materiels evaluation

1. Laboratory Evaluation of Critical Properties and
Attributes of Calcined Bauxite and Steel Slag
Aggregates for Pavement Friction Surfacing
Demei Yu, Ph.D.1
; Rui Xiong, Ph.D.2
; Shuo Li, Ph.D.3
; Peiliang Cong, Ph.D.4
;
Ayesha Shah, Ph.D.5
; and Yi Jiang, Ph.D.6
Abstract: The long-term friction performance of safety-focused friction surfacing, especially high-friction surface treatment (HFST), relies
primarily on the properties of aggregate. Nevertheless, inconsistencies exist in the properties and attributes and requirements for aggregates
across the country. A study was conducted to evaluate the properties of the calcined bauxite and steel slag aggregates selected for HFST.
Differences were identified between the British Standard (BS) and AASHTO test methods for aggregate abrasion and polishing. Laboratory
tests were conducted to determine the mechanical, physical, chemical, and geometric properties of the selected aggregates. It was found
that the Micro-Deval abrasion (MDA) test is a repeatable test. A size effect existed in both the abrasion and polishing tests. It was concluded
that steel slag may be used as an alternative aggregate for friction surfacing. The requirements for aggregates for HFST were established in
terms of the critical property attributes, particularly the Los Angeles abrasion (LAA), MDA, and polish value PV-10, which can be readily
implemented by state Departments of Transportation. DOI: 10.1061/(ASCE)MT.1943-5533.0002806. © 2019 American Society of Civil
Engineers.
Introduction
At roadway horizontal curves, interchange ramps, or intersections,
pavement surface tends to become polished rapidly and experience
a dramatic friction loss due to frequent and excessive braking
of vehicles, which may lead to reduced controllability of the vehicle
and increased stop distance, particularly when pavement is wet.
FHWA (2016) reported that although horizontal curves make up
about 5% of the nation’s roadways, 23% of fatal crashes occurred
on horizontal curves. In response, safety-focused friction surfacing
has been used to enhance pavement friction. In particular, the so-
called high-friction surface treatment (HFST) has been increasingly
used as a cost-effective solution to extreme friction demands
across the country (FHWA 2012). HFST is composed of a layer of
high-quality aggregate, most commonly calcined bauxite, bonded
to the existing pavement surface using a specialized resin binder.
AASHTO has published a provisional standard, AASHTO PP79,
“Standard practice for high friction surface treatment for asphalt
and concrete pavements (AASHTO 2014b),” to formulate the ap-
plication of HFST. To date, great efforts have been made to evaluate
the friction performance of HFST and the properties and attributes
of aggregates by researchers across the country (Izeppi et al. 2010;
Heitzman et al. 2015; Merritt et al. 2015).
Nevertheless, there are still several important issues to be
addressed. First, the mechanical properties, particularly polishing
and abrasion, are recognized as important property attributes for the
aggregates for friction surfacing. The specification requirements for
polishing and abrasion currently adopted by state DOTs were de-
veloped according to those for high-friction surfacing in the United
Kingdom (UK), where aggregate polishing and abrasion are as-
sessed in terms of the aggregate abrasion value (AAV) and polished
stone value (PSV) outlined in BS EN 1097, “Tests for mechanical
and physical properties of aggregates-determination of the polished
stone value (BSI 2009).” However, AAV is currently not adopted by
state departments of transportation (DOTs) in the US. Moreover,
the requirements implemented in the UK were developed in
1970s (James 1971; Denning 1977). To date, the calcination tech-
nologies have advanced to provide calcined bauxite with improved
properties. In addition, the UK and US test methods such as BS EN
1097 and AASHTO T279, “Standard method of test for acceler-
ated polishing of aggregates using the British wheel (AASHTO
2014a),” on aggregate polishing differ in many aspects. Second,
AASHTO PP79 requires the use of calcined bauxite for HFST and
specifies its mechanical properties with only the Los Angeles
abrasion (LAA) loss of 20% max. It is only during the past few
years that the data has been available to assess the polishing and
abrasion properties of calcined bauxite aggregate used for HFST
in the country. Other properties such as physical and geometric
properties may also affect the friction of HFST.
1
Visiting Research Assistant, School of Construction Management,
Purdue Univ., West Lafayette, IN 47906; Assistant Professor, School of
Transportation and Civil Engineering, Fujian Agriculture and Forestry
Univ., Fuzhou 350002, China. Email: yudemei119@163.com
2
Visiting Research Associate, School of Construction Management,
Purdue Univ., West Lafayette, IN 47906; Associate Professor, School of
Materials Science and Engineering, Chang’an Univ., Xian 710064, China.
