Cement Stabilization Of Soils - FPA

Cement Stabilization of SoilsMatthew W. Singel, P.E.Program ManagerSoil Cement/Roller-Compacted Concrete

Cement-Based PavementMaterialsCement eNo Wearing edFlowable lledWater Contentrse Required

ConcreteSoil-CementCementitious Gel or PasteHydration Products coats all particles fills voids all particles not coated voids not filled linkages bind soilagglomerations together

Soil-Cement Materials in aPavement SectionCemFull ent-Tre-Depath R ted Baeclasmat eionCement-ModifiedSoil

APPLICATIONS

Reasons to Modify Improve the properties of the subgrade soilReduce volume change caused by moistureImprove wet strengthImprove compactibility Expedite construction by improving subgradesupport in wet weatherEliminate muddy construction sitesCreate an all-weather work platformIt is important to remember thatsoil modification is different than soil stabilization

Construction Problemswith Silts or Sandy Soils Fine-grained and difficult to compactPoor gradationLow bearing capacityLow cohesiveness and shear strengthUnstable under construction equipment

Construction Problemswith Clay Soils High plasticity and cohesivenessFine-grained and poorly gradedHigh shrink and swell potentialExpansive when wetLow bearing strength when moistand deform under loadDifficult to dry outDifficult to compact

Solutions for poor subgrade soils Excavate/replacewith select fillAggregate9 Soil9 Increase thebase/pavementthicknessContain usingfabrics or othergeotextilesModify soils witha calcium-basedadditive such asportland cement

BENEFITS

Benefits of Cement-Modified Soil Small addition of cement tosoils to change propertiesEliminates need forremoval/replacement ofinferior soilsLow cost soil improvementImproves pavement supportForms weather-resistantwork platformProvides permanent nonleaching modification

By treating the soil with cement,the detrimental properties of claycan be improved through thefollowing three onPozzolanicReaction

Cement Reactions with Clay PrimaryIon exchange between calcium in cementand clay which occurs immediately SecondaryNormal cement hydration contributes tostrength gain

Primary Reaction Cation exchange reactions occur Intensifies the grouping of the clayparticles by neutralizing the negativesurface charges Produces Calcium Hydroxide – Ca(OH)2 –(hydrated lime)

Cation ExchangeClay particleSodium ions Negativelychargedclay surface OriginalspacingDipolar H2O Calcium ions Reducedspacingafter ionexchangeandshrinkageof waterlayer

Particle RestructuringUnmodified clay particlesClay particles afterflocculation / agglomeration

Secondary Reaction Clay participates in the secondary process Clay is converted to calcium form Calcium ions combine with dissolved silicaand alumina in the clay to create additionalcementitious materials Strength gain occurs

Cement HydrationCement Water Calcium Silicate Hydrate(Cementitious Gel)- plus –Calcium Hydroxide(Hydrated Lime)

Hydrationunhydratedcement grainclay particleclay-cementbondscement hydration products(CSH and CAH)

Pozzolanic ReactionHydrated Lime Silica Calcium Silicate HydrateHydrated Lime Alumina Calcium Aluminate HydrateSupplied byCementHydrationClayMineralsCementitiousGelNote: Without silica or alumina-based clay minerals,this process does not occur (e.g. sandy or silty soils).

Pozzolanic Reactioncementitiousmaterial fromcement hydrationCa(OH)2Ca(OH)2clay particle(SiO2, Al2O3)cementitiousmaterial frompozzolanicreactions(CSH and CAH)Ca(OH)2Ca(OH)2claycementbondscalcium hydroxidefrom cement

Time of Modification Processes1. ParticleRestructuringImmediateto a fewhours2. Cement HydrationLargest strengthgain between1 day and 1 month3. Pozzolanic ReactionSlowly, overmonths andyears

DESIGN

Laboratory TestsSieve Analysis (ASTM C136) Atterberg Limits (ASTM D4318) Moisture-Density (ASTM D558) Durability Tests Wet-Dry (ASTM D559)Freeze-Thaw (ASTM D560)Soluble Sulfates (ASTM D516) Compressive Strength (ASTM D1633)

