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UPDATE ON ICAR 507: THE SIGNIFICANCE AND APPLICATION OF THEMICRO-DEVAL TEST
G. Daniel Williams
MS Candidate in Civil Engineering, The University of Texas at AustinAustin, Texas, USA
Kevin HampelMS Candidate in Civil Engineering, The University of Texas at AustinAustin, Texas, USA
John J. AllenManaging Associate Director, International Center for Aggregates Research,The University of Texas at AustinAustin, Texas, USA
David W. Fowler Dean T.U. Taylor Professor in Civil Engineering, The University of Texas at AustinAustin, Texas, USA
ABSTRACT
The aggregate industry needs a test that better correlates test results to field performance.
Micro-Deval has shown potential as a good indicator for field performance. The micro-Deval
wet abrasion test for coarse aggregate is studied in this project to determine the ability of the testto predict field performance for various uses and mineralogical backgrounds when used alone or
in combination with other aggregate tests. Aggregate properties such as particle shape, surface
texture, and mineralogy are studied to determine their effect on the amount of micro-Deval loss.
Aggregates were obtained from across the United States and Canada with varying field
performance ratings, uses, and mineralogy. Testing is underway and the micro-Deval test is
showing promise as an indicator of field performance when used in combination with other
aggregate qualifying tests.
Keywords: micro-Deval; abrasion; wet aggregates; coarse aggregate properties; field
performance; wet attrition.
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INTRODUCTION
From the 1920s to the 1940s, many tests such as the Los Angeles (L.A.) abrasion test
(adopted by ASTM in 1939) and the sulfate soundness test (adopted by ASTM in 1931) were
created by researchers and adopted by American Association of State Highway and
Transportation Officials (AASHTO) and American Society of Testing and Materials (ASTM).
These tests had fundamentally sound intentions attempting to model the forces experienced by
the aggregates in field conditions, but acceptance limits were determined in relation to the range
of test values experienced [1] due to a lack of field performance history and data. Most of these
tests gained popularity despite this lack of correlation to field performance and were introduced
into aggregate qualification standards.
The L.A. abrasion and impact test (AASHTO T 96), for example, is the most widely
specified test in North America to determine the impact and abrasion resistance of coarse
aggregate [2]. Its development attempted to overcome the short comings of the Deval test which
was established in 1878 and adopted by ASTM in 1908. The main short coming of the Deval test
consisted of a lack of a correlation with the performance of aggregates in pavements [3].
Research has shown that the L.A. abrasion test is a poor indicator of field performance [4-6].
Senior and Rogers [7] have shown that brittle, crystalline particles tend to shatter under the
impact load while fine-grained aggregates such as slates tend to absorb some of the impact and produce lower losses.
One major disadvantage of the L.A. abrasion test is its inability to test aggregates in a
moist environment. Aggregate in the field is rarely dry and the effects of moisture may
significantly alter aggregate mechanical properties [7]. Larson et al. [8] studied the effects of
moisture on aggregate tested in the L.A. abrasion apparatus. He found that running 250
revolutions dry followed by 250 revolutions wet produced a better correlation with field
performance. He also noted that collecting the entire test specimen from the drum was difficult
since the fines tended to adhere to the inside of the drum. These findings gave opening to a new
abrasion test designed specifically to include the effects of moisture on the mechanical properties
of aggregate.
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The micro-Deval test was developed in France in the 1960s to include the effects of
moisture on the mechanical properties of aggregate. Although, the test did not gain popularity in
the United States and Canada until the early to mid-1990s, the micro-Deval abrasion test is
growing in use across North America. Many state and provincial agencies have begun using the
test knowing that the introduction of water affects the behavior of some aggregates. The fact that
aggregate in use is rarely dry combined with the relatively short time it takes to get a micro-
Deval abrasion result has encouraged the use of this relatively new test procedure. Some have
started using the test for comparison purposes while others have made the test procedure a
supplement to qualification standards.
Due to little or no correlation between some of the current tests and field performance,
some of these agencies have adopted the micro-Deval test despite a lack of confidence in therecommended acceptance limits. In order to gain confidence in the test and set realistic limits for
various uses of aggregate (e.g. in concrete pavements, hot mix asphalt, base courses, etc.) the
micro-Deval test needs to be correlated with aggregates of known field performance. Early
testing performed by Rogers and Senior with the Ontario Ministry of Transportation in the 1980s
and 90s has shown a general trend correlating the field performance of aggregates with micro-
Deval loss. While not perfect, the correlation is much better than other tests such as the L.A.
abrasion.
