Mix Design & Construction of RCCg

Wayne Adaska, P.E. Director, Public WorksPortland Cement Association

Mixture DesignMixture Design

Dry enough to support vibratory pp yrollerWet enough to permit adequate distribution of paste

Mixture DesignMixture Design

Differs from conventional concrete pavementsDiffers from conventional concrete pavements

–Not air-entrained

–Lower water content

–Lower paste content

Larger fine aggregate content–Larger fine aggregate content

–Nominal max. size aggregate +/- 5/8 in.gg g

Proportioning MethodsProportioning Methods

S l th d il blSeveral methods available:

–Concrete consistency testsConcrete consistency tests

–Soil compaction methods

–Optimal paste volume method

–Solid suspensions model

Always allow time and money for field trialAlways allow time and money for field trial

Aggregate SelectionAggregate Selection

Aggregate selection very importantResponsible for mix workability,

ti fsegregation, ease of consolidationP bl d dPre-blended or stored separately

Aggregate Selection

Select a sound, well-graded aggregateg gg g–For stability under vibratory roller, aggregate

interlock for load transfer, highest density, g yreduced segregation

Crushed or uncrushed gravel or crushed stonegCrushed aggregates:

Require more compactive effort–Require more compactive effort–Require more water

P id t t bilit l ti–Provide greater stability, less segregation–Provide higher flexural strength

Aggregate Selection

Highway base course asphalt or concreteHighway base course, asphalt or concrete aggregates can be used5/8 in NMSA5/8 in. NMSA – Provides smooth surface, reduces segregation

Higher fine aggregate content than conventionalHigher fine aggregate content than conventional– Economic advantage using non-washed and pit-run

aggregates including dense graded aggregate base – Provide adequate stability under vibratory roller

2%-8% passing #200 sieve – Supplements paste to fill voids and maintain tight surface

Optimum Combined Gradation (Shilstone Method)

The Coarseness Factor Chart provides on overview of the mixtureoverview of the mixture

The 0.45 Power Chart shows a trend

Percent of aggregate retained on individual sieves (8/18 rule) shows detailsindividual sieves (8/18 rule) shows details

Aggregate GradationAggregate GradationSieve Size Percent Passing Actual

in mm Minimum Maximum Gradation1" 25 100 100 100

3/4" 19 95 100 1003/4 19 95 100 1001/2" 12.5 75 90 85.23/8" 9.5 65 85 75.0#4 4 75 40 60 57 0#4 4.75 40 60 57.0#8 2.36 25 50 43.5

#16 1.18 20 40 34.2#30 0.6 10 30 24.3#50 0.3 7 20 10.6#100 0 15 5 15 2 1#100 0.15 5 15 2.1#200 0.075 2 8 0.7

Coarseness Factor (CF) = % retained on 3/8 in. ÷ % retained on # 8 sieve x 100

Workability Factor (WF) = % passing #8 sieve + [ 2.5 x (lb/yd3 of cementitious material – 564) / 94]÷÷

( )

Soil Compaction MethodSoil Compaction Method

Select cementitious materials–Portland cement: Type I or II (C150 or C1157)Portland cement: Type I or II (C150 or C1157)–Blended cement: (C595 or C1157)–Fly Ash (C618) Slag (C989) or silica fume–Fly Ash (C618), Slag (C989) or silica fume

(C1240) –Normally 400-600 lb/cy total cementitious–Normally 400-600 lb/cy total cementitious

(12% to 17% of dry weight)–If used fly ash proportions typically 15% to–If used, fly ash proportions typically 15% to

25%; silica fume typically 5% to 10%

Soil Compaction MethodSoil Compaction Method

Determine moisture content–Construct moisture/density curveConstruct moisture/density curve–Modified proctor ASTM D1557

A di t t t (–Assume a median cement content (e.g. 500 pcy)

Moisture-Density RelationshipMoisture Density Relationship

144

143

144

lb/c

f)

141

142

Den

sity

(l

140

141

2% 3% 4% 5% 6% 7% 8%

Dry

2% 3% 4% 5% 6% 7% 8%

Moisture Content

Modified vs Standard ProctorModified vs Standard Proctor

Soil Compaction MethodSoil Compaction Method

D t i titi t i l t tDetermine cementitious materials content–Use optimum moisture content–Run cement series

• e.g., 11%, 13%, 15%, 17%

–Select cement content which yields appropriate strength.

