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

2 Roads Pavement Forum 17 November 2004 “ 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 Concrete drying shrinkage research...

3 Roads Pavement Forum 17 November 2004 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

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

5 Roads Pavement Forum 17 November 2004 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%

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

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

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

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

10 Roads Pavement Forum 17 November 2004 Dolerite concrete Quartzite concrete

11 Roads Pavement Forum 17 November 2004 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

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

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

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

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

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

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

18 Roads Pavement Forum 17 November 2004 Early concrete temperature changes

19 Roads Pavement Forum 17 November 2004 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

20 Roads Pavement Forum 17 November 2004 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