1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 BENEFITS OF PORTLAND-LIMESTONE CEMENT FOR CONCRETE
WITH ROUNDED GRAVEL AGGREGATES AND
HIGHER FLY ASH REPLACEMENT RATES
Jay Shannon
Graduate Research Assistant
Civil and Environmental Engineering
Mississippi State University (MSU)
501 Hardy Road-Mail Stop 9546, Mississippi State, MS 39762
662-325-3050 (ph) 662-325-7189 (fax) [email protected]
Isaac L. Howard, PhD, PE
Associate Professor
Materials and Construction Industries Chair
Civil and Environmental Engineering
Mississippi State University (MSU)
501 Hardy Road-Mail Stop 9546, Mississippi State, MS 39762
662-325-7193 (ph) 662-325-7189 (fax) [email protected]
Corresponding Author
V. Tim Cost, PE, F.ACI
Senior Technical Service Engineer
Holcim (US) Inc.
121 Hampton Hills Blvd., Canton, MS 39046
601-856-2487 (ph) [email protected]
Wayne M. Wilson, PE, LEED AP
Senior Technical Service Engineer
Holcim (US) Inc.
4678 Arbor Crest Place, Suwanee, GA 30024
770-789-3254 (ph) [email protected]
Paper Prepared for Consideration for Presentation and Publication at the 94th Annual Meeting of
the Transportation Research Board.
Original Submission: August 1, 2014
Revised Submission: November 9, 2014
5,490 Words, 5 Figures (1250 words), 3 Tables (750 words) = 7,490 Total Equivalent Words
1 Shannon et al.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 ABSTRACT
Recently, portland-limestone cement (PLC) has garnered increased interest in the US due to
potentially greater environmental sustainability and enhancement of certain concrete properties
and/or performance. Combined with supplementary cementitious materials (SCMs), these
benefits can be further extended. This paper builds on past works of the authors, tailored to
Mississippi’s current concrete practices, by evaluating concrete mixtures with rounded gravel
aggregates and greater replacement of cement with SCMs (primarily fly ash).
In total, 15 different cementitious combinations were used in concrete and cement paste
mixtures. Concrete specimens from 30 mixtures (360 specimens) were tested, featuring various
combinations of cements, SCMs, and admixtures. Replicates of these 30 mixtures were created
in cement paste mixtures (540 specimens). Major variables included SCM type, replacement
rate, and cement source. Mixtures were tested for compressive strength, time of setting or
thermal setting indication, and slump and air content, in the case of concrete mixtures. A small
subsection of concrete mixtures was also examined using petrography.
Results indicated that use of PLC vs. ordinary portland cement (OPC) resulted in notable
compressive strength improvements in mixtures with high Class C fly ash replacement
(especially 40%). Slump and air content were not statistically different in PLC vs. OPC
mixtures; however time of setting was lower in mixtures with PLC. Hydration-related
distinctions (PLC vs. OPC mixtures) were evident in petrographic images, with some observed
differences in cement paste character and the paste-to-aggregate interfacial transition zone (ITZ).
2 Shannon et al.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 INTRODUCTION AND BACKGROUND
State Departments of Transportation (DOTs), other agencies, and private industry continue to
demand increased sustainability. Utilization of more sustainable materials (e.g. concrete) is an
effective approach to take since DOTs use large material quantities. Historically, however,
improved sustainability is largely attained at some performance tradeoff; i.e. improved
performance or sustainability.
Portland-limestone cement (PLC) is this paper’s primary interest. AASHTO M240 (as of
a 2012 revision) now includes a Type 1L cement designation for PLC. A key point is how PLC
can facilitate increased or more effective use of supplementary cementitious materials (SCMs).
The main premise supported through this paper and companion efforts by the authors is that PLC
use and high SCM replacement can add value to projects from performance and sustainability
perspectives.
Improved sustainability is generally achieved in concrete via reducing clinker use.
Replacing a portion of portland cement clinker with uncalcined limestone (e.g. 5% to 15%), as
performed with PLC, coupled with increased replacement of portland cement with SCMs can
have meaningful sustainability implications. AASHTO M240 Type 1L PLC is a more
sustainable alternative to AASHTO M85 Type I ordinary portland cement (OPC). It contains less
clinker, which is the source of most of concrete’s CO2 footprint and embodied energy. Improved
performance (e.g. strength performance) with PLC is achieved through material synergies
(interaction of elements that when combined exceed the sum of their individual contributions).
PLC interest has increased in recent years, especially with the new specifications, which
should further facilitate marketplace use and acceptance. Various studies have been conducted to
clarify PLC’s perceived benefits and to optimize properties and use protocols for performance
(1-4). There have been several laboratory based research studies indicating promising PLC
behavior (e.g. 5-7), and there has also been successful use of PLC with 50% SCM replacement in
structural concrete for a southeastern U.S. college football stadium expansion and renovation
project (8). Complementary key findings from (5-8) are summarized in later sections.
