MAINTENANCE OF CRACKED PAVEMENTS WITHIN THE FORMAT PROJECT

Transcription

1 MAINTENANCE OF CRACKED PAVEMENTS WITHIN THE FORMAT PROJECT M.L. Antunes 1, A. van Dommelen 2, P. Sanders 3, J.M. Balay 4 and E.L. Gamiz 5 (1) Laboratório Nacional de Engenharia Civil, Portugal (2) Rijkswaterstaat, Dienst Weg- en Waterbouwkunde, the Netherlands (3) TRL Ltd. United Kingdom (4) Laboratoire Central des Ponts et Chaussées, France (5) Autopistas del Mare Nostrum S.A., Spain Abstract The FORMAT project (Fully Optimised Road Maintenance) is designed to enhance the efficiency and safety of the European road network by providing the means to reduce the number, duration and size of road works for pavement maintenance purposes. Four topics key to road pavement maintenance form the subject of this extensive research effort: maintenance techniques, cost benefit analysis, safety at roadworks and pavement condition monitoring. Part of the research being conducted includes the assessment of methods for maintaining cracked pavements. This paper focuses on accelerated load testing in full scale facilities at TRL (UK) and LCPC (France) of treatments that will address cracking and on the construction of a pilot trial on a motorway in Spain. The maintenance treatments being evaluated in the accelerated load tests are wheel track inlays of high modulus binder course under a thin surfacing at TRL and a thin surfacing incorporating a geogrid at LCPC. In the pilot trial on a motorway in southern Spain, the construction of asphalt overlays incorporating geogrids laid over jointed concrete pavements will be evaluated. This paper describes the experiments conducted and presents the results achieved so far. 1. Introduction The FORMAT (Fully Optimised Road Maintenance) project is supported by the European Commission, under the 5th Framework Programme, Key Action Sustainable Mobility and Intermodality. It started in February 2002, with a planned duration of 3 years. Twenty organisations including national road owners, national highway research laboratories, universities, highway contractors and international trade associations from fourteen European countries and from the USA are involved. The aim of this research project is to enhance the efficiency and safety of road maintenance works by appropriate planning, timing and execution of work zone operations.

2 Four topics, key to road pavement maintenance form the subject of this extensive research effort are conducted within four scientific Work Packages [1]: Pavement maintenance techniques and procedures (WP 3 Technology ); Associated cost-benefit analysis methods (WP 4 Cost Benefit Analysis ); Safety at work sites (WP5 Safety ); High speed monitoring of pavement condition (WP6 Monitoring ). The objective of FORMAT WP3 Technology is to identify and assess innovative maintenance techniques and procedures for maintaining both bituminous and concrete roads, which will reduce user delays and safety hazards at road works. The research being conducted within Work Package 3 includes the assessment of selected maintenance techniques for cracked flexible pavements using Accelerated Loading Tests (ALT) performed at TRL and LCPC facilities and a pilot trial concerning different overlay options for a cracked jointed concrete pavement on an actual pavement site in Spain. This paper describes these research studies. 2. Selection of maintenance treatments for evaluation The work started with the assessment of the main reasons for performing maintenance works in Europe, identifying the main deterioration mechanisms in different types of pavement structures (flexible, rigid and composite), and the condition indicators that are used to describe the condition of the pavements and to evaluate the need to perform maintenance works. Cracking was identified as one of the mechanisms with particular relevance to European road pavements. A list of maintenance techniques and procedures for application that are considered best suited for the main types of problems identified was collated based on a database of maintenance treatments developed by COST Action 343 [2], with further input provided by the FORMAT team members. The efficiency of these treatments for rectifying the problems associated with the deterioration mechanisms arising in different types of pavements were noted when information was available. The most promising maintenance treatments and procedures for application were selected for evaluation in Accelerated Loading Tests (ALT) and in pilot studies. These were treatments that were considered to have potential for correcting the main defects in the principal European road network, and that were considered as innovative by the FORMAT team [3]. The following three types of maintenance treatments were among those selected for evaluation in the ALT and in the pilot studies: the use of a thin bituminous surface incorporating a geogrid, placed over a cracked flexible pavement; the use of wheel-track inlays with high modulus binder course, which can be applied both for correcting cracking in the wheel path and rutting in flexible pavements; a thin surfacing is applied on the full width of the pavement after the inlay has been performed. the use of cement grouting under cracked concrete slabs for strengthening of the existing pavement, followed by the placement of a bituminous overlay with or without a geogrid. The performance the first two selected maintenance treatments is being assessed relative to a well known conventional treatment, laid alongside the treatments being evaluated. The third treatment, concerning concrete slab maintenance, is not possible to evaluate in the ALT, but it will be applied in a pilot test. Given the limited timeframe of the

