The construction and repair of road infrastructure must nowadays integrate future scarcity issues of raw materials such as petroleum products. Considering the existing road network in France the repair is a major issue. Grids, including fiberglass, are an efficient and economical solution for building asphalt pavements to increase their lifespan and slow reflective cracking.
Today, the grids are increasingly used in France and in many countries, to improve the <br />life of the pavement. Applications are, both, new roads, repair and <br />the reinforcement of cracked pavements. They relate to road pavements but also, increasingly, the <br />industrial or hub ports and airport runways using treated materials <br /> with hydraulic binders or concrete. Grids, including fiberglass, have amply demonstrated, on <br />site, their ability to improve the fatigue life of the asphalt layers, and to delay or <br />prevent reflective cracking of old pavements reinforced. However, there is no <br />now consensus on the characterization tests to carry out, nor on the approaches to calculating or <br />designing of reinforced pavements. The project, which combines why both research laboratories and industrial partners, is to develop more rational and mechanical approaches to the evaluation grids, and for the calculation of reinforced pavements. This is up three locks, which are hindering the development of this technique: <br />- A better understanding of the stresses to which the grids are subjected during the implementation, <br />especially during the movement of construction machinery on the grid when compacting layers <br />pavements, to optimize the resistance of the grids to these stresses. <br />- To study the mechanical behavior of interfaces between the reinforced layers and their support <br />to optimize the characteristics of the interfaces (choice of the emulsion, assay) <br />- Improve prediction of lifetimes reinforced pavement, through study and modeling <br />fatigue behavior grids, reinforced coated and interfaces, and confirmation of <br />the approach by a fatigue test on the full-scale fatigue carrousel.
To achieve these objectives, various laboratory tests will be developed or adapted to simulate stresses that the grid, and the reinforced material meet at the implementation and all throughout their lifetime :
- Monotonous tensile tests at different temperatures, fatigue, creep-recovery on the grid
- Indentation tests to simulate punching suffered by the grid during compaction.
- Mechanical strength testing of grid interfaces / mix.
- Flexural fatigue tests alternating 4 points.
Conducting field tests will study in real conditions, the behavior of grids during the construction phase and damage created to implement and then on real structures instrumented will study their functioning in the floor, and their effect on the life of pavements. These tests are necessary to validate the results laboratory and developed computational models, will be conducted on the fatigue carrousel.
Moreover, end of the experiment, a test milling and recycling of the product will be carried out in order to validate the assumptions recycling at end of life of the composite floor.
An important modeling work is also planned, in interpreting laboratory tests and in situ behavior modeling of reinforced structures.
This research will be complemented by technical, economic and
environmental study to establish:
- The economic benefits of the art (comparison of costs (material, work) and monetization of discomfort to the user-related projects)
- Changes in environmental impacts brought about by the use of coated reinforced grids, in new pavement and pavement reinforcement, comparing different usage scenarios with conventional techniques without grid solutions. A life-cycle assessment will be carried out
Using the software ECORCE 2.0.
Work and results achieved:
- Task 2 (Laboratory Materials Study)
• 2.1 Characterization of the mechanical behavior of composite fiberglass-bituminous concretes composites and their constituents
A) The grid wires
The mechanical characterization of the new materials and those recovered from the test boards was carried out. There appears to be a considerable damage to the surface of the grid wires.
• 2.2 Study of the bonding of the grid / asphalt interfaces
WST test: Maïssa Gharbi's thesis on the mechanical resistance of the grid / asphalt interfaces started on 1/10/2015. The «Wedge Splitting« type test for the resistance of interfaces was developed. Its operation is in the modeling phase by G. Koval.
• 2.3 Damage to the grids by punching
- analysis of surfaces of asphalt to statistically characterize the geometry of the punches
- characterization of the defects observed on the grids after the application of the asphalt. Design and realization (CAD / CAM machining) of steel punches.
- laboratory reproduction of defects under fiber indentation before fatigue tests
- Task 3 (Full-scale testing)
• 3.1: Production of experimental boards and study of the damage to the implementation
Five experimental boards (length 5 to 10 m) were carried out on the site of IFSTTAR in November 2015:
- Task 4: .modelling
Modeling work is currently under way on the simulation of 4-point fatigue bending tests on grid / asphalt composite and on multifissed structure modeling using the boundary element method.
- Task 5: Sustainability assessment of technical solutions
• 5.2: Environmental assessment
Data on the production of the grids studied were measured on site to carry out an environmental impact assessment based on stroke.