OBJECTIVES AND SCOPE
This paper’s primary objective is to evaluate a high SCM replacement PLC data set designed to
guide implementation in the state of Mississippi, considering both Mississippi Department of
Transportation (MDOT) and private industry applications, with relatively few protocol changes
compared to traditional concrete practices. As suggested in the discussion to follow, concrete
mixes made with rounded gravel aggregates and a single SCM (generally fly ash) are the most
common case in Mississippi, thus the principal focus. As such, the scope of this investigation is
intentionally narrow. While rounded gravel aggregates are not common to all markets, they are
heavily used for concrete in Mississippi as well as numerous other regions of the U.S. A
nationwide review of aggregates production by type (9) shows numerous locations of siliceous
gravel aggregates mining across the US and suggests that, while use of crushed aggregates is
increasing more rapidly than that of natural gravels, there are still similar quantities of each in
use today in the US. Thus the data and conclusions presented are also believed to have
pertinence outside Mississippi.
Rounded gravel aggregates sometimes pose certain concrete quality challenges that may
tend to detract from strength. Potential issues include entrained air void clustering and inherent
difficulties with paste-aggregate bond. Some studies have documented more extreme strength
loss when fly ash was used in concrete mixes with rounded gravel aggregates (10, 11). Concrete
3 Shannon et al.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 data produced in previous studies by the authors has suggested that PLC may help to relieve or
even reverse such strength loss trends, making a more complete study of performance associated
with this set of materials of even greater interest.
While PLC has a longer history of use in several other countries where its performance
has been well researched and documented, the combinations of materials featured in this study
present a somewhat unique research opportunity. PLC synergies that enhance performance are
fineness related (4, 5), and cements are typically produced at lower Blaine fineness values (i.e.
they are coarser) in most other countries. Class C fly ash is also generally unique to the US,
thanks to the chemical composition of coal from the western US. PLC’s interaction with fly ash
has not been heavily studied, especially relating to strength synergies and higher replacement
rates. PLC’s use in concrete with Class C fly ash and rounded gravel aggregates is even less
documented.
RELEVANT CONCRETE PRACTICES IN MISSISSIPPI
Materials and protocols selected for testing considered the current state of practice for concrete
in Mississippi. The most common ready-mix plant configuration would include two cementitious
material silos, one for cement and one for an SCM. Additional silos are less common. Thus use
of a single SCM in the mix design is most common, and this choice seemed especially
appropriate for the study since many state DOTs (including MDOT, presently) do not yet allow
multiple SCMs in concrete.
SCM selection in Mississippi is driven almost entirely by economics. Though slag
cement is recognized as having higher potential concrete performance attributes and usually
costs somewhat less than portland cement, fly ash is widely available in the state and is generally
far lower in cost than slag cement. While there are occasional justifications for slag cement based
on performance requirements in projects, the need for special durability measures in Mississippi
concrete (mitigation of alkali-aggregate reactivity or potential sulfate attack, etc.) that would
suggest slag cement are less common than in many states. While ternary concrete mixes with
both fly ash and slag cement and higher total cementitious replacement have become somewhat
common in adjacent states (esp. LA), this trend has not become prevalent in Mississippi.
MDOT’s Central Materials Laboratory provided information related to concrete practices
on MDOT projects from mid fall of 2007 to mid summer of 2014. During that time frame,
approximately 1700 structural concrete mixtures were submitted for approval and approximately
96% contained fly ash, 1% contained slag cement, and 93% contained rounded gravel
aggregates. Note that the number of mixes approved and the amount of concrete placed are not
necessarily related, and the database does not necessarily reflect unique mix designs, as the same
mix may be used on multiple projects. Non-structural applications are not reflected here.
The three largest concrete producers in Mississippi provided information related to
aggregate and SCM use (MDOT or non-MDOT work) that was in general agreement with the
information from MDOT. Gravel was the predominant coarse aggregate. Limestone is used in a
few areas where economics are favorable, and may also be used even at a higher cost when
requested, justified based on project type (e.g. for joint sawing purposes), or for other
performance requirements.
MDOT currently allows up to 25% fly ash replacement of cement in concrete mixtures.
Many states are reported to be considering moving toward higher replacement rate limits in the
interest of sustainability, performance, and innovation. These trends considered, along with the
documented synergistic effects of PLC with Class C fly ash at higher replacement levels (5, 7),
4 Shannon et al.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 40% SCM replacement of cement with Class C fly ash was selected as a main focus. Some data
with slag cement are also included, for comparison.
The following section provides PLC vs. OPC test data related to SCM replacement rates,
mostly at 40%(+). Concrete economics in Mississippi would be well served with mix designs
that use higher fly ash replacement and rounded gravel aggregates, and the premise of this paper
is that PLC use stands to enhance the performance and applicability of such mix designs.
COMPANION RESEARCH
Cementitious blends containing portland cement, fly ash, and slag cement (i.e. two SCM
systems), have recent documented success with PLC (7, 8). While not directly applicable to this
paper, key aspects of companion efforts with two SCM systems have been presented to show
PLC’s versatility in terms of increased SCM use potential. Companion comparisons with single
SCM systems are also provided.