3 FORMAT project, the assessment concentrates on the feasibility, speed of application and on the improvement in pavement condition. Traffic and safety aspects during application of the treatment are also being assessed in this pilot test. 3. Design of the Accelerated Loading Test experiments In the FORMAT project it was decided to test each innovative treatment in parallel with a conventional treatment for its effectiveness to correct distress, its performance under repeated loading and their possible side-effects. The evaluation is based on the following performance indicators: a) cracking; b) other surface defects; b) profile (transverse, longitudinal); c) deflection; d) texture; and e) skid resistance. The tests are being complemented with further investigations, such as saw-cut along transverse profiles in the tested pavement to investigate in-depth distresses. Due to differences in the nature of both treatments, the design of the two cracking experiments differs in practical details. In the experiment at LCPC a treatment is being tested which is intended to be applied on a pavement with existing cracking, without removing the cracked layers. Therefore the design of the experiment includes sufficient loading of the pavement to induce this cracking before application of the innovative and reference treatments. In this experiment it is important to record precisely the moment of reappearance of cracks and their development, which will mean that frequent inspection for possible cracking is a key element in the set-up of the experiment. The experiment at TRL concerns a treatment, which involves the full replacement of cracked or rutted surface layers in the wheel tracks of well designed pavements, with a high modulus binder course. With this replacement, all cracks will be removed. Therefore it is not necessary to try to induce cracking by trafficking the pavement before application of the treatment. Furthermore it is clear that both the wheel path inlay and the conventional full width inlay, which serves as reference, will fully correct the existing surface cracking. Extensive research at TRL has demonstrated that, for the type of pavement structure being tested, the cracks initialise at the surface and propagate downwards usually only as deep as the binder course. The main questions are whether the long term reappearance of surface cracking is different, and if the treatment is sufficiently feasible and has no negative side-effects. 4. Accelerated Loading Tests at TRL 4.1 ALT Facility The TRL indoor Pavement Test Facility (PTF) is a linear test facility with test pit dimensions 25 m x 10 m x 3 m. The size of the test facility allows use of full-size construction plant Typically a pavement test section is 2.4 m wide, 10 m long and is often split into 2 or 3 sections along its length. Testing is carried out at ambient temperature or controlled to a maximum of 40 O C. Loading can be varied between 23 kn 100 kn, with a lateral wander of +/- 450 mm, and may be performed with either a Single or Dual wheel assembly. The speed of loading can be varied between 1 and 20 km/h. 4.2 Objective of the trial The objective of the testing is to evaluate the performance of a high modulus asphalt binder course, applied as an inlay to the wheel path alone, plus a thin asphalt wearing

4 course. This treatment is being trialled principally to provide an approved treatment for wheeltrack rutting or cracking, two of the main problems on the European road network. If successful, the treatment will result in a saving in materials, time and energy over the more usual full lane width treatment. A new flexible pavement structure has been built, consisting of 300 mm of asphalt laid on a foundation comprising a clay subgrade and a granular sub-base. The layout of the test section is shown in Figure 1. 30mm Masterpave Thin Wearing Course 60mm Binder course 210mm HDM Base course HDM 50 - HMB 15 - Heavy Duty Macadam with 50 pen grade binder High Modulus Binder course with 15 pen grade binder HMB15 Wheelpath Inlay HDM50 HMB15 Full Lane Width Inlay Fig. 1 Test section at TRL Figure 2 shows the construction of the test section. The width of the weel track inlay is 1 m. Experiments carried out in Austria have shown that this width will cover almost 95% of the truck wheel passes [4]. 4.3 Testing Testing is performed using a super single 40 kn wheel load on two wheel tracks. The wheel loads have a lateral wander which simulates the trafic distribution, over a width of ± 350 mm. On the first wheel track the performance of the HMB material is tested and directly compared to that of the adjacent HDM material. On the other test track, wheel loads is applied to the wheel track inlay treatment which will test both the ability of the HMB material to resist loading and the construction configuration itself. Fig. 2 Construction of the wheel track inlay at TRL ALT facility