Email: xiongr61@126.com
3
Research Engineer, Research Division, Indiana Dept. of Transporta-
tion, West Lafayette, IN 47906 (corresponding author). Email: sli@
indot.in.gov
4
Visiting Research Scholar, School of Construction Management,
Purdue Univ., West Lafayette, IN 47906; Professor, School of Materials
Science and Engineering, Chang’an Univ., Xian 710064, China. Email:
congpl88@163.com
5
Research Engineer, North Central SuperPave Center, Purdue Univ.,
West Lafayette, IN 47906. Email: bano@purdue.edu
6
Professor, School of Construction Management, Purdue Univ., West
Lafayette, IN 47906. ORCID: https://orcid.org/0000-0003-2055-680X.
Email: jian2@purdue.edu
Note. This manuscript was submitted on November 13, 2018; approved
on March 4, 2019; published online on May 25, 2019. Discussion period
open until October 25, 2019; separate discussions must be submitted for
individual papers. This paper is part of the Journal of Materials in Civil
Engineering, © ASCE, ISSN 0899-1561.
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2. It is also worth mentioning that the refractory calcined
bauxite currently used for HFST nationwide is imported from other
countries. It is the authors’ opinion that for both economic and
environmental reasons, local polish-resistant aggregates should be
considered in addressing friction issues, particularly for locations
with less extreme friction demands and bridge deck preservation. In
reality, steel slag is currently utilized to enhance surface friction for
heavy traffic asphalt pavements by the INDOT (2016). Recently,
INDOT completed an award-winning project to make a compre-
hensive evaluation of HFST, including aggregate properties and
surface friction characteristics (AASHTO 2018). The current paper
documents one part of the study, the results of laboratory tests and
analysis on the critical properties and attributes of the selected
calcined bauxite and steel slag. The research results on the surface
friction of HFST system can be found elsewhere (Li et al. 2018).
To the authors’ knowledge, the original test and analysis results
presented in this paper are very useful to thoroughly assess the criti-
cal property aspects of aggregates for friction surfacing, better
understand the distinguishing features of different aggregate tests,
and accurately determine the unique properties of calcined bauxite
and steel slag. Moreover, such information is very useful for state
DOTs’ materials engineers to improve specifications on HFST
aggregates and make more informed decisions and better use of
alternative aggregates for friction surfacing.
Abrasion Resistance Tests, Results, and Analysis
Current Abrasion Resistance Indicators
AAV is the indicator currently used in the UK to measure the abra-
sion of aggregate, i.e., the resistance of aggregate to surface wear by
abrasion under traffic, for high-friction surfacing. AAV is computed
as the weight percentage loss of the aggregate sample after 500
revolutions using the Dorry abrasion machine. However, the AAV
test is currently not adopted by state DOTs. Instead, the LAA,
Micro-Deval abrasion (MDA), or both as outlined in AASHTO
T96, “Standard method of test for resistance to degradation
of small-size coarse aggregate by abrasion and impact in the
Los Angeles machine (AASHTO 2015)” and AASHTO T327,
“Standard method of test for resistance of coarse aggregate to deg-
radation by abrasion in the micro-Deval apparatus (AASHTO
2012a),” respectively, are utilized to evaluate the aggregate abra-
sion. The LAA loss is a measure of the degradation of mineral
aggregates of standard grading resulting from a combination of ac-
tions, including abrasion, impact, and grinding. The test is carried
out by rotating the sample in a steel drum with a charge of steel
balls and determining the difference between the mass of the origi-
nal sample and the mass of the sample retained on 1.70-mm sieve,
expressed as percentage loss by mass of the original sample. MDA
is a measure of the abrasion resistance and durability of aggregates
resulting from a combination of abrasions and grinding in the pres-
ence of water. The MDA loss is measured with the test method
carried out by rotating the sample in a steel jar filled with water
and a charge of steel balls and determining the loss of the sample,
i.e., the amount of aggregate passing 1.18-mm sieve, as a ratio of
the mass of the original sample.
Notwithstanding that the LAA and MDA tests appear similar,
there are three major differences that set these two tests apart:
(1) the original sample shall be immersed in water for a minimum
of one hour in the MDA test, but oven-dried in the LAA test; (2) the
rotating jar contains 2.0 L water during the MDA test, but no water
is added during the LAA test; and (3) the charge in the LAA test has
a total mass (5,000 g) equal to that in the MDA test, however, the
former consists of 46/48 mm diameter steel balls and the latter
consists of 9.5 mm diameter steel balls. It was reported that the
LAA test is actually a measure of aggregate impact and crushing
strength because the mode of action involves impact of particles
against steel balls, against each, and against the walls of the cyl-
inder, and the LAA loss would seldom reflect actual abrasion in
practice (Alexanderm and Mindess 2005; Rogers and Senior 1994).