The main highlights obtained in 2/3 of the project are: - Evaluation of the behavior of the grids after having undergone the implementation
- WST to characterize the cracking of the interface
- Study of the indentation of the grids by the asphalt during the implementation and study of the damage of the wires. Realization of model indents.
- Overall, tests have shown that measurements at the laboratory scale are representative of full-scale behavior, provided that industrial production is perfectly controlled. Minor adjustments will be necessary. This makes it possible to envisage passing the test on fatigue and the modeling serenely.
Models for the WST, 4PB, and fatigue test track are being developed.
BCRRA 2017 (Athènes), 2 articles présentés : - In situ damage evaluation of geogrid used in AC pavement //
Wedge Splitting Characterisation of the bond between asphalt layers reinforced with glass
- EATA 2017 : 1 poster accepté et présenté : Experimental evaluation of the interface fracture energy for composite pavements
- ISAP 2018 : 1 article soumis
- CFM 2017 : 1 article présenté : Characterization of Debonding at the Interface
between Layers of Heterogeneous Materials coming from Roads
- Le 2 mars, Maïssa Gharbi a participé au concours «Ma thèse en 180 secondes«.
- Séminaire JERI 08/11/2016 : EPFL Lausanne (P. Hornych)
Road infrastructures construction and renovation in the framework of sustainable development should nowadays include future scarcity issues, such as oil byproducts. Considering the existing road heritage, at least in France, renovation constitutes a major challenge. The ageing of infrastructures requires the development of Ecological reengineering affordable solutions, which allow for total, partial, even gradual, renovation.
In the area of new construction, the question is to develop and implement solutions minimizing environmental and energy impacts, under managed costs, during the construction phase but also throughout the pavement lifespan.
Grids, notably glass fiber grids, are an efficient and economical solution for asphalt pavement stiffening, to increase their lifespan and slow down the coming up to the surface of cracks, as well on new pavements as well as for reinforcement.
Grids are used for reinforcement, to improve the traction performances and cracking resistance. As for every composite product, this is of paramount importance that the support and the matrix constitute a “unique” product in situ. Moreover, this cover should not lose performance during the application and when it is subject to constraints related to stress under traffic loadings. Nowadays, the grids are more and more used to improve the pavement lifespan, but this use mainly lays upon empirical rules, which are based on learnings from past experience.
This project aims at gathering laboratories studies, observations from full size tests and modelings, in order to:
• Improve the grids design: arrangement of threads and resins, opening of the stitch.
• Improve the tests used for the laboratory characterisation of the grids mechanical performances: traction, indentation and fatigue tests on grids, resistance tests during implementation, fatigue tests on reinforced asphalt concrete
• Better understand, through laboratory and full size tests, the impact of implementation conditions on the grids behavior, the sticking of asphalt concrete layers, and their modus operandi in pavement, with various asphalt materials (hot, warm)
• Develop models suitable for describing the mechanical behavior and evaluating the reinforced materials lifespan.
• Verify the possibility of integral recycling of these materials
• Engineer evaluation methods of economical impacts and apply a method for analysing the life cycle assessment to evaluate environmental impacts of the reinforcement process.
As expected results, one can list the optimisation of the grid mechanical properties in the context of existing pavements reinforcement and new pavements, relating experimental studies in laboratory with in situ studies on in situ and fatigue test tracks.
The scientific and theoretical originality lies in the engineering of a model coupling fatigue and damage to predict the influence of the reinforcement grids on fatigue behavior of a reinforced pavement structure.
Special attention will be devoted to the issue of quantification of grid spoiling during its implementation and sticking. This last idea will be the object of a laboratory test.
Finally, the environmental impact of road strengthening by fiberglass grids will be considered from the manufacture of the grid to its full recycling and its use with warm mix asphalts, these latter being set to grow.
Monsieur Cyrille Chazallon (Laboratoire des sciences de l'ingénieur, de l'informatique et de l'imagerie)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
INSA-ICUBE Laboratoire des sciences de l'ingénieur, de l'informatique et de l'imagerie
ICS Institut Charles Sadron
IFSTTAR Institut Français des Sciences et Technologies des Transports, de l’Aménagement et des Réseaux
COLAS COLAS S.A.
6 D SOLUTIONS
Help of the ANR 894,262 euros
Beginning and duration of the scientific project: September 2014 - 42 Months