ADMIXTURE SOIL IMPROVEMENT 1 INTRODUCTION ADMIXTURE SOIL IMPROVEMENT SOIL IMPROVEMENT ⬢ ⬢ ⬢ Engineering properties of soil can be enhanced through addition or subtraction of materials to or from the soil. The mechanics may be physical or chemical in nature. In most cases, changes in soil properties is permanent. 3 STABILIZATION Improvement of soil through the use of admixtures is often called soil stabilization. 4 SOIL ADMIXTURE MATERIALS Natural Soils Chemical Reagents Binders Polymers Industrial By-Products Salts Poly-Fibers Bitumen/Tar 5 BENEFITS OF ADMIXTURE SOIL IMPROVEMENT ⬢ ⬢ ⬢ ⬢ ⬢ ⬢ ⬢ ⬢ Cost savings Drying up of wet soil Strength improvement Volume stability Reduced soil deformations Reduced erodibility Permeability control Dust control 6 SOIL IMPROVEMENTS HAVE BEEN RESPONSIBLE FOR: ⬢ ⬢ ⬢ ⬢ ⬢ ⬢ ⬢ ⬢ ⬢ Improved working platforms and workability of soils Reduced thickness of roadway layers Slope Stabilization Foundation/Structural Support Excavation Support Liquefaction Support Reduced Leakage/Seepage Stabilization of Marine Sediments Environmental Remediation 7 STABILIZATION PROJECTS Stabilization Projects are almost always site specific. 8 2 ADMIXTURE MATERIALS ADMIXTURE MATERIALS DEPEND ON: ⬢ ⬢ ⬢ ⬢ ⬢ ⬢ ⬢ Soil Type to be treated Purpose of use Engineering properties desired Minimum requirements of engineering properties Availability of Materials Cost Environmental concern 10 NATURAL SOIL ADMIXTURES 11 NATURAL SOIL ADMIXTURES Most of the engineering properties of the ground are the direct result of soil grain sizes and the density of the packing of the grains. High density increases strength, stiffness, durability, and lowers compressibility, and permeability. 12 OPTIMUM PARTICLE SIZE DISTRIBUTION 𝑑 𝑛 100(𝐷) ⬢ 𝑝= ⬢ Where: ⬡ p = Percent passing sieve with a nominal grain Diameter ⬡ d = Aggregate size being considered ⬡ D = Maximum aggregate size ⬡ n = Parameters, (0.45-0.50 for typical pavement layers) 13 MECHANICAL STABILIZATION Mechanical solutions involve physically changing the properties of the soil in order to affect its characteristics. 14 GRADATION CONTROL Addition or removal of certain grain sizes and control of grain size distribution can aid in achieving many desirable properties and can increase a soil’s workability. In some instances, a more uniform gradation is required for improved drainage. 15 UNIFORMLY GRADED SOILS Uniformly graded soils can be found in nature but often must be generated by grading or screening. 16 UNIFORMLY GRADED SOILS Most roadway design guidelines and engineering fills require specific gradations not found in nature. To meet these specifications, it’s necesssary to control the grain size distribution of soils. Screening the materials can help achieve this. 17 BENTONITE CLAY A “natural” soil additve being used by itself or in conjuction with other admixtures. This lowers the permeability in naturally occuring soil. It has also been apply in slurry form for hydraulic barriers (cutoffs). 18 AGRREGATE GRADING REQUIREMENTS 19 AGRREGATE GRADING REQUIREMENTS 20 GRADING RECOMMENDATIONS FOR PAVEMENT UNDERLAYERS 21 CEMENT AND LIMES 22 CEMENT AND LIME Cement ⬢ Most widely used stabilizing agent. ⬢ Contains lime but has its own source of additional reactants (pozzolans) Lime ⬢ Purported to be the oldest known stabilizing admixture (ie. Rome’s Appian Way) 23 APPIAN WAY 24 POZZOLAN A pozzolan is a siliceous or siliceous and aliminous material that by itself is not cementitious. But in finely divided form and with moisture, will react chemcially with calclium hydroxide to form cementitious compound. 