Cost et al. (5) investigated PLC largely via laboratory cement paste testing. Cementitious
systems included 0% SCM, 25% Class F fly ash, and 25% Class C fly ash. Some concrete data
was available that used gravel aggregates. Linear trendlines with regression through the origin
(RTO) were performed with OPC on the x-axis and PLC on the y-axis (i.e. slopes larger than 1
indicate PLC performs better). Concrete compressive strength slopes were 0.97, 1.07, and 1.13
for 0% SCM, 25% Class F fly ash, and 25% Class C fly ash, respectively. Pertinent conclusions
and recommendations of (5) were that higher than traditional replacement rates with some SCMs
appear possible without performance loss, and that additional research should be performed to
explore practical limits of improving concrete performance with extended SCM use.
Cost et al. (6) tested concrete mixes produced with Georgia granite (Size 57) and
alluvial/marine sand. Cementitious systems included 0% SCM, 25% fly ash (C and F), and 40%
slag cement, with characteristics common to DOT applications. Complimentary OPC and PLC
were supplied from five plants and handled as source-blind samples. The key conclusion was
that the PLCs supplied performed almost identically to corresponding OPCs.
Cost et al. (7) tested cement paste and concrete produced with Alabama limestone (Size
57), intermediate size rounded gravel (Size 8), and natural sand. Cementitious systems included
0% SCM, 40% fly ash (C and F), and 30% slag cement with 20% Class C fly ash (50% total
replacement). Complimentary OPC and PLC were supplied from four plants and handled as
source-blind samples (some of the same materials from (6) were used). The study evaluated
increasing SCM replacement levels via PLC. With 0% SCMs, OPC and PLC behavior was very
similar for a given plant. Consistent concrete strength benefits were observed with PLCs relative
to OPCs for 40% Class C fly ash and 30% slag cement with 20% Class C fly ash. Strength
benefits were modest for 40% Class F fly ash. PLC lowered time of setting relative to OPC.
Howard et al. (8) evaluated 50% SCM replacement (30% slag cement and 20% Class C
fly ash) using the same aggregate sources as (7). One of the study’s most meaningful findings
was that PLC strength gain at 7 days or earlier with 50% SCM replacement was noticeably better
than OPC. Concrete with 50% SCM replacement of PLC was produced and successfully used on
a concrete project over a several month period. Cost (11) documented strength challenges with
rounded gravel aggregates and fly ash in concrete that seemed to be mitigated via use of PLC.
EXPERIMENTAL PROGRAM
The experimental program explored the potential for PLCs in concrete with high cementitious
replacement rates to improve concrete sustainability, economy, and performance. Concrete
5 Shannon et al.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 mixtures were designed to be similar to typical general-purpose mixes in Mississippi and those
being produced at a nearby ready-mixed concrete facility. Specimens included 540 cement paste
(CP) cylinders and 360 concrete cylinders. Tests included traditional fresh concrete properties,
compressive strength, time of setting, and petrography. Cement paste batches were proportioned
similarly to the concrete mixtures but with no coarse or fine aggregates. These have been found
to be useful as a quick indicator of performance trends including setting, but were also included
in this plan of work to potentially help distinguish concrete trends influenced by paste-aggregate
bond from trends that were the result of paste enhancements alone.
With the exception of high cementitious replacement rates, the test mixtures would
generally meet category requirements for several MDOT concrete classes. Note that not all
requirements for these concrete classes were included in mix design focus (e.g. sulfate
resistance), but proportions were similar to those required in MDOT specifications.
Materials Incorporated
Materials included 8 cement samples from 4 sources (OPC and PLC from each), 2 SCMs (Class
C fly ash and slag cement), 3 aggregates (1 coarse, 1 intermediate, and 1 fine), and 3 admixtures
(mid-range water reducer, high-range water reducer, and a workability retainer). Properties of
these materials are provided in Tables 1 to 3.