In the MDA test, however, the use of saturated aggregate samples
can better reflect the effects of the environment and therefore the
durability of aggregate properties. Rotating the sample in the steel
jar with 2.0 L of water can not only maintain aggregate surface in
wet condition, but also reduce the action of impact by the steel
balls. In addition, the use of smaller steel balls reduces the impact
action. Consequently, the impact action by the steel balls becomes
small and surface wear by abrasion and grinding prevails. There is
an association between the AAV and MDA tests and the MDA test
is simpler to complete than the AAV test (Senior and Rogers 1991).
LAA and MDA Test Results and Analysis
Both LAA and MDA tests were conducted on the samples of the
selected calcined bauxite and steel slag. Presented in Table 1 are
the results of LAA testing performed on the calcined bauxite
and steel slag aggregates of Gradings C (4.75–9.5 mm) and D
(2.36–4.75 mm), respectively. There were two reasons to choose
both Gradings C and D for LAA testing. First, Grading D better
represents the standard size of the calcined bauxite aggregate used
in HFST nationwide. Second, it was indicated that no specific trend
could be observed on the influence of aggregate grading on the
LAA loss (Kandhal and Parker 1998; Rangaraju and Edlinski
2008). Although this was thought to result from the lack of con-
sistency in ball charge and particle surface area, such issue was
considered worthy of further investigation because very little infor-
mation is currently available on LAA for both calcined bauxite
and steel slag. Grading C represents the main size of steel slag
commonly used in asphalt mixtures by INDOT (2016).
It is shown that for the calcined bauxite aggregate, the average
LAA loss is 9.3% and 12.3% with Grading C and Grading D, re-
spectively. The latter is 3.0% greater than the former. For the steel
slag aggregate, the average LAA loss is 13.1% and 14.0% with
Gradings C and D, respectively. The latter is 0.9% greater than
the former. Overall, steel slag experienced greater LAA loss than
calcined bauxite, and however, the differences decreased as the ag-
gregate size increased. The average LAA loss of the steel slag is
approximately 41% and 14% greater than the average LAA of the
calcined bauxite for Gradings C and D, respectively. It is evident
that the LAA loss increased as the aggregate size decreased for both
the calcined bauxite and steel slag aggregates. Nevertheless, the
LAA loss of steel slag was less sensitive to the aggregate size than
that of calcined bauxite. This indicates that the differences between
the calcined bauxite and steel slag LAA losses may become much
less as the aggregate size decreases. In addition, the specification
for LAA in AASHTO PP79, i.e., 20% max, is too loose, and in
Table 1. Los Angeles abrasion (LAA) test results
Sample No.
Calcined bauxite
(% by mass)
Steel slag
(% by mass)
Grading C Grading D Grading C Grading D
1 9.1 12.3 13.2 14.0
2 9.5 12.3 13.0 13.9
Average 9.30 12.30 13.10 13.95
Stdev 0.28 0.00 0.14 0.07
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3. reality, has no real meaning for the selected calcined bauxite and
steel slag.
There are three standard aggregate gradings, including 9.5–19.0,
4.75–12.5, and 4.75–9.5 mm in the MDA test. The grading with a
maximum nominal size of 9.5 mm was chosen for conducting the
MDA testing to better represent the aggregate size commonly used
for HFST. Table 2 presents the MDA test results for both the cal-
cined bauxite and steel slag aggregate samples. It is shown that for
both the calcined bauxite and steel slag aggregates, all the three
samples yielded very consistent test results and the standard devia-
tions are very subtle. This may imply that the MDA test is a very
repeatable test. The average MDA loss is 5.2% for the calcined
bauxite aggregate and 6.1% for the steel slag aggregate. Therefore,
the steel slag can be a promising alternative for small size aggre-
gates used for friction surfacing in terms of abrasion resistance.
