Project Title: Chemical Stabilization of Clay Design Department Presenter: Stephan Cheong Date: February 5,2015

  Introduction to Soil Stabilization  Chemical Admixtures  Application of Soil Stabilization  Environmental Impacts  Engineering Properties of Clay  Standard Engineering Tests  Project Limits  Results and Analysis  Discussion  Flexible Pavement Design  Economical Consideration of Flexible Pavement  Benefits of Soil Stabilization  Conclusion  Recommendations Outline of Presentation

  Permanent physical and chemical alteration of soils to enhance their physical properties.  To create an improved soil material possessing the desired engineering properties.  Chemical stabilization relies on the use of an admixture to alter the chemical properties of the soil. Introduction to Soil Stabilization

  The chemical additives used to modify the chemical properties of a clay soil in this research are listed below: o Rice Husk Ash – Silicate Based Chemical Admixtures

 o Sodium Hydroxide – Sodium Based o Lime – Calcium Based Chemical Admixtures

  Road Pavements  Foundations Application of Soil Stabilization

 Environmental Parameter Sodium HydroxideRice HuskLime PHYSICAL Air: Dust Control measures when transported Not RequiredRequired Water QualitySodium toxicity results from high concentration of Sodium in water but decreases acidity of water due to low pH Water quality is not affected Ionizes to Calcium cations in water which is beneficial for human and fish health Social Health and SafetySeverely Hazardous Substance Harmless Substance Environmental Impacts

  Their vulnerability to slow volume changes that can occur independent of loading due to swelling or shrinkage.  The degree of weathering they have undergone which leads to the destruction of interparticle bond.  Reductions in strength and elastic modulus with a general increase in plasticity. Engineering Properties of Clays

 Standard TestsKey Engineering Properties Liquid and Plastic Limit {ASTM D } Plasticity Index Shrinkage Limit {ASTM D } Shrinkage Potential Specific Gravity {ASTM D } Soil Density Standard Engineering Tests

 Standard TestsKey Engineering Properties Modified Proctor {ASTM D } Compaction California Bearing Ratio {ASTM D } Subgrade Strength Settlement Potential of Cohesive Soils {ASTM D } Soil Permeability and Percent Settlement

  Location of Disturbed Tested Sample: University of Guyana  Selected Test Specimens: Soil mixed with 5%, 10%, 15% NaOH, 3%, 5%, 8% Lime and 20%, 25% and 30% RHA.  Soil mixed with 8% Lime, 30% RHA and 10% NaOH was more effective in stabilizing clay soils. Project Limits

 Soil TypeSpecific Gravity Values Plasticity Index /% Soil Type *Plasticity Chart (ASTM D 2487) Shrinkage Limit/% Untreated Clay Soil CH13.62 Soil + 30% RHA MH 3.90 Soil + 8% Lime MH8.90 Soil + 10% NaOH MH7.47 Results and Analysis

 Soil TypeMaximum Modified Proctor Dry Density / lb/ft 3 California Bearing Ratio Subgrade Strength *Based on AASHTO Pavement Thickness Design Guide Untreated Clay Soil Low Soil + 30% RHA Low Soil + 8% Lime Low Soil + 10% NaOH Medium Results and Analysis

 Soil Type Settlement Potential of Cohesive Soils {Remolded Samples} Hydraulic Conductivity, k z (m/yr ) Untreated Clay Soil Soil + 30% RHA Soil + 8% Lime Soil + 10% NaOH

 Seating Pressure σ vo (KPa) Untreated Clay Soil Soil + 8% LimeSoil + 30% RHA Soil + 10% NaOH - Percent Settlement /% of Remolded Samples Percent Rebound Settlement /% of Remolded Samples Results and Analysis

 Discussion Increased Compaction Stabilized Soil% Variation from Clay 10% NaOH5% 8%Lime-3% 30% RHA-17% Increased Density Stabilized Soil% Variation from Clay 10% NaOH10% 8%Lime-7% 30% RHA-9%

 Discussion Increased Load Bearing Capacity (Subgrade Strength) Increased Hydraulic Conductivity Stabilized Soil% Variation from Clay 10% NaOH60% 8%Lime1160% 30% RHA1300% Stabilized Soil% Variation from Clay 10% NaOH90% 8%Lime37% 30% RHA7%

 Stabilized Soil% Variation from Clay (S) % Variation from Clay (R.S) 10% NaOH43% 8%Lime53%48% 30% RHA37%33% Discussion  Reduction in Settlement and Rebound Settlement

 Flexible Pavement Design (AASHTO 1993) Input Values for Nomograph Reliability (R)%=95 Overall Standard Deviation (So) = 0.40 Estimated Future traffic, 18 Kip ESALs, w 18 = 10 × 10 6 m=1 (drainage provided) Final Serviceability limit = 4.5 Initial Serviceability limit = 2.5 Design Serviceability loss = 2.0 Layer Coefficient Asphaltic Concrete; a 1 = 0.365, E AC = 300,000 psi Aggregate base; a 2 = 0.13, CBR = 70 White Sand/Sand Clay; a 3 =0.11, CBR = 30 White Sand; a 4 = , CBR = 20

 Subgrade Type Design Structural Number SN (DES) d 1 (AC) d 2 (AB) d 3 (WS/SC) d 4 (WS) Subgrade Resilient Modulus /MPa Clay Clay + 30%RHA Clay + 8%Lime Clay + 10%NaOH Structural Number and Layer Thickness (AASHTO 1993)

 SubgradeCost of Stabilized Material/Mile (GYD) Cost of Road Material / Mile (GYD) Total Road Pavement Cost per Mile (GYD) Clay-$133M Clay + 30%RHA0$121.4M Clay + 8%Lime$10M$100M$110M Clay + 10%NaOH $27M$79M$106M Economical Considerations of Flexible Pavement o Lane Width = 12Ft; Stabilized Depth = 12in; Road Length = 1mile

  From a financial point of view, Stabilization produces the following relevant benefits: 1)Increased Long-term performance of pavement structures 2)Saving of significant amounts of non-renewable resources 3)Transforms inexpensive earth materials into effective construction materials  Despite positive benefits of stabilization, the engineering properties derived can vary widely due to heterogeneity in soil composition, differences in micro and macro structure among soils. Economical Benefits of Stabilization

 Benefits of Soil Stabilization  Stabilization can: o increase the strength of a soil o control the shrink-swell properties of a soil o Replace mechanical methods of stabilization which can be more costly. o improve stress-strain properties, permeability, and durability.

  All three admixture can potentially stabilize Guyana’s coastal clays.  The Sodium Hydroxide admixture proved to be the most effective investigated admixture.  Lime was slightly more effective in controlling settlement and improving permeability.  Rice husk ash was more effective in controlling volume changes and improving permeability. Conclusion

  A complete and thorough Environmental and Social Impact Assessment will be required.  The following items which are not part of the scope of research are recommended areas of further study; 1)Correlation Between Laboratory Strength and In-situ Strength 2)Impact of Subgrade Stabilization on Life-Cycle Cost of Pavements 3)Mixing the Proportions of Two Stabilizers Recommendations