Correlation between the micro-Deval test results and field performance ratings should be
established early. AASHTO has adopted the micro-Deval test procedure (TP 58) and other
agencies are looking to adopt the test procedure as well. As more agencies develop acceptance
standards, a clear understanding of the effect of aggregate mineralogy, shape, surface texture,
and/or use on the micro-Deval abrasion loss is needed. For example, an aggregate used as a base
course may not need to be subjected to the same acceptance limits as that same aggregate used in
concrete.
RESEARCH OBJECTIVE
Prior to adoption of the test procedure and its specified allowable limits, careful
consideration, testing, and correlation must be performed to reduce the number of aggregates that
would be judged incorrectly. Aggregate producers will benefit through satisfactory aggregates
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not being labeled unacceptable. Departments of Transportation (DOTs) will gain by avoiding
costly pavement repairs due to the degradation of an unsatisfactory aggregate which might have
passed a high micro-Deval acceptance limit. It is beneficial to everyone involved in the
aggregate industry to establish accurate acceptance limits early based on field performance.
This project looks at the correlation of micro-Deval abrasion loss and field performance
of aggregates as well as a number of other tests whose results were also correlated with field
performance. Each aggregate sample will be subjected to a test suite composed of twelve tests
including the micro-Deval, L.A. abrasion, magnesium sulfate soundness, Canadian Freeze-Thaw,
AASHTO Freeze-Thaw, Aggregate Crushing Value, Wet Crushing Value, absorption, specific
gravity, percent flat and elongated particles, percent crushed particles, and petrographic
examination. The results of each of the tests mentioned are being compared with micro-Deval
test results to see if a correlation between two tests is able to distinguish better acceptance limitswith respect to field performance.
AGGREGATE ACQUISITION
Initial Survey
The first step of the testing process was to determine the extent of knowledge and use of
the micro-Deval test. A survey was distributed to the forty-eight contiguous state DOTs, most
Canadian provincial transportation ministries, and a few aggregate producers. The survey aimed to obtain information on current aggregate qualifying tests in use, confidence in the results of
these tests, knowledge of the micro-Deval test, interest in the micro-Deval test, and knowledge
of aggregate sources which might be linked to failures in hot-mixed asphalt, Portland cement
concrete, bases, and subbases. 52 of the 55 (95 percent) surveys sent were completed and
returned. This high response rate along with the information attained on the form revealed
considerable interest in the micro-Deval test. Every responder indicated interest in receiving
project updates and findings as well as a copy of the report upon completion. The responses from
the survey indicated that most agencies were familiar with micro-Deval, but many were unsure
of the role of the micro-Deval test. Many responders, mentioned being familiar with National
Center for Asphalt Technology (NCAT) report number 98-4 [9] or NCAT report number 02-09
[10].
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Acquisition Logistics
The initial survey response indicated which aggregates could be provided. Along with the
identification of sources, field performance ratings were also requested for each source. This
gave the ICAR 507 project team an idea of the aggregates it would be receiving and what gaps
would need to be filled by future aggregate requests. It was quickly found that providers were
more likely to offer aggregates of good and fair field performance. Naturally, most providers did
not want to claim their aggregate source as poor so more effort was put into obtaining aggregates
of poor field performance.
Attempts were also made to ensure there were enough sources for each usage category:
hot-mixed asphalt, Portland cement concrete, and base/subbase. Because each use entails
different applied forces from transportation, mixing, placement, compaction, and transportation
loads, different acceptance criteria may be valid. Collection of aggregates of many usages was
easily achieved as many sources were used in two or more categories previously listed.
Finally, samples of numerous mineralogical backgrounds were sought. Based on the
work performed by Cooley, Jr. et al. [10], it was found that granites, for example, may not need
to be subjected to the same acceptance criteria as limestones and sandstones or gravels.
Therefore, samples were accumulated from across the United State and Canada so this could beinvestigated. 31 states and seven provinces have participated in the study to date with
communications on-going in six other states. This helps guarantee a broader view and acceptance
of the micro-Deval test.
The amount of aggregate initially requested was two or three 55 gallon drums of each
source. This large amount was needed for two reasons, the project team discussed making
specimens for performance testing, and the test suite had not been finalized. The team realized it
was more beneficial to use the performance rating found through actual field performance
because of redundancy, cost requirements, and time requirements. Henceforth, aggregates were
only requested if there was an established field performance for the source. Sieve analysis
showed only one fifty-five gallon drum of aggregate was needed if the grading could be limited
to the aggregate passing the 25 mm (1 inch) sieve and retained on the 4.75 mm (No. 4) sieve
with approximately fifty percent retained on the 12.5 mm (1/2 inch) sieve. When this gradation
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was unable to be provided, calculations were performed to determine the amount of aggregate
needed.