ASTM C136Standard Test Methodfor Sieve Analysisof Fine and Coarse Aggregates

Particle SizeDistributionGravelSandSiltClay

Hydrometer

ASTM D4318Standard Test Methodsfor Liquid Limit, Plastic Limit,and Plasticity Indexof Soils

Plasticity Index (PI) The range of moisture through which a soil deformsunder loading The measure of a soil’s affinity to retain moisture Plasticity Index is the difference between theLiquid Limit and the Plastic Limit of a soil PI LL - PL

Expansive Soils andPI pansive2 or less0 to 102 to 410 to 20ModeratelyExpansiveHighlyExpansiveMore than 4 20 and above

ASTM D558Standard Test Methodsfor Moisture-Density Relationsof Soil-Cement Mixtures

Standard Proctor Moldand Rammers

Moisture/Density Relationship

Moisture/Density Relationship125Dry Density (lb/cf)Maximum Dry Density120115110105Optimum Moisture Content1005%7%9%11%13%Moisture ContentASTM D55815%17%

ASTM D559Standard Test Methodsfor Wetting and DryingCompacted Soil-CementMixtures

Wet-Dry Tests Three cement contents testedSeparate specimens for W-D and F-TStandard Proctors used at optimum moistureand maximum dry densityMoist cured for 7 days

Wet-Dry Tests Wet-DrySoaked in water for5 hoursDried at70 C (158 F)for 42 hoursBrushedRepeat 12 times

ASTM D516Standard Test Methodfor Sulfate Ion in Water

0.00% to 0.30% - Sulfate Levels Too Low to be of Concern0.31% to 0.50% - Sulfate Levels of Moderate Risk0.51% to 0.80% - Sulfate Levels of Moderate to High Risk0.81% and up - Sulfate Levels of High and Unacceptable Risk

ASTM D1633Standard Test Methodfor Compressive Strengthof Molded Soil-CementCylinders

CMS Strength DeterminationThe objective of CMS is to amendundesirable properties of problemsoils or substandard materials so thatthey are suitable for use inconstruction. The amount of cementadded to the soil is less than thatrequired to produce a hardened massbut is enough to improve theengineering properties of the soil.It is important to remember thatsoil modification is different than soil stabilization

CTB Strength Determination Unconfined Compressive Strength TestingUsed by most State DOT’s and FAASimple and quick procedure7-day strengths rangingfrom 300 psi to 800 psi(2.1 MPa to 5.5 MPa) aregenerally recommendedStrengths vary accordingto project requirements300 to 400 psi (2.1 to 2.8 MPa) mixed-in-placeand 600 to 800 psi (4.1 to 5.5 MPa) plant mixed

FDR Strength Determination Unconfined Compressive Strength TestingASTM D1633Used by most State DOT’s and the FAASimple and quick procedure7-day strengths rangingfrom 300 psi to 400 psi(2.1 MPa to 2.8 MPa) aregenerally recommendedProven strength (support)under heavy traffic conditionsProven durability (performance)in both wet/dry and freeze/thawenvironments

Please keep in mind thatstrength and durabilityare NOT the same thing!The purpose of themix design procedureis to select thecorrect additive thatmost closely balancesboth strength ANDperformance for theroadway materials!

Early Research InvolvingCement-Modified Soils “Cement Modification of Clay Soils”A. P. Christensen Portland Cement Association 1969Studied the effects of treating clay soils with small amountsof portland cementHe compared: Plasticity Index (PI) reduction shrinkage limits cohesiveness unconfined and triaxial compressive strengths

Study Soils Eight were clays, three were clay and siltyclay loamsFour were classification AASHTO A-6Seven were classification AASHTO A-7-6 The predominant soil used in the study was aTexas clay (Montmorillonite) Cement percentages used were 3% and 5% byweight of dry soil

Effect of Modificationon Plasticity IndexPlasticity Index (%)504140363332273022201918131010740Soil 2UntreatedSoil 53% CementSoil 9Soil 105% Cement

General Results ofChristensen’s Study Portland cement increased the shrinkagelimits of clay soils to values greater thanoptimum moisture Soils with a Plasticity Index (PI) between18 and 29 were reduced to 10 or less aftera 24-hour compaction delay

Current Research InvolvingCement-Modified Soils “Tube Suction Test for Stabilized Materials” Tom Scullion, P.E. Texas Transportation Institute 2001 Evaluated the moisture susceptibility of subgradesoils used in roadway pavements Recognized an empirical relationship betweenlaboratory electrical conductivity values andexpected performance (durability) of subgradematerials in the field

Tightly BoundLoosely BoundViscous Water

Tube Suction Test (TST)for Moisture Susceptibility

Using the Dielectric Probedielectric - n. A nonconductor of electricity.

