“Moving Advancements into Practice”

MAP Brief October 2014

Describing promising technologies that can be used now to enhance concrete paving practices

Aggregate Gradations for Concrete Pavement

Mixtures
www.cproadmap.org

October 2014 Introduction

ROAD MAP TRACK 1 Most modern concrete mixtures have more the specified smoothness and the textured
than 70% of their volume composed of ag- finish to reduce noise and improve skid re-
PROJECT TITLE gregate. Aggregate is typically an inexpen- sistance. While mixtures containing excessive
Aggregate Gradations for material on the #8 through #200 can lead to
sive ingredient that can reduce the amount
Concrete Pavement Mixtures
of shrinkage and subsequent cracking. stickiness, harsh surface finishing, and prob-
However, proportioning high aggregate lems with poor consolidation, mixtures with
TECHNICAL WRITERS
Tyler Ley volumes in a mixture is a complex subject. low amounts retained on the #30 through
Oklahoma State University The gradation, volume, shape, and texture #200 can create segregation [4]. In addition,
of aggregates make major contributions to many specifications limit the material on
Daniel Cook
Oklahoma State University the workability, paste content required, and the #200 sieve and smaller, as it has a direct
mechanical properties of a concrete mixture. impact on the water required in a mixture
Each of these issues will be further dis- due to fine particles being made of clay-like
EDITOR
Sabrina Shields-Cook cussed in detail in the sections below. particles [6]. However, if these particles were
not clays then it might be possible to use
SPONSOR larger amounts.
Workability
Federal Highway Administration
The workability requirements of a concrete
Paste Content
MORE INFORMATION mixture can drastically change depending
Tyler Ley on the application. The unique construc- Commonly, mixtures only use enough paste
Oklahoma State University tion process of slip formed paving requires volume to achieve the required workabil-
tyler.ley@okstate.edu ity. One method for determining the paste
the workability of a mixture to be flowable
405-744-5257
enough under vibration for consolidation content through a concrete mixture has been
but still able to hold an edge after the vibra- through the voids content of the aggregate
tion has stopped and the side forms are [7]. Not only does the paste content play a
removed [1, 2]. This property of a concrete role in cracking risk, but the paste content is
The Long-Term Plan for Concrete is called thixotropy, and is controlled by the a primary controller of cost, shrinkage, and
Pavement Research and paste properties of a mixture and the aggre- heat generated in a mixture. These reasons
Technology (CP Road Map) is a
national research plan developed gate volume and gradation [3]. demonstrate the importance of aggregate
and jointly implemented by the gradation for reducing the paste content of a
concrete pavement stakeholder The aggregate gradation plays a major role mixture. However, the aggregate gradation
community. Publications and
other support services are in the constructability of a slip formed pave- with the minimum voids content does not
provided by the Operations
Support Group and funded by
ment. For example, if the aggregate grada- necessarily lead to superior mixtures.
TPF-5(286). tion contains high amounts on any given
Moving Advancements into sieve size, it negatively impacts the ability of
Practice (MAP) Briefs describe
a mixture to be consolidated under vibra-
Mechanical Properties
innovative research and
promising technologies that can tion [4]. Also, the material on the #8 through Since aggregates make up a large volume
be used now to enhance concrete
paving practices. The June 2014
the #30 sieve plays an important role in the of the concrete, the type of aggregate has a
MAP Brief provides information cohesion of the concrete or the ability for major impact on the mechanical properties
relevant to Track 1 of the CP Road
Map: Materials and Mixes for it to hold an edge [4, 5]. Mixtures lacking of the concrete [3, 8, 9]. Aggregates largely
Concrete Pavements. these sieve sizes are at greater risk of edge control the stiffness and creep of a concrete
This MAP Brief is available at slumping and possibly segregation. mixture. However, these properties are more
www.cproadmap.
org/publications/ dependent on the aggregate type and volume
MAPbriefOctober2014.pdf. Finally, a mixture needs to have the right than on the aggregate gradation.
balance of mortar and coarse aggregate for
 CP Road MAP Brief October 2014

One mechanical property of focus for concrete producers is Coarseness Factor Chart
the compressive and flexural strength of the concrete. This
The Coarseness Factor Chart (figure 1) developed by Jim Shil-
parameter is primarily controlled by the water/cementitious
stone, Sr. is an empirical approach to aggregate proportioning
materials (w/cm) ratio of the paste and the type and volume
based on his experience in producing lean concrete mixtures
of the aggregate. The aggregate gradation does play a minor
with acceptable workability and reduced segregation [11, 12].
role in determining the strength of concrete through modifi-
The Coarseness Factor Chart plots two different parameters
cation of the amount of interfacial zone around aggregates,
that help divide a combined aggregate gradation into coarse,
increased aggregate interlock, and relative stiffness of the
intermediate, and fine aggregate sections. The Coarseness Fac-
paste to the aggregate.
tor represents the ratio of coarse to intermediate aggregate and
the Workability Factor represents the ratio of sand and cement
How do I find a good gradation? to coarse and intermediate aggregate.