Polishing Resistance Tests, Results, and Analysis
Current Polishing Resistance Indicators
The polishing property of aggregate refers to as the resistance of
coarse aggregates to polishing action of vehicle tires under condi-
tions similar to those on road surfaces. PSV is currently used to
measure the polishing property of aggregate in the UK, and is de-
termined with the BS EN 1097 method. In the US, the aggregate
polishing property is measured with a parameter similar to PVS,
i.e., PV-10, the polish value after 10 hours polishing determined
with the AASHTO T279 method. Summarized in Table 3 are
the key features of both the BS EN 1097 and AASHTO T279 meth-
ods. The BS EN 1097 method applies a total load of 725 10 N on
the specimen surface, however, the AASHTO T279 method applies
a total load of 391 4.5 N on the specimen surface. In the BS EN
1097 method, the specimen is polished in two phases with two
different abrasive materials. In the first phase, the specimen is sub-
jected to a polishing action of three hours by feeding the corn emery
and water both at 27 9 g=min. In the second phase, the specimen
is subjected to a polishing action of three hours by feeding the
emery flour at 3 1 g=min and water at 6 1 g=min. In the
AASHTO T279 method, the specimen is subjected continuously
to a polishing action of 10 h by feeding the silicon carbide grit
of 0.075–0.15 mm at 6 2 g=min and water at 50–75 mL=min.
In particular, when measuring the friction, i.e., British pendulum
number (BPN) at the end of polish conditioning, the method out-
lined in BS EN 13036, “Road and airfield surface characteristics-
test methods Part 4: Method for measurement of slip/skid resistance
of a surface: the pendulum test (BSI 2011),” uses the F-scale, how-
ever, the AASHTO T278, “Standard method of test for surface
frictional properties using the British pendulum tester (AASHTO
2012b),” uses the main scale. Shown in Fig. 1 is a typical British
pendulum tester with both F- and main scales on the scale plate.
Approximately, the BPN in terms of the main scale is 0.6 times
the BPN in terms of the F-scale. In general, the main scale is in-
tended for use in the test of road surfaces with a 76.2-mm-wide
slider and the F-scale in the test of aggregates with a 31.75-mm-
wide slider in the laboratory. Although the AASHTO T278 method
uses the main scale, it uses the 31.75-mm-wide slider, instead of the
76.2-mm-wide slider. Obviously, the PSV measured with the BS
EN 1097 method differs from the PSV, i.e., PV-10 measured with
the AASHTO T279 method in many aspects, including load, pol-
ishing process and time duration, abrasion material, and measuring
scale. Therefore, the PSV determined in accordance with BS EN
1097 test method does not necessarily agree with the PV-10
measured in accordance with AASHTO T279 method.
PSV Test Results and Analysis
Fig. 2 shows the photos of two PSV test coupons (curved
specimens) made of 6.3–9.5 and 1–3-mm aggregates, respectively.
There are two specified aggregate sizes, including the standard and
alternative sizes for aggregates to be tested in accordance with the
AASHTO T279 method. The standard aggregate size is 9.5–
12.5 mm and the alternative aggregate size is 6.3–9.5 mm. How-
ever, the calcined bauxite aggregate of 1–3 mm had been widely
used for HFST. The PSV testing was initially conducted by the
Table 2. Micro-Deval abrasion (MDA) test results
Sample No. Calcined bauxite (% by mass) Steel slag (% by mass)
1 5.3 6.1
2 5.2 6.1
3 5.2 6.1
Average 5.23 6.10
Stdev 0.06 0.0
Table 3. Comparison of BS EN 1097 and AASHTO T279 standard test methods
Category Content BS EN 1097 AASHTO T279
Apparatus Road wheel ϕ406 3 mm; 44.5 0.5 mm wide ϕ406.4 mm; 44.45 mm wide
Rubber-tired wheel Solid, ϕ200 3 mm; 38 2 mm wide ϕ203.2 mma
Rubber hardness 69 3 IRHDb
69 3 IRHD
Materials Control stone PSV Quartz dolerite: 49.5–55.5 20–30 Ottawa sand: 850–600 μm
Abrasive 1. Corn emery, passing 0.60 mm Silicon carbide grit: 150–75 μm
2. Emery flour, passing 0.05 mm
Specimen Dimension 90.6 0.5 × 44.5 0.5 × 12.5 mm 88.9 × 44.45 × 16 mm
Aggregate size 10–7.2 mmc
9.5–6.4 mm
Procedures Load on road wheel 725 10 N 391.44 4.45 N (88 1 lbf)
Temperature 20 5°C 23.9 2.8°C
Road wheel speed 320 5 rpm 320 5 rpm
Polishing time 6 h: corn emery, 3 h, emery flour, 3 h 10 h
Abrasive feed rate 1. Corn emery: 27 9 g=min, water: 27 9 g=min 1. Silicon carbide: 6 2 g=min
2. Emery flour: 3 1 g=min, water: 6 2 g=min 2. Water: 50–75 mL=min
Report BPN PSV (F-scale) PV-i/PV-n (main scale)
a
Alternative tire No. 3 in AASHTO T279.
b
International rubber hardness degrees.
c
7.2-mm sieve is the standard grid sieve.