5 5. Accelerated Loading Tests at LCPC 5.1 ALT Facility The LCPC facility comprises 3 circular test tracks, with dimensions 110 m x 6 m x 3 m, located outside, with no control of environmental conditions (temperature, rainfall). However, the track which will be used for the FORMAT project allows for control of the water table in the test pit. Several wheel arrangements can be used, namely single, dual or tandem wheels. The wheel load can vary from 45kN on a single wheel up to 135 kn on a tridem single. The maximum test speed is 70 km/h and lateral distribution of loads can be controlled. Figure 3 shows the LCPC test facility. Fig 3 LCPC Accelerated Load Test facility 5.2 Objective of the trial The repair of cracked bituminous pavements is often done through the application of bituminous overlays, whose thickness will depend on the amount and depth of cracking in the existing layers. For conventional overlays, the minimum thickness is generally 40 mm. This trial aims at the evaluation of a thin overlay (25mm thick) reinforced with a geogrid. The geogrid is expected to increase the resistance of the overlay to reflective cracking. 5.3 Testing A conventional flexible pavement structure was built at the LCPC test track. This section is being loaded until the pavement is damaged. If needed, the water table will be raised is order to achieve the desired level of cracking in the worn pavement. Three sections will then be built, with different maintenance techniques, as illustrated in Figure 4. The thin overlay reinforced with geogrid will be tested alongside with a thin overlay without any reinforcement and a conventional 40 mm thick bituminous overlay. 10m 10m 10m Conventional Very thin bituminous overlay bituminous overlay 4 cm thick without geogrid Fig. 4 Test sections at LCPC Very thin bituminous overlay 2.5 cm incorporating geogrid

6 6. Analysis of ALT results In the experiment at LCPC, the cracks before application of the treatments will be mapped and their severity will be recorded. The extent of cracking will be expressed as the total length of cracks for each severity class (light, moderate and severe). Ideally, the three treatments will be applied in such a way that the extent and severity of cracks in the underlying structures is similar. During the ALT after application of the treatments, frequent inspections are performed on each section to detect new cracks and to record their development and severity as a function of time and loading. The effectiveness of the innovative treatment will be based on a comparison of the rate and severity with which the cracks reappear and redevelop for the innovative and for the conventional treatments. The thin unreinforced treatment will not be directly used for assessing the effectiveness but will give the possibility to see the effect from the geogrid separately from the effect of different overlay thickness. Additional analysis will concern development of bearing capacity (FWD), skid resistance, rutting, texture (sand patch), longitudinal unevenness and drainability, to determine if the treatment has any side effects. It should be noted that side effects can be both negative (i.e that the treatment is detrimental for other pavement properties) or positive (meaning that the treatment is also effective in improving other pavement properties). The TRL experiment will primarily focus on possible side-effects of the treatment (for which especially the construction of the two longitudinal vertical joints and the achieved material quality close to the joints will be critical), the feasibility of the treatment and the development of guidance on good practice for inlaying. This will be mainly based on numerous tests on the bituminous materials, including compositional analysis, indirect tensile stiffness tests, density profile of cores (using Xray scanner), laboratory wheel tracking, repeated load asphalt test with vacuum confinement (VRLAT), ISTM on cores taken across edges of trench and nuclear density measurement across the inlay and at the interface of trench and pavement. At the conclusion of the trial, a transverse section will be cut across each section of the pavement to obtain direct information about the quality of the joint and possible distress. The ALT testing will play a less important role (it is mainly intended to assess the rutting performance of the treatment). However it should provide an indication of the effect of the vertical joints on longitudinal cracking in the surface layer above it, or of the possible effect of a lesser compaction near the joints on permanent deformations. This last aspect may follow from the rutting experiment by comparing the section with high modulus wheel path inlay with the section with full width high modulus inlay. 7. Pilot study on maintenance of jointed concrete pavements 7.1 Design of the experiment A 3 km long motorway stretch under the responsibility of AUMAR (Autopistas del Mare Nostrum), in Spain, was selected as a pilot test section. The pavement is 25 years old and consists of 0,25 m thick jointed unreinforced concrete slabs, with no dowel bars, placed over a 0,15 m lean concrete base and a 0,50 m gravel sub-base. At present 76% of the pavement slabs are severely cracked, which is attributed to poor foundation support. The maintenance technique selected for this pavement consists of the following steps:

