Construction Considerations in Concrete Pavement Recycling Considerations (FINAL... · Construction...
Transcript of Construction Considerations in Concrete Pavement Recycling Considerations (FINAL... · Construction...
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Construction Considerations in Concrete Pavement Recycling
Gary FickTrinity Construction Management
Services
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Construction Considerations in Concrete Pavement Recycling
• Webinar OutlineRCA basicsEquipmentMaterialsProcessConstraintsDesign considerationsExample project scenarios
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Recycling Basics
• Commercial recycle yard• Mobilization of a crusher to a projectHaul materials to a crusher siteOn-grade processing
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Commercial Recycle Yard
• Mixture of source materialsConcreteMasonryAsphalt
• RCA specifications (gradation and deleterious materials) impact the potential use of this type of material
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On-Site Crusher
• Crushing, screening and stockpiling at a central locationInterchange ramps within the R.O.W. or
similar areas are ideal• Broken concrete is hauled to the crusher site• RCA is hauled back to the grade
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Typical RCA Site13
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On-Grade Crusher
• Mobile crusher processes the broken concrete on the grade
• No haul-off or haul back of RCA
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Typical On-Grade Crushing15
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RCA Equipment• Jaw crusher can be used as a primary
crusherAllows feeding of larger sized pieces of
broken concrete (24”)Helps to separate steel from the broken
concrete
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RCA Equipment• Impact crusher is the most common for RCA
applications• Most steel (dowels, crcp and mesh) should be
removed prior to crushing• Smaller feed size (approx. 12” minus)
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RCA Process
• In almost all cases, a screen is used to properly size the materialAllows for increased production by
returning oversized material to the crusherCan be used to split material on a mid-
sized sieve (e.g. 3/8”) when specifications require
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RCA Process
• Equipment used to produce RCA is identical to that used in a quarry producing virgin aggregatesSimilar QC results for gradation
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RCA Process• What about existing sealant?• What about existing bituminous patch
materials?Unnecessary to remove prior to crushingVolume of these materials is negligible when compared
to the volume of concrete being recycled
… except when RCA is used as a coarse aggregate for the new concrete pavement
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RCA Process• Breaking pavement
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RCA Process• Removing SteelCRCP, dowels and meshTie-bars can be left in the broken concreteSteel is usually hauled to a salvage facility
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RCA Process• Loading and hauling
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RCA Process• Crushing and sizing
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RCA Process• Hydraulic hammer breaking over-size rubble
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RCA Process• Excavator feeding crusher
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RCA Process• Crusher
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RCA Process• Magnet
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RCA Process• Sizing screensOversized returns to crusherFinished product transferred by conveyor
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RCA Process
• Oversize return
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RCA Process• Stockpiling – use proper techniques to
minimize segregation
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On-Grade Recycling• Same equipment• No hauling requiredSignificant cost savingsReduced exposure to traffic
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On-Grade Recycling• Typically used as granular baseDense graded or semi-drainable
• Stockpile on the existing shoulder if subgrade manipulation is required
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RCA Summary
• A controlled processBreakingCrushingSizingStockpilingReturn to project as quality aggregate for
subbase, base, concrete, etc.
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RCA Design/Construction Considerations• Material applicationsUnbound granular baseBound granular base (cement
treated)(plant mixed)Granular shoulder/backfillConcrete aggregateOther
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RCA Design/Construction Considerations• Construction processes for RCAShaping and compacting of unbound base
is the same as for virgin materialHowever, absorption is higher so even
more water will be necessary to attain optimum
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RCA Design/Construction Considerations• Construction processes for RCAPlant mixed materials are batched just like
virgin materialsStockpiles must be kept moist (above SSD) to avoid
absorption during the batching processSpecific gravity of RCA is lower than virgin materials,
therefore it will take less mass per CY of batched materials as compared to virgin aggregates
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RCA Design/Construction Considerations• Fines in RCAApprox. 1% to 2% passing the #200 from
crushing clean concrete pavementAdditional fines come from excavating
underlying soils when loading the broken concreteGradation specifications should consider:Underlying material – subgrade vs. treated baseModify specification as needed (reduce the low end of
% passing the #200)
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RCA Design/Construction Considerations• Fines content comes predominantly from the
underlying materials
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RCA Design/Construction Considerations• Residual mortar particles in RCA used as
concrete aggregate#4 and larger particles composed of mortarPotential for higher absorptionSome projects have shown more distressFurther crushing can break these particles down, but
leads to inefficiencies (production and by-product)
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RCA Design/Construction Considerations• Should RCA be mandated/specified, or
should the market determine the most efficient means of constructing the project?
