mixtures. In this study, the potential use of a CR asphalt mixture as base course of an Italian motorway was evaluated. The studied mixture was produced in a central plant employing high-reclaimed asphalt (RA) content and used to construct two experimental sections along an in-service Italian motorway. In particular, a special mixing procedure, involving the use of water vapour and bituminous emulsion, was tested. A third experimental section was constructed with the same layer thickness using the AC mixture currently used in rehabilitation projects, incorporating 30% of RA. Volumetric properties, stiffness, resistance to permanent deformation and fatigue behaviour of mixtures were investigated by performing tests on samples cored from the three test sections and on laboratory-compacted samples. Results of the mechanical tests showed that CR mixtures provide lower stiffness modulus and lower resistance to repeated loading, but better resistance to permanent deformation when compared with AC. This behaviour can be explained due to the presence of cementitious bonds that reduce thermal sensitivity and viscous response.

Mechanical Testing of Interlayer Bonding in Asphalt Pavements

Steadily increasing requirements on pavement performance properties, in terms of bearing capacity and durability, as well as new innovative developments regarding pavement materials and construction, are observed worldwide. In this context interlayer bonding at the interfaces of multi-layered bituminous systems is recognized as a key issue for the evaluation of the effects, in terms of stress-strain distribution, produced by traffic loads in road pavements. For this reason a correct assessment of interlayer bonding is of primary importance, and research efforts should be addressed in order to improve the lack of correlation and/or harmonization among test methods. Following this principle RILEM TG 4 organized an interlaboratory test in order to compare the different test procedures to assess the interlayer bonding properties of asphalt pavement. The results of the experimental research are presented with a preliminary overview of basic elements, test methods and experimental investigations on interlayer bonding. Then the RILEM TG 4 experimental activities, based on the construction of three real- scale pavement sections, are presented in detail. Each pavement section was composed of two layers, and three different interface conditions were chosen. The first pavement was laid without interface treatment and the others with two different types of emulsion. Fourteen laboratories from 11 countries participated in this study and carried out shear or torque tests on 1,400 cores. The maximum shear or torque load and the corresponding displacement were measured, and the shear or torque strength was calculated as a function of the following parameters: diameter, test temperature, test speed, stress applied normal to the interface and age of the specimen. The results of this study are presented in terms of precision and correlations regarding the parameters which results in useful information on asphalt pavement interlayer bond tests.

Laboratory characterisation and field validation of geogrid-reinforced asphalt pavements

In order to improve the mechanical properties of pavements, reinforcement systems can be employed in asphalt layers. However, the presence of a grid at the interface causes an interlayer de-bonding effect. Moreover, a real challenge is related to the proper in situ installation of grids. The present research aims to evaluate the effectiveness of pavement rehabilitation with fibreglass geogrids. To this purpose, a real-scale field trial was constructed and monitored through Falling Weight Deflectometer measurements. Interface shear tests and flexural tests were also carried out on double-layered samples prepared in the laboratory reproducing real-scale field trial characteristics. Moreover, shear tests were also performed on in situ cored specimens. Results mainly showed that a proper installation of the reinforcement is fundamental in order to obtain suitable test results and good pavement performance.

Synthesis of standards and procedures for specimen preparation and in-field evaluation of cold-recycled asphalt mixtures

The use of recycled asphalt (RA) materials in pavement rehabilitation processes is continuously increasing as recycling techniques, such as cold recycling (CR), are being utilised in increasing magnitude and greater awareness for use of recycled materials and consideration of sustainable practices is becoming common in the construction industry. The focus of this paper is on developing a state of the art and state of the practice summary of processes used for classification of RA as well as the curing and specimen preparation practices for cold-recycled asphalt mixtures. A variety of topics were explored through an exhaustive literature search, these include RA production methods, definition of RA materials, stockpiling practices, industrial operations, specimen curing and preparation practices and in-field evaluation of cold-recycled rehabilitation. This paper was developed through efforts of CR task group (TG6) of RILEM Technical Committee on Testing and Characterization of Sustainable Innovative Bituminous Materials and Systems (TC-237 SIB).

Analysis of Structural Compatibility at Interface Between Asphalt Concrete Pavements and Orthotropic Steel Deck Surfaces

Orthotropic steel deck is the most suitable solution for long-span bridges by virtue of its low weight and good mechanical properties. However, this deck shows a lack of adhesion with ordinary paving materials; for this reason special bonding coats are usually applied on the steel surface. Polymer-modified bitumen, asphalt-based mastic, epoxy asphalt, and reinforced asphalt membrane have been used at the interface between the hot-mix asphalt (HMA) course and steel bridge decks. A description of these materials and their construction process is provided. In some extreme situations mechanical reinforcement is necessary to provide adequate bonding between the steel deck and the asphalt pavement. The aim of this study was the laboratory evaluation of the shear properties of smooth and reinforced steel interfaces, which were coated with a polymer-modified bitumen and placed between the steel deck and conventional HMA. A suitable specimen preparation procedure was first defined. Shear resistance was evaluated with the ASTRA shear test device to investigate the effects of temperature and normal stress on different types of HMA–steel interfaces. The results showed that reinforced steel interfaces guaranteed higher performance than did smooth interfaces, especially with increasing temperature. Reinforced steel interfaces can be considered as a reliable solution in cases of high-shear traffic-induced stresses.

New method to estimate the “re-activated” binder amount in recycled hot-mix asphalt

The magnitude of the binder re-activation within the reclaimed asphalt pavement (RAP) fraction is a major concern when recycled hot-mix asphalt (HMA) is produced, since it directly affects the final performance of the mix. Currently, no reliable methods to predict the RAP binder re-activation are available and the lack of such information prevents the quantification of the proper amount of virgin binder to be added to the recycled HMA.This study proposes a new method to estimate the re-activated binder amount based on the surface area (SA) of RAP aggregates. Laboratory results demonstrated the effectiveness of the SA approach in the case of RAP amounts typically used for hot-recycled HMA. Moreover, the experimental investigation suggested that revised coefficients are needed for the evaluation of the SA to account for the presence of clumps when high amounts of fine RAP aggregates are used.