Field Performance Rating
Since one of the goals of this report is to correlate micro-Deval test results with field
performance of aggregates, the field performance rating is crucial. Originally, the performance
ratings given in the responses to the initial survey were intended to be used as the performance
rating of each aggregate source. As the project developed and more published literature was
reviewed, it was felt that strictly using the ratings provided in the survey responses could result
in a subjective rating system. To define a more objective rating system, two rating systems were
found from past research. These were found in published work by Senior and Rogers [7] and Wu
et al. [9].
Senior and Rogers [7] developed a rating scale for the field performance evaluation
criteria of coarse aggregates used in granular base and asphaltic and Portland cement concrete:
Good used for many years with no reported failures, pop-outs, or other signs of
poor durability,
Fair used at least once where pop-outs or some reduced service life had resulted,
but pavement or structure life extended for over 10 years, and
Poor used once with noticeable disintegration of pavement after one winter,
severely restricting pavement life.
The second published rating scale found was that of Wu et al. [9]. Wu et al. looked into
characterizing aggregates used in asphaltic concrete only. The scale was as follows:
Good used for many years with no significant degradation problem during
construction and no significant pop-outs, raveling, or potholing during service life,
Fair used at least once where some degradation occurred during construction
and/or some pop-outs, raveling, and potholing developed, but pavement life extended for over 8
years, and
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Poor used at least once where raveling, pop-outs, or combinations developed
during the first two years, severely restricting pavement [use]
ICAR 507 utilized the same three-step rating system (good, fair, and poor) shared by both
studies listed above. The good and fair ratings used by the ICAR 507 project were similar to
those used by Senior and Rogers since this project dealt with bases, hot-mixed asphalts, and
portland cement concretes. The poor rating was similar to the one used by Wu et al. in that two
years separated poor from fair instead of the one year used by Senior and Rogers. The final
performance rating system accepted for use consisted of the following:
Good used for 10 or more years with no reported non-chemical problems, Fair used at least once where minor non-chemically related failures require
minor repairs, but average life extends beyond 10 years, and
Poor used at least once where severe degradation or failure occurred within 2
years of service or during construction which severely inhibits and/or prevents the use of the
application.
In addition to the performance rating scale being developed, a final survey was
constructed as well. This survey consisted of a series of questions about each source including
which applications the source was used in and any problems experienced due to its use. The goalof the survey was to make the rating system as objective as possible.
Following a phone interview, ICAR 507 personnel determined the performance rating
based on the information provided. By ICAR 507 personnel determining the field performance
rating, all samples could be compared on equal terms. In no case was a sample rated good or
poor that was initially rated the other extreme. In some cases though, a sample was initially rated
good but was determined to be fair.
TESTING METHODOLOGY
While choosing the aggregate tests to be included within this study, several factors were
taken into consideration. Great importance was placed on tests of widespread current use by state
and provincial departments of transportation. Since this research primarily focuses on the micro-
Deval test, attention was given to tests whose results would either correlate with or compliment
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micro-Deval results in comparisons with field performance. Relationship to field performance
and the ability of each test to adequately predict field performance was considered. Relationship
to basic aggregate properties was also considered. The following is a description of methodology
used to determine which tests would be included in this research.
Abrasion Tests
Los Angeles Abrasion and Impact Test (AASHTO T 96)
The L.A. abrasion test was decided on due to its popularity among transportation officials
as found through the initial survey. According to Amirkhanian [11], 26 percent of surveyed
agencies were unaware where their L.A. abrasion specification loss limits originated. Studies by
Minor [4], Rogers et al. [5], and Richard and Scarlett [6] have shown poor correlations betweenthe L.A. abrasion test and field performance. While the L.A. abrasion test can predict the
mechanical breakdown of aggregate in stockpiling, transportation, and construction, it does not
correlate well with field performance.
The L.A. abrasion test [12] calls for an aggregate sample to be placed in a revolving drum
along with a set number of steel charges. The drum repeatedly picks up and drops the sample and
charges by means of a shelf located inside the drum. While the name of the test implies both
abrasion and impact, the L.A. abrasion test correlates well with other impact tests such as the
Aggregate Impact value (BS 812: 110) and Aggregate Crushing Value (BS 812: 110) as shown
Hudec [13] and Al-Harthi [14].
Micro-Deval Abrasion Test (AASHTO TP 58)
The micro-Deval test, developed in France during the 1960s, looks at the effects of
moisture on the abrasion resistance of mineral aggregates. The test (AASHTO TP 58 [15])
involves placing 1500 g of soaked, graded aggregate and two liters of water into a five liter jar.
