INFLUENCE OF HIGH NITRATE SALTS CONCENTRATIONS ON DIMENSIONAL - PowerPoint PPT Presentation

INFLUENCE OF HIGH NITRATE SALTS CONCENTRATIONS ON DIMENSIONAL VARIATIONS OF MORTARS UNDER WET-CURING P. Bénard, C. Cau-dit-Coumes, S. Garrault, A. Nonat

Cementation Widely applied technique for the conditioning of aqueous streams resulting from nuclear decommisioning process Water from the waste : used for cement hydration Characterised by a high salinity (300g/L) Aim of the study : investigate the dimensionnal variation under water of mortars prepared with nitrate rich solutions Potential accidental scenario

EXPERIMENTAL Sulphate resistant cement : CEM I 52.5 (1000g of cement, 374 g of sand and 350 g of solution) Mixed with solutions of KNO 3 or NaNO 3 (normalized mixing) Cast into 4x4x16 cm moulds for 3 days (20°C/ 95% R.H.) Demoulding Placed into measured cell filled with demineralised water

EXPERIMENTAL The length changes : displacement gauges consisting in linear variable differential transducers (LVDT) LVDT Sampling Thermocouple port Thermostated room Mobile ∼ ∼ ∼ ∼ ∼ ∼ steel bar ∼ ∼ ∼ ∼ ∼ ∼ Curing solution ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ 4x4x16 cm ∼ ∼ ∼ ∼ ∼ ∼ Measurement specimen ∼ ∼ ∼ ∼ ∼ ∼ bolt ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ Measurement recorded every 30 minutes over 90 days

EXPERIMENTAL Solution analyzed ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ at 3, 14, 42 and 68 days ∼ ∼ ∼ ∼ ∼ ∼ by I.C.P OES ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼

EXPERIMENTAL Solution analyzed ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ at 3, 14, 42 and 68 days ∼ ∼ ∼ ∼ ∼ ∼ by I.C.P OES ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ At the end : Porosity determined using Mercury intrusion porosimetry Weighed and measured

RESULTS [NaNO 3 ] 3,52 mol/L 700 référence NaNO3 2 mol/L 600 KNO3 2 mol/L KNO3 2,97 mol/L allongement / µm.m -1 [KNO 3 ] 2,97 mol/L NaNO3 3,52mol/L 500 400 Length change [NaNO 3 ] 2 mol/L 300 [KNO 3 ] 2 mol/L 200 Reference 100 0 0 10 20 30 40 50 60 70 80 Time (days) échéance / jours

RESULTS [NaNO 3 ] 3,52 mol/L 700 référence NaNO3 2 mol/L 600 Rapid expansion KNO3 2 mol/L KNO3 2,97 mol/L allongement / µm.m -1 [KNO 3 ] 2,97 mol/L NaNO3 3,52mol/L 500 400 Length change [NaNO 3 ] 2 mol/L 300 [KNO 3 ] 2 mol/L 200 Reference 100 0 0 10 20 30 40 50 60 70 80 Time (days) échéance / jours

RESULTS [NaNO 3 ] 3,52 mol/L 700 référence NaNO3 2 mol/L 600 KNO3 2 mol/L KNO3 2,97 mol/L allongement / µm.m -1 [KNO 3 ] 2,97 mol/L NaNO3 3,52mol/L 500 400 Length change [NaNO 3 ] 2 mol/L 300 [KNO 3 ] 2 mol/L 200 Reference 100 0 0 10 20 30 40 50 60 70 80 Time (days) échéance / jours

RESULTS Two processes may be involved: - diffusion - osmosis

RESULTS Two processes may be involved: - diffusion Pore solution High concentration (Na + /K + , NO 3 - ) Concentration gradient the curing solution (water)

RESULTS Two processes may be involved: - diffusion Pore solution High concentration (Na + /K + , NO 3 - ) Concentration gradient Ions the curing solution (water) Ions Reducing the concentration gradients

Lenght change (µm/m) length change (µm/m) 400 350 300 250 200 150 100 50 0 90 80 NaNO3 2 mol/L KNO3 2 mol/L Dl/l (µm/m) Dl/l (µm/m) 70 60 RESULTS Time (days) time (days) 50 40 30 20 10 0 250 200 150 100 50 0 Alkaline concentration (mmol/L) alkaline concentration (mmol/L)

Lenght change (µm/m) length change (µm/m) 400 350 300 250 200 150 100 50 0 90 80 NaNO3 2 mol/L KNO3 2 mol/L Dl/l (µm/m) Dl/l (µm/m) 70 60 RESULTS Time (days) time (days) 50 40 30 20 10 0 250 200 150 100 50 0 Alkaline concentration (mmol/L) alkaline concentration (mmol/L)

