Soil Basics 91St Transportation Short Course Dallas N

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Soil Basics 91st Transportation Short Course Dallas N. Little Snead Chair and Regents Professor, Zachry Dept. of Civil Engineering Senior Research Fellow, TTI May be not quite so basic 91st Transportation Short Course Dallas N. Little Snead Chair and Regents Professor, Zachry Dept. of Civil Engineering Senior Research Fellow, TTI Materials Science and Engineering Mechanics of Flexible Pavement of Flexible Pavement Materials Outline

• Basic information – Natural Resource County Soil Surveys General geotechnical information Soil series and associations • Crystalline v. amorphous Energy state Reactivity • Clay minerals Volumetric instability • Improving properties via stabilization (importance of basic knowledge) traditional Ionic polymer Natural Processes that Shape Soils

• Weathering is the biochemical alteration of Earth's rocks, soils and minerals through direct contact with the planet's atmosphere. • Eluviation: removal of materials chemically, with chemical changes during downward movement. • Illuviation: deposition of chemically altered materials in lower horizon • Translocation: movement without chemical alteration

http://www.cst.cmich.edu/users/Franc1M/esc334/images/origin%20of%20soil/profile.gif Soil Maps

State Highway 130 Corridor

Silicate Solids

Crystallline: Quartz

Crystalline: Non-crystalline: Non-crystalline: silicon dioxide silicon dioxide Sodium-silicate 7 glass Excess volume v. mineral stability

Excess volume Excess volume v. mineral stability Kaolinite Smectite

Negative surface charge and high SSA attract (up to 800 m2/g) • Cations • Water

Ca(OH)2 reacts with • SiO2 and Al2O3 • To form CSH/CAH Microstructure of Greek Na-Smectite under High Electrolyte Concentration (a) at Saturation and after Drying: (b) 105 Pa, (c) 106 Pa Calcium Based Stabilizers Lime, Portland cement, fly ash (with and without activator) Transmission Electron Microscope Images of Clay- Water Lattice: Effect of Salt/Concentration

Clay Layers

DDL 35100 A

tactoid

Clay Layersd 0.00118.6 A

a. 1M NaCl – near saturation -3 b. 10 M CaCl2 – near saturation Microstructure of Greek Na-Smectite under High Electrolyte Concentration (a) at Saturation and after Drying: (b) 105 Pa, (c) 106 Pa Resilient Modulus of LSS

35000

30000

25000

20000

15000

10000 Resilient Moduus, psi Moduus, Resilient 5000

0 opt 2% 15% Moisture State Natural LSS Acid Based Phase Diagram

Na-Montmorillonite treated with Hydrogen Ion Stabilizer (HIS) releases 퐴푙3+ from the octahedral layer.

pH = 1 pH = 4 X-Ray Diffraction

Smectite peak

Untreated Na-Montmorillonite

Na-Montmorillonite Treated with dilute (1:20) HIS Na-Montmorillonite Treated with concentrated HIS Interlayer Alumina Hydroxyl

Silica Tetrahedral Silica Tetrahedral

Aluminium Octahedral Aluminium Octahedral

Silica Tetrahedral Silica Tetrahedral

+ + + + Interlayer Cation + + + + + + + + Aluminum Hydroxyl ++ + + + + + + + + + (퐶푎 /푁푎 ) + + + + + + + + + + + + + + + + interlayer

Silica Tetrahedral Silica Tetrahedral

Aluminium Octahedral Aluminium Octahedral

Silica Tetrahedral Silica Tetrahedral

Untreated Montmorillonite HIS treated Montmorillonite Interlayer Alumina Hydroxyl

Silica Tetrahedral “Silica Sheet Wreckage” ?

Aluminium Octahedral “Alumina Sheet Wreckage” ?

