Special formwork avoids scabbling

The task

Construction of large concrete structures.

The problem

A construction company was awarded a contract to build one of the stations for the London Underground Jubilee Line Extension. The station design included a reinforced concrete base slab 300 m long, 25 m wide and 3 m deep. The slab was cast in situ in 43 sections, each 7 m long. The sections were cast one after another using the previous section to support one side and a specially constructed formwork stop end to support the other. With this method of construction it is important that the new concrete makes an effective bond with the old. When wooden formwork is used, this bond can only be achieved by removing the top surface of the concrete to reveal the aggregate underneath. This is often done with impulsive tools in a process known as scabbling. In this case, the tools were used for about 2 hours per day and exposed operators to high vibration magnitudes (typically 18 m/s2). At that work rate, each stop end would have taken approximately eight worker shifts to scabble with a vibration exposure well above the limit value.

The solution

The company used an expanded metal material to construct the formwork for the stop end mating surfaces. The material was ribbed and featured bent tabs of mesh which, when concrete was poured behind it, become embedded in the concrete, forming a bond. The formwork was left in place once the concrete had cured and when the next section was poured, it formed a bond with the outer surface of the expanded metal that was as strong as a traditional scabbled joint. No scabbling was necessary.

Scraping away excess material during pouring

Scraping away excess material during pouring

Example of in situ cast concrete showing expanded metal formwork

Example of in situ cast concrete showing expanded metal formwork

The result

  • The operators were not exposed to any vibration.
  • It was installed more quickly than using wooden formwork as it allowed the next section of concrete to be poured before the previous section was fully cured (set).
  • Noise and dust levels were also reduced.

