Post on 28-Jun-2020
Advances in CivilEngineering Materials
Rodrigo Antunes1 and Mang Tia2
DOI: 10.1520/ACEM20180030
Effects of Aggregate Packing onConcrete Strength andConsistency
VOL. 7 / NO. 1 / 2018
Copyright by ASTM Int'l (all rights reserved); Thu Sep 6 16:29:02 EDT 2018Downloaded/printed byUniversity of Florida (University of Florida) pursuant to License Agreement. No further reproductions authorized.
REVIEW PAPER
Rodrigo Antunes1 and Mang Tia2
Effects of Aggregate Packing on ConcreteStrength and Consistency
Reference
Antunes, R. and Tia, M., “Effects of Aggregate Packing on Concrete Strength and Consistency,”
Advances in Civil Engineering Materials, Vol. 7, No. 1, 2018, pp. 479–495, https://doi.org/10.1520/
ACEM20180030. ISSN 2379-1357
ABSTRACT
Designing concrete based on aggregate packing and optimized gradations can
result in 25 % less cement content to reach a targeted compressive strength and less
water-reducing admixture to obtain a required consistency. In this research, two
studies were conducted: (1) an experimental analysis to determine the effects of
aggregate packing on concrete strength and consistency; and (2) an investigation
of the relationship between the traditional dry-rodded and the vibrated aggregate
packing. Excellent correlation was found between 240 packing results, which can
be applied to the modified mixture design method presented. Also, 40 slump and
120 compressive strength standard tests were performed to evaluate the effects
of reducing cement content by 7.5, 15, 20, and 25 % to slump and compressive
strength of concrete mixtures. The compressive strength of the optimized
mixture demonstrated less susceptibility to variations due to cement content
reductions when compared to nonoptimized mixtures. The Modified Coarse
Factor Chart can be used to design an optimized concrete mixture efficiently in
conjunction with aggregate gradation and packing, cement content, and concrete
consistency.
Keywords
limestone, silica sand, optimized gradation, aggregate, packing, portland cement, concrete,
mixture design, admixture
Manuscript received March 16,
2018; accepted for publication
July 20, 2018; published online
September 7, 2018.
1 Department of Civil and Coastal
Engineering, University of Florida,
PO Box 116580, Gainesville, FL
32611, USA (Corresponding
author), e-mail: rodrigo.antunes@
ufl.edu, https://orcid.org/
0000-0002-1878-382X
2 Department of Civil and Coastal
Engineering, University of Florida,
PO Box 116580, Gainesville, FL
32611, USA
Advances in Civil Engineering Materials
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doi:10.1520/ACEM20180030 / Vol. 7 / No. 1 / 2018 / available online at www.astm.org
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Introduction
Optimized aggregate blends may improve the concrete performance and be used to de-
sign concretes with lower cementitious material content [1]. Usually, 70 to 80 % of
concrete is composed of aggregate, which significantly dominates the mechanical
and physical properties of this composite material, both by the quality and quantity
of the aggregates [2–4]. The characteristics of the aggregates, such as maximum size,
particle size distribution, and aggregate packing, besides proportioning, profoundly
affect the performance of concrete.
This study aims to evaluate the effects of aggregate packing on the concrete strength
and consistency as well as to investigate the relation between the traditional dry-rodded
and the vibrated aggregate packing by adopting the Vebe apparatus. The methodological
approach consists of relating optimized and nonoptimized aggregate gradation parameters
to the properties of fresh and hardened concrete mixtures under different aggregate pack-
ing and cement contents.
This investigation argues that designing concrete based on aggregate packing and
optimization can result in the reduction of water-reducing admixture contents in order
to reach a target workability of the fresh concrete, as well as in significant reduction of
cementitious material consumption to reach a desired compressive strength.
Background
AGGREGATE OPTIMIZATION
Traditional optimized aggregate gradations have been specified and endorsed to provide
concrete improvement. In contrast, very few, if any, comprehensive methods are readily
available at the disposal of engineers to perform aggregate optimization [5].
Theoretical and empirical approaches can be used to obtain a typically optimized
aggregate gradation [5,6], and the underlying premise behind each method is similar.
A well-graded aggregate, that is, one that covers all aggregate particle sizes, usually con-
tains a higher percentage of particles with intermediate sizes and smaller portions at the
extremes. Such gradation takes on what is often described as a haystack shape when plot-
ted on a percent retained chart.