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4. authors on the test coupons made of 6.3–9.5-mm aggregates for
both the calcined bauxite and steel slag, and the results are pre-
sented in Table 4. The average PV-10 values are 35.4 and 27.8
for the calcined bauxite and steel slag, respectively, and are much
less than the published typical PSV, i.e., 70 for the calcined bauxite
(Hosking and Tubey 1972) and 63 for steel slag (Stock et al. 1996).
There are two possible reasons. First, this is due in great part to that
in the UK, the typical PSV numbers were measured with 1–3-mm
aggregate rather than 6.3–9.5-mm aggregate. Second, the default
differences between the BS and AASHTO test methods, particu-
larly the measuring scale for BPN as noted earlier, could also con-
tribute to the low PV-10 values. After weighing all the factors,
another set of polishing tests were conducted using 1–3-mm aggre-
gate and the results are also presented in Table 4.
For the calcined bauxite, the PV-i (the initial polish value) and
PV-10 for the 1–3-mm aggregate, respectively, are 64% and 67%
greater than those for the 6.3–9.5-mm aggregate. For the steel slag,
the PV-i and PV-10 for the 1–3-mm aggregate, respectively, are
84% and 86% greater than those for the 6.3–9.5-mm aggregate.
Evidently, there is an effect of size on the PSV of aggregate. Both
the PV-i and PV-10 values for the 1–3-mm aggregate demonstrate
greater variations than those for the 6.3–9.5-mm aggregate. The
main reason is that when preparing the test coupons, the 1–3-mm
aggregate particles were too small to be individually placed in the
mold like coarse aggregate particles. Instead, the 1–3-mm aggre-
gate particles were first spread on the bottom of the mold to achieve
a desired single layer, and then epoxy was added over the particles
(Fig. 2), which might cause greater variability. On average, the PSV
for the 1–3-mm calcined bauxite aggregate decreased from 79.1
(PV-i) to 59.1 (PV-10) after 10 h of polishing, representing a re-
duction of 25% in polishing resistance. For the 1–3-mm steel slag
aggregate, the PSV decreased from 74.6 (PV-i) to 51.7 (PV-10)
after 10 h of polishing, representing a reduction of 31% in polishing
resistance. The PV-10 values are 59.1 and 51.7 with reference to the
main scale and 98.6 and 86.2 with reference to the F-scale for
the calcined bauxite and steel slag aggregates, respectively. Evi-
dently, both the calcined bauxite and steel slag demonstrated a
PV-10 value that is much greater than 70, i.e., the PSV measured
with the F-scale in the UK. This may also indicate that the steel slag
aggregate of 1–3 mm is highly polish-resistant, and therefore, can
be a promising alternative for aggregates for friction surfacing.
Presented in Fig. 3 are the variations of PSV with aggregate size
for the calcined bauxite aggregates. The black column represents
the average PV-10 measured using the AASHTO T279 method
(Table 4). The dark grey column represents the average PSV mea-
sured in accordance with the BS EN 1097 method by a laboratory
in the UK (Georgia Eusner, personal communication, April 14,
2015). Again, the variations of both PSV and PV-10 demonstrate
an obvious size effect. It is shown that both the PSV and PV-10
values increase as the aggregate size decreases. However, it seems
that PV-10 increases more rapidly than PSV. For the 1–3-mm
aggregate, the PV-10 with reference to the F-scale is much greater
Fig. 1. F- and main scales on scale plate of British pendulum tester.
(Image by Shuo Li.)
Fig. 2. Polished stone value (PSV) test coupons. (Image by Shuo Li.)
Table 4. Laboratory polished stone value (PSV) test results
Sample no.
Calcined bauxite Steel slag
6.3–9.5 mm 1–3 mm 6.3–9.5 mm 1–3 mm
PV-i PV-10 PV-i PV-10 PV-i PV-10 PV-i PV-10
1 50.0 35.0 80.5 59.8 40 26 73.8 50.3
2 46.0 37.0 80.5 58.5 41 28 77.3 50.3
3 48.0 35.0 81.3 64.0 40 26 76.0 56.5
4 48.0 35.0 74.0 54.3 40 31 71.3 49.8
5 49.0 35.0 — — 42 28 — —
Averagea
48.2 (80.3) 35.4 (59.0) 79.1 (ofs) 59.1 (98.6) 40.6 (67.6) 27.8 (46.3) 74.6 (ofs) 51.7 (86.2)
Stdev 1.48 0.89 3.40 4.00 0.89 2.05 2.63 3.19
Note: ofs = out of scale.
a
Measured on the main scale (F-scale).