25 LIME ⬢ One of the most used admixture for permanent, long-term stabilization. (poor quality, fine grained soils) ⬢ Effective in rapid, short-term solutions for enabling or expediting construction where wet soil conditions are present. 26 LIME ⬢ ⬢ ⬢ Used heavily for roadways, airfields, drainage canals, and foundation soils. In addition to drying wet soil, it reduces plasticity and improves stability. Quality lime stabilization can be achieved with 2-8% lime, if more is needed, another admixture type like cement may be more economical. 27 LIME ⬢ ⬢ ⬢ ⬢ Terminology for lime (ASTM C51) depends on the amount of magnesium (MgCO3) it contains. High calcium lime containing 0-5% MgCO3 (Magnesium Carbonate) Magnesian Lime Containing 5-35% MgCO3 Dolomitic lime containing 35-46% MgCO3 28 QUICKLIME A white, caustic, alkaline crystalline solid that is most commonly made by thermal decomposition of limestone or other calcium carbonate material containing the mineral calcite (CaCO3 or MgCO3). This is also called burnt lime. 29 QUICKLIME ⬢ Quicklime is commercially available in a number of sizes (ASTM C51) ⬡ Large lump lime – max of 20cm dia. (8 in.) ⬡ Crushed or pebble lime – 0.6 to 6.3cm dia. (0.25in. – 2.5in.) ⬡ Ground lime – 0.6cm and smaller. ⬡ Pulverized Lime – passes #20 sieve ⬡ Pelletized lime – 2.5 cm (1in.) sized pellets or briquettes, molded form fines. 30 QUICKLIME ⬢ Quicklime is made by heating the source material above 825ºC (1517ºF) in a process called calcination which drives off CO2 leaving calcium oxide. CaCO3 + MgCO3 → CaO + MgO + CO2 One of the advantages of using quicklime is the intense heat generated during hydration (up to 150ºC) ⬡ ⬢ ⬡ CaO(s) + H2O(l)Ca(OH)2(aq) ⬡ ∆Hr = 63.7kJ/mol of CaO; 490BTU/lb = 273cal/g 31 QUICKLIME ⬢ The water content reduces due to hydration of the lime. ⬡ 1kg CaO absorbs 0.32kg of water through hydration. ⬡ Decrease of moisture from hydration is given by the equation: ⬡ Δw = wo – (wo – 0.32as)/(1+1.32as) ⬡ Where: ● Δw = decrease of moisture from hydration ● wo = original soil water content ● as = mass ratio of lime to soil 32 QUICKLIME ⬢ Moisture is lost due to the evaporation due to the heat generated by the hydration of quicklime. ⬡ Δw =0.45as 33 QUICKLIME ⬢ Quicklime is volatile and must be kept sealed until use. ⬢ It’s perishable and must be “fresh” (<60 days) to be useful. ⬢ It reacts with CO2 in the air and ultimately revert back to a nonreactive form of CaCO3. 34 HYDRATED LIME ⬢ A more “user-friendly” approach compared to quicklime. ⬢ Made by adding ~1% water to crushed granular quicklime. ⬢ Dry to the touch but with sufficient water to convert oxides to hydroxides. ⬢ Only found as a fine powder or a slurry 35 LIME KILN DUST (LKD) ⬢ Collected from the draft of the calcining process of lime production. ⬢ Typically contain only 18-30% total oxides with 7-15% alumina and silica oxides. ⬢ Best for silts and sands 36 REACTIVE SOILS ⬢ Whether quicklime or hydrated lime is used, numerous fundamental reactions can occur in reactive soils. ⬢ Reactive soils are soils that have a gain in unconfined compressive strength of at least 350 kpa (51 psi) 37 REACTIVE SOILS ⬢ Reactions include both longterm and short-term reactions. ⬢ For long-term cementation, adequate lime must be added to maintain available calcium to keep pozzolanic reactions going. This is evaluated by maintaining a high ph level of pore water 38 CLAY MINERALOGY Clay particles carry a net negative charge on their surface. The net negative charge of the clay attracts the positive end of the dipolar water molecule. The outer edge of the water layer will attract positive charges still in the form of water. This