TABLE 1. Properties of OPC and PLC Cements
Cement ID
A-1
A-2
C-1
C-2
5.5
5.3
5.0
4.5
Al2O3 (%)
0.023 0.021 0.008 0.018
Cl (%)
63.9 63.4 64.2 64.3
CaO (%)
3.4
3.4
3.5
3.3
Fe2O3 (%)
0.65 0.61 0.35 0.43
K2O (%)
0.8
0.8
1.0
1.1
MgO (%)
0.13 0.12 0.18 0.16
Na2O (%)
19.1 17.8 20.3 19.1
SiO2 (%)
3.2
3.9
3.1
3.2
SO3 (%)
0.56 0.52 0.41 0.44
Na eq (%)
2.19 8.83 0.10 8.46
Limestone (%)
2.37 4.71 1.18 4.2
LOI (%)
2
422
522
403
549
Blaine (m /kg)
95
95
115
105
Vicat Initial (min)
170
160
190
170
Vicat Final (min)
1 Day Strength (MPa) 18.2 19.9 18.0 20.9
3 Day Strength (MPa) 29.7 31.8 25.9 30.7
7 Day Strength (MPa) 34.6 38.0 31.6 37.9
28 Day Strength (MPa) 41.4 42.8 44.0 45.3
D-1
4.4
0.007
63.1
3.3
0.67
2.8
0.09
20.3
3.2
0.52
0.27
1.54
421
140
250
15.2
27.0
30.2
39.3
D-3
4.0
0.010
63.1
3.2
0.71
2.7
0.07
17.9
3.4
0.54
14.02
6.95
556
100
225
17.1
27.4
32.3
39.7
E-1
4.6
0.010
63.1
3.2
0.52
3.1
0.07
19.0
3.3
0.41
4.07
2.63
407
105
205
15.0
25.8
31.8
42.1
E-2
4.0
0.009
63.9
2.9
0.44
3.1
0.07
16.7
3.3
0.36
15.69
7.29
681
90
175
20.1
29.2
35.6
41.2
Strength data collected with C109.
While this paper focuses on mixtures with Class C fly ash, data from some concrete using
slag cement were also reported for comparison. The 4 cement sources are all approved for
MDOT projects and supply cement in Mississippi. These 4 plants are located in Calera,
Demopolis, Leeds, and Theodore, Alabama. Cement sources were each given a random
6 Shannon et al.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 designation (A through E). Note that source IDs reflect multiple samples from some sources used
in other studies, though only data using one OPC and one PLC from each source is reported in
this paper. Chemical and physical analysis data for each of the cements was developed in testing
conducted at the laboratories of the Holcim Theodore, AL plant.
There are several acceptable testing alternatives provided for documentation of limestone
content in cement specifications, but for consistency only one measurement type, based on CO2
content, was used for comparative analyses of limestone content; results are listed in Table 1.
This method is one of those used for reporting limestone contents according to AASHTO M85,
but is not required by M240 or ASTM C1157. It should be noted that CO2 calculations may give
slightly higher values for limestone content than those documented by actual production data,
due to other minor sources of CO2 present in cement besides limestone. Each of the PLCs
included in this study contained limestone percentages within the 5% to 15% range specified by
M240 for Type 1L cements, based on production data.
The SCM sources selected are commonly used in Mississippi. The slag cement is
supplied as ASTM C989, Grade 100, and was provided by Holcim from a location near
Birmingham, Alabama. The ASTM C618, Class C fly ash was provided by Headwaters, also
near Birmingham, Alabama.
TABLE 2. Properties of Supplementary Cementitious Materials
Property
ASTM C618 Class
SiO2 (%)
Al2O3 (%)
Fe2O3 (%)
SO3 (%)
CaO (%)
Moisture (%)
LOI (%)
Available Akalies (%)
Fineness (%)
Strength Activity Index 7 day
(% of control)
Strength Activity Index 28 Day
(% of control)
Water Requirement (% control)
Density (Mg/m3)
20 21 22 23 24 25 26 27 28 29 30 31 Fly Ash
C Ash
38.3
20.5
6.3
1.6
22.1
0.04
0.4
1.5
15.7
101
Property
ASTM C989 Grade
S (%)
SO3 (%)
Fineness (%)
Blaine (m2/kg)
Air content (%)
Strength Activity Index 7 Day (%)
Strength Activity Index 28 Day (%)
Slag
100
0.5
0.8
0.5
574
4.7
84
128
107
95
2.63
Aggregates included size 57 rounded gravel, size 8 rounded gravel, and natural sand, all
selected as typical aggregates used in Mississippi. The size 57 material was re-sieved prior to
testing to ensure that segregation did not occur.
Admixtures used were BASF products: Pozzolith 322 N (ASTM C494 Type A/B/D
water reducer), RheoTEC Z-60 (ASTM C494 Type S workability retainer), and Glenium 7500
(ASTM C494 Type A/F high-range water reducer). Dosage rates selected were based on
manufacturer’s suggested dosage per cementitious content and past experience. Two different
admixture scenarios were used: Dosage [1] – 419 ml/m3 (320 ml/yd3) Pozzolith 322 N, 1046
ml/m3 (800 ml/yd3) RheoTEC Z-60, 1256 ml/m3 (960 ml/yd3) Glenium 7500, and Dosage [2] –
837 ml/m3 (640 ml/yd3) Glenium 7500 alone.
7 Shannon et al.
1 TABLE 3. Properties of Aggregates
Material
Location
Bulk Specific Gravity (Gsb) - SSD
Bulk Specific Gravity (Gsb) - OD
F.M.