Strength vs Cement ContentStrength vs. Cement Content

6,000

6,500

sive

725

697

5 000

5,500

,

Com

pres

sng

th (

psi)

667

636

4,500

5,000

28

-Day

CS

tren 636

603

5694,00010% 12% 14% 16% 18%

Cement Content

569

AdmixturesAdmixtures

R t d t d b d tRetarder or water reducer can be used to increase working timeSilica fume (7%) has resulted in significant strength gainsAir entrainment not yet technologically possible, butp–Experience has shown RCC can be made

freeze/thaw resistant

Freeze-Thaw DurabilityField performance excellent, although not air entrainedentrainedMinor surface paste (1/16”) erodes, then t bilistabilizes

RCC results variable under ASTM C666 (F/T) and C672 (Deicer scaling)Tests appear to be too severe based on ppactual experienceDurability tests used for masonry concreteDurability tests used for masonry concrete and precast units possibly more appropriate

Freeze-Thaw Durability

Sample RCC Mix Designs

Port of Tacoma Units Intermodal Yard CTL Mix Canada Mix

Coarse Aggregate lb/cy 1,700 2,106 2,210Fine Aggregate lb/cy 1,700 1,378 1,338

MSA in 5/8 3/4 1/2MSA in 5/8 3/4 1/2% Finer Than #200 % 3 - 7 2 1

Cement lb/cy 450 504 470Fly Ash lb/cy 100 0 36 (silica fume)Water lb/cy 257 211 172Water lb/cy 257 211 172

Admixture oz/cwt none none 5 (WR)w/c ratio - 0.47 0.42 0.34

Unit Weight lb/cy 154.3 152.0 153.1C i 3 d i 1 810 5 460Compressive: 3 day psi 1,810 5,460 -Compressive: 28 day psi 6,050 7,900 -

Flexural: 3 day psi 525 690 1,205Flexural: 28 day psi 770 900 1,640

Construction

Construction RequirementsConstruction Requirements

Subgrade preparationMixing processg pTransportingPlacingPlacing CompactingJointingCuringg

Continuous Pug Mill

High-volume applicationsapplicationsExcellent mixing efficiency for dryefficiency for dry materials250 to 500+ tons/hr250 to 500 tons/hrMobile, erected on site

Central Concrete Batch PlantCentral Concrete Batch Plant

Highly accurate proportioningLocal availabilitySmaller output capacityLonger mix times than conventional concreteFrequent cleaningDedicated production

Dry Concrete Batch PlantDry Concrete Batch Plant

Highest local availability2-step processp p–Feed into transit

mixers–Discharge into dumps

Very slow productionVery slow productionFrequent cleaningSegregation possibleSegregation possible

Dry Concrete Batch Plant

SupplementarySupplementary mixer can aid in thorough mixing and plant throughput.

Mobile Mixers

Transporting

Rear dump trucks normally usedMinimize transport timeCovers required for long hauls, or h t/ i d ditihot/windy conditions

Transporting

Load in multiple piles

Placing

Layer thicknessy–4 in. minimum–8 in. maximum (10 in. with heavy-duty pavers)( y y p )

Timing sequence–Adjacent lanes placed within 60 minutes for–Adjacent lanes placed within 60 minutes for

“fresh joint”, unless retarders used–Multiple lifts placed within 60 minutes for bondMultiple lifts placed within 60 minutes for bond

Production should match paver capacityContinuous forward motion for best smoothness–Continuous forward motion for best smoothness