causes the “double water layer”, or “diffuse water layer” 39 CLAY MINERALOGY 40 CLAY MINERALOGY A clay soil with a flocculated structure will have higher peak strength but is more brittle, it will have lower compressibility and swell potential and a higher permeability. a. b. Flocculated Dispersed 41 SOIL-LIME REACTIONS Short term ⬡ Rapid Hydration – can dry the soil ⬡ Flocculation ⬡ Agglomeration – combining of particles to form large particles ⬡ Dry wet soil, reduce plasticity, reduce attraction for water, improve workability, stable working platform. 42 SOIL-LIME REACTIONS Long Term ⬡ Pozzolanic reactions or cementation occurs. The resulting cementitious end products are permanent and formed from nonreversible reactions that may continue for days, months, and even years. 43 SOIL-LIME REACTIONS Soils containing suitable amount of silica or alumina clay minerals or the fine material already in Portland cement, react with the calcium and water to produce insoluble calcium silica hydrates. Additional Lime can react with moisture in order to form (or reform) calcium carbonate. 44 CONCERNS OF USING LIME AND CEMENT STABILIZATION ⬢ ⬢ Reactions with sulfate-rich soils can lead to expansions and in turn can damage the overlying pavements. Lime stabilization is known to alter compaction characteristics; causing an increase in OMC and reduction in maximum density. 45 CEMENT ⬢ Most effective and economical for granular soils, ineffective for cohesive soils. ⬢ Ideal for well-graded, granular soils including gravelly soils and sands with small amounts of silts and clay 46 CEMENT Definitions derived for cement stabilization (FHWA) ⬢ Portland Cement – A hydraulic cement produced by pulverizing clinker consisting essentially of hydraulic calcium silicates, and usually containing one or more of the forms of calcium sulfate as an interground condition. ⬢ Cement-Stabilized Soil – A mixture of soil and measured amounts of Portland cement and water, which is thoroughly mixed, compacted to a high density, and protected against moisture loss during a specific curing period. 47 CEMENT Definitions derived for cement stabilization (FHWA) ⬢ Soil-Cement – A hardened material formed by curing a mechanically compacted, intimate mixture of pulverized soil, Portland cement, and water. ⬢ Cement-Modified Soil – An unhardened (or semihardened) intimate mixture of pulverized soil, Portland cement, and water. Significantly smaller cement contents are used in cement-modified soil than in soil-cement. 48 CEMENT Definitions derived for cement stabilization (FHWA) ⬢ Plastic Soil Cement – A hardened or semi hardened intimate mixture of pulverized soil, Portland cement and water, where the soil and cement is mixed at a high-water content such that the material can be pumped. This mixture is often placed without compaction and is best suited for most soils except for clayey or organic soils. ⬢ The primary difference between categories of cement soil mixture is the amount of cement added. The more fine-grained and the higher the plasticity, the more cement is required for stabilization 49 SHRINKAGE Shrinkage occurs due to hydration and moisture loss. This can cause cracks in the surface. This can be prevented by limiting the plasticity and thorough pulverization of the soil, and proper curing. For high cement contents, controlled cracks can allow and design for planned shrinkage. 50 FLY ASH 51 FLY ASH ⬢ Used as a substitute or supplement for concrete. ⬢ It is a by-product of coal fired electric generation facilities. ⬢ There are two components of ash-generated: - top ash : collected by cyclone or electrostatic precipitators - bottom ash: a granular aggregate collected by gravity ⬢ Consists of silt and clay-sized, cohesionless particles with relatively low specific gravity. 