Post on 15-May-2020
8th Annual Concrete Pavement Workshop,
January 21, 2009
Combined Aggregate Gradings – Why all the fuss?
- James M. Shilstone, Jr.
www.shilstone.com 1
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
8th Annual Concrete Pavement Workshop,
January 21, 2009
Combined Aggregate Gradings – Why all the fuss?
- James M. Shilstone, Jr.
www.shilstone.com 2
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
8th Annual Concrete Pavement Workshop,
January 21, 2009
Combined Aggregate Gradings – Why all the fuss?
- James M. Shilstone, Jr.
www.shilstone.com 3
Coarseness Factor ChartCoarseness Factor Chart
19901990’’s Aggregate Distributions Aggregate Distribution
HAYSTACK HAYSTACK -- ““OptimumOptimum””
8th Annual Concrete Pavement Workshop,
January 21, 2009
Combined Aggregate Gradings – Why all the fuss?
- James M. Shilstone, Jr.
www.shilstone.com 4
Workability ZonesWorkability Zones
WATER DEMANDWATER DEMAND
RESULTS OF GAP GRADINGRESULTS OF GAP GRADING
8th Annual Concrete Pavement Workshop,
January 21, 2009
Combined Aggregate Gradings – Why all the fuss?
- James M. Shilstone, Jr.
www.shilstone.com 5
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
8th Annual Concrete Pavement Workshop,
January 21, 2009
Combined Aggregate Gradings – Why all the fuss?
- James M. Shilstone, Jr.
www.shilstone.com 6
.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
8th Annual Concrete Pavement Workshop,
January 21, 2009
Combined Aggregate Gradings – Why all the fuss?
- James M. Shilstone, Jr.
www.shilstone.com 7
8/18 Grading Spec8/18 Grading Spec
Concrete producers Concrete producers
respond.respond.
Concrete InternationalConcrete International
March, 2005March, 2005
8th Annual Concrete Pavement Workshop,
January 21, 2009
Combined Aggregate Gradings – Why all the fuss?
- James M. Shilstone, Jr.
www.shilstone.com 8
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.”
8th Annual Concrete Pavement Workshop,
January 21, 2009
Combined Aggregate Gradings – Why all the fuss?
- James M. Shilstone, Jr.
www.shilstone.com 9
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
8th Annual Concrete Pavement Workshop,
January 21, 2009
Combined Aggregate Gradings – Why all the fuss?
- James M. Shilstone, Jr.
www.shilstone.com 10
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
8th Annual Concrete Pavement Workshop,
January 21, 2009
Combined Aggregate Gradings – Why all the fuss?
- James M. Shilstone, Jr.
www.shilstone.com 11
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
8th Annual Concrete Pavement Workshop,
January 21, 2009
Combined Aggregate Gradings – Why all the fuss?
- James M. Shilstone, Jr.
www.shilstone.com 12
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