Achieving a traditional optimized gradation usually requires the combination of at
least three differently sized aggregates. However, most concrete typically contains two ag-
gregates: (1) fine aggregate, with particles smaller than 4.75 mm; and (2) coarse aggregate,
with particles larger than 4.75 mm. The combination of two aggregates is usually not well
graded because of the absence of intermediate-sized particles, having a peak-valley-peak
distribution.
The commonly used techniques to develop traditional optimized aggregate grada-
tions are: (1) the percent retained chart; (2) the power chart; and (3) the Modified
Coarseness Factor Chart (MCFC). All aim to determine a target gradation, and thus select
an optimized blend of the available aggregates [5].
To clarify the MCFC applications, first it is essential to define the Coarseness Factor
(CF), the adjusted Workability Factor (WFadj), and the parameters Q, ISA, and W, as
shown in Eqs 1 and 2.
CF = ½Q=ðQ + ISAÞ� × 100 % (1)
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where:
CF= coarseness factor,
Q= cumulative percent retained on the sieve 9.5 mm,
ISA= percent retained within sieves 2.36 and 9.5 mm.
WFadj =W + ð2.5% × ΔC=WTÞ (2)
where:
WFadj= adjusted workability factor,
W= cumulative percent passing the 2.36-mm sieve,
ΔC= cement content difference to 335 kg/m3,
WT=weight of cement bag, 42.6 kg.
The MCFC is an empirically developed chart that is widely used to plot CF andWFadjas a single point representing fine and coarse aggregate proportions by using two equa-
tions. Mixtures appearing near the center of Zone II consistently provide good workability
[7], so that many of the traditional optimized gradation concrete practitioners recommend
that gradations be plotted within the center of Zone II for slip-formed concrete [8]. In
contrast, for some, the MCFC is considered not helpful in comprehending slip-formed
consistency behavior [9].
AGGREGATE PACKING
Aggregate packing is relevant to concrete since it relates to the volume of cement paste
needed to fill the gaps in between the aggregates and to separate particles. Typically, dry-
rodded packing is used in current official mixture designs in the United States. However, in
Europe, vibrocompaction has been successfully used as a packing method [10].
Aggregate packing k is the ratio between the actual volume of the solid particles Pv and
the compacted bulk volume V. Packing depends on three main parameters: (1) size of the
grains, (2) shape of the grains, and (3) packing method. Usually, aggregate packing of
rounded aggregate blends appears to be about 12 % greater than the outcomes obtained
from crushed aggregate blends [11]. Most theoretical models consider monosized or random
spherical particle shapes to determine aggregate packing [10]. Consequently, theoretical sim-
ulations may generate fewer voids to fill with cement paste than experimental packings. As a
result, these spherical blends may lead to excessive optimistic results in which less cement
paste is required to fill the gaps between grains. Hence, most simulations may unrealistically
predict the use of 12 % less cement paste content in actual concrete mixtures.
On the other hand, some models have successfully adopted characteristic diameter
and packing to reduce error in outcomes when compared to the Toufar’s theoretical pack-
ing curve. It is thought that comparing actual packing test results to the Toufar’s curve can
increase adherence to actual results and reduce the need for experiments [12].
Some parameters need to be calculated to determine aggregate packing. The volume
of solid particles Pv is the actual aggregate particles volume [10] as shown in Eq 3.
Pv =W=ρ (3)
where:
Pv= volume of solid particles, m3,
W=mass of the aggregates, kg,
ρ= density of the aggregates, kg/m3.
Compacted bulk volume V is the volume occupied by the particles after the compac-
tion, as expressed in Eq 4.
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V =W=M (4)
where:
V= compacted bulk volume, m3,
W=mass of the aggregates, kg,
M= compacted unit weight of the aggregates, kg/m3.
Furthermore, aggregate packing k is defined as the ratio between the volume of solid
particles Pv and compacted bulk volume V [10], as seen in Eq 5.
k = Pv=V (5)
where:
k= aggregate packing,
Pv= volume of solid particles, m3,
V= compacted bulk volume, m3.
