combined aggregate grading – why all the fuss?shilstone.com/library/aci-ut-2009-paving.pdf ·...

8th Annual Concrete Pavement Workshop,

January 21, 2009

Combined Aggregate Gradings – Why all the fuss?

- James M. Shilstone, Jr.

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Combined Aggregate Grading Combined Aggregate Grading

–– Why all the fuss?Why all the fuss?

-- James M. Shilstone, Jr.James M. Shilstone, Jr.

8th Annual Concrete Pavement WorkshopUtah ACPA, LTAP, ACI

What are we talking about?What are we talking about?

1.1. Do well graded aggregate Do well graded aggregate

concrete mixes outconcrete mixes out--perform gap perform gap

graded mixes?graded mixes?

2.2. Do current combined grading Do current combined grading

specifications result in better specifications result in better

concrete?concrete?

Claims in balanceClaims in balance

SSI, Home

Depot, Walmart

FHWA, ACPA, DOTs

ShilstoneNRMCA

CI Article


January 21, 2009



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Do well graded Do well graded

aggregate concrete aggregate concrete

mixes outmixes out--perform perform

gap graded mixes?gap graded mixes?

C33 C33 -- 1923 Graded Mix1923 Graded Mix

Proportion coarse Proportion coarse aggagg ––ACI 211ACI 211


January 21, 2009



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Coarseness Factor ChartCoarseness Factor Chart

19901990’’s Aggregate Distributions Aggregate Distribution

HAYSTACK HAYSTACK -- ““OptimumOptimum””


January 21, 2009



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Workability ZonesWorkability Zones

WATER DEMANDWATER DEMAND

RESULTS OF GAP GRADINGRESULTS OF GAP GRADING


January 21, 2009



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Colorado Bridge DeckColorado Bridge Deck

Wisconsin Wisconsin UnivUniv/DOT Research/DOT ResearchOptimized Aggregate ConclusionOptimized Aggregate Conclusion

�� Compressive strengthCompressive strength -- plus 10 to 20%plus 10 to 20%

�� Air entraining agentAir entraining agent -- minus 20 to 30%minus 20 to 30%

�� Potential water demandPotential water demand -- minus 20 to minus 20 to

30%30%

�� Potential high spacing factorPotential high spacing factor for air voidsfor air voids

�� Reduced segregationReduced segregation and and higher densityhigher density

following extended vibrationfollowing extended vibration

Wisconsin DOT/Wisconsin DOT/UnivUnivEffects of particle distribution on segregationEffects of particle distribution on segregation


January 21, 2009



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.45 Power Chart.45 Power Chart

Benefits attributed to Benefits attributed to

well graded aggregate mixeswell graded aggregate mixes

�� Increased strengthIncreased strength

�� Decreased shrinkage & crackingDecreased shrinkage & cracking

�� Decreased permeabilityDecreased permeability

�� Better workability, Better workability, pumpabilitypumpability

�� Decreased curling in slabsDecreased curling in slabs

�� Less blistering & Less blistering & delaminationdelamination

�� Decreased air lossDecreased air loss

�� Better ride on pavementsBetter ride on pavements

�� Decreased segregationDecreased segregation

http://http://library.modot.mo.govlibrary.modot.mo.gov/RDT//RDT/

reports/Ri98035/RDT05001.pdfreports/Ri98035/RDT05001.pdf


January 21, 2009



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8/18 Grading Spec8/18 Grading Spec

Concrete producers Concrete producers

respond.respond.

Concrete InternationalConcrete International

March, 2005March, 2005


January 21, 2009



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http://http://www.nrmca.orgwww.nrmca.org/research//research/

D340%20AGR%20report%20phaseA2.pdfD340%20AGR%20report%20phaseA2.pdf

NRMCA FindingsNRMCA Findings

1. Water demand: Similar (67%) and higher (33%) of the

cases

2. Bleeding water amount: Similar (75%) and higher (25%) of the cases

3. Strength: Similar (67%) and lower (22%) of the cases

4. Shrinkage: Similar (92%) and higher (8%) of the cases

5. Finishability: Better FR with higher coarseness factor and lower workability factor (about 68/33) and similar FR with intermediate coarseness factor and workability factor

(about 60/35)

6. Segregation: Lower segregation with intermediate coarseness factor and workability factor (about 60/35) and similar or higher segregation with higher coarseness factor and lower workability factor (about 68/33)

NRMCA StatementsNRMCA Statements

� “..none of these empirical approaches have been scientifically tested in the laboratory to see if it leads to maximum aggregate packing density or lower cementitious paste for a given amount of workability.”

� “The intermediate coarse aggregate (No. 8) was obtained from the same quarry as the larger coarse aggregates (No. 467, No. 57). This was done in order to keep the particle shape consistent and discount the influence that a different particle shape can have on test results.”


January 21, 2009



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Mischaracterization ofMischaracterization of

well graded aggregateswell graded aggregates

Problems with currentProblems with current

well graded aggregate specswell graded aggregate specs

�� DonDon’’t take into consideration particle t take into consideration particle

shape and textureshape and texture

�� May require the use of 3, 4 or 5 May require the use of 3, 4 or 5

aggregates (and bins)aggregates (and bins)

�� Some particle sizes may not be Some particle sizes may not be

locally availablelocally available

�� May inhibit research into viable May inhibit research into viable

alternativesalternatives

8/18 Grading Spec8/18 Grading Spec


January 21, 2009



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NRMCA ConclusionsNRMCA Conclusions

� Based on the results of this study, it can

be concluded that there is no assurance

that a concrete specification that includes

a requirement for WG through compliance

with CF and/or 8-18 charts will lead to

reduced mixing water content or lower

shrinkage as is typically the goal with

these controls on aggregate grading.

NRMCA ConclusionsNRMCA Conclusions

� The above conclusion does not mean that

aggregate grading is unimportant for

concrete performance.

� In summary CF and 8-18 charts are

potential concrete mixture optimization

tools. These should not be invoked as

requirements in project specifications.

NRMCA AcknowledgementsNRMCA Acknowledgements

� The authors would like to thankDr. Cesar Constantino and Mr. James Cook of Titan America, FL, and Mr. Roger Tate of Heidelberger Technology Center, GA for participating in the round robin test program


January 21, 2009




Do current combined Do current combined

grading specs result in grading specs result in

better concrete?better concrete?

What have combined grading What have combined grading

specs done for the industry?specs done for the industry?

�� Diverted emphasis from just Diverted emphasis from just

strength, slump and air contentstrength, slump and air content

�� Forced the industry to recognize that Forced the industry to recognize that

changes in standards have affected changes in standards have affected

concrete qualityconcrete quality

�� Focused attention on contractor Focused attention on contractor

needsneeds

�� Recognized the need for reduced Recognized the need for reduced

water in concrete mixeswater in concrete mixes

Blind Men & the ElephantBlind Men & the Elephant


January 21, 2009




Should combined Should combined

aggregate grading be aggregate grading be

specified by the designer?specified by the designer?

No No –– but until we have a better way but until we have a better way

to specify our needs, combined to specify our needs, combined

grading specs should continue.grading specs should continue.

www.shilstone.comwww.shilstone.com/library/library

combined aggregate grading – why all the fuss?shilstone.com/library/aci-ut-2009-paving.pdf ·...

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