Following soaking of the aggregate for a minimum of one hour prior to running the test, 5000 g
of steel charges, 9.5 mm (3/8 in) in diameter, are added to the jar in addition to the sample and
water. The jar is then placed into the micro-Deval apparatus and rotated at 100 revolutions per
minute for two hours. Upon completion of the required number of revolutions, the sample is
screened over a 1.18 mm (No. 16) sieve and oven dried to constant mass at 110C (230F).
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Unlike the L.A. abrasion test drum, the micro-Deval test drum does not have a shelf to
lift and drop the sample and subject it to impact loads causing fragmentation. Degradation is a
product of abrasion between the aggregate particles and steel charges in the presence of water.
The micro-Deval test has been shown to correlate well with field performance but its
application is still unclear. In 1998 Rogers has suggested that micro-Deval be used as an
aggregate qualifying test due to its correlation with field performance [16]. The test could be
used to replace the magnesium sulfate test due to the high correlation found by Rogers and
Senior [7]. The precision of the micro-Deval test alerts changes in aggregate type at quarries by
yielding different losses in the micro-Deval test, which can inform quarry personnel when to
perform sulfate soundness testing, saving time and money.
Soundness Tests
Sulfate Soundness Tests (AASHTO T 104)
Soundness tests have been used by transportation agencies and testing laboratories in
North America for Many years. Since its birth, many have debated the merit of this test as an
indicator of field performance. Although some have found the sulfate test to be an adequate
predictor of performance [2, 9, 17-19], some have reported cases where the sulfate tests have
lacked the ability to consistently relate to field performance [20-22]. The crystal growth of salts
within the pores of aggregates does not subject the aggregate to the same expansive forces as the
freezing of water [2]. In addition, several researchers report large variability in the results of
soundness testing [23-25]. Nevertheless, the sulfate soundness test is one of the most commonly
used qualification test in the United States. Hanna et al. [1] showed that the sulfate soundness
test is the soundness test of choice for 31 of the 43 respondents to a national survey. Because of
its widespread use, a sulfate soundness test was an obvious choice for this research.
Although several reported using magnesium sulfate during phone interviews with DOTrepresentatives, Hanna et al. reported in 2003 that a majority of the states using sulfate soundness
testing use sodium sulfate soundness [1]. Despite this, the magnesium sulfate test has several
favorable characteristics that warrant its use in this research instead of sodium sulfate.
Magnesium sulfate is a much harsher test [26] producing more loss by mass. In addition,
magnesium sulfate has been shown to have less variation in solubility in the temperature range of
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testing making it a much more dependable and reproducible test [1, 21]. Moreover, sodium
sulfate has three different crystalline forms at the temperature of testing making the preparation
of solution difficult [21], whereas, magnesium sulfate has only one at that temperature.
Researchers have even called for agencies change to the magnesium sulfate test due to the
difficulty in preparing and operating the sodium sulfate test [26, 27]. Therefore, the AASTHO
T 104 [28] magnesium sulfate soundness test was chosen for use in this research to ensure more
reliable results.
Canadian Freeze-Thaw Test (CSA A23.2-24A)
Although not widespread, some agencies use freezing and thawing tests as a supplement
to the sulfate soundness test. Of those that do, the majority test the durability of aggregates by
the freezing and thawing of concrete specimens containing those aggregates. Many believe that
the tests currently available for the unconfined freezing and thawing of aggregates, such as
AASHTO T103, create unrealistically harsh conditions. However, Volger reported that 7 states
within the U.S. use some form of unconfined freeze-thaw test on aggregates [29]. As a result, the
decision was made to use an unconfined freeze-thaw test in this research.
Deciding on a test method proved difficult. Wide variations in the use of AASHTOs T
103 standard are allowed as no cooling rate or absolute minimum temperature is defined [30].
Both of these variables have been shown to affect degradation due to freezing and thawing and
the relationship of the results to field performance [31-33]. Moreover, personal communications
with state agencies or testing laboratories revealed wide differences in the test method. Some
reported freezing aggregate mostly submerged then thawing with a 70 degree forced air draft.
Another agency reported vacuum saturating samples and testing them suspended in plastic bags.
Still another reported vacuum saturating the aggregate and freezing them in metal pans. All of
these methods are roughly a variation of a test that has been shown to be unrealistically harsh.