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5. than the PSV more likely due to the default differences between the
BS EN 1097 and AASHTO T279 methods. There is no evidence to
suggest which method is more suitable or more effective than the
other one.
Other Properties and Attributes Important to
Friction Surfacing
Chemical Compositions and Test Results
The calcined bauxite for HFST is commonly imported from China.
It is produced by calcining raw bauxite at a temperature of 1,450°C–
1,700°C and consists of mainly corundum (α-Al2O3) and mullite
(3Al2O3 · 2SiO2) phases and a very small glass phase (Zhong and
Li 1981). The chemical compositions of the calcined bauxite affect
not only its lattice, phase, and microstructure, but also its physical
and mechanical properties. As a rule of thumb, the strength, stiff-
ness, and hardness of the calcined bauxite increase as the content of
Al2O3 increases. Steel slag is the major byproduct from converting
molten iron to steel in a basic oxygen furnace (BOF) or melting
steel scrap to make new steel in an electric arc furnace (EAF). Both
BOF and EAF steel slags consist primarily of oxides such as CaO
(lime), FeO, SiO2, and MgO. For a specific steel slag, the chemical
constituents are combined to form the main mineral phases that
determine its unique physical and mechanical properties, such as
polishing, abrasion, hardness, and compressive strength. It was also
commented that Al2O3 does contribute to the hardness of steel slag
(Patrick Malfitano and Doug Fromm, personal communication,
April 13, 2015).
Table 5 shows the chemical compositions of the calcined baux-
ite measured in accordance with ASTM C311 (ASTM 2017) in the
current paper and the typical values provided by the supplier (GLM
2015). Al2O3 has the highest percentages. Variations can be seen
between the measured and typical values. The proportions of ox-
ides in calcined bauxite depend not only on raw bauxite, but also on
calcination conditions, especially kiln type, fuel type, flame tem-
perature, and feed amount and speed. Therefore, the oxide propor-
tions may vary from plant to plant, batch to batch, and even across a
single batch. Table 6 presents the chemical compositions of the
steel slags, including the selected BOF steel slag and two others
reported elsewhere (Yildirim and Prezzi 2009). The major oxides
such as CaO and FeO represent more than 59% of the total
concentration. Significant differences can be seen in chemical com-
positions between BOF and EAF steel slags. The proportions
of oxides in steel slags depend on the feed material, type of steel
made, and furnace condition, and may vary from plant to plant and
from batch to batch.
Physical and Geometric Properties and Test Results
Density is one of the important physical properties for aggregates.
For calcined bauxite, density indicates if the raw bauxite is fully
calcined. Partially calcined bauxite tends to have lower strength,
toughness, and volumetric stability. For steel slag, density varies
with the cooling conditions (Lewis 1982). In general, the higher
density of aggregate, the greater strength and durability of the ag-
gregate. The initial moisture content of aggregate is another factor
that affects the durability of HFST. A higher initial moisture content
tends to create more free water on the surface of aggregate that will
affect the adhesion between aggregate and epoxy binder. It has also
been recognized that the friction of pavement surface varies with
the aggregate geometric attributes. The macrotexture of HFST sur-
face depends to a great extent on the size, shape, and angularity of
the aggregate and plays a critical role in high-speed crashes on wet
pavement. In addition, the feature of aggregate particle surface
affects the surface friction, particularly the long term friction per-
formance. The authors examined the calcined bauxite aggregate
samples. It was found out that the rounded particles accounted
for 7% of the total weight. Therefore, the fine aggregate angularity
(FAA) (AASHTO 2017) test was conducted to measure the shape
of the aggregate particles and the degree of surface irregularities of
the aggregate particles.
Table 7 shows the results of specific gravity, moisture content,
and FAA tests performed on both the calcined bauxite and steel slag
aggregate samples. The calcined bauxite aggregate has a very high
density. The moisture content of 0.81% is much greater than 0.2%,
the maximum moisture content specified in AASHTO PP79, and
0.3%, the typical value from the supplier, but much less than 3%,
the maximum water absorption for the calcined bauxite (NDRC
2005). The steel slag aggregate sample is solid with a specific grav-
ity of 3.59 and a moisture content of 1.11%. In general, BOF steel
slag has a density higher and a water absorption lower than EAF
steel slag. This may be attributed to that BOF steel slag usually has
a higher iron oxide content than EAF steel slag. The FAAvalues are
48% and 46% for the calcined bauxite and steel slag aggregate
samples, respectively, and are greater than 45%, the minimum
FAA for heavy traffic asphalt mixtures (INDOT 2016).
Fig. 3. Variations of polished stone value (PSV) with aggregate size for
calcined bauxite.