Absorption
Unit Weight (kg/m3)
Sand Equivalency
3.81 cm (1.50 in)
3.18 cm (1.25 in)
2.54 cm (1.00 in)
1.90 cm (0.75 in)
1.27 cm (0.50 in)
0.97 cm (0.38 in)
Percent Passing
No. 4
No. 8
No. 16
No. 30
No. 40
No. 50
No. 100
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Size 57 Gravel
Columbus, MS
2.47
2.39
6.82
3.15
1525
--100
100
95.4
82.4
51.7
30.3
4.3
0.7
-----------
Size 8 Rounded Gravel
Columbus, MS
2.46
2.39
5.70
3.08
------------100
100
29.3
0.3
0.3
---------
Natural Sand
Columbus, MS
2.61
2.59
2.61
0.66
--86.8%
--------100
100
99.3
83.1
72.8
61.1
44.2
20.9
1.5
Values based on typical aggregate properties as reported by source. Individual batch values differed insignificantly
Test Methods
Cement Paste Preparation, Compressive Strength, and Setting Indication
CP specimens were 5.1 cm by 10.2 cm cylinders. CP specimens contained only cementitious
materials, water, and admixtures, and were fabricated as described in (5), using a w/cm ratio of
0.50, with admixture dosage [1] except as noted. Compressive strength (fcp) testing was
conducted at 1, 7, 14, 28, 56, and 180 days using a hydraulic load frame with attachments to
accommodate cylinder size. Unbonded caps were used in accordance with ASTM C1231.
Specimens tested for compressive strength at 1 day were also used for setting time indication; all
other specimens were stored in a moist curing room meeting ASTM C192. Setting time
indication was determined from thermal data using procedures summarized in (5).
Concrete Fabrication, Compressive Strength, Time of Setting, and Fresh Property Testing
Concrete mix designs were of similar proportions as the CP batches, with aggregates added. The
majority of concrete mixes used a w/cm ratio of 0.43 and admixture dosage [1]. Several mixes
from a different data set were of similar proportions except for the use of a w/cm ratio of 0.52
and admixture dosage [2]. Aggregate quantities for each mixture were approximately 890 kg/m3
size 57 gravel, 208 kg/m3 size 8 gravel, and 841 kg/m3 natural sand, based on saturated surface
dry moisture conditions. Total cementitious content was approximately 320 kg/m3 (540 lb/yd3).
The indicated cement replacement rate is in each case the percentage by weight of the total
cementitious content (e.g. 50% fly ash indicates 160 kg/m3 fly ash content and 160 kg/m3 cement
content).
Concrete specimens were 10.2 cm by 20.3 cm cylinders fabricated in accordance with
ASTM C192. Concrete was mixed in batches of 0.05 m3 in a laboratory concrete mixer, each
batch producing 12 cylinders. Immediately after mixing, concrete was tested for slump, air
8 Shannon et al.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 content, and unit weight in accordance with C143, C231, and C138, respectively. Cylinders
were then fabricated at the mixing site, covered, and initial curing began. A small portion of the
batch was used to conduct time of setting testing according to C403. After initial curing, the
specimens were removed from molds and stored in a curing room meeting the curing
environment requirements of C192 until testing. Concrete compressive strength (fc) testing, using
the unbonded caps as described in C1231, was conducted at 7, 14, 28, and 56 days in accordance
with C39.
Petrographic Investigation
Four specimens that were subjected to compressive testing after a 56 day cure were evaluated via
petrography, with special attention to distinctions in the ITZ that might suggest differences in
paste-aggregate bond of OPC vs. PLC mixtures. These test cylinder specimens were prepared by
removing any sections damaged in testing using a standard block saw, and cutting to a sample
size of 9.5 cm (3.75 in) by 12.7 cm (5 in), 2.5 cm (1 in) thick. Each specimen was prepared for
optical microscopic examination according to ASTM C856. Observations were made and
reference images collected using a digital microscope with magnification up to 200X.
TEST RESULTS
Fresh Concrete Property Trends
Comparisons of fresh concrete properties of otherwise similar OPC and PLC mixtures provide
some insight into PLC vs. OPC early performance distinctions. Concrete slump and air for the
baseline mixtures were predicted to be about 20.3 cm (8.0 in) and 2.0%, respectively, based on
mix designs. In total 15 matched pairs were used in t-tests to determine significant differences in
properties. These matched pairs included multiple sources, multiple replacement levels, and
multiple admixture dosages as indicated in Figures 1-4. Mean values for slump were 20.5 cm for
OPC and 20.1 cm for PLC. Test results found a p-value of 0.3280 indicating that these slumps
were not statistically different. Mean air contents were 2.53% for both OPC and PLC.
Time of setting trends were evaluated using the same 15 concrete pairs and an additional
14 CP pairs. Mean concrete time of setting was 6.56 hr for OPC and 5.87 hr for PLC, and test
results found a p-value of 0.0003, indicating that the times of setting were indeed statistically
different. CP setting indication results yielded means of 15.57 hr for OPC and 12.89 hr for PLC,
with a p-value of 0.0092, again indicating that the CP setting indication was statistically
different.
