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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