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1、SUBGRADE STABILISATION USING CHEMICAL AGENTSTao Wang 11616947Zheng Liu 11882952JingWei LI 11588035Han Zhang 11539044 IntroductionThe subgrade is the in situ material upon which the pavement structure is placed.Subgrade performance generally depends on two characteristics, load bearing capacity and v

2、olume change.Poor subgrade can not be avoided in most cases. As poor subgrade, such as soft soil, can not provide enough load bearing capacity for pavement structure, it could cause deformation.Pavement Failure from unstable soils Two ApproachRemoval and ReplacementPoor subgrade soil can be removed

3、and replaced with stronger materials.Using chemical agentsStabilizing the subgrade with an appropriate chemical stabilizer( such as lime, cement and fly ash）increase subgrade stiffness and reduces expansion tendencies. LimeCementCement kiln dustGround Granulated Blast Furnace Slag (GGBFS) Chemical A

4、gents What is limeLime has been used as a stabilizing agent for problematic soil since the 1930s in the southern of the USA.Lime include quicklime (calcium oxide CaO), hydrated lime (calcium hydroxide CaOH2), and lime slurry.Quicklime is manufactured by chemically transforming calcium carbonate (lim

5、estome CaCO3) into calcium oxide.Hydrated lime is created when quicklime chemically reacts with water. Lime Treatment how it workDryingIf quicklime is used, it immediately hydrate and release heat. It will reduce the soils moisture holding capacity, because the quicklime can react with the water fro

6、m soil.ModificationAfter initial mixing, the calcium ions will migrate to the surface of the clay and displace water and other ions. The Plasticity Index of the soil will decrease dramatically.StabilizationThe calcium will react with silica and alumina to form calcium-silicate-hydrate (CSH) and calc

7、ium-aluminate-hydrate (CAH). These two things are cementitious products. These process can improve the load bearing capacity of soil, and make the soil impermeable. EquationCement StabilisationCement is one of the most common construction materials that being used in pavement constructions in terms

8、of cement stabilization, it can be use in light traffic roadways Advantages of cement stabiliserEnvironmental friendlyCheapReduce the sensitivity to moisture (Reduce risks of loss bearing capacity in wet conditions. Therefore the ability of resisting rutting and other types of deformation is improve

9、d.)Increase durability of road surface and decrease the maintenancecement stabiliser Portland Cement Stabilisercan be used to stabilise large range of soils, from granular soils to low plasticity clays. Highly plastic clays are most effectively stabilized with lime.Portland Cement StabiliserThe Port

10、land cement stabiliser is suitable for gravel soils which have maximum 45 precents of soils aggregates larger than 4 sieve, and the soil plasticity index should be less than 20. Commonly for the road pavement subgrade construction, the cements setting time should be less than 2 hours. Cement kiln du

11、st （CKD）IntroductionCement kiln dust (CKD) is a finely-divided particulate material carried in the air stream of a cement kiln.Using CKD is to improve the texture, increase the strength and reduce the swell characteristics of the various soilsComposition of Cement Kiln DustIn general, CKDs are parti

12、culate mixtures of partially calcined and unreacted raw feed, clinker dust, and fuel ash, enriched with alkali sulfates, halides, and other volatiles.Constituentor PropertyPercentageLowMeanHighSiO26.016.528.5Al2O33.24.49.6Fe2 O30.82.75.9CaOFrom 9 sourcesFrom 13 sources16.08.347.612.665.020.2MgO0.82.

13、34.8SO30.77.126.3Na2O0.080.83.2K2O1.085.526.2Loss on Ignition2.516.032.0Analyses of CKDs from Nine Different Sources CKD StudyWaters and Schwieger A limited study on the effects of CKD on a moderately plastic soil (liquid limit = 50) as compared with lime. The addition of 6% CKD lowered the plastici

14、ty index the same amount as 4% quicklimeDescriptionCure timeLLPLPINative soilN/A501931Native soil with 6% CKD2 hours452817Native soil with 6% CKD48 hours422814Native soil with 6% CKD7 days422814Native soil with 4% Quicklime48 hours413110Native soil with 4% Quicklime48 hours39336Atterberg Limits of N

15、ative and Treated SoilCKD StudyFu. C.N. - QISThe effectiveness of CKD in reducing plasticity for a soil with high plasticity (LL = 79, PI = 62). Changes in PI with the addition of CKD or Lime TestingThe testing procedure is cited from Robert L., Elizabeth (2004).Eight different soils classified as C

16、H, CL, ML, SM and SP were selected for use in the admixture evaluation.TestASTMTestASTMGrain Size AnalysisD 422SwellKDOT SpecAtterberg LimitsD4318Freeze-thawD 560Specific GravityD 854Wet-dryD 559pH Lime StabilizationD 6276Unconfined CompressionD1633, 5102Moisture-Density RelationshipD 698Standard Te

17、sting ProceduresResultsAtterberg LimitsChanges in the liquid limit were irregular with increases for some soils and decreases for others. However, increases in the plastic limit were consistently large enough to lower the plasticity index for all soils. Unconfined Compression StrengthUnconfined comp

18、ressive (UC) strength at optimum moisture increased approximately 100 to 200% for most soils.UC Strength Native vs. CKD treatedResultsSoil Stiffness with TimeStiffness values for CKD treated samples were substantially higher than for native samples within a short time after compaction. However there was little additional stiffness gain observed after the first few hours.SwellCKD performed very well in swell testing for the entire range of soils, This performance is likely a funct