POWER CHART
Fundamentals on maximum density of aggregate gradations have been known for about
100 years [8]. Initially, the power curve index n was proposed as 0.50 [13] and was later
adjusted to 0.45 [14]. Since then, each sieve opening is raised to the 0.45 power on the
cumulative percent passing chart. It is typically a straight line representing the maximum
aggregate blend density, connecting the origin to the aggregates’ nominal maximum size
(NMS). Aggregate proportions can be obtained based on the best-fit curve of the straight
line [8]. It is recognized that concrete mixtures using very dense gradations produce harsh
concretes [14,15].
Although there are other types of ideal gradation references, such as Rissel, Graf, and
Boloney, this investigation was based on the Fuller and Thompson curve equation based
on the maximum size (MS) of aggregates as shown in Eq 6.
Pd = 100 × ðd=DmaxÞn (6)
where:
Pd= particles passing a sieve opening, %,
d= sieve opening, mm,
Dmax=maximum sieve opening, mm,
n= 0.45.
ENTRAPPED AIR IN CONCRETE
Entrapped air voids are typically spherical with diameters as large as 3 mm. Air bubbles are
usually trapped in cement paste during the mixing process. Often, for a given consistency,
the lower the cement paste volume, the lower the entrapped air content in concrete [16].
SLUMP OF FRESH CONCRETE
The slump is a direct measurement of fresh concrete consistency and is part of the work-
ability in conjunction with cohesiveness. Usually, the water content is directly proportional
to the slump. Also, the slump of concrete can increase with the addition of water-reducing
admixtures without increasing the water content. However, typically no more than 2 %
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(by weight of cement) of water-reducing admixtures are added to concrete to increase
consistency while reducing water content by 5 % [16].
Concrete workability can also be enhanced by adding intermediate-sized aggregates,
which can fill major voids in the aggregate portion of portland cement concrete and reduce
internal friction. Mixtures deficient in aggregates retained between sieves 2.36 and 9.5 mm
are expected to require more mortar to provide needed mobility [7].
COMPRESSIVE STRENGTH OF CONCRETE
It is widely known that water-cement ratio (w/c) is the critical factor influencing the com-
pressive strength of concrete. This is usually true since the strength of aggregates is much
higher than that of the cement paste matrix and interfacial transition zone (ITZ). However,
for a given consistency and cement content of high- and moderate-strength concretes, the
compressive strength of the matrix tends to increase if the NMS of coarse aggregate in-
creases. Also, it is known that the ITZ dramatically influences the tensile strength. Then, if
the NMS of coarse aggregate increases, the ITZ tends to be weaker, decreasing the tensile-
compressive strength ratio [16].
Materials and Methods
AGGREGATES
The fine aggregate (FA) used was silica sand from the supplier GA397 according to the
Florida Department of Transportation (FDOT) producers list. Intermediate coarse aggre-
gate (IA) used was the Miami Oolite Limestone #89 from the mine 87,090 (supplier code
TM447). Coarse aggregate (CA) was the Miami Oolite Limestone #57 from the same IA
quarry. Tables 1–3 show the FA, IA, and CA properties, respectively.
For aggregate packing testing, all aggregates were oven-dried. For concrete mixing,
moisture content tests were performed with specimens taken simultaneously when ma-
terials were batched. Right before mixing, moisture content was determined. Thus, aggre-
gates and water contents were adjusted accordingly.
PORTLAND CEMENT
The portland cement Type I/II used in this experimental study was provided by Suwannee
American Cement Company (Branford, FL). Physical properties and chemical composi-
tion met current requirements of the ASTM C150/C150M-17 [17], Standard Specification
for Portland Cement.
TABLE 1Physical properties of fine aggregate.
Physical Properties Standard Value
Materials <75 μm ASTM C117-17 [28] 0.2 %
Fineness Modulus ASTM C136-14 [29] 2.34
SSD Specific Gravity ASTM C128-15 [30] 2.70
Apparent Specific Gravity ASTM C128-15 [30] 2.75
Bulk Specific Gravity ASTM C128-15 [30] 2.69
Absorption ASTM C128-15 [30] 0.3 %
Note: ASTM C136-14, Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates; ASTM C128, StandardTest Method for Relative Density (Specific Gravity) and Absorption of Fine Aggregate; SSD, saturated-surface drycondition of aggregates.
