Carbon nanotubes for application in soil stabilization

Transcription

1 Carbon nanotubes for application in soil stabilization M. Graça Rasteiro CIEPQPF, Department of Chemical Engineering-UC, Portugal António Alberto S. Correia Department of Civil Engineering-UC, Portugal

2 Outline 1 Chemical stabilization of soft soils 3 Results (study of the influence of using CNTs and of the influence of using surfactant) 4 Conclusions 2/31

3 1 Chemical stabilization of a soil Construction process 3/31 Hayward Baker Inc. Keller Group Binder with or without water Physical/chemical reactions Stabilized Soil Soil

4 OBJECTIVE Chemical Stabilization ADDITIVES Filler + Carbon Nanotubes (CNT) - nanometric scale effects Single Wall Multiple Wall - MWCNT 4/31

5 Soft Soil - Baixo Mondego Portugal Chemical composition CaO (%) SiO 2 (%) Al 2 O 3 (%) Fe 2 O 3 (%) MgO (%) K 2 O (%) High plasticity, high water content (80.9%) Soil conditioned in a thermo-hygrometric chamber (temperature = 20 ºC, relative humidity = 95%) Binder- Portland Cement -CEM I 42.5 (dosage = 175 kg binder/m 3 soil) CaO SiO 2 Al 2 O 3 Fe 2 O 3 MgO SO 3 Cl - Specific surface ζ (%) (%) (%) (%) (%) (%) (%) (m 2 /kg) (mv) ph 5/31

6 Carbon Nanotubes f av nanometric (10-9 m) Single Wall (SWCNT) Double or Multiple Wall (MWCNT) Less expensive 6/31 PROBLEM Tendency to form aggregates Difficulty of dispersion

7 MWCNT used (CNT 7000 Nanocyl) f = 9,5 nm L = nm Specific surface m 2 /kg CEM r = 1,7 g/cm 3 z = -25,4 mv 7/31 Excellent mechanical characteristics tensile strength = 60 GPa (100 times steel) Young modulus = 1 TPa (5 times steel) strain at failure = 12% (ductile behaviour)

8 Ultra-sonic energy (20 khz) aqueous medium - power: 30W and 500W - time: 1, 2, 5, 10, 15 and 20 min 20 min 500W - Temperature raises up to 46ºC => 10 min cooling system required (T-22ºC) Addition of surfactant Dispersions preparation 5 min 30W - polycarboxylate Glycerox Amber concentrations: 0.5, 1 and 3% WITHOUT (w/w) WITH 8/31

9 Dispersions preparation Surfactant characterization (e.g. polycarboxylate) Z-average = 4.65 nm D z - hydrodynamic diameter (DLS dynamic light scattering) 9/31

10 Dispersions preparation Surfactant characterization (e.g. polycarboxylate) MW = kda (R 2 = 0.992) 10/31 MW- molecular weight (SLS static light scattering) Debye plot

11 Surfactant characterization Dispersions preparation m (mpa.s) MW (kda) - SLS D z (nm) - DLS charge Polycarboxylate* Nonionic Glycerox* Nonionic Amber 4001 # Amphoteric * Comercial polymer # taylored poilymer developed by aquatech+ 11/31

12 Evaluation of dispersions quality Dispersions quality was evaluated by DLS (particle size distribution & polydispersity index) e.g. polycarboxylate (3% w/w) with MWCNT MWCNT = 0.001% lower CNT concentration MWCNT = 0.01% MWCNT = 0.1% 12/31

13 Evaluation of dispersions quality Dispersions quality was evaluated by DLS (particle size distribution & polydispersity index) e.g. Glycerox with MWCNT = 0.01% (w/w) Glycerox = 1% Glycerox = 0.5% 1% < optimum < 3% Glycerox = 3% 13/31

14 Evaluation of dispersions quality Dispersions quality was evaluated by DLS (particle size distribution & polydispersity index) e.g. Amber4001 with MWCNT = 0.01% (w/w) Amber = 1% optimum 1 to 3% Amber = 0.5% Amber = 3% 14/31

