1. 1 Barbara Lubelli 1, Rob P.J. van Hees 1,2, Henk P. Huinink 3 Hygric dilation behaviour of NaCl contaminated lime-cement mortar 1 Delft University of Technology, The Netherlands 2 TNO BenO, Delft, The Netherlands 3 Eindhoven University of Technology, The Netherlands 7 th European Conference SAUVEUR Prague 31 st May -2 nd June 2006

2. 2 COMPASS Project Compatibility of plasters and renders with salt loaded substrates in historic buildings (2002-2005) Main partners: TNO BenO – NL (coordinator) LRMH – F TUE – NL TUD – NL CSIC IET – ES LNEC - P Main aims: Model of transport & degradation mechanism Requirements for plasters and renders Accelerated crystallisation test Experts system www.compass-salt.org

3. 3 NaCl damage mechanism Sodium chloride does not reach high super-saturation “However, as it is not possible to obtain higher supersaturation than m/m0=2.2 of NaCl in levitated droplets, the occurrence of even higher supersaturation in pore solution is unlikely” [Steiger M., J. Cryst. Growth, 282,(3-4) 2005] “During this experiments with NaCl no supersaturation is found…” [Pel L. et al., Applied Physics letters, 81 (15) 2002] In spite of this… The NaCl damage mechanism is not fully understood. therefore it can hardly develop high crystallization pressures.

4. 4 …damage occurs Venice (I) La Rochelle (F) Brouwershaven (NL)

5. 5 Damage due to NaCl No crypto-florescences No expansive reaction

6. 6 Hypothesis: differential dilation High salt conc. Low salt conc. shear stresses at the interface

7. 7 Experimental set-up salt contamination by capillary rise from the bottom surface lateral sides sealed with epoxy resin evaporation surface support LVDT

8. 8 Hygric dilation Dilation occurs during crystallization

9. 9 Hygric dilation If the RH equ is not crossed, no irreversible dilation occurs

10. 10 Damage mechanism The dilation is irreversible and leads to damage

11. 11 NaNO 3 and KCl

12. 12 ESEM investigation - NaCl Salt layer Pores >0.5  m empty NaCl: salt layer

13. 13 ESEM investigation – NaNO 3 and KCl

14. 14 ESEM investigation – NaCl + inh. agglomeration of NaCl crystals NaCl crystals not adhering to the substrate NaCl + inh.: no salt layer

15. 15 Hygric behaviour NaCl + inh. No dilation occurs in presence of the inhibitor

16. 16 Hygric behaviour – NaCl + inh. No dilation and no damage occurs in presence of a crystallization inhibitor

17. 17 Conclusions NaCl modifies the hygric dilation behaviour of a material. Damage may result from the differential dilation between zones having different salt loads A damage mechanism based on the mechanical interaction between salt and pore wall is proposed. NaCl crystallizing as a layer on the pore walls causes irreversible dilation and damage during crystallization. No dilation and no damage is observed when the same salt crystallizes without adhering to the pore wall.

18. 18 Thanks for your attention