Much work has been done to take the information from a Coarseness Factor (CF) = (Q/R)*100
sieve analysis and develop methods and tools that help us- Q= cumulative % retained on the 3/8” sieve
ers better understand the gradation and provide insight in R= cumulative % retained on the no. 8 sieve
how the gradation affects concrete performance. However,
not all of these tools have proved useful when applied in Workability Factor (WF) = W + (2.5(C-564)/94)
the field. A more detailed description of several approaches W= cumulative % passing the no. 8 sieve
and their importance is discussed below. C= cementitious material content (lbs. /yd³)

The chart has been divided into five different zones that report-
Gap-Graded vs Well-Graded edly predict the workability of a mixture. Some states require
that mixtures for slip formed pavements fall within a narrower
Discussion has long circulated about the performance dif-
ference between gap-graded and well-graded aggregate
systems [3, 4, 5, 8, 9, 10, 11, 12]. Both of these terms are
broad expressions that do not have well defined mean-
ings. Well-graded aggregate systems are interpreted as
gradations with a uniform amount of material retained on
adjacent sieve sizes. These mixtures can be used to produce
workable mixtures with reduced paste contents and tend to
obtain lower voids content of the combined aggregate gra-
dation [9]. However, mixtures with the idealized grading do
not always show superior performance [3, 4, 9, 10].

Gap-graded aggregate systems have low and high amounts

retained on a given range of sieve sizes. Recent work has
suggested that high amounts (> 20% retained) on a given
sieve size has a significant impact on workability, while
having low amounts did not drastically impact workability
[4]. However, most of the literature agrees that a range of
gradations can be used with little effect on the performance 47
of the concrete [3, 4, 9, 10].
IV
42
Maximum Nominal Aggregate Size
Workability Factor (%)

III
Historically, it has been suggested that one should use the 37
II
gradation with the largest maximum nominal aggregate
that is available and constructible in a concrete mixture. It is 32
I
suggested that when the aggregate with maximum size of
aggregate is used, then less water (or paste) will be required 27
to achieve a given workability. While this may be commonly V
used in practice, the use of larger aggregate sizes does not
22
guarantee improved workability [4]. The use of a larger 80 70 60 50 40 30
maximum nominal aggregate size expands the number of Coarseness Factor (%)
sieves sizes and can help reduce high sieve size amounts for
2 a gradation. Figure 1. Power 45 Chart (top) and Coarseness Factor Chart (bottom)
 CP Road MAP Brief October 2014

region within Zone II [5]. While some contractors report gradation of more than 500 different mixtures with 8 differ-
improved constructability, others have found challenges with ent aggregate sources [4, 13]. Since the Slump Test has not
mixtures at the exact same locations [4, 13]. This suggests been shown to adequately evaluate the workability of low
that other criteria control the workability of these mixtures. flowable mixtures, a quick and inexpensive test was devel-
oped called the Box Test [2].
Power 45 Curve This test investigates the concrete’s response to vibration
In this approach (shown in figure 1), the gradation is plotted while still being able to hold an edge after the vibration is
on the cumulative percent passing chart with the sieve sizes stopped and the side forms are removed. Unconsolidated
raised to the power of 0.45 [3, 14, 15]. Although a range of concrete is placed in a 1 ft3 collapsible wood form and vibrat-
exponents have been proposed based on the characteristics ed in a consistent manner. Next, the wood forms are removed
of the aggregates, the use of 0.45 is the most common value and the sides of the concrete are inspected for excessive
[16]. Theoretically, a system lying on a straight line from the voids. If the sides have excessive voids, the mixture did not
smallest to largest particles will achieve a maximum density consolidate under the vibration and is not satisfactory. Also,
[14]. Experience has shown that it is not always possible to the edges of the concrete can be inspected for edge slumping.
stay on or above the line for particles smaller than #30 [4, Examples of satisfactory and unsatisfactory performance in
13]. Others have reported that systems too close to the line the Box Test are shown in figure 2.
produce mixtures that are not workable [5, 10, 13].
Based on comparing the workability impacts on aggregate
gradation, a new set of limits for the Individual Percent
Individual Percent Retained Chart Retained Chart were established with new upper and lower
Another graphical method for evaluating the distribution of bounds that resemble the silhouette of a tarantula. The
a gradation is using the Individual Percent Retained Chart. results also provide recommendations of the coarse sand
This chart is commonly called the “8-18 chart” due to a amount needed for cohesion (the amount retained on the
minimum of 8% and a maximum of 18% required as grada- #8, #16, and #30 shall be greater than 15%) and fine sand for
tion limits for sieves between 1” and #30; others have called workability (between 24% and 34% retained on the #30 -
it the “Haystack Chart” due to the results resembling a stack #200). Also, a limit for the ASTM D 4791 flatness of the coarse
of hay [5]. This graph is useful as it allows the gradation to aggregate has been proposed [4]. More information can be
be plotted and the excessive or deficient amount of material found at www.optimizedgraded.com.
to be easily observed. Recent research supported by field per-
When these results were compared to the gradations of
formance on the Individual Percent Retained Chart has led to
hundreds of successfully placed lean concrete pavement
the creation of the Tarantula Curve [4].
mixtures in Minnesota and Iowa, there was agreement
between the recommendations of the Tarantula Curve and
Tarantula Curve the contractor-produced mixture designs. This suggests that,
A new set of limits for the Individual Percent Retained chart through trial and error, the contractors were finding mixtures
were developed by comparing the workability and aggregate with a number of different materials that closely matched the
recommendations made by the Tarantula Curve (figure 3).