15 Evaluation of dispersions quality Dispersions quality was evaluated by DLS (particle size distribution & polydispersity index) concentration (% w/w) MWCNT (% w/w) D z * (nm) - DLS Polycarboxylate Glycerox Amber /31 * for a MWCNT = 0.01% (w/w)

16 What is a soil? Natural material Composed of solid particles, liquid (water) and gas (air) Solid particles can have any relative arrangement Liquid / gas are present in the voids between solid particles 16/31

17 What is a stabilized soil? Composite material (soil-water-cement) Physico-chemical interactions (hydration reactions) Cementitious bonds between soil particles New stronger and stiffer matrix 17/31

18 What is a stabilized soil? Composite material (soil-water-cement) Physico-chemical interactions (hydration reactions) Cementitious bonds between soil particles New stronger and stiffer matrix Unconfined compressive strength tests - UCS 18/31 Preparation of samples (mixture soil-binder-surfactant-mwcnt) Curing time = 7 days in a tank at 20ºC (vertical pressure of 24 kpa) UCS test (deformation rate = 1%/min) Measurements: - vertical Force - vertical deformation

19 Tests Summary Dispersions quality was evaluated by DLS Mechanical behavior was evaluated by UCS surfactant Solution concentration (% w/w) Water - Polycarboxylate 3 MWCNT (% w/w) 19/31 Glycerox Amber

20 3 Results binder = 175 kg/m 3 MWCNT = 0 Water 400 C maximum load = q u max stiffness = E u /

21 3 Results binder = 175 kg/m 3 MWCNT = 0,001% Water C C+MWCNTs MWCNT q u E u /

22 3 Results binder = 175 kg/m 3 MWCNT = 0 Polycarboxylate (3%) C C+MWCNTs C (Pc) Polycar q u E u /

23 3 Results binder = 175 kg/m 3 MWCNT = 0.001% Polycarboxylate (3%) q u + 34% C C+MWCNTs C (Pc) C+MWCNTs (Pc) MWCNT + Policarb E u % q u E u /

24 3 Results binder = 175 kg/m 3 MWCNT = 0.01% Glycerox (2%) q u + 60% C C + Glycerox C+ Glycerox + MWCNTs MWCNT + Glycerox q u E u E u % 24/

25 3 Results binder = 175 kg/m 3 MWCNT = 0.01% Amber 4001 (1%) q u + 77% C C + Amber4001 C+ Amber MWCNTs MWCNT + Glycerox q u E u E u % 50 25/

26 3 Results SEM of soil-binder-mwcnts Good dispersion obtained MWCNTs 26/31

27 3 Results Conceptual model soil-binder-mwcnts MWCNTs 27/31

28 3 Results Conceptual model soil-binder-mwcnts Cementitious bonds (thicker) more stronger and stiffer 28/31

29 29/31 3 Results MWCNT improved the mechanical parameters of the stabilized soil Without surfactant, good dispersion cannot be guaranteed for the higher MWCNT dosages and this is reflected on the mechanical parameters of the stabilized soil (q umax and E u50 decrease) If surfactant is used higher amounts of MWCNT can be incorporated in the binder, with a higher positive effect on the mechanical performance indicators: q umax and E u50 increase for MWCNTs concentrations up to 0.01%.

30 4 Conclusions The presence of nanoparticles in a soil cement matrix contributes to reduce interparticle spacing, promoting a stiffer soil skeleton matrix. Mechanical enhancement is increased if the quality of the MWCNTs dispersion improves. Surfactants can improve that dispersion. The addition of even a very small quantity of MWCNT (0.001% or 0.01%) effectively dispersed, improved significantly the mechanical properties of a soil chemically stabilized with cement (77% and 116% improvement, respectively for q umax and E u50 ). 30/31 FUTURE WORK: TAILORED SURFACTANTS WITH DIFFERENT MOLECULAR WEIGHT AND/OR CHARGE

31 Thank you for your attention M. Graça Rasteiro, António Alberto S. Correia, 31/31 Acknowledgments: P.D.F. Casaleiro and D.T.R. Figueiredo (MSc students) aquatech (David Hunkeler) and Cimpor