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AGGREGATE BLENDS
Proportions of aggregate blends required a broad range of combinations. The 14 combina-
tions shown in Table4 have the percent of IA varying from 0 to 20%, usually reducing half of
the percentage from the CA and the other half from the FA. Blends SD1 and SD2 are binary;
PK1 and PK2 are ternary with 10 % IA; PK3 and PK4 are also ternary, however with 20 % IA.
The combinations PK5, PK6, PK7, PK8, and PK9 have IA contents within 2.5 and 17.5 %.
TABLE 2Physical properties of intermediate aggregate.
Physical Properties Standard Value
Materials <75 μm ASTM C117-17 [28] 1.7 %
NMS ASTM C33-16e1 [31] 3/8 in.
SSD Specific Gravity ASTM C127-15 [32] 2.45
Apparent Specific Gravity ASTM C127-15 [32] 2.61
Bulk Specific Gravity ASTM C127-15 [32] 2.35
Absorption ASTM C127-15 [32] 4.2 %
Note: ASTM C33/C33M-16e1, Standard Specification for Concrete Aggregates; ASTM C127-15, Standard Test Method forRelative Density (Specific Gravity) and Absorption of Coarse Aggregate; SSD, saturated-surface dry condition of aggregates.
TABLE 3Physical properties of coarse aggregate.
Physical Properties Standard Value
Materials <75 μm ASTM C117-17 [28] 1.5 %
NMS ASTM C33-16e1 [31] 3/4 in.
SSD Specific Gravity ASTM C127-15 [32] 2.42
Apparent Specific Gravity ASTM C127-15 [32] 2.59
Bulk Specific Gravity ASTM C127-15 [32] 2.32
Absorption ASTM C127-15 [32] 3.9 %
Note: SSD, saturated-surface dry condition of aggregates.
TABLE 4Aggregate blend proportions.
Blend CA, % IA, % FA, % Total, %
OPT 56.700 10.300 33.000 100
OPT1 47.125 5.750 47.125 100
OPT2 41.000 18.000 41.000 100
SD1 60.000 0.000 40.000 100
SD2 57.450 0.000 42.550 100
PK1 55.000 10.000 35.000 100
PK2 45.000 10.000 45.000 100
PK3 50.000 20.000 30.000 100
PK4 40.000 20.000 40.000 100
PK5 58.200 11.200 30.600 100
PK6 47.500 5.000 47.500 100
PK7 42.500 15.000 42.500 100
PK8 48.750 2.500 48.750 100
PK9 41.250 17.500 41.250 100
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The acronym “SD” refers to standard mixes containing two aggregates, typically one
finer and one coarser. Also, the acronym “PK” identifies blends specifically developed for
packing tests, while “OPT” represents an optimized blend.
Although all blends were used in the packing tests, a similar-shape gradation curve
procedure was used to select the blends to mix into concrete following Antunes and Tia
[18]. Aggregate blends with a similar shape of gradation plots were thus selected.
Gradation plots of blends PK6, PK7, PK9, and OPT, as shown in Fig. 1, are representative
samples of gradation plots of the aggregate blends used.
AGGREGATE PACKING TESTING PROCEDURE
Two methods were used to test aggregate packing: (1) the dry-rodding method according to
ASTM C29/C29M-17a [19], Test Method for Bulk Density (“Unit Weight”) and Voids in
Aggregate, and (2) the vibration method per ASTM C1170/C1170M-14e1 [20], Standard
Method for Determining Consistency and Density of Roller-Compacted Concrete Using a
Vibrating Table. Because of the experimental nature of this study, a relatively wide range
of combinations of the three aggregates was carefully selected. The sample size required by
the statistical model was 24, specifying a minimum of 12 determinations of dry-rodded and
12 trials of vibrated aggregate blends, resulting in a 5 % type 1 error (95 % confidence), and 1
% type 2 error. The twelve tests on each blend were divided into three independently pre-
pared specimens tested four times each. The weighed binary and ternary aggregate blends
had the same average dry weights: 12.8 kg for dry-rodded and 8.6 kg for vibrated packing.
Aggregate packing of each binary and ternary aggregate blend was systematically
determined to achieve accurate results. A total of 240 results were obtained: 120 for
dry-rodded and 120 for vibrated specimens.
