Recent evidence has demonstrated that the deterioration of thick, well constructed flexible pavements is not structural and that deterioration generally starts at the surface in the form of cracking and rutting. Such behaviour of long life roads emphasises the need for accurate repeatable and economical methods of monitoring and correcting these defects before they affect the structural integrity of the pavement. This paper describes the development of a system for the automatic detection of surface cracking. Automatic analysis depends on obtaining uniformly bright images of high quality. These are collected at survey speeds of up to 80 km/h using novel linescan video cameras operating with artificial illumination. Surveys can thus proceed either by day or night. Purpose built hardware on board the survey vehicle assembles the line images into video frames prior to automatic processing to identify cracks. Firmware is used to carry out part of this processing in real time, the remainder of the processing being carried out off-line on a PC. In such a system the correct application of defect information depends on accurate knowledge of its location. In the UK such referencing is currently provided by accurately measuring the distance travelled with respect to automatically recognised studs on the road surface. An improved system using GPS is also being investigated. Such a system provides enormous benefits by reducing considerably the need for hazardous and relatively expensive slow speed visual condition surveys as well as eliminating the inconsistency and subjectivity of manual interpretation. This development will be a major contribution to the effective monitoring and maintenance of flexible pavements. For the covering abstract, see IRRD E100539.
This paper describes the development and operation of a practical system for the collection of images of the road pavement surface at traffic speed and the automatic identification of cracks appearing in those images. In view of the large number of images collected and the need for reliable and consistent results, automatic analysis is required. A process, based on a combination of on-board real time and off-line image processing, has therefore been devised which identifies cracks at speeds close to real time. Such automatic analysis depends on obtaining images of high quality and uniform brightness and this is achieved using novel line scan cameras and controlled artificial illumination. Surveys can thus proceed during either day or night. Purpose built hardware assembles the line images into video frames prior to processing. The correct application of the information provided by the system depends on accurate knowledge of crack location. In the UK location referencing is currently provided by accurately measuring the distance travelled with respect to automatically recognised studs on the road surface and laser-read bar codes beside the road. Improved methods using buried radio tags and GPS are now being investigated. Location referencing information based on these methods is automaticailly stored in the hidden lines of each video frame collected by the cameras. Such a crack monitoring system provides enormous benefits by reducing considerably the need for hazardous and relatively expensive slow speed video condition surveys as well as eliminating the inconsistency and subjectivity of manual interpretation. (A) For the covering abstract see IRRD E100847.
This paper summarises an investigation by the Transport and Road Research Laboratory (TRRL) of the result of comparative trials of falling weight deflectometer (FWD) systems used by four survey contractors in the UK. The main purposes of this study of a range of road surfaces were to: (1) provide information on the consistency of different FWD systems, with respect to their estimates of pavement layer stiffness and residual life and their recommendations for maintenance treatments; (2) compare the FWD estimates of residual life and recommended treatment with those provided by current practice in the UK. Each survey contractor was allocated half a day to survey each of four sites, and was requested to evaluate pavement layer stiffness at each test location. Results were obtained on: (1) deflection measurements; (2) bound layer stiffness; (3) foundation stiffness; (4) residual life; (5) recommended maintenance treatments. The deflection measurements, made by the different FWDs tested, showed good consistency. It was found that an indication of layer stiffness could be obtained using the services of the four survey contractors. The present FWD design methods predicted residual lives significantly longer than, and often strengthening treatments significantly different from, reference values based on the TRRL design method using delfectograph measurements. (TRRL)
Effective use of the large sums of money now being spent world wide on strengthening roads requires a design system capable of matching spending to needs; it should establish priorities for work and also the nature and extent of strengthening on the roads selected for treatment. Economical solutions can generally be obtained if a relatively thick overlay is applied before the structural integrity of the road pavement is seriously impaired, when the road is in a critical and not a failed condition. The transport and Road Research Laboratory has therefore developed a method for the planning of structural strengthening that can predict the remaining life of the pavement so that the strengthening can be timed to coincide with the onset of critical conditions; the method can also design the necessary thickness of overlay required to extend the life of a road to carry the predicted future traffic. Papers to previous conferences have described earlier stages in the development of the method from a systematic study of the relation between the deflection under a loaded wheel and the performance of pavements in the laboratory's many full-scale road experiments; the work has been supported by detailed observations of the deflection behaviour of pilot-scale pavements and by analytical techniques. This paper outlines the