Interpreting TST Results

Sample Test Data1816Dielectric Value141210Cement 5.5%C 3.5% FA 8%8Cement 7.5%64200246Time (days)81012

Summary of RecommendedLaboratory Test Procedure

General Results of the TexasTransportation Institute’sResearch A final dielectric value less than 16appears to be indicative of a stabilizedsubgrade material adequately resistant tomoisture susceptibility Reliable durability predictions can bemade in two-thirds the time of theconventional W-D and F-T Tests

CONSTRUCTION

Subgrades before and after CMS

TESTING

Primary Testing RequirementsGradationA common gradationrequirement is for100% to pass the1.5-inch (38 mm)sieve and a minimumof 60% to pass theNo. 4 (4.75 mm)sieve (ASTM C136).MoistureDensityA common moisturerequirement is to bewithin 2% of thelaboratory establishedoptimum moisturecontent (ASTM D558).A common densityrequirement is to bebetween 95% and98% of theestablished laboratorystandard Proctordensity (ASTM D558).

Secondary Testing s forsubgrade depths canvary from as little as6 inches (150 mm)up to 2 feet (0.6 m)depending ongoverning agency.Measures in-placeengineering valuesusing structural layerstiffness, klbf/in(MN/m) and Young’sModulus of a material,kpsi (MPa).Modified subgrade MUST bestable before next pavementcourse is constructed!Proof-rolling is the mostcommonly accepted practice.

But what about strength?The objective of CMS is to amendundesirable properties of problemsoils or substandard materials so thatthey are suitable for use inconstruction. The amount of cementadded to the soil is less than thatrequired to produce a hardened massbut is enough to improve theengineering properties of the soil.It is important to remember thatsoil modification is different than soil stabilization

PERFORMANCE

CMS can be used as a subgradefor either flexible or rigidpavement structures

The final impact of CMS

Summary:Cement-Modified Soil Cement factors normally 2% to 5%Significant and immediate reductions in thesoil’s Plasticity IndexIncreases bearing ability of granular orplastic soilsProduces workable foundation for bases forboth rigid and flexible pavements

Summary:Cement Effects Strength improves immediately and increasesover years No long-term effects from leaching Compaction can occur immediately with no“mellowing period” necessary

Full-Depth ReclamationMatthew W. Singel, PE

Full-Depth Reclamationwith Cement Applications Design Construction Testing Performance

Definition of Reclamation Method of flexible pavement reconstruction thatutilizes the existing asphalt, base, and subgradematerial to produce a new stabilized base coursefor an asphalt, chip seal, or concrete wearingsurface.Alternative Terms:Full-Depth Recycling (FDR)Cement Stabilized Reclaimed Base (CSRB)Cement Recycled Asphalt and Base (CRAB)Cement Recycled Asphalt Pavement (CRA )

The New BaseThe new cement recycled base will bestronger, more uniform, and moremoisture resistant than the originalbase, resulting in a long, lowmaintenance life

Inside a Reclaimer

Soil-Cement Materials in aPavement SectionCemFull ent-Tr-Depth eatedBReclam aseCeatiomenntMod ifiedSoil

Equipment and MaterialsRecycling vs. New BaseTrucks(Number)18012Material(tons)Landfill(cu yd)Diesel(gal)45003002700030005001 Mile of 24’-wide 2-lane road,6” base 2” asphalt surfaceNewRecycle

Pavement Loadings .An Increasing Trend

Rural Interstates - Growth700Percent Growth (%)650%600LOAD500400300200ADT150%100Source: Highway Statistics 7819761974197219700

Pavement DistressAlligator Cracking

Pavement DistressRutting

Pavement DistressBase Failure

Pavement DistressMoisture Infiltration

Pavement DistressPotholes