52 TWO CLASSES OF FLY ASH (ASTM) Class F ⬢ produced from the combustion of bituminous anthracite and some lignite coals. ⬢ provides a greater reduction in permeability of concrete. Class C ⬢ Its component allows it to be self-cementing ⬢ It will improve the durability of cement 53 54 BENEFITS OF USING ASH ⬢ Reusing a waste product ⬢ Reducing the use of high CO2 “footprint” cement ⬢ Minimizing the environmentally destructive need to transport expensive engineering fill materials 55 FURNACE SLAG 56 FURNACE SLAG ⬢ Granulated material formed during the processing of iron blast furnace slag generated from steel manufacturing. ⬢ Sometimes referred as slag cement ⬢ Provide strength gain without the repercussions of generating secondary expansive materials 57 SALTS, CHLORIDES, AND SILICATES 58 SALTS, CHLORIDES, AND SILICATES ⬢ Variety of salts have been used as stabilizing agents: Calcium Chloride and sodium chloride are two salts that are commonly used 59 STABILIZING AGENTS 60 CALCIUM CHLORIDE AND SODIUM CHLORIDE ⬢ ⬢ It can be produced ⬢ Used to control directly from moisture and improve limestone compaction densities Used as an aid to in sandy granular soils compaction, especially for gravels 61 POTASSIUM CHLORIDE (KCl) ⬢ Used for modification of cohesive, expensive clay soils with the objective of reducing swell potential. ⬢ The objective is to attract and maintain water so that the soil will be “preswelled”. 62 SODIUM SILICATES ⬢ Used as dust palliatives ⬢ It results in high soil PH, making them available for cementation reactions ⬢ Works best with silica sands and other lime-rich admixtures 63 PHOSPHORIC / POLYSPHORIC ACID ⬢ Used to modify asphalt binders to prevent rutting and brittle failures ⬢ Was used as a stabilizer in mid 1900s as it shows increase in strength and water resistance of soils. ⬢ At present, no clear conclusion to the benefits of using phosphoric acid as an additive to salt. 64 BITUMINOUS ADMIXTURES (ASPHALTS, BITUMEN, TAR) 65 BITUMINOUS ADMIXTURE ⬢ Includes ⬡ Asphalt cement/binders ⬡ Cutback Asphalt ⬡ Emulsified Asphalt 66 BITUMINOUS ADMIXTURE Asphalt Bitumen Tar Bitumen mixed with other aggregates. Obtained from the refining process of crude oil. A sticky petroleum for binding other materials. Obtained from the destructive distillation (Burning without oxygen) of bituminous coal 67 BITUMINOUS ADMIXTURE ⬢ Can be found naturally (tar in sands) ⬢ Generated by distillation of organic matter (wood, peat, crude oil processing) ⬢ By-product of coke production 68 BITUMINOUS ADMIXTURES ⬢ The aim of bituminous admixtures is water repulsion and increase in cohesive strength of soils. ⬢ The difference between asphalts and calcium-rich admixtures is that no chemical reactions take place when asphalts are mixed with soils. 69 BITUMINOUS ADMIXTURES ⬢ Asphalt binders may be used as hot mix or cold mix applications ⬢ Hot mix asphalt (HMA) are generally premixed in batches and applied in mixed form while cold mix asphalts are often applied to the soil in place. 70 ASPHALT CEMENTS/BINDERS (ASTM 6373 or AASHTO M 20, M 226, M 320) ⬢ Commonly used for roadway pavements. ⬢ Typically applied as hot mix ( >200°F = 182°C) ⬢ High temp. aids in better mixing and workability. 71 CUTBACK ASPHALT ⬢ A combination of asphalt cement and a petroleum solvent. ⬢ Reduces the viscosity of asphalt at low temperatures for use as tack/prime coats, fog seals, and slurry seals. ⬢ Solvent evaporates and leaves asphalt cement residue on the application. ⬢ For patching and repairs in colder weather. 