RESULTS Two processes may be involved: - osmosis Π curing solution the curing solution (water) Π pore solution ΔΠ = osmotic pressure gradient Pore solution High concentration (Na + /K + , NO 3 - )

RESULTS Two processes may be involved: - osmosis the curing solution (water) water water Pore solution High concentration (Na + /K + , NO 3 - )

RESULTS Two processes may be involved: - osmosis the curing solution (water) water mechanical pressure =G. γ G = Young modulus (Pa) water and γ = length change (m/m) Pore solution High concentration (Na + /K + , NO 3 - )

RESULTS Two processes may be involved: - osmosis the curing solution (water) Equilibrium : water ΔΠ = mechanical pressure = G. γ G = Young modulus (Pa) and γ = length change (m/m) water Pore solution High concentration (Na + /K + , NO 3 - )

RESULTS Two processes may be involved: - osmosis the curing solution (water) Equilibrium : water ΔΠ = mechanical pressure = G. γ G = Young modulus (Pa) and γ = length change (m/m) water Pore solution High concentration (Na + /K + , NO 3 - )

RESULTS Two processes may be involved: - osmosis Π curing solution Π = 2 C alkalis .R.T C alkalis = concentration of Na + or K + (mol/m 3 ), with R = gas constant (8.314 J.K -1 .mol -1 ), T = temperature (K) Π pore solution

RESULTS Two processes may be involved: - osmosis Π curing solution Π = 2 C alkalis .R.T C alkalis = determined by ICP.OES Π pore solution

RESULTS Two processes may be involved: - osmosis Π curing solution Π = 2 C alkalis .R.T C alkalis = determined by ICP.OES Π pore solution mass balance n alkalis (pore) (considering also alkalis from cement)

RESULTS Two processes may be involved: - osmosis Π curing solution Π pore solution n alkalis (pore)

RESULTS Cumulated Hg volume (mL/g) Cumulated Hg volume (mL/g) 0,12 0,12 0,1 0,1 0,08 0,08 0,06 0,06 0,04 0,04 0,02 0,02 0 0 1000 1000 100 100 10 10 1 1 0,1 0,1 0,01 0,01 0,001 0,001 Pore diameter (µm) Pore diameter (µm) Volume of pores solution

RESULTS Two processes may be involved: - osmosis Π curing solution Π pore solution Π = 2 C alkalis .R.T

RESULTS Two processes may be involved: - osmosis Π curing solution Π pore solution Π = 2 C alkalis .R.T

RESULTS G. γ = ΔΠ γ ΔΠ ( Pa)

RESULTS G. γ = ΔΠ γ 1 = 23 GPa slope ΔΠ ( Pa)

Mass increase at the end of experiment RESULTS

Mass increase at the end of experiment RESULTS

RESULTS Mass increase at the end of experiment -Not due to osmosis (effect should increase with ionic concentration of mixing solution)

RESULTS Mass increase at the end of experiment -Not due to osmosis (effect should increase with ionic concentration of mixing solution) -Mass gain can result to two antagonist processes : water penetration / diffusion of salts Weight loss

At the end of experiments RESULTS

At the end of experiments RESULTS

RESULTS Mass increase at the end of experiment -Not due to osmosis (effect should increase with ionic concentration of mixing solution) -Mass gain can result to two antagonist processes : water penetration/diffusion of salts -Difference in the degree of hydration

NaNO 3 3.53 mol/L NaNO 3 3.53 mol/L Reference Reference Nitrates retard cement hydration RESULTS Time (d) Time (d) Time (d) Portlandite content (%) Portlandite content (%) Portlandite content (%)

RESULTS Nitrates retard cement hydration Reference Reference Portlandite content (%) Portlandite content (%) Portlandite content (%) NaNO 3 3.53 mol/L NaNO 3 3.53 mol/L Time (d) Time (d) Time (d) Mass gain can be due to water uptake due to capillary suction =compensation for water depletion by hydration

RESULTS Mass gain can be due to water uptake due to capillary suction =compensation for water depletion by hydration Degree of hydration

CONCLUSIONS Mortars prepared with solutions of KNO 3 or NaNO 3 exhibited expansion Expansion increases with the nitrate concentration in the mixing solution, whatever the associated cation. Swelling was controlled by a concentration effect which involved diffusion and osmosis: -diffusion of the ions of the pore solution into the less concentrated curing solution, - water uptake by the material due to the osmotic pressure gradient between the pore and curing solutions.