7 - to improve the slab support, therefore eliminating the cause of cracking, making the best possible use of the existing pavement structure; - to place an overlay that will increase, to a certain extent, the pavement s bearing capacity and will restore the riding condition. Within a 3 km section, 3 sub-sections were defined, for application of each of the three maintenance options summarised in Table 1. Table 1 Maintenance options to be trialed in the pilot study Option Description Nº Phase 1 Phase 2 1 Crack and joint Diamond grinding + Joint sealing ; no overlay 2 sealing + Foundation Bituminous overlay using conventional mixtures (70 mm thick) 3 stabilisation by grouting Geotextile + Bituminous overlay using modified binders (60 mm thick) The assessment of the different solutions will be performed by visual inspection and crack mapping, longitudinal unevenness and FWD testing before and after each of the construction phases. The speed of crack propagation for the tested solutions will be compared with the existing data on performance of other options, previously collected by AUMAR. Figure 5 gives an example of such data. % Reflective cracks at the surface 100% 90% 80% 70% 60% 50% 40% 30% Option Nº 1 - "Vandellos" Option Nº 2 - "All sections" Option Nº 2 - "Castellón" Option Nº 2 - "Vandellos" Option Nº 4 - "Vandellos" Option Nº 3 - "Vandellos" 20% 10% 0% Maintenance option Nº1 - geotextile +100mm asphalt overlay Millions of commercial vehicles Maintenance option Nº2-100mm asphalt overlay Maintenance option Nº3-20mm levelling + geotextile + 60mm asphalt overlay Maintenance option Nº4-20mm levelling + 20mm sand-bitumen + 40mm asphalt Fig. 5 Existing data on crack propagation 7.2 Application of the maintenance treatments The first phase of application of maintenance treatments to the pilot test section is taking place between April and June 2003 and consists of the following operations: - Hole drilling, either in the slabs of the slow lane or in the shoulder, followed by cleaning operations; - Joint and crack sealing, preferably with durable materials; - Cement grout injection at controlled pressure (Figure 6) - Cleaning. The second phase takes place in September October This phase will consist in the conclusion of the treatments for sealing and improving pavement evenness,

8 combined with some degree of strengthening, in the case of the solutions with bituminous overlays (see Table 1). Fig. 6 Cement grout injection 8. Final remarks This paper describes some experiments undergoing in the frame of the FORMAT project, which include the assessment of methods for maintaining cracked pavements through accelerated load testing in full scale facilities of pavements where selected maintenance treatments are applied. The research also includes the construction of a pilot trial in Spain, concerning maintenance treatments for cracked concrete pavements. At the time the paper was delivered, application of the maintenance treatments was ongoing and results were not yet available concerning the performance of the selected treatments. During the conference, results from the studies will be presented. 9. References 1. FORMAT. Inception Report, FORMAT Deliverable Report D1, July 2002.DWW Delft, The Netherlands 2. COST Action 343 Reduction in Road Closures by Improved Maintenance Procedures Final Report of Working Group 1: Maintenance Options, European Commission. 3. FORMAT, Selection of Maintenance Techniques and Procedures for Implementation, FORMAT Deliverable Report D2, January DWW Delft, The Netherlands 4. Blab, R. Analytical methods for modelling deformation behaviour of flexible pavements (in German), ISTU Wien, 2001