Accelerated ageing of a stabilised/ solidified contaminated soil at elevated temperatures. Burden Chitambira

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Posy Higgins
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1 Accelerated ageing f a stabilised/ slidified cntaminated sil at elevated temperatures Burden Chitambira

2 Outline West Draytn site Shrt-term labratry tests Accelerated ageing Experimental Results Cnclusin

3 Intrductin Limited field lng-term perfrmance data Predictin f lng term behaviur at the design stage saves time and cst. Sustainability Lng term effectiveness validatin is paramunt t success and sustainability f any remediatin technlgy. Accelerating the ageing prcess Link shrt-term labratry results t real time lng-term field results. Accelerating methds Elevated temperatures Carbnatin

4 West Draytn site Site - 2m f made grund verlying 3-4m f natural sands and gravels. Cntaminated with heavy metals and petrleum hydrcarbns. Cntaminants in sand & gravel: Cntaminant Cncentratin (mg/kg dry sil) Lead 2800 Cpper 1300 Nickel 105 Zinc 1600 Cadmium 9 Ttal Sulphate 2000 Mineral Oil 570

5 Site treatment Site treated in 1995 by in-situ S/S using 7 cement gruts and implemented using a mixing auger. Mix E : Cement:pfa:Lime Water:Dry grut Sil:Grut 2.5 : 8.0 : : : 1 Site cred at 2 mnths t 5 years. Uncnfined cmpressive strength (UCS) Leachability and leachate ph Permeability Durability freeze-thaw and wet-dry

6 Labratry samples Mdel sil - Gravel (50%), sand (37%), silt (6.5%) and clay (6.5%). Spiked with Pb(NO 3 ) 2, CuSO 4, Ni(NO 3 ) 2, ZnCl, Cd(NO 3 ) 2 and mineral il. Cast int mulds 100mm x 50mm diameter. Sme degree f setting befre subjecting t heat treatment. Sample curing: Elevated temperature nly - ven, wax cated. Oven fr 1 week fllwed by 20% carbnatin in an incubatr at 90% RH. Samples cured fr 28, 60 and 90 days Tested in triplicate fr UCS, duplicate fr NRA leachate ph.

7 Accelerated ageing Elevated Temperatures Degree f hydratin increases with curing time and temperature. The Arrhenius equatin used t accunt fr cmpressive strength develpment. k E = a A exp RT Equatin 1 It can be shwn that the equivalent time t e, which represents the time required at the reference temperature T t btain the same strength (UCS) as that btained at an elevated temperature T in time t, is: t e = t exp E a R 1 T 1 T Equatin 2

8 Accelerated ageing Carbnatin A slw natural prcess leading t frmatin f CaCO 3 and silica gel frm C-S-H r just CaCO 3 frm Ca(OH) 2. The mechanisms and kinetics f carbnatin are cmplex.

9 Results Elevated temperatures UCS (kpa) C 45 C 60 C Figure Age (Days) NRA leachate ph Temperature 21 C 45 C 60 C 1 mnth mnths

10 Results elevated temperatures + carbnatin UCS (kpa) C 45 C 60 C Figure Age (Days) NRA leachate ph Temperature 21 C 45 C 60 C 1 mnth mnths

11 Time-temperature superpsitin Plt the UCS vs. time results n a natural lg-lg scale. Adpt results at rm temperature as the reference T Shift all ther results alng the x-axis relative t T. Obtain shift factrs (a T ). Ln [UCS (kpa)] C 45 C 60 C Ln [Age (Days)] Figure 3 Plt f the shifted curves fr temperature alne data

12 Time-temperature superpsitin Temperature alne Plt the shift factrs (a T ), previusly btained against (1/T -1/T), the slpe f the curve is Ea/R. 5 Shift factr ( a T) y = 6200x (1/T -1/T) Figure 4 Plt f shift factrs against difference in temperature reciprcals

13 Time-temperature superpsitin Ea is the nly unknwn in; t e = t exp E a R 1 T 1 T Equatin 2 Therefre t e can be evaluated. Similar shifting and pltting f shift factrs was carried ut fr the elevated temperatures and carbnatin cmbinatin. Equivalent time t e, after 3 mnths curing Elevated temperature Elevated temperatures + carbnatin 2.9 years 5.2 years

14 Time-temperature superpsitin Crrelatin between site and labratry results Prperty Site Elevated temperatures UCS (MPa) (extraplated) Elevated temperatures + carbnatin 2.6 Direct cmparisn nt pssible due t differences Site sil vs. freshly spiked mdel sil Mre chemicals in site sil Densities different Better crrelatin when similar sil was used. Ea/R btained fr the temperature + carbnatin case 24% higher than that fr temperature alne. Mre carbnatin resulted in less UCS.

15 Cnclusin UCS fllwed the trend; elevated temperature mix > site mix > elevated temperature + carbnatin mix. Suitable scenari - lnger initial temperature curing fllwed by a shrt carbnatin perid. Arrhenius equatin was shwn t be applicable t bth elevated temperatures and temperature + carbnatin. A much better crrelatin btained when same materials were cmpared. Clse t site cmbinatin f cnditins (level f carbnatin, chemicals etc) wuld give better cmparisn with site.

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