Placing Equipment

High-density paversg y p– Vibrating screed– Dual tamping bars– High initial density, 90-95%g y,– Reduces subsequent

compaction– High-volume placement g p

(1,000 to 2,000 cubic yards per shift)

– Designed for harsh mixes– Smoothest RCC surface

Placement Equipment

Transfer equipment keeps paver fully charged

Placing Equipment

Conventional asphalt pavers– Provide some initial density

(80-85%)

– Relatively smooth surface

– May require modification

– Increased maintenance

Compaction

Proper compactionProper compaction is critical for strength and durabilityyCompact to 98% Modified ProctorVibratory rollerRubber-tire roller

Compaction Very ImportantCompaction Very Important

Construction JointsConstruction Joints

Most critical area of projectMost critical area of projectMust be constructed properly for durabilityE b d/i t l k l b tEnsures bond/interlock, so slab acts monolithicallyTh t f t ti j i tThree types of construction joints:– “Fresh joints”

“Cold joints”– Cold joints– “Horizontal joints”

Fresh JointFresh Joint

Edges CriticalEdges Critical

Compaction more difficult

Segregation more likely

Try to minimize number of cold joints

Care needed to match grade from cold gto fresh joint

Edge Compaction

Compacting shoeCompacting shoe

Edge CompactionEdge Compaction

Avoid Edge SegregationAvoid Edge Segregation

Matching Fresh to Cold JointMatching Fresh to Cold Joint

Cracking/JointingCracking/Jointing

Saw cut jointsSaw-cut joints unnecessary for performancepNatural cracks provide excellent load transferSaw-cut joints control cracks for aesthetic purposes

Natural CracksNatural Cracks

Most economical15 to 60 ft spacingOften first cracks appear within 24 hoursN k idthNarrow crack widthsSeal if > 1/4 in.Provide load transferProvide load transferMinimal raveling

New, UnsealedCrack

10-yr OldSealed Crack

Saw-Cut Joints

More aesthetically pleasingSoff cut very effectiveSoff-cut very effective, shortly following placementpNeed to saw within 12 hours to avoid

t ll d kiuncontrolled cracking1/3 to 1/4 depthSeal joints similar toSeal joints similar to conventional concrete

Curingg

EXTREMELY IMPORTANTEXTREMELY IMPORTANTEnsures surface durability; reduces dusting Low moisture content in RCC; no bleed waterThree methods:Three methods:–Moist cure

Concrete curing compound–Concrete curing compound–Asphalt emulsion

Water Cure

Typically 7-day specified

Concrete Curing Compoundg p

White-pigmented concrete curing compoundsApplication rate depends on surface texture

Surface Texture

Intermodal Yard, TX Sludge Drying Bed, TX

Honda, ALWarehouse Facility, WI

Quality Control

Quality ControlQuality Control

Aggregate quality gradation & moistureAggregate quality, gradation & moisturePlant calibrationDensity testsSmoothnessSurface textureThicknessThicknessStrength

ASTM D1557

ASTM C1435

ASTM C1435

Typically 3/8 in. over 10-ft length

More Information

www.cement.org/pavements

Questions?Discover how beautiful concrete can be

Specifications for Mix DesignSpecifications for Mix Design

Prescriptive: Provides required properties of a product material or piece of equipmentof a product, material or piece of equipment and the method of installation.

Performance: Provides the required results, criteria by which the performance will be judged and the method by which it will be verified.

Prescriptive ExamplesPrescriptive Examples

A t d tiAggregate gradation

Mix design including cement contentMix design including cement content

Type of mixing plantyp g p

Type of paver

Type and size of compaction equipment

Method of curing

Performance ExamplesPerformance Examples

Minimum strength

Minimum densityMinimum density

Production rateProduction rate

Thickness

Smoothness

Combined SpecificationCombined Specification

Mix design/Compressive strength

Type of mixing plant/Production rate

Type and size of compactor/Density

Minimum number of passes/Density