method concentrating on the latest work to complete its development, evidence of its validty and examples of its use. Extensive experimental data is presented that has been used to develop charts relating deflection to pavement temperature so that deflections measured over a range of temperatures on different pavements can be corrected to equivalent design deflections at a standard temperature of 20 deg c. The development of pavement deterioration and its relation to deflection levels is illustrated, in particular the increasing uncertainty as pavement failure approaches, uncertainty that may be avoided by suitable definition of critical conditions and timely maintenance intervention. Typical evidence is presented defining experimental relations between deflection and critical life. The information has been consolidated into design charts for the prediction of remaining pavement life to the onset of critical conditions; separate design charts have been produced for the four main types of road base used in the United Kingdom. Measurements on a number of in-service pavements demonstrate the validity of the charts over a wide range of traffic. Observations of the reduction in deflection achieved by different types of overlay material are presented. These results have been combined with information on the performance of overlaid pavements to produce overlay design charts. Levels of probability of achieving a particular residual life or, in the case of an overlay, an extension of life are defined on the design charts. Maintenance decisions based primarily on deflection but supported by other information have been made on many
A SERIES OF TRIALS HAS BEEN UNDERTAKEN TO INVESTIGATE (1) THE MANUFACTURE OF MASTIC ASPHALT ON A CONVENTIONAL ROLLED- ASPHALT MIXING PLANT WITH AN ADDITIONAL DRYER, AND (2) THE MACHINE-LAYING OF MASTIC ASPHALT. BOTH WATERPROOFING-GRADE MASTIC ASPHALT (BASED ON B.S. 988:1966) AND PAVING-GRADE MASTIC ASPHALT WITH 42.5 PER CENT OF COARSE AGGREGATE (BASED ON B.S. 1447:1962) HAVE BEEN USED IN THESE TRIALS. IT HAS BEEN DEMONSTRATED THAT IT IS FEASIBLE AND PRACTICAL TO MANUFACTURE MASTIC ASPHALT ON AN ASPHALT MIXING PLANT WITH A NORMAL MIXING CYCLE. IT IS ALSO POSSIBLE TO LAY MASTIC ASPHALT MECHANICALLY, ALTHOUGH THERE ARE PROBLEMS IN COMBATING TRANSVERSE FLOW OF THE HOT MATERIAL WHEN LAYING ON A CROSS-FALL AND THE LONGITUDINAL JOINT TRENDS NOT TO BE COMPLETELY SATISFACTORY; THIS IS A QUESTION OF LEVEL AND APPERANCE, THERE BEING NO PROBLEM OF OBTAINING A WATER-TIGHT JOINT. THE EFFECT OF 'BLOWING' IN RELATION TO THE NATURE OF THE SUBSTANCE HAS BEEN BRIEFLY STUDIED. A REVIEW IS MADE OF THE REMAINING STEPS IN THE RESEARCH WHICH ARE CONSIDERED NECESSARY TO PRODUCE VIABLE PROCESSES FOR THE MANUFACTURE AND LAYING OF MASTIC ASPHALT AT A RELATIVELY HIGH RATE OF OUTPUT. /A/RRL/
In the Wibau Dustless (SL) Asphalt Plant the binder is added to the aggregate before it is dried and heated in contrast to a conventional plant in which the sequence of events is reversed. This new process virtually eliminates the discharge of dust into the atmosphere without the need to provide expensive dust collecting equipment and has other possible economic advantages deriving from its ability to carry out production in two stages. A group representing the Department of the Environment's Transport and Road Research Laboratory and Engineering Intelligence Division, and the asphalt and coated macadam association have visited five plants in western Europe in order to assess their ability to produce satisfactory bituminous materials. It was found that a wide range of dense materials containing penetration grade bitumen binders was being produced satisfactorily on the Wibau SL plant at output temperatures above 120 degrees c. This suggests that the process could be employed to manufacture many of the dense bituminous mixtures used in Great Britain. Although the limited evidence available suggested that materials produced by the SL process should have an adequate road performance, for full acceptance further evidence of the performance under traffic is required. The use of the process for a wider range of materials and its use in the two-stage form requires further investigation. /Author/TRRL/
A European Long-Life Pavements Group (ELLPAG) has been formed under the auspices of FEHRL (Forum of European National Highway Research Laboratories) to report on the current state of knowledge on long-life pavements in Europe in particular on the very practical issue of how to design, build and maintain pavements to give long structural lives. This paper summarises the findings of the first 12 month phase of the project which has delivered a report reviewing the current state-of-the-art of fully flexible long life pavements based on the combined knowledge of the European pavement community. The report includes chapters on new pavement design, assessment and upgrading, maintenance and treatment design, economics and, finally, identifying knowledge gaps. Future phases will look at the state-of-the-art of all other major pavement types as well as promoting research programmes to solve the knowledge gaps identified. The group is funded by the members' respective Road Administrations. For the covering abstract see ITRD E121480.
The UK Highways Agency Road Research Information System (HARRIS) is described. This system which operates at traffic speed, provides an economical means of automatically condition surveying roads with special reference to the detection of cracks from 2mm wide. The HARRIS prototype vehicle and the vehicle developed to carry out the traffic-speed condtion surveys, the Road Assessment Vehicle (RAV) are described. Data are collected on longitudinal profile, road evenness and texture depths as well as cracking. Measurements from the RAV will be downloaded, verified and linked with the Highway Agency's road referencing system using software developed by the Highways Agency. The data will be fed into the Highways Agency Pavement Management System (HAPMS) which is currently under development. For the covering abstract see ITRD E118788.
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