Vibrated aggregate packing tests were conducted as follows: (1) specimens were
mixed thoroughly before horizontal layers of aggregate were poured into the measure
in three equal layers, which were vibrated for 30 seconds each; (2) distance between cyl-
inder rim and the top of the specimens was measured at four evenly distributed locations.
Fig. 2a and b shows the Vebe apparatus and specimen measurement, respectively.
FIG. 1
Gradation curves of selected
aggregate blends.
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AGGREGATE OPTIMIZATION PROCEDURE
Gradation optimization technique provides the ability to employ multisource aggregates
to be blended and optimized. Optimizations were performed as follows: (1) all aggregate
gradations were determined using the standard sieve series; (2) aggregate blends were math-
ematically combined based on the initial trial proportions; (3) NMS of combined blends
were determined to identify eventual intermediate aggregate effect on aggregate system;
(4) the percent passing and percent retained charts were prepared; (5) desired gradations,
typically following the theoretical maximum density line, were determined based on the
Talbot and Richart [14] power curve equation (n= 0.45); (6) CF and WFadj of combined
gradations were calculated and plotted on the MCFC; (7) traditional optimized gradation
proportions were calculated by interaction of individual gradations to reach the Workability
Box (WB) surroundings of 33 %≤WFadj≤ 37 % and CF= 60 %, aiming the maximum
consistency for w/c= 0.50; and (8) the percent passing and percent retained charts of both
combined and optimized blends were plotted against the desired curve for final comparison.
MIXTURE DESIGN PROCEDURE
Twenty FDOT Class I (pavement) for slip-formed concrete mixtures were designed and
prepared in the laboratory to evaluate the possibility of reducing the cement content by
between 7.5 and 25 %. One of the goals was to obtain a mixture with sufficient cement
paste to consolidate the concrete while keeping the edge stiff. Following the FDOT
Section 346 [21], Portland Cement Concrete, and the FDOT Section 9.2 [22],
Structural Concrete Production Facilities Guide, all mixtures required a minimum com-
pressive strength of 29 MPa and minimum cement content of 279 kg/m3. The decision
to adopt a constant and maximum allowed w/c ratio of 0.50 aimed to (1) evidence con-
sistency behavior without water-reducing admixture aid, (2) analyze the lowest possible
FIG. 2 Aggregate packing test: (a) Vebe apparatus and (b) step two of the vibrated packing test on ternary aggregate blends,
measuring distance between the top vibrated specimen and measure rim.
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compressive strength and highest consistency behaviors under different cement contents,
and (3) highlight the aggregate packing and optimization effects on concrete properties.
Table 5 shows the mixture designs summary.
The following tests were performed on fresh and hardened concrete: (1) air content as
per ASTM C173/C173M-16 [23], Air Content of Freshly Mixed Concrete by the Volumetric
Method; (2) slump according to ASTM C143/C143M-15a [24], Standard Test Method for
Slump of Hydraulic-Cement Concrete; and (3) compressive strength at 28 days following
ASTM C39/C39M-18 [25], Test Method for Compressive Strength of Cylindrical Concrete
Specimens. Fig. 3 presents the adjusted mixture design procedure adopted, based on ACI
211.1 [26], Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass
Concrete. Although the procedure is not new, for mixtures with predetermined aggregate
proportions, the ACI 211.1 [26] mix design procedure was followed for the cement and
water content determination. An adaptation was necessary because (1) the aggregate pro-
portions were given, and aggregate weights were known; (2) packing (k) was given, cement
paste (CP) to fill voids (CPv) and separate particles (CPs) were known; and (3) CP index
could be applied to reduce or increase CPs as demonstrated in Fig. 4.
CONCRETE MIXING AND TESTING
Cement and aggregates were stored in laboratory conditions at room temperature between
20°C and 30°C. A total of 20 mixtures were designed and batched twice. Thus, a total of 40
samples of fresh concrete were tested for a slump to investigate the consistency and uni-
formity of the fresh concrete. Also, 40 samples were tested for unit weight of fresh concrete
to ensure the yield volume and for air content. Also, 120 specimens were tested for com-
pressive strength (3 specimens per mixture) at the age of 28 days to evaluate whether the
material reached the expected strength. Single compression results were occasionally
TABLE 5Concrete mixture designs.