A B C
Figure 2. The mixture in image A showed good performance and the mixtures in image B and C did not. Image A shows a mixture that showed
good consolidation and no edge slumping. Image B shows a mixture with good consolidation and poor edge slumping. Vertical lines have
been added to highlight the edge slumping. Image C shows a mixture with poor consolidation.

3
 CP Road MAP Brief October 2014

4. Cook, D., A. Ghaeezah, T. Ley, and B. Russell,

Investigation of Optimized Graded Concrete for
Oklahoma-Phase 1. Oklahoma City, Oklahoma.:
Oklahoma Department of Transportation; 2013.
5. Richard, DN., Aggregate Gradation Optimization-
Literature Search. Missouri Department of Trans-
port. RDT 05-001. Jefferson, Missouri: MDOT;
2005.
6. Quiroga, P., Ahn, A, and Flower DW. Concrete Mix-
tures with High Microfines. ACI Materials Journal.
103 (4). ACI; 2006, p. 258-264.
7. Yurdakul, E. Proportioning for Performance-Based
Figure 3 . The Tarantula Curve with the recommended limits of coarse and Concrete pavement Mixtures. Dissertation. Iowa
fine sand.
State University. Ames, Iowa; 2013
8. National Stone, Sand, and Gravel Association. The
What if I cannot obtain the recommended Aggregates Handbook. 2nd ed. Alexandria, Virginia:
Sheridan Books, Inc; 2013.
gradation? 9. Neville, AM. Properties of Concrete. 5th ed. San
Concrete pavements have been placed with aggregate grada- Francisco, CA: Prentice Hall; 2012
tions that fall outside the recommended limits. Sometimes it
may not be economically feasible to reject these gradations or
10. Abrams, D. Proportioning Concrete Mixtures. ACI
find alternatives.
Journal Proceedings. (18) 2. ACI; 1922, p. 174-181.
11. Shilstone, JM. Concrete Mixture Optimization.
Due to the aggregate gradation, these mixtures may need higher Concrete International. 12 (6) Farmington Hills,
amounts of paste for satisfactory workability or may require MI: ACI; 1990, p. 33-39.
edge forms to minimize edge slumping. This will increase
project cost, reduce constructability of the pavement, and lead 12. Shilstone JM. Performance Specifications for Con-
to greater cracking of the concrete. These mixtures may be crete Pavements. Concrete International. 13 (12)
improved by blending different aggregate sources so that the Farmington Hills, MI: ACI; 1991. p. 28-34.
resultant grading is closer to the suggested values. 13. Ley, T, Cook, D, Fick, G. Concrete Pavement Mix-
ture Design and Analysis (MDA): Effect of Aggre-
gate Systems on Concrete Mixture Properties. Iowa:
References National Concrete Pavement Technology Center;
2012.
1. Taylor, P.C., S. Hosmatka, G. Voigt, and et al, Integrated
Materials and Construction Practices for Concrete Pave- 14. Fuller, W, Thompson, S. The Laws of Proportioning
ment: A State-of-the-Practice Manual. 2nd edition. U.S. Concrete. Transactions of ASCE. New York, NY:
Department of Transportation. Washington, DC: FHWA; ASCE; 1907.
2007. 15. Talbot, AN, Richart, FE. The Strength of Concrete,
2. Cook, M.D., A. Ghaeezadah, and Ley, M.T. A Work- Its Relation to the Cement Aggregates and Water.
ability Test for Slip Formed Concrete Pavements. Con- Engineering Experiment Station. Bulletin 137. Ur-
struction and Building Materials. 68. Elsevier; 2014, p. bana, IL; University of Illinois; 1923
376-383 16. Anson-Cartwright, M. Optimization of Aggregate
3. Powers TC. The Properties of Fresh Concrete. New York: Gradation Combinations to Improve Concrete Sus-
John Wiley & Sons, Inc.; 1968 tainability. Thesis in Civil Engineering, University of
Toronto. 2011.

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4 endorses products or manufacturers mentioned herein.