Link URLs in this page

  1. Vibrationhttps://www.hse.gov.uk/vIBRAtIon/index.htm
  2. Hand arm vibrationhttps://www.hse.gov.uk/vIBRAtIon/hav/index.htm
  3. About this websitehttps://www.hse.gov.uk/vIBRAtIon/hav/about.htm
  4. Key messageshttps://www.hse.gov.uk/vIBRAtIon/hav/keymessages.htm
  5. Worried about your handshttps://www.hse.gov.uk/vIBRAtIon/hav/yourhands.htm
  6. Overview - Advice for employershttps://www.hse.gov.uk/vIBRAtIon/hav/advicetoemployers/index.htm
  7. Employers responsibilitieshttps://www.hse.gov.uk/vIBRAtIon/hav/advicetoemployers/responsibilities.htm
  8. Assess riskhttps://www.hse.gov.uk/vIBRAtIon/hav/advicetoemployers/assessrisks.htm
  9. Overview - How to protect workershttps://www.hse.gov.uk/vIBRAtIon/hav/advicetoemployers/protect.htm
  10. Control riskhttps://www.hse.gov.uk/vIBRAtIon/hav/advicetoemployers/controlrisks.htm
  11. Information and traininghttps://www.hse.gov.uk/vIBRAtIon/hav/advicetoemployers/information.htm
  12. Health surveillancehttps://www.hse.gov.uk/vIBRAtIon/hav/advicetoemployers/healthsurveillance.htm
  13. Overview - Good practicehttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/index.htm
  14. Overview - Foundrieshttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/foundries/index.htm
  15. Eliminate fettling by improving casting qualityhttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/foundries/fettlingelimination.htm
  16. Machining as a substitute for fettlinghttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/foundries/machining.htm
  17. Automatic fettlinghttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/foundries/automaticfettling.htm
  18. Jig-mounting of grindershttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/foundries/jigmounting.htm
  19. Semi-automatic cut off machinehttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/foundries/cutoffmachine.htm
  20. Isolated casting cut offhttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/foundries/isolatedcasting.htm
  21. Installation of hydraulic cropping machinehttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/foundries/hydrauliccropping.htm
  22. Shell knockout 1https://www.hse.gov.uk/vIBRAtIon/hav/campaign/foundries/castingshell.htm
  23. Shell knockout 2https://www.hse.gov.uk/vIBRAtIon/hav/campaign/foundries/contactcastingshell.htm
  24. Hydraulic pushouthttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/foundries/furnaceliningremoval.htm
  25. Ladle slag chippinghttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/foundries/chippingslag.htm
  26. Overview - Constructionhttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/construction/index.htm
  27. Preparing a code of practicehttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/construction/tunnelling.htm
  28. Construction Industry Council guidancehttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/construction/cicguidance.htm
  29. Mounted breakerhttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/construction/mountedroadbreaker.htm
  30. Directional drillinghttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/construction/directionaldrilling.htm
  31. Crushing concretehttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/construction/crushingconcrete.htm
  32. Bursting concretehttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/construction/burstingconcrete.htm
  33. Diamond wire cuttinghttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/construction/diamondwire.htm
  34. Water jettinghttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/construction/waterjetting.htm
  35. Codes of Practice from the Water Jetting Associationhttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/construction/codeofpractice.htm
  36. Grit blastinghttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/construction/gritblasting.htm
  37. Paint-on retarderhttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/construction/paintonmaterial.htm
  38. Special formworkhttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/construction/specialformwork.htm
  39. Overview - Steel fabricationhttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/fabrication/index.htm
  40. Machininghttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/fabrication/cncmachining.htm
  41. Laser cuttinghttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/fabrication/lasercutter.htm
  42. Plasma cuttinghttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/fabrication/plasmacutting.htm
  43. Noise reduction in the ship repair industry – research report 1992https://www.hse.gov.uk/vIBRAtIon/hav/campaign/fabrication/noisereduction.htm
  44. Abrasive blastershttps://www.hse.gov.uk/vIBRAtIon/hav/campaign/fabrication/abrasiveblasters.htm
  45. Overview - Regulationshttps://www.hse.gov.uk/vIBRAtIon/hav/regulations.htm
  46. Inspector briefinghttps://www.hse.gov.uk/vIBRAtIon/hav/inspectorbriefing.htm
  47. Overview - Resourceshttps://www.hse.gov.uk/vIBRAtIon/hav/information.htm
  48. Publicationshttps://www.hse.gov.uk/vIBRAtIon/hav/publications.htm
  49. Researchhttps://www.hse.gov.uk/vIBRAtIon/hav/research.htm
  50. Statisticshttps://www.hse.gov.uk/vIBRAtIon/hav/statistics.htm
  51. Useful linkshttps://www.hse.gov.uk/vIBRAtIon/hav/links.htm
  52. Vibration calculatorhttps://www.hse.gov.uk/vIBRAtIon/hav/calculator-guide.htm
  53. Overview - Case studieshttps://www.hse.gov.uk/vIBRAtIon/hav/casestudies/index.htm
  54. (HAVS) in two motor companieshttps://www.hse.gov.uk/vIBRAtIon/hav/casestudies/enforceex.htm
  55. Monitoring exposure to Hand-Arm Vibrationhttps://www.hse.gov.uk/vIBRAtIon/hav/casestudies/mhav-carlwest.htm
  56. Overview - Supply project eventshttps://www.hse.gov.uk/vIBRAtIon/hav/project-events.htm
  57. Controlling vibrationhttps://www.hse.gov.uk/vIBRAtIon/hav/controlling-vibration.htm
  58. Q & A on hand toolshttps://www.hse.gov.uk/vIBRAtIon/hav/hand-tools-qa.htm
  59. Q & A on using a vibration consultanthttps://www.hse.gov.uk/vIBRAtIon/hav/qa-consultant.htm
  60. Q & A on health surveillancehttps://www.hse.gov.uk/vIBRAtIon/hav/qa-surveillance.htm
  61. Tunnelling and Pipejacking: Guidance for Designers https://www.hse.gov.uk/construction/pdf/pjaguidance.pdf
  62. Pile cropping. A review of current practice https://www.hse.gov.uk/vIBRAtIon/assets/docs/pilecrop.pdf
  63. Hand-arm vibration at work: A brief guide https://www.hse.gov.uk/pubns/indg175.htm
  64. Advice for employershttps://www.hse.gov.uk/vIBRAtIon/hav/advicetoemployers/index.htm
  65. Regulationshttps://www.hse.gov.uk/vIBRAtIon/hav/regulations.htm
  66. How to protect workershttps://www.hse.gov.uk/vIBRAtIon/hav/advicetoemployers/protect.htm
  67. Constructionhttps://www.hse.gov.uk/construction/index.htm
  68. Engineeringhttps://www.hse.gov.uk/engineering/index.htm
  69. Motor vehicle repairhttps://www.hse.gov.uk/mvr/index.htm
  70. Noisehttps://www.hse.gov.uk/noise/index.htm
  71. Quarrieshttps://www.hse.gov.uk/quarries/index.htm
  72. Agriculturehttps://www.hse.gov.uk/agriculture/index.htm

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Updated: 2021-05-20