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Concrete Drying Shrinkage

Concrete Drying Shrinkage. 17 November 2004 Roads Pavement Forum Sebasti Badenhorst, Pr. Eng Holcim (South Africa) (Pty) Ltd. Concrete drying shrinkage research. “ To look is one thing. To see what you look at is another To understand what you see is another.

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Concrete Drying Shrinkage

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  1. Concrete Drying Shrinkage 17 November 2004 Roads Pavement Forum Sebasti Badenhorst, Pr. Eng Holcim (South Africa) (Pty) Ltd

  2. Concrete drying shrinkage research ... “ To look is one thing. To see what you look at is another To understand what you see is another. To learn from what you understand is something else But to act on what you learn is all that really matters” Sir Winston Churchill Roads Pavement Forum 17 November 2004

  3. Performance-based specifications for shrinkage “ To look is one thing. To see what you look at is another…” WC COLTO - Standard Specification for Road and Bridge Works for State Road Authorities 1998 Shrinkage shall not exceed 0,04% , tested in accordance with SABS 1085 Roads Pavement Forum 17 November 2004

  4. Shrinkage tests... SABS Method 1085:2001 - Initial drying and wetting expansion of concrete Controversial… severe drying... 50 to 55 C,15 to 25% RH Cycles of heating and cooling Small concrete samples Poorly defined end point Roads Pavement Forum 17 November 2004

  5. An investigation to review SABS 1085 “...To understand what you see is another….” WC • Establish how the SABS 1085 shrinkage test result relate to other international shrinkage tests methods? • International shrinkage test methods are based on natural (moderate) drying conditions • Temperature between 22 to 25ºC • Relative humidity between 50 to 70% Roads Pavement Forum 17 November 2004

  6. Laboratory investigation... 28 Concretes...different combinations… • aggregates • cements Same size specimens • SABS 1085 • natural drying test ...compared results... Roads Pavement Forum 17 November 2004

  7. Results of investigation…aggregate type Roads Pavement Forum 17 November 2004

  8. Results of investigation…cements Roads Pavement Forum 17 November 2004

  9. Hilton Concrete Pavement trials… “...To learn from what you understand is something else…” WC Roads Pavement Forum 17 November 2004

  10. Quartzite concrete Dolerite concrete Roads Pavement Forum 17 November 2004

  11. Shrinkage investigation at Hilton • Seven pairs of crack measuring gauges installed • Perpendicular and centred to crack inducing plate • Non doweled joints • Determine movement at joints with time Crack inducing plate Crack measuring gauges Roads Pavement Forum 17 November 2004

  12. Environmental conditions …day of casting Dolerite concrete 21,5°C 37% RH 13,3°C 72% RH Quartzite concrete Roads Pavement Forum 17 November 2004

  13. Laboratory shrinkage testing University of Witwatersrand… 6 samples …creep and shrinkage…quartzite and dolerite Cement and Concrete Institute …shrinkage tests... SABS Method 1085 Roads Pavement Forum 17 November 2004

  14. Results…natural drying ...laboratory shrinkage • Quartzite higher shrinkage potential • Dolerite lower shrinkage potential Roads Pavement Forum 17 November 2004

  15. Results … SABS 1085 shrinkage • Dolerite concrete, meets COLTO specification • Quartzite concrete fails COLTO specification • SABS 1085 does not account for variability Roads Pavement Forum 17 November 2004

  16. Field results • Quartzite cracked less, in spite of higher shrinkage potential Roads Pavement Forum 17 November 2004

  17. Crack width…dolerite concrete Roads Pavement Forum 17 November 2004

  18. Early concrete temperature changes Roads Pavement Forum 17 November 2004

  19. Conclusions... • Environmental condition at time of construction of greater significance in the formation of cracks than the shrinkage potential determined in the laboratory • Changes in early temperature...significant effect on crack propagation • Difference between... crack potential…shrinkage potential Roads Pavement Forum 17 November 2004

  20. Further work... “...But to act on what you learn is all that really matters” WC • Draft of SANRAL specification, clause referring to SABS 1085 scraped • CnCPave updated with revised shrinkage prediction model, no longer refer to SABS 1085 • Draft ISO test method…based on natural drying tests... extrapolate the results from 28-days…under investigation Roads Pavement Forum 17 November 2004

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