Blend ID PC. Red., % w/c Cement, kg/m3 Water, kg/m3 CA, kg/m3 IA, kg/m3 FA, kg/m3
OPT#1 0 0.50 374 187 952 173 554
OPT#2 7.5 0.50 346 173 984 179 573
OPT#3 15 0.50 318 159 1,016 185 591
OPT#4 20 0.50 299 150 1,037 188 604
OPT#5 25 0.50 280 140 1,058 192 616
PK7#1 0 0.50 374 187 714 252 714
PK7#2 7.5 0.50 346 173 737 260 737
PK7#3 15 0.50 318 159 761 269 761
PK7#4 20 0.50 299 150 777 274 777
PK7#5 25 0.50 280 140 793 280 793
PK6#1 0 0.50 374 187 798 84 798
PK6#2 7.5 0.50 346 173 824 87 824
PK6#3 15 0.50 318 159 851 90 851
PK6#4 20 0.50 299 150 869 91 869
PK6#5 25 0.50 280 140 887 93 887
PK9#1 0 0.50 374 187 693 294 693
PK9#2 7.5 0.50 346 173 716 304 716
PK9#3 15 0.50 318 159 739 314 739
PK9#4 20 0.50 299 150 754 320 754
PK9#5 25 0.50 280 140 770 327 770
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FIG. 3 Fluxogram of the adapted concrete mixture design.
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rejected because of excessive strength deviation from the group. The results were calcu-
lated from the average of the remaining specimens.
The procedure adopted during each concrete batching and mixing followed ASTM
C192/C192M-16a [27], Standard Practice for Making and Curing Concrete Test Specimens
in the Laboratory. Materials were batched 24 hours before mixing and stored in buckets
with lids. Aggregate specimens for moisture content were simultaneously taken, and the
aggregate and mixing water contents were adjusted right before mixing. Concrete spec-
imens were placed into water curing tanks within 30 minutes after removal from the cylin-
drical molds. The curing water was lime water kept at an average temperature of 23°C.
Fig. 5a and b shows the slump test and the cylindrical specimen being tested for com-
pressive strength, respectively.
FIG. 5 Fresh and hardened concrete testing: (a) slump test and (b) the cylindrical specimen being tested for compressive strength.
FIG. 4 Increase of aggregate proportion in concrete that is due to the reduction in cement paste volume.
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Results and Discussion
In this study, the objectives were to (1) evaluate the effects of aggregate packing on slip-
formed concrete strength and consistency and (2) evaluate the relationship between dry-
rodded and vibrated packing methods. To reach the first objective, standard tests were
performed on fresh and hardened concrete to investigate the relationship between the
concrete properties and the gradation parameters, such as MCFC factors and aggregate
packing. For the second objective, comparisons were made between the two packing meth-
ods: the traditional dry-rodded, kr, and the vibrated, kv, using a Vebe apparatus.
Since concrete is a composite material, the methodological approach was to evaluate
the fresh and hardened behaviors of concrete using different aggregate blends and cement
contents. Each selected mixture had its cement content reduced by 7.5, 15, 20, and 25 %.
The compressive strength of each mixture was plotted against the cement reductions to
evaluate the strength of concrete under different cement contents. Slump outcomes were also
plotted against the cement reductions to evaluate workability. The possibility of using slump,
packing, gradation, and cement content to design concrete mixtures more efficiently was also
investigated.
Lastly, dry-rodded and vibrated aggregate packing tests were performed with the same
selected aggregate blends, and the results were plotted to seek the best-fit trend line. Table 6
displays the testing outcomes. Fresh concrete air content data ranged from 0.7 to 3.7 %.
COMPRESSIVE STRENGTH AND CEMENT CONTENT
Since each of the 4 aggregate-blend mixtures was tested twice with 5 different cement
contents, a total of 40 mixes were prepared. Every mixture had the same w/c ratio of
TABLE 6
Test results.
