Track sub-structural stiffness is a major factor in the deterioration of track geometric quality as a result of the rail traffic that passes over it. Whilst track geometric quality has been measured at normal line speed for many years, determination of the condition of the substructure has only been possible at discrete locations using stationary devices or invasive manual inspection. This paper describes the problems caused by differential track system stiffness and progress with research that seeks to identify and implement a suitable technology that will enable the measurement of track structural stiffness at normal linespeed. Acquisition of this information on a production basis and use of it in conjunction with other condition data collected routinely offers Network Rail the opportunity to progress towards more effective targeting of track maintenance and renewal resources through greater knowledge of whole track system condition. (6 pages)
This report describes a series of road trials of two proprietary thin surfacing techniques, UL-M (1 site) and Safepave (7 sites), and summarises the performance of the materials during their early service life. Most of the claims for the materials appear to be confirmed, but there are reservations regarding surface texture. Visual surveys on these heavily trafficked sites generally show significant consolidation of material in the wheel-paths; however, low-speed (50 km/h) skidding resistance measured using SCRIM is unaffected and is being maintained at an acceptable level in all cases. Monitoring to date shows generally good integrity and adhesion of the surfacing. However, isolated areas of material loss have been observed, particuarly at junctions, on some Safepave sites where turning vehicles have caused scuffing and pull-out of material. Where Safepave was used on a jointed concrete pavement, the technique of saw-cut and seal at expansion joints appears to be the most effective method for minimising reflective cracking at joints. On some of the flexible construction Safepave sites, no pre-treatment was carried out to cracks in the surface or to other defects and consequently many defects have re-appeared, necessitating further maintenance. Preliminary maintenance and minor repairs prior to the application of Safepave will assist in ensuring maximum life from the new surfacing. (A)
The initial research in the UK on the performance of the crack and seat process in inhibiting reflection cracking in asphalt overlays on jointed unreinforced concrete pavements and on pavements with cement-bound roadbases was reported by Potter and Mercer in the 3rd RILEM conference. Since then, 3 more years of monitoring the condition of the trials has confirmed the good performance of the treatment. TRL has developed an analytical structural design method for determining the thickness of asphalt overlay required on cracked and seated jointed unreinforced concrete pavements to carry the anticipated future traffic. Designs have been produced for use on UK motorways and trunk roads carrying cumulative traffic levels up to 100 million standard 8.2 tonne axles. This paper presents the performance of the research trials that has led to the developmet of the UK crack and seat specification. The on site monitoring and analysis necessary for the successful application of the technique is also described. It also demonstrates how, with effective partnering, validated research results can be implemented quickly for the benefit of the whole community. The analytical structural design method is described and typical design examples are presented. (A)
Crack and seat has become an established technique for the cost-effective rehabilitation of flexible composite roads in the UK. However, as the treatment requires exposure of the underlying lean concrete base, it has, in the past, required the transportation and disposal of large amounts of asphalt planings and the placement of a new hot mix asphalt overlay. Cemex UK Construction Services Limited (Cemex) were appointed as the main contractor for a major crack and seat maintenance scheme on the A46 trunk road in Warwickshire. In order to improve the sustainability of the maintenance treatment, Cemex sought to incorporate a layer of ViaFoam Cold Recycled Base Material (CRBM) in the new overlay. This material would be produced by Cemex in an ex situ process utilising the asphalt planings arising from the crack and seat phase of the scheme. As this was believed to be the first time in the UK that a recycled material has been used over a crack and seat treated cement bound layer, verification was required that the proposed construction would satisfy the design requirements for both components. This report contains details of the design approach used, observations during the construction of the scheme, presents the results of the in situ and laboratory testing and presents a discussion of potential future applicability of the combined treatment. An estimation of the reduction in CO2 emissions owing to the use of the combination of crack and seat and ViaFoam in comparison to two conventional alternatives is also presented. (A)
Thin surfacing systems, as the term is currently understood, were introduced into the United Kingdom in 1991. On some sites used for the system to gain Highways Agency approval, the thin surfacing systems are approaching the end of their assumed design lives whilst others have only been in service for just over two years. Therefore, it is opportune to begin to evaluate information collected from these sites to establish a better understanding of their design life. In this report, published information and the data currently available from the trial sites has been reviewed to confirm the suitability of proprietary thin surfacings for use in the United Kingdom. For the review, the systems have been grouped into five general categories with data on early sites being available from four of the categories. Selected sites are being monitored by visual inspection, by SCRIMtex surveys and by measuring recovered binder properties from cores. This report gives the results, and their analysis, after the first (of three) year of monitoring, from which tentative estimates of the average service lives of four different categories of thin surfacing system have been proposed. (A)
The 2007 annual UK Falling Weight Deflectometer (FWD) correlation trial was held on the 24th and 25th April 2007 at TRL, on behalf of the Highways Agency. This is the eighth mandatory FWD correlation trial to be held in the UK with the objective being to monitor the performance of all FWDs (and Heavy Weight Deflectometers, HWDs) operating on the HA trunk road network. The performance of seventeen individual machines was assessed by examining and monitoring the results from the machines operating on specified test sections of the TRL Small Roads System (SRS). Only machines that are considered to have demonstrated satisfactory performance in the correlation trial are subsequently approved for use on the HA trunk road network. This report describes the conduct and findings of the correlation trial. (A)
This report is prepared for Defence Estates (DE) of the Ministry of Defence (MoD) under contract number WS21/4013: 'Provision of research and consultancy services'. TRL Limited (formerly the Transport Research Laboratory) were commissioned by DE to prepare guidelines for crack and seat maintenance of pavements at DE airfields and thus disseminate the knowledge that has been gained through full-scale trials that have taken place at RAF Coningsby and RAF Lyneham. The overall purpose of the guide is to provide enough information to enable those engineers not familiar with crack and seat technology to specify and use the technique effectively for the maintenance of unreinforced concrete pavements and flexible composite pavements at airfields. A background is provided which includes a description of the mechanisms that result in the occurrence of reflection cracking and options for maintenance. The crack and seat methodology and procedures are detailed and a specification and notes for guidance are given for the use of crack and seat on airfield pavements. Detailed guidance is given to help DE project managers supervise and check the works on site. (A)
One of the headline objectives of the UK Highways Agency (HA) is to reduce congestion and improve road safety whilst undertaking highway maintenance. To this end the HA has invested significant resources in appropriate technology to collect road condition and structural data at traffic speed. Surface condition surveys of the English strategic road network are already carried out using survey vehicles operating up to 100 km/h, however until recently there was no traffic speed facility for measuring the structural condition of the road network. Deflection measurements remain the most reliable non-destructive method for determining the structural condition of flexible pavements and therefore in 2000 the HA instructed TRL to examine available technology for measuring deflection at traffic speed. In 2005 they followed this up by asking TRL to procure a prototype Danish Traffic Speed Deflectometer (TSD), on their behalf, and tasked them with developing it into a survey tool capable of providing an estimate of structural condition and implementing network level surveys on the English Strategic Road Network. This paper presents the long and challenging process of taking an innovative technique, assessing its effectiveness, developing it into a robust approach, and applying it to a live road network.
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