SCM Replacement Rate Effects for Class C Fly Ash and Slag Cement
One cement source (source C) was used for OPC vs. PLC comparisons in mixtures using Class C
fly ash or slag cement at varying replacement rates (40%, 50%, and 60% for fly ash and 50%,
60%, and 70% for slag cement). Figure 1 shows concrete fc and CP fcp data for fly ash mixtures.
Parts (a) and (c) illustrate fc and fcp differences between fly ash replacement rates at test days of
7, 14, 28, and 56 days. In total 14 concrete mixtures (168 specimens) and 14 CP mixtures (252
specimens) were used to produce the data shown in these bar charts. An equality plot of OPC to
PLC trends is included in parts (b) and (d). Note that part (b) includes all data from part (a) as
well as the small sample of 0.52 w/cm mixtures with the alternate [2] admixture dosage. Part (d)
also includes more data than part (c) in the form of fcp from the additional paste test ages (1 and
180) not included in bar charts and the small set of mixtures with admixture dosage [2].
9 Shannon et al.
1 60
60
w/cm 0.43, Admix 1
w/cm 0.52, Admix 2
OPC
fc (MPa)
40
30
20
40
30
20
0
0
Test Day 7 14 28 56 7 14 28 56 7 14 28 56
50% Ash
60% Ash
40% Ash
0
a) Concrete fc
80
OPC
70
PLC
60
50
40
30
20
10
0
Test Day 7 14 28 56 7 14 28 56 7 14 28 56
50% Ash
60% Ash
40% Ash
PLC fcp (MPa)
fcp (MPa)
10
20
30
40
OPC fc (MPa)
50
60
b) Concrete Equality
90
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 y = 1.28x
R² = 0.71
10
10
2 3 50
PLC
PLC fc (MPa)
50
90
80
70
60
50
40
30
20
10
0
w/cm 0.50, Admix 1
w/cm 0.50, Admix 2
y = 1.23x
R² = 0.90
0
10 20 30 40 50 60 70 80 90
OPC fcp (MPa)
c) Cement Paste fcp
d) Cement Paste Equality
FIGURE 1. Incremental Replacement Rate Class C Fly Ash Results
Figure 1 parts (b) and (d) show that on average, all 3 fly ash replacement rates resulted in
higher compressive strengths with PLC than OPC. The overall percent increase, as illustrated in
the equality plots, was similar in both concrete and CP specimens, though there are clearly
different trends when similar replacement rates are compared, concrete vs. CP. In concrete
mixtures, 40% replacement produced the greatest fc values and ratio of PLC to OPC fc. As
replacement levels increased, both fc and the ratio of PLC to OPC fc decreased. In CP mixtures
this trend was essentially reversed, on average, as higher replacement mixtures generally
outgained lower replacement in both areas. This observation (different trends, concrete vs. CP)
may suggest different concrete paste-aggregate bond effects as influenced by the percentage of
fly ash in the mix. The mixtures with different w/cm and admixture dosage fell within a
reasonable range of the other PLC to OPC ratios portrayed in the equality plots.
Figure 2 shows concrete fc and CP fcp data for slag cement mixtures in the same format as
Figure 1. While the focus of the paper is on Class C fly ash replacement effects, slag cement
comparison trends may also be of interest and may help add to the understanding of performance
synergies of SCM-PLC systems in concrete as influenced by both chemistry and physical
10 Shannon et al.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 (fineness) cementitious properties. In this case only a single w/cm ratio (0.43 for concrete) and
admixture dosage [1] were used. Concrete and CP with slag cement reflected PLC strength
benefits at 7 days (note circled data points on equality plots, parts (b) and (d)), but at later ages
the benefits were usually less pronounced. Concrete performance at later ages was actually quite
similar, PLC vs. OPC. There are still some interesting trends and distinctions in trends between
concrete and CP performance, however.
Concrete strengths are on average noticeably greater for slag cement mixtures than fly
ash mixtures, especially at higher replacement rates, even though CP strengths are generally
lower. This suggests better inherent paste-aggregate bond with slag cement in all cases than with
fly ash, possibly related, in part, to the higher fineness of slag cement and relative coarseness of
fly ash particles. These impacts in fly ash mixtures are somewhat mitigated with PLC, which
contributes a high proportion of very fine (limestone) particles that enhance the overall particle
size distribution.
60
60
40
30
20
30
20
a) Concrete fc
0
OPC
PLC
40
30
20
10
0
Test Day 7 14 28 56 7 14 28 56 7 14 28 56
70% Slag
60% Slag
50% Slag
PLC fcp (MPa)
fcp (MPa)
10
20
30
40
OPC f c (MPa)
50
60
b) Concrete fc Equality
60
17 18 19 20 21 22 23 y = 1.00x
R² = 0.49
0
0
Test Day 7 14 28 56 7 14 28 56 7 14 28 56
60% Slag
70% Slag
50% Slag
50
7 Day
40
10
10
15 16 50
PLC f c (MPa)
fc (MPa)
50
OPC
PLC
90
80
70
60
50
40
30
20
10
0
7 Day
y = 1.12x
R² = 0.78
0
10 20 30 40 50 60 70 80 90
OPC fcp (MPa)
c) Cement Paste fcp
d) Cement Paste fc Equality
FIGURE 2. Incremental Replacement Rate Slag Cement Results
Multiple Cement Sources Compared in 0% and 40% Class C Fly Ash Mixtures
The question may be posed whether the beneficial trends observed for PLC (vs. OPC) from one
source will be common to other cement sources. To address this and to contrast general
11 Shannon et al.
performance trend differences of mixtures with no SCMs and those with 40% Class C fly ash,
mixtures with OPC and PLC samples from each of the 4 sources have been used to develop the
comparisons shown in Figures 3 and 4.