Blend ID kr kv CF WFadj MCFC Zone
Comp. Strength
(28 days), MPa SD, MPa Slump, mm
OPT#1 0.727 0.759 60 37 II 45.4 0.2 229
PK9#1 0.733 0.823 51 45 IV 44.7 1.4 133
PK7#1 0.729 0.798 52 46 IV 45.3 1.1 178
PK6#1 0.722 0.791 63 50 IV 44.8 0.7 95
OPT#2 0.727 0.759 60 36 II 45.1 1.5 133
PK9#2 0.733 0.823 51 44 IV 45.0 2.0 64
PK7#2 0.729 0.798 52 45 IV 43.3 1.1 89
PK6#2 0.722 0.791 63 49 IV 43.0 0.8 51
OPT#3 0.727 0.759 60 34 II 46.2 1.1 76
PK9#3 0.733 0.823 51 42 II 45.1 0.9 13
PK7#3 0.729 0.798 52 43 IV 41.8 0.2 25
PK6#3 0.722 0.791 63 47 IV 41.4 0.7 19
OPT#4 0.727 0.759 60 33 II 45.3 0.5 32
PK9#4 0.733 0.823 51 41 II 43.9 0.2 6
PK7#4 0.729 0.798 52 42 II 43.0 1.5 13
PK6#4 0.722 0.791 63 46 IV 41.4 0.1 6
OPT#5 0.727 0.759 60 33 II 43.6 0.5 25
PK9#5 0.733 0.823 51 41 II 39.9 0.6 6
PK7#5 0.729 0.798 52 42 II 39.8 0.0 6
PK6#5 0.722 0.791 63 46 IV 39.3 0.0 0
Note: SD, standard deviation.
490 ANTUNES AND TIA ON AGGREGATE PACKING AND CONCRETE
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0.50 and five different cement contents. However, aggregate proportions remained the
same regardless of the cement content. At least three 100 by 200-mm cylindrical specimens
were cast for each mixture to be evaluated for compressive strength at 28 days, with a total
of 6 specimens per mix design, or a grand total of 120 specimens. Fig. 6 shows the average
compressive strengths plotted against the cement content reductions, featuring a low aver-
age standard deviation of 0.8 MPa.
When no cement content was reduced, all mixes presented a similar compressive
strength around 45 MPa. At 25 % cement reduction, nonoptimized mixtures (PK7,
PK9, and PK6) presented a similar compressive strength of about 39.6 MPa, while the
traditional optimized mixture (OPT) had a compressive strength of 43.6 MPa. Also,
the compressive strength of OPT mixtures remained constant and higher than the non-
optimized mixes for all cement content levels.
Changes in strength were not significant since optimized mixes gave fairly constant
strength at a greater extent, while nonoptimized mixes gave approximately 12 % reduction
in strength where cement content was reduced by 25 %. All mixtures presented a com-
pressive strength higher than the target design value (29 MPa), even with 25 % less cement
in their compositions.
CONSISTENCY AND CEMENT CONTENT
The objective was to test the concrete slump within a wide range of cement contents to
identify a trend. Some of the mixes would not be of practical use in concrete pavements
considering their slump results.
The slump of each mixture was the average of at least two determinations, with a total
of 40 tests (Fig. 7). Optimized mixtures presented 229-mm slump at no cement content
reduction, compared to the lowest 95 mm displayed among the nonoptimized mixtures.
With no water-reducing admixtures added, outcomes indicate that nonoptimized
mixtures reached the designed slump of 50 mm at 10 % cement reduction.
Meanwhile, optimized mixtures reached 50 mm slump at 18 % cement reduction.
DRY-RODDED AND VIBRATED AGGREGATE PACKING
The relationship between dry-rodded packing, well known as dry-rodded unit weight as
stated in ASTM C29/C29M-17a [19], and vibrated aggregate packing was investigated.
Past publications have documented the low reliability of theoretical models, suggesting
that experimental results would compare well to the Toufar model if the aggregate
FIG. 6
Compressive strength behavior
of optimized and nonoptimized
mixtures under different
cement contents.
ANTUNES AND TIA ON AGGREGATE PACKING AND CONCRETE 491
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diameter and experimental packing were used to calibrate results. Thus, an experimental
approach was used in this study to address the effects of aggregate packing on compressive
strength and slump, and the outcomes can add to the existing academic literature, with a
focus on southern U.S, limestone and silica sand.
The results of 240 tests (Fig. 8) indicated a strong linear relationship (R2= 0.98)
between dry-rodded and vibrated aggregate packing, which is thought to be due to con-
stant and steady higher energy applied to the vibrated specimens. Aggregate and concrete
producers can benefit from this outcome given the higher accuracy of absolute volumes of
aggregates transported and concrete produced.