Table 5. Chemical compositions (% by mass) of calcined bauxite
Chemical Current paper GLM (2015)
Al2O3 86.93 88.1
SiO2 6.82 5.1
Fe2O3 1.63 1.45
TiO2 3.45 3.7
CaO þ MgO 0.45 0.47
K2O þ Na2O 0.21 0.18
Table 6. Chemical compositions (% by mass) of steel slag
Chemical
BOF EAF (ladle)
Current study
Yildirim and
Prezzi (2009)
Yildirim and
Prezzi (2009)
CaO 38.49 39.4 47.52
FeO 29.53 30.23 7.61
SiO2 12.52 11.97 4.64
MgO 10.22 7.69 7.35
MnO 4.24 2.74 1
Al2O3 5.71 2.16 22.59
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6. Requirements for Aggregate Properties and
Attributes
Current Requirements by State DOTs
Summarized in Table 8 are the requirements for the aggregate prop-
erties for HFST by eleven state DOTs (ATSSA 2016). All these
agencies except the Georgia DOT use only calcined bauxite. The
Georgia DOT allows the use of either calcined bauxite or highly
resistant granite. All agencies have requirements for LAA; one
agency (Virginia DOT) has the requirement for MDA; five agencies
have requirements for PSV; three agencies have requirements for
aggregate soundness; and two agencies have set forth a requirement
for aggregate acid insolubility in terms of the acid insoluble residue
(AIR). Obviously, the current state DOT requirements vary consid-
erably in aggregate properties and attributes, aggregate gradation
or size, quantitative provision, and test method. In addition, there
is a lack of consistency with the requirements between different
mechanical properties, particularly LAA and PSV.
The ASTM E660 method (ASTM 2015) uses aggregates of
9.5–12.7 mm (2015), and the results do not necessarily agree with
the measurements using the AASHTO T279 method. However,
AASHTO T279 has been more commonly used to evaluate the
polishing attribute of aggregate. It should also be pointed out that
it was reported that the AIR test does not directly measure the hard-
ness of aggregate (Fowler and Rached 2012), and aggregates that
pass the MDA test would likely pass the sulfate soundness test
(Cuelho et al. 2008). Therefore, the requirements for soundness
or AIR may ultimately become unnecessary if LAA or MDA has
been considered. As noted earlier, the only requirements for the
properties of calcined bauxite in AASHTO PP79 include the
LAA loss (20% max), Al2O3 content (87% min), and moisture
content (0.2%). AASHTO PP79 is a provisional standard adopted
on a temporary basis for the refractory calcined bauxite originated
from China, where the refractory grade calcined bauxite is divided
into seven grades in terms of the Al2O3 content (NDRC 2005).
Recommended Requirements
The friction of HFST or friction surfacing relies primarily on the
aggregate abrasion and polish attributes. Also, the large aggregate
particles in HFST are embedded to about half of the aggregate
height and may experience large impact force, and thus, the aggre-
gate abrasion attribute such as LAA can be utilized to measure the
resistance of aggregate to fragmentation. Fig. 4 shows the relation-
ships among LAA, MDA, and PV-10 for the aggregates commonly
used by INDOT. For natural aggregates (≤9.5 mm), the LAA
values are 20% or more, the MDA values are 6% or more, and the
PV-10 values (main scale) are around 26–34. The abrasion perfor-
mance of the selected steel slag is superior to the natural aggregates.
Because the Pearson correlation analysis suggested a strong corre-
lation between LAA and MDA (r ¼ 0.837), either LAA or MDA
loss can be used to measure the abrasion resistance of aggregate.
However, the PV-10 values fluctuate greatly from aggregate to
aggregate (see the bottom of Fig. 4). The Pearson correlation
analysis indicated a very weak correlation between PV-10 and
LAA (r ¼ −0.432) or MDA (r ¼ −0.467). This implies that for
a specific type of aggregate, high abrasion resistance does not nec-
essarily guarantee high polish resistance. Therefore, PSV should be
considered for aggregates for HFST or friction surfacing.
Table 7. Specific gravity, moisture content, and fine aggregate angularity
(FAA) test results
Aggregate Specific gravity Moisture content (%) FAA (%)
Calcined bauxite 3.38 0.81 48
Steel slag 3.59 1.11 46
Table 8. Current requirements for aggregate properties by state DOTs
State DOT
LAA
(%, max.)
MDA
(%, max.)
PSV
(min.)
Soundness
(%, max.)
AIRa
(%, min.)