Figure 3 shows OPC and PLC data for all cement sources with no SCM (100% of the
cementitious content is cement) and 40% fly ash for both concrete and CP. A total of 16
concrete mixtures (192 specimens) and 16 paste mixtures (288 specimens) are represented. All
mixtures were made at a w/cm of 0.43 and admixture dosage [1]. In “No SCM” concrete
mixtures, part (a), OPC fc was slightly greater than PLC for cement sources A and C, but very
slightly lower for cement sources D and E. Overall, these differences (without fly ash) were
essentially negligible, which is consistent with other published data sets. Similar mixtures in CP
specimens, as seen in part (c), favored OPC with source A and PLC with source C and somewhat
with sources D and E. Though CP trends show more variability, again these overall differences
are not especially meaningful. In 40% fly ash mixtures, PLC strengths clearly excelled beyond
those of OPC in all CP (part (d)) and concrete (part (b)) comparisons, and by similar, meaningful
margins, in most cases.
fc (MPa)
60
OPC
"A"
"C"
PLC
"D"
60
"E"
50
50
40
40
fc (MPa)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 30
17 18 20
10
10
"D"
"E"
7 14 28 56 7 14 28 56 7 14 28 56 7 14 28 56
Test Day
a) Concrete fc No SCM
70
"C"
0
7 14 28 56 7 14 28 56 7 14 28 56 7 14 28 56
Test Day
80
"A"
PLC
30
20
0
OPC
OPC
"A"
"C"
b) Concrete fc 40% Ash
PLC
"D"
60
"E"
OPC
"A"
"C"
PLC
"D"
"E"
50
50
fcp (MPa)
fcp (MPa)
60
40
30
40
30
20
20
10
10
0
0
19 20 21 22 23 7 14 28 56 7 14 28 56 7 14 28 56 7 14 28 56
Test Day
7 14 28 56 7 14 28 56 7 14 28 56 7 14 28 56
Test Day
c) Cement Paste fcp No SCM
d) Cement Paste fcp 40% Ash
FIGURE 3. 0% and 40% Class C Fly Ash Strength Results, 4 Cement Sources
12 Shannon et al.
Figure 4 presents equality plots for the mixtures depicted in Figure 3, with results for all sources
shown without differentiation. In parts (a) and (c), concrete and CP mixtures without SCMs
show little or no difference in strength performance on average, OPC vs. PLC. Figure 4 (a)
shows a modest favoring toward PLC, but with considerable scatter, this isn’t believed to be
especially meaningful. In parts (b) and (d), 40% fly ash mixtures indicate considerable
advantages with PLC, with much greater benefits in concrete (equality line slope of 1.46 and
every data point favoring PLC) than CP. Again, this is thought to be somewhat related to the
particle size contributions of PLC to the fly ash concrete mixtures and possibly to associated
improvements in paste-aggregate bond.
60
60
50
50
PLC fc (MPa)
PLC fc (MPa)
1 2 3 4 5 6 7 8 9 10 40
30
20
y = 0.98x
R² = 0.74
10
10
20
30
40
OPC fc (MPa)
50
y = 1.46x
R² = 0.64
0
60
a) Concrete No SCM
70
60
60
50
50
40
30
20
y = 1.07x
R² = 0.67
10
10
20
30
40
OPC fc (MPa)
50
60
b) Concrete 40% Fly Ash
70
PLC fcp (MPa)
PLC fp (MPa)
20
0
0
40
30
20
y = 1.22x
R² = 0.91
10
0
0
0
13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 30
10
0
11 12 40
10
20
30
40
50
OPC fcp (MPa)
60
70
0
10
20
30
40
50
OPC fcp (MPa)
60
70
c) Cement Paste No SCM
d) Cement Paste 40% Fly Ash
FIGURE 4. 0% and 40% Class C Fly Ash Equality Plots, 4 Cement Sources
Concrete Petrography Results
Concrete Petrography was performed on 4 specimens (No SCM OPC, No SCM PLC, 40% fly
ash OPC, and 40% fly ash PLC) from mixtures using cement source C, in the interest of
exploring observed strength trends thought to be possibly related to paste-aggregate bond
differences. Results are presented in Figure 5 along with an example specimen in part (a). In the
“No SCM” mixtures, the OPC paste portion was generally darker in color with a less uniform,
more mottled appearance than the PLC paste portion. OPC paste appeared coarser with a
medium texture, while PLC paste looked finer with a more medium fine texture ((b) and (c)).
