Enhancing Wet Shotcrete Performance: Methods and Influencing Factors

1. Wet Shotcrete Performance – Laboratory Test, Methods and influencing Factors in Practice Dr. Peter BoosHeidelbergCement, Zentrallabor HC Nord, Ennigerloh Dr. Martina Dietermann HeidelbergCement, Entwicklung und Anwendung, Leimen

2. Agenda • Wet shotcrete • HeidelbergCement pull-off test • Laboratory shotcrete rig • Influencing factors in practice • Optimized cement for shotcrete application • Summary

3. Shotcrete, high performance product consisting of … Cement + + + + addition admixture water aggregates + non-alkaline accelerator

4. Requirements on wet shotcrete 100 J3 10 J2 compressive strength [MPa] J1 1 0.1 0.01 0.01 0.1 1 10 100 time [h]

5. Requirements on wet shotcrete 100 Assessment of accelerated solidification by using the HC pull-off test J3 10 J2 compressive strength [MPa] J1 1 > J2 0.1 0.01 0.01 0.1 1 10 100 time [h]

6. Requirements on wet shotcrete 100 J3 10 J2 compressive strength [MPa] J1 1 0.1 Assessment of early strength develop-ment by using the shotcrete rig 0.01 0.01 0.1 1 10 100 time [h]

7. Agenda • Wet shotcrete • HeidelbergCement pull-off test • Laboratory shotcrete rig • Influencing factors in practice • Optimized cement for shotcrete application • Summary

8. HeidelbergCement pull-off test dissolver dissolver axis beaker Cement paste vertically positioned axis electromagnetic force

9. HeidelbergCement pull-off test

10. Agenda • Wet shotcrete • HeidelbergCement pull-off test • Laboratory shotcrete rig • Influencing factors in practice • Optimized cement for shotcrete application • Summary

11. Laboratory shotcrete rig Film

12. Recipes for the laboratory shotcrete rig

13. Results 100 B2 (450/150) J3 B3 (400/70) 10 J2 B4 (400/90) Compressive strength [MPa] J1 1 0.1 0.01 0.01 0.1 1 10 100 time [h]

14. Results 100 J3 10 J2 Compressive strength [MPa] J1 1 0.1 0.01 0.01 0.1 1 10 100 time [h] Practise Lab-test B2

15. Agenda • Wet shotcrete • HeidelbergCement pull-off test • Laboratory shotcrete rig • Influencing factors in practice • Optimized cement for shotcrete application • Summary

16. Influencing factors in practice fresh concrete temperature??? ambient-temperature??? w/c-factor???

17. Influence of w/c-factor and fresh concrete temperature 14 12 10 8 accelerator demand HC-pull-off test [M.-%] 6 4 2 w/c = 0.40 w/c = 0.50 w/c = 0.55 0 14 16 18 20 temperature [°C]

18. Influence of fresh concrete temperature 100 J3 10 J2 compressive strength [MPa] J1 1 0.1 0.01 0.01 0.1 1 10 100 time [h] TB = 20 °C TB = 26 °C

19. Influence of the ambient temperature 100 J3 10 J2 ? compressive strength [MPa] J1 1 0.1 0.01 0.01 0.1 1 10 100 time [h] TAir = 7 °C TL = 10 °C TL = 20 °C TAir = 20 °C

20. Influence of the ambient temperature 20 15 temperature [°C] 10 5 0 0 2 4 6 8 10 12 14 16 18 20 22 time [h] temp.air Cooling of concrete temp.concrete

21. Agenda • Wet shotcrete • HeidelbergCement pull-off test • Laboratory shotcrete rig • Influencing factors in practice • Optimized cement for shotcrete application • Summary

22. Optimized cement for shotcrete application 100 J3 10 J2 Compressive strength [MPa] J1 1 0.1 0.01 0.01 0.1 1 10 100 time [h] before optimization after optimization

23. Agenda • Wet shotcrete • HeidelbergCement pull-off test • Laboratory shotcrete rig • Influencing factors in practice • Optimized cement for shotcrete application • Summary

24. Summary Accelerator efficacy of cement-accelerator combination can be tested by using the new HC pull-off test The following early strength development can be reliably tested by using the HC shotcrete rig Essential external influences on shotcrete performance are: Solidification: w/c-factor Further strength development: ambient temperature Optimized cement-accelerator combination show solidification between J2 and J3 and are gaining - even at low ambient air temperature - continuously strength.