An experimental approach was performed by Antunes and Tia [18] to investigate how
k of silica sand and limestone correlates to ISA contents in aggregate blends. Overall, the
lowest packing (k) variation (1.7 %) occurred when ISA was between 25 and 27 % by weight,
indicating that blends containing 25 to 27 % of particles within sieves 2.36 and 9.5 mm (ISA)
might be considered optimal. In other words, a lower variation in packing can increase the
predictability of the concrete consistency since concrete is typically designed based on
dry-rodded unit weight (dry-rodded packing) and vibrated during placement.
FIG. 7
Slump behavior of optimized
and nonoptimized mixtures
under different cement
contents.
FIG. 8
A linear relationship between
dry-rodded and vibrated
aggregate packing.
492 ANTUNES AND TIA ON AGGREGATE PACKING AND CONCRETE
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MCFC AND CONCRETE MIXTURE DESIGN
Aggregate blend gradations are displayed in Fig. 1, providing parameters for CF andWFadjcalculations. Fig. 9 shows the MCFC with aggregate factors related to each concrete mix-
ture and varied cement contents.
Results show that optimized mixtures plotted near the center of the WB and had the
highest slumps in comparison to mixtures with the same cement content. Nonoptimized
mixes plotted away from the WB and presented slumps inversely proportional to their
distance to the WB. On the other hand, the slump results of each blend showed a direct
relationship to cement content. The slump of the optimized mixture was 229 mm at 0 %
reduction and 25 mm at 25 % reduction. In comparison, the average slump of the non-
optimized mixtures was 135 mm at 0 % reduction and 4 mm at 25 % reduction. The
cement content variation provides a local alteration on the location of the WFadj plotted
on the MCFC, in which the higher the cement content, the higher theWFadj. This may be
explained by the proportionally higher water content associated with the higher cement
content since all mixes had a fixed w/c of 0.50.
Results also indicate a nonlinearity in aggregate packing outcomes when plotted on
the MCFC. At the WB, the optimized blend had packing of 0.727 and 0.759 for the
dry-rodded and vibrated specimens, respectively, increasing to the average 0.731 and
0.811 between Zones II and IV (PK7 and PK9), and decreasing to 0.722 and 0.791 in
Zone IV (PK6).
Conclusions
This study provided a theoretical and experimental analysis of the effects of aggregate
packing on concrete strength and consistency. Also, an investigation of the relationship
between the traditional dry-rodded and the vibrated aggregate packing was performed.
The results can contribute to filling the gap in the literature addressing southern U.S. lime-
stone and silica sand. The main findings are as follows:
(1) Slump and compressive strength of optimized concrete mixtures are less sensitiveto cement content reductions (0 to 25 %) than nonoptimized mixtures. This can be
FIG. 9
MCFC with aggregate packing
and slump for all cement
contents tested, adapted from
Ref. [7].
ANTUNES AND TIA ON AGGREGATE PACKING AND CONCRETE 493
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explained by the fact that the greater content of limestone particles in the optimizedmix reduces the fine-coarse aggregate friction, as well as the influence of theaggregate-cement paste interfacial zone on the concrete strength.
(2) Optimized mixtures require less water-reducing admixture to reach the desiredconsistency because of less friction between aggregate particles, which can requireboth less cement paste and admixtures to reach the desired workability.
(3) Dry-rodded and vibrated aggregate packing present a robust linear relationship(R2= 0.98) since the energy applied to the vibrated specimens was steady andhigher than the energy applied by rodding.
(4) Aggregate packing cannot be used alone to optimize gradations and should be usedin conjunction with aggregate gradation, slump, and cement content because pack-ing results indicate nonlinearity with aggregate proportions. Conversely, the linearrelationship between aggregate proportions and concrete slump is one of thetheoretical bases of the ACI 211.1 mix design procedure.
Finally, designing concrete based on packing, consistency, and aggregate gradation
can result in 25 % less cement content to reach an expected compressive strength and less
water-reducing admixture to obtain a required consistency.
ACKNOWLEDGMENTS
We thank the Brazilian Coordination for the Improvement of Higher Education Personnel
for the financial support. We acknowledge the support from the State Materials Office of
the FDOT for aggregate donation and Vebe apparatus usage.
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