72 EMULSIFIED ASPHALT ⬢ Common with cold mix asphalt concrete ⬢ From emulsifying asphalt in water (with soap/detergent) ⬢ Taken the place of cutback asphalt due to environmental concern. 73 CUTBACK ASPHALT VS EMULSIFIED ASPHALT Cutback Asphalt ⬢ Emulsified Asphalt 85% asphalt cement and 15% cutter by weight. ⬢ Asphalt emulsions consists of onlye 2/3 of asphalt cement. ⬢ This can lead to a less then expected volume of binder. 74 APPLICATIONS ⬢ ⬢ ⬢ ⬢ ⬢ ⬢ ⬢ Used for tack coasts. (Adhesive between old and new asphalt layers or for a new wearing surface.) Waterproofing Dust palliatives Erosion control Water conveyance structures Moisture loss prevention Stabilizer 75 ASPHALT SEAL COATS ⬢ Thin layer of asphalt material applied to pavement surfaces for added wear protection and waterproofing. ⬢ Extends the wear and life of the pavement. 76 TYPICAL PROBLEMS WITH ASPHALT STABILIZED SOILS ⬢ Stripping ⬢ Deteriorates with age, drying, and repeated loading (fatigue) ⬡ Crocodile cracks ⬡ Potholes ⬡ Heaving ⬡ Raveling ⬡ Rutting 77 TYPICAL PROBLEMS WITH ASPHALT STABILIZED SOILS (CONT.) ⬢ ⬢ While adding bitumen to a soil will increase cohesive strength to a point, excessive bitumen typically decreases unconfined compressive strength depending on aggregate type. Fatigue strength is 55-60% of peak strength. 78 POLYMERS AND RESINS 79 POLYMERS AND RESINS ⬢ ⬢ ⬢ Typically available as liquids, foams, or gels Chemically derived resins were found to be toxic and harmful to the environment and have been taken off the market. (acrylics, lignosulfonates, and epoxies) Can be available as premixed solutions (requiring no water), or as dry powder. 80 APPLICATIONS ⬢ ⬢ ⬢ ⬢ ⬢ ⬢ ⬢ Stabilizes soil while keeping its natural appearance For grouting Dust control Strengthening of near-surface soils Rapid improvement of unpaved rural roadways Attractive option for military maneuvers (roads, airfields, helipads, etc.) Erosion resistance 81 ECOALTERNATIVES ⬢ ⬢ Many new additives are now on the market touting “ecofriendly” and “green” engineering, like Soilwork’s Soiltac. Same strength gain and reduced swell from lime application. ⬡ Reduced water usage ⬡ No need for Remixing ⬡ Reduced Energy consumption ⬡ Reduced carbon footprint ⬡ Lower Permeability ⬡ No adverse reaction to sulfates 82 ECOALTERNATIVES ⬢ Polymeric admixtures such as SS-100 from Chemilink. ⬡ Improvement of soils in tropical areas (Southeast Asia) ⬡ More suitable for these areas compared to lime, cement, and fly ash. 83 FIBERS 84 FIBERS ⬢ Dates back thousands of years when straw was mixed with clay. ⬢ Can be synthetic (polyester, polyethylene, polypropylene, or fiberglass), and can be natural (coir or papyrus) 85 FIBERS ⬢ Utilized for both sands and finegrained soils as well as some asphalt applications. ⬢ Provides tensile strength to soils which in turn increases shear strength. ⬢ Fibers are blended with existing soil using rotary mixers similar to the ones used with limes, cement, or fly ash. 86 COMBINED MATERIALS 87 COMBINED MATERIALS ⬢ ⬢ ⬢ One material may provide an effective treatment of a particular attribute while the other may not. An admixture may also provide a pretreatment of soil making a more effective treatment by additional admixture materials. Less economical but the end result may not be possible with only using a single kind of admixture. 88 OTHER RECYCLED MATERIALS 89 RECYCLED MATERIALS ⬢ Recycled rubber from waste tires ⬢ Plastic waste from water bottles mixed with soil ⬢ Crushed concrete ⬡ “Rubblization” ⬢ Municipal solid waste ash ⬢ Steel slag fines 90