Silica Tetrahedral

+ + + + + + + + + + + + + + + + + + + + + + + + Aluminum Hydroxyl + + + + + + + + + + + + + + + + + + + + + + + + + + interlayer + + + + + + + + + + + + + + + + + + + + + +

Silica Tetrahedral

Aluminium Octahedral

Silica Tetrahedral

HIS treated Montmorillonite Impact of HIEC Stabilization on Volume Change (Swell- Shrink) in Soils

Suction Compressibility Index, 훾ℎ is a critical parameter in the estimation of Vertical Movement in expansive soils. ∆푉 훾 = 푉 Measured in lab using ℎ ∆푝퐹 Pressure Plate Test ASTM D836

63.5 Untreated HIEC Suction Sample Soil Treated Soil 훾ℎ drops by 63 Interval I.D. nearly 50% (pF) γh γh

) 62.5 3 2.70-3.20 0.045 0.022 after 62 HC1 3.20-3.70 0.068 0.037 treatment! 61.5 3.70-4.20 0.094 0.044 2.70-3.20 0.034 0.009 61 HC2 3.20-3.70 0.045 0.019 3.70-4.20 0.050 0.018 Volume (cm Volume 60.5 Natural Soil 2.70-3.20 0.023 0.011 HIEC 60 HC3 3.20-3.70 0.076 0.019 3.70-4.20 0.056 0.028 59.5 0 1 2 3 4 5 matric suction, pF Impact of Chemical Stabilization on Resilient Modulus (Mr) of Soils

Hydrogen Ion Exchange Chemical (HIEC) : Increases Mr by 40% Lime Treatment: Increases Mr by 100%

200 Lime Treated Soil

Natural Soil

150 HIEC

100 Mr Mr (Mpa)

0 24 25 26 27 28 29 Moisture Content (%) Polymer Soil Stabilization using Polyelectrolyte Complexes (PECs)

Polyanion + Polycation PEC PEC Complex Formation

Polyanion Polycation

PEC

J. Van der Gucht, et al., Polyelectrolyte complexes: bulk phases and colloidal systems. Journal of colloid and Interface Science 361, Water soluble anionic and cationic PECs via Polycation(PSS) and 407-422 (2011) nonstoichiometric mixing of Polyanions and Polycations. Polyanion (PDADMAC) Soil Stabilization using Polyelectrolyte Complexes (PECs)

Bridging Mechanism Bridge edge-to-edge Moisture Resistant Hydrophobic core

Bridging Edges of Clays using Anionic PECs

Negatively charged PECs can be effective in stabilizing clays since the poly-anion chains are extended and bridge several particles. Also the presence of divalent cations (such as Calcium from Lime) and longer chain polymers (greater molecular weight) make the process more effective.

Polymer v. Traditional Stabilization

0.5 Untreated Limestone 0.45

) 0.4 0.5 Limestone + 9 wt.% Cement 0.35

0.3 Limestone + 2 wt.% PEC 0.25 (PSS:PDADMAC=1:0.4)

0.2 Limestone + 2 wt.% PEC 0.15 (PSS:PDADMAC=1:0.8)

Fracture Toughness, (MPa.M K Toughness, Fracture 0.1 Limestone + 9 wt.% Cement + 2 wt.% PEC 0.05 (PSS:PDADMAC=1:0.8)

Polyelectrolyte Complex - TAMU Protonated edges at low pH Sulfonated Hydrophobic “body” Functionality – bond with clay edges Ettringite Stoichiometry

Stoichiometric proportions:1 mole ettringite

1 mole of tricalcium aluminate C3 A 3 moles of gypsum (CSH2 )

26 moles of water H 2O

3- Columns of (Al)(OH)6 octahedral (red), 2+ Ca (blue), and H2O (grey) 2- SO4 and water (yellow) are seated in channels between the columns Risk Assessment: Two Soils

Mineralogical Model of Soil 1 Mineralogical Model of Soil 2 (Similar to Taylor Formation) (Similar to Eagle Ford Formation)

SO4 3,000 ppm SO4 3,000 ppm Aluminum Availability and Mineralogy

1216ppm

1.216ppm

log (Ca) = -2.469 log (Na) = -1.355 log (Al) = -2.498 log (SO4) = -2.503 Thermodynamic model represented by a Herbert and Little,pH 2006 = 12.8 predominance diagram Stoichiometric Volume Increase, % 14

6 Percent Change Change Percent 4

0 0.00 1.00 2.00

3,000 5,000 Percent SO4 ppm ppm Final Steps: Nucleation and Growth before Compaction Conclusions

• Basics of soil structure and mineralogy define Properties and predict performance Predict impact of chemical additives • Basics allow us to understand and to develop methods to prevent deleterious reactions • Sources of information Geotechnical reports NRCSS