13 Shannon et al.
1 2 3 a) Example Specimen
b) No SCM OPC 20X
c) No SCM PLC 20X
4 5 d) 40% Ash OPC 20X
e) 40% Ash PLC 20X
f) 40% Ash OPC 200X
6 7 8 g) 40% Ash PLC 200X
h) No SCM OPC 50X
i) No SCM PLC 50X
FIGURE 5. Petrography Images 14 Shannon et al.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 In the fly ash mixtures, general paste texture appeared finer with a slight chalky like
appearance relative to the no SCM mixtures. The OPC with fly ash appeared slightly coarser
overall relative to the PLC fly ash mixture ((d) and (e)). The presence of white to translucent,
irregularly-shaped particles was observed in both OPC and PLC fly ash mixtures. The material
composition of these particles was not determined; however, the material volume of the particles
did appear slightly higher in the OPC fly ash mixture. The volume of unhydrated fly ash
particles appeared slightly higher in the OPC fly ash paste portion than the PLC fly ash paste
portion ((f) and (g)). These observations suggest more uniform and complete cementitious
material hydration in the PLC mixtures.
Paste portions of the No SCM PLC near the paste-aggregate ITZ were notably lighter in
color, softer, and of a higher w/cm ratio than similar areas in the PLC mixture ((h) and (i)). In
fly ash mixtures, the lighter color paste-aggregate rings observed in the No SCM OPC mixture
were less pronounced and the relative difference in the paste-aggregate ITZ was less apparent.
Both OPC and PLC mixtures had similar color, hardness, and w/cm characteristics in the pasteaggregate ITZ. These observations are inconclusive with respect to explaining any pasteaggregate bond differences (PLC vs. OPC with fly ash), though it should be pointed out that PLC
vs. OPC strength trends were similar for concrete and CP mixtures with these materials, and the
other petrography observations discussed above do suggest more complete hydration conditions
in the PLC concrete mixtures.
SUMMARY AND CONCLUSIONS
Data presented clearly supports that PLC can be used to enhance the performance (e.g. strength
performance) of concrete containing rounded gravel aggregates and increased Class C fly ash
replacement of portland cement. Implementation benefits would appear to be many, including
increased sustainability by way of an economically competitive and well performing concrete
mixture. These benefits could be realized for Mississippi, and other applicable areas as well.
PLC produced higher strengths than OPC in essentially all mixtures with fly ash
replacement, and concrete at the 40% replacement level notably excelled. Strengths of concrete
mixtures with slag cement were higher than those with fly ash overall, though OPC vs. PLC
distinctions were less apparent. There were differing trends for concrete and cement paste (CP)
in both cases.
When cements from 4 sources were compared, CP fcp results for mixtures without SCMs
varied by source, with OPC favored for some sources and PLC for others. Concrete fc results
without SCMs also showed variability by source, with 2 sources moderately favoring OPC and 2
sources moderately favoring PLC. In mixtures with 40% fly ash, notably higher strength results
were produced with PLC than OPC for all sources, in both concrete and CP.
Fresh concrete properties of slump and air content were not statistically different between
PLC and OPC mixtures. Time of setting was found to be lower in PLC mixtures by
approximately 0.7 hr in concrete and setting indication lower by about 2.7 hr in CP.
Petrography revealed lighter, less uniform paste portions in OPC compared to PLC,
possibly indicative of more complete cementitious hydration with PLC. The addition of fly ash
appeared to lessen the differences between OPC and PLC paste appearance. OPC mixtures also
appeared to have higher w/cm at the paste-aggregate ITZ.
The differences in performance trends of concrete and CP may suggest that pasteaggregate bond is a component of some strength differences seen in mixtures with SCMs, which
15 Shannon et al.
1 2 3 4 could be associated with particle size distribution effects influenced by significant fineness
differences of the SCMs, as well as cement types (OPC vs. PLC).
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 The MSU Cement and Concrete Industries Excellence Fund supported a portion of the efforts
presented. During the time frame of the work presented, Argos USA, CEMEX, Holcim (US),
and an anonymous donor made financial contributions. Holcim (US) also supported a portion of
the efforts presented through research grants. Materials were donated by: Argos USA, CEMEX,
Headwaters Resources, Holcim (US), Lehigh Cement Company, and MMC Materials. Cement
testing services were performed in-kind by Holcim at the Theodore, AL plant. Industry and
agency data were provided by B&B Concrete Co., Delta Industries, MMC Materials, and
MDOT. Individuals who have supported the effort include Dr. Imad Aleithawe, Adam Browne,
Alissa Collins, David Collins, Bill Goodloe, Rodney Grogan, Doug Gruber, Les Howell, Al
Innis, Gary Knight, Mark Stovall, Bill Waters, and Stephen Wilcox.
ACKNOWLEDGEMENTS
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