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https://nap.nationalacademies.org/catalog/27432/critical-issues-in-transportation-for-2024-and-beyond

EFFECT OF STEEL GRIDS ON THE DURABILITY OF THE ROAD

TERASVERKON KAYTTO TIERAKENTEIDEN KOERAKENNUSKOHTEISSA; SYNTEESI.

This is a synthesis of the test results with steel grids in test road constructions, the STEELSYNT project. The behaviour of the reinforcements has been studied in many research projects. The test material for this synthesis has been: the TPPT (Pavement Structures Research Programme) test constructions, the European reinforcement research programme called Reflex and some HVS test projects (like 'Steep slope' or 'Frost test'). HVS (Heavy Vehicle Simulator) is a mobile accelerated loading test facility. The aim of the synthesis was to define the practical benefit of the usage of steel grids concerning following matters: 1) permanent deformations (rutting), 2) cracks caused by fatigue, 3) cracks caused by reflection, 4) cracks caused by frost heave, 5) longitudinal unevenness and other matters. All test results both in laboratory and in field conditions showed that rutting (the depth of the rut) can be remarkably reduced by using steel grids. In average this reduction lies between 40-60%. There are some tests that indicate even 60% reduction of rut depths. The effect of the steel grid is small in structures with thick bound layers or otherwise good bearing capacity. The reduction of rutting of 40%-60% means that the service life of a reinforced pavement is about 50-100% longer than the service life of an unreinforced pavement in respect to rutting. The efficiency of the reinforcement depends on the conditions where it is used. The reinforcement works best in the cases where the bearing capacity of the pavement is low. If the bearing capacity of the pavement is high, reinforcement does not reduce the rate of rutting much. In the tests the surface moduli - which indicate bearing capacity - have been measured with falling weight deflectometer or with Benkelmann beam. The HVS test results indicate that other reinforcement materials than steel can function as well as steel grids in the bound layers. At least the glass fibre reinforcement Polyfelt PGM-G100/100 performed well, even a little better than its reference steel grid. Test results show that steel grid delays fatigue to some extent. In the 'Frost test', where the subgrade was very weak because of thawing, this delay was about 20%-30%. In the Reflex tests a steel grid with the pitch size of # 75 mm delayed fatigue only slightly and a steel grid with the pitch size # 150 mm had no better performance than unreinforced pavement. The calculations in Reflex projects indicate some 5%-10% reduction to the resilient strains in the reinforced pavement compared with unreinforced pavement. According to the statistics (database of Finnish Road Administration) an overlay with a steel grid seems to reduce both rutting and cracking more effectively than an overlay without a grid, when the speed of the cracking or rutting was high before the rehabilitation. The same applies for a grid in the unbound base. The Reflex project prognoses that reflection cracking of a cement bound gravel base can be reduced 35% by steel grids. Some other unspecified research results indicate that cracking due to the widening of the road can be reduced by reinforcements. No amount of this reduction was presented. A steel grid prevents the development of longitudinal frost cracks in the reinforced area according to the TPPT test results and over twenty years of field experience with reinforced and unreinforced structures. The longitudinal cracks usually move to the edges of the road where grid reinforcement ends. Steel grid also mitigates the transverse frost cracking by curtailing the width of the cracks and by preventing the development of small cracks. The grid should be installed in the whole width of the road to prevent cracking caused by frost heave or rutting of a narrow road. If a steel grid is used to reduce rutting of a wide road it should be installed in the whole width of a lane. No overlapping of the steel grid is needed in longitudinal direction to prevent cracks caused by frost heave. On the contrary the space between adjacent grids can be up to 500 mm, if the frost heave is less than 100 mm. If the frost heave is bigger than 100 mm, the grids should be installed with edge joint (close to each other with no space between them). The TPPT test structures show that the frost heave differences in the cross section can be levelled with steel grids. Reflex project recommends that at least 50 mm asphalt layer should be spread upon the steel grid. The used steel grid can be quite light. The researches so far have not found that longitudinal unevenness could be levelled with reinforcements.

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  • Corporate Authors:

    TIEHALLINTO, FINNISH ROAD ADMINISTRATION

    OPASTINSILTA 12 A
    HELSINKI,   Finland  FIN-00520
  • Authors:
    • Korkiala-Tanttu, L
    • Kivikoski, H
    • RATHMAYER, H
    • TORNQVIST, J
  • Publication Date: 2003

Language

  • Finnish

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Filing Info

  • Accession Number: 00970143
  • Record Type: Publication
  • Source Agency: VTT Technical Research Centre of Finland
  • ISBN: 951-803-096-0
  • Files: ITRD
  • Created Date: Mar 5 2004 12:00AM