• Where should RCA be used?What are the objectives?CostSustainabilityQualityOther
It depends …
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RCA Design/Construction Considerations - Constraints• RCA use and applications is impacted by:Availability of space for recyclingEnvironmental permitting restrictionsCost of virgin materials
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RCA Design/Construction Considerations - Constraints• RCA use and applications is impacted by:Volume of RCA available from the projectTiming of that availability (phasing)Material specifications
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RCA Design/Construction Considerations• Existing divided highway (5 mile project)8” JPCPHMA shoulders6” granular base
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RCA Design/Construction Considerations• Phase ITemporary HMA widening of NBPlace traffic on widened NB0 CY of RCA available5,642 CY of virgin granular base required
for widening
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RCA Design/Construction Considerations• Phase IIReconstruct SB12” JPCP on 6” RCA granular base
– RCA available = 46,933 CY– RCA required = 52,800 CY– Virgin required = 5,867 CY (≈ 11%)
8” JPCP shoulders on salvaged granular base– Salvaged available = 60,133 CY– Salvaged required = 69,412 CY– Virgin required = 9,279 CY (≈ 13%)
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RCA Design/Construction Considerations• Phase II
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RCA Design/Construction Considerations• Phase IIIReconstruct NB12” JPCP on 6” RCA granular base
– RCA available = 46,933 CY– RCA required = 52,800 CY– Virgin required = 5,867 CY (≈ 11%)
8” JPCP shoulders on salvaged granular base– Salvaged available = 69,207 CY– Salvaged required = 28,101 CY– Excess salvaged granular base = 41,106 CY
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RCA Design/Construction Considerations• Phase III
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RCA Design/Construction Considerations• What about other RCA applications for the
same hypothetical project?4” cement treated granular base4” cement treated drainable baseIncorporated as coarse aggregate in the
JPCP
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RCA Design/Construction Considerations• Specified gradation impacts the amount of
RCA recoveredDrainable base specifications have fewer
fines than a granular baseCoarse aggregate for concrete has fewer
fines than drainable bases
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RCA Design/Construction Considerations• Specified gradation impacts the amount of
RCA recovered
Sieve
RCA Granular Base Percent Passing
Drainable BasePercentPassing
Concrete Stone Percent Passing
1 ½" 100 100 100
1" 95-100 95-100 95-100
¾" 65-85 75-85
½" 55-65 25-60
⅜" 40-60 40-50
#4 25-45 15-25 0-10
#8 0-5 0-5
#10 15-30
#40 5-15 0-5
#200 0-10 0-3 0-2
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RCA Design/Construction Considerations• RCA as granular base93,866 CY available93,866 CY used
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RCA Design/Construction Considerations• RCA as cement treated drainable base93,866 CY available79,786 CY used14,080 CY screened and stockpiled
• Where can this material be incorporated in the project?
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RCA Design/Construction Considerations• RCA as coarse aggregate for concrete93,866 CY available65,706 CY used28,160 CY screened and stockpiled
• Where can this material be incorporated in the project?
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RCA Design/Construction Considerations• Back to the hypothetical projectPhase III had approx. 41,000 CY of excess
salvaged granular baseUse as granular base under the 12” JPCP?This leaves ±35,000 CY of RCA that could be used for
coarse aggregate in the JPCPApprox. 20,000 CY needed for the JPCPThis leaves ±10,000 CY of excess fines and ± 5,000
CY of excess RCA
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RCA Design/Construction Considerations• Verify that the contractor is complying with:Environmental regulations (dust and runoff)Safety regulations
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RCA Design/Construction Considerations (summary)• There are many options for the use of RCASpecifications should allow RCA wherever
possibleModify durability requirements (LA Abrasion, sodium
sulfate, C 666, etc) to allow RCAReduce the spec. for the low end of the material
passing the #200Gradation QC should be performed at the same
frequency as for virgin aggregates• Let the market determine how/where to
incorporate RCA cost effectively
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