Alabama 20b
— 38c
— —
California 10b
— — 30d
90
Florida 10b
— — — —
Georgia 10b
— — — —
Illinois 20e
— — — —
Iowa 20f
— 70g
— —
Pennsylvania 20f
— 38f
— —
South Carolina 20f
— 70g
— —
South Dakota 30f
— 65g
12h
—
Texas 10e
— — 30d
90
Virginia 20b
5 — — —
a
AIR represents acid insoluble residue.
b
No grading specified.
c
AASHTO T279, accelerated polish value.
d
Magnesium sulfate.
e
Grading D.
f
Grading C.
g
ASTM E660, three-wheel polish value.
h
Sodium sulfate.
Fig. 4. Relationships among Los Angeles abrasion (LAA), Micro-Deval
abrasion (MDA), and polish value (PV-10) (aggregate size ≤ 9.5 mm).
© ASCE 04019155-6 J. Mater. Civ. Eng.
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7. As noted earlier, the content of Al2O3 plays a critical role in
ensuring the mechanical properties of calcined bauxite and steel
slag used for HFST or friction surfacing, but depends on the many
factors. In addition, FAA is very effective at measuring the shape
and surface irregularity of aggregate particles for HFST, and has
already implemented for thin-overlay HMA mixtures by INDOT
(2016). Density is one of the important physical properties for
a specific aggregate; nevertheless, it is directly related to the
mechanical properties of the aggregate. Moisture content [ASTM
C566 (ASTM 2013)] affects the adhesion between aggregate and
binder, therefore, the durability of HFST. It should also be stressed
that alternative aggregates have been successfully used in a wide
range of pavement treatment applications, particularly the so-called
color surface treatment (CST) that is increasingly receiving atten-
tion. Aggregate blending may also be an option for friction surfac-
ing, such as thin bonded overlays for bridge decks (NVDOT 2015).
Therefore, it is practically useful to develop a more broad-based
specification that provides both specific and generic requirements
for HFST and other friction surfacing. Table 9 presents the recom-
mended aggregate properties and requirements established by
taking into consideration the original test results, current practices,
and friction performance. The generic requirements may apply to
any possible standard and alternative aggregates for friction surfac-
ing. Specially, the content of Al2O3 only applies for both calcined
bauxite and steel slag; and FAA applies for HFST with 1–3-mm
aggregates.
Conclusions
The PSVof BS EN 1097 accelerated polishing test differs from the
PV-10 of AASHTO T279 accelerated polishing test in many as-
pects, including load, polishing time duration, abrasion material
and procedure, and reading scale. No unique correlation between
PSV and PV-10 has been reported so far. No evidence has been
reported to suggest which one is more accurate for measuring
polishing resistance. The MDA test is a more repeatable abrasion
test. The exposed aggregate particles in HFST protrude above the
binder and undergo greater shear force and impact from vehicle
tires. The resistance of aggregate to the shear force and impact
of tires may be measured in terms of the LAA loss.
The steel slag aggregate experienced greater LAA losses than
the calcined bauxite aggregate. However, the difference between
the LAA losses of the calcined bauxite and steel slag aggregates
became much smaller as aggregate size decreased. The LAA loss
increased as the aggregate size decreased. Nevertheless, the LAA
loss of the steel slag was much less sensitive to aggregate size than
that of the calcined bauxite. The steel slag aggregate demonstrated
greater MDA losses than the calcined bauxite aggregate. The
accelerated polishing test results demonstrated an obvious size ef-
fect. The 1–3-mm aggregates yielded greater polishing resistance
than the 6.3–9.5-mm aggregates for both calcined bauxite and
steel slag. The selected steel slag can be a promising alternative for
1–3-mm aggregates for HFST or friction surfacing in terms of both
aggregate abrasion and polishing resistances.
The mechanical, physical and geometric properties of aggregate
are critically important for HFST or friction surfacing to provide
durable surface friction performance. Specification requirements
for these critical properties of aggregates can be readily established
in terms of PV-10, LAA (or MDA), moisture content, and FAA that
are currently adopted by AASHTO or ASTM and widely utilized
by state DOTs.
Acknowledgments
This work was supported by the Joint Transportation Research
Program (JTRP) administered by Indiana Department of Transpor-
tation and Purdue University. The authors would like to thank
the study advisory committee members, including Bill Tompkins,
Tim Wells, Mike Holowaty, Matt Beeson, Mike Prather, Scott
Chandler, Chris Moore, Ed Spahr, Enass Zayed, and Rick Drum
for their guidance. Special thanks are extended to Bob Rees and
Bart Williamson for their assistance in laboratory testing. The
authors recognize the help from Frank Julian, David Merritt, Doug
Fromm, Patrick Malfitano, Georgia Eusner, George Wang, and
Mike Blackwell.
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