A few other tests have been developed for determining the potential resistance to freezing
and thawing. Two of these tests are the Iowa Pore Index Test and the Washington Hydraulic
Fracture test. Rogers has shown a good correlation between the Iowa Pore Index test and the
durability of aggregates in Ontario, and the final version of the WHFT appears to be satisfactory
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[1]. However, through communications with state agencies evidence of widespread use these
tests could not be found and were not chosen for this research.
The Canadian Standards Association, however, has adopted an unconfined freezing and
thawing test of aggregates that has been designed to model actual field conditions and maximize
the relationship to field performance [31]. Research at the Ministry of Transpiration of Ontario
determined the optimum cooling rate and minimum freezing temperature of unconfined freeze-
thaw tests to maximize loss and relationship to field conditions. These observations are also in
accordance with the observations of others. The optimum salt solution strength and the effect of
the number of cycles was also determined.
As mentioned above, all of these variables have been shown by MTO and other authors
to significantly affect freeze-thaw durability [31-33]. The science behind the CSA specification
has addressed these issues, whereas AASHTOs T 103 and its variations have not. The CSA
standard has also been recommended by the National Cooperative Highway Research Program
[1], and the T 103 method has not. Moreover, the CSA test method can be completed with a
fraction of the time and difficultly required by the T 103 method. Testing the aggregates for this
research with some variation of T 103 would have required the acquisition of equipment the
project could not afford, and this would be done for a test that has been shown to be inadequate
and is used in various forms by only 7 DOTs. Due to the good correlation with field performance, the ease and quickness of the test, the NCHRP recommendation, and the
overwhelming scientific support, the CSA A23.2-24A specification was chosen for this research.
However, recognizing that the CSA version of unconfined freeze-thaw testing is not well known
among U.S. departments of transportation, a side study of the present micro-Deval research is
being conducted to determine if a correlation exists between AASHTO T 103 and the CSA
standard.
The method used for the Canadian Freeze-Thaw testing follows the CSA A23.2-24A
testing standard [34]. After washing, oven drying, and sieving the aggregate, samples are
prepared by hand sieving the material according to the following gradation:
3/4 in 1/2 in 1250 grams
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1/2 in 3/8 in 1000 grams
3/8 in No. 4 500 grams
Each size fraction prepared is then individually placed in autoclavable mason jars. Thesamples are soaked in the jars for 24 hours in a 3% sodium chloride solution. After soaking, the
solution is drained from the samples, and air tight lids are placed on the jars to ensure 100
percent humidity. The samples are cooled to a temperature of -18 C (0 F) for 16 hours
overnight. They are removed and allowed to thaw at room temperature for approximately 8
hours. After the fifth cycle the jars are filled with water and rinsed five times. Finally, the
samples are oven dried to constant mass at 110 C (230 F) in a convection-type oven and sieved
over the original sieve sizes. The percent loss is calculated, and the final loss is determined by
the weighted average of the percent loss of the three jars.
For the purposes of conducting this test a blast freezer was purchased, and adjustments
were made to control the freezing rate according to the optimal freezing rate as determined by
MTO [31]. The freezing rate of the freezer was monitored over twelve practice runs to ensure
consistent freezing, and fans were placed in the freezer chamber to ensure uniform freezing of all
samples. Personnel are present in the afternoons to turn on the freezer for cooling and in the
mornings to open the freezer doors for thawing. Although the samples are not removed from the
chamber every morning, a high-powered box fan circulates air at room temperature through thechamber. The samples are then rotated as specified before freezing again that afternoon. The
remainder of the test is conducted exactly as stated in the specification and above.
AASHTO Freeze-Thaw Test (AASHTO T 103)
The procedure selected for the AASHTO freeze-thaw test was procedure C of the T 103
specification. The samples will be hand sieved according to the following gradation:
3/4 in to 3/8 in 1000 5 grams
Consisting of:
3/4 in to 1/2 in 330 5 grams
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1/2 in to 3/8 in 670 5 grams
3/8 in to No. 4 300 5 grams
Each sample will be vacuum saturated by subjecting them to a vacuum with an air pressure not over 3.4 kPa (25.4 mm of mercury) and then introducing de-ionized water to the
samples. After saturation they will be placed in Teflon coated baking pans to prevent corrosion
with a plastic seal to prevent evaporation. The samples will then undergo twenty-five cycles with
6 hours of freezing to a temperature less than -26C (-15F) followed by 6 hours of thawing to a
temperature of 21 to 24C (70 to 75F). Although the procedure calls for thawing in water, this
test will be conducted with air thawing. The expense and technical difficulties of acquiring or
building a machine to air freeze samples while thawing them in water are beyond the capabilities
of this project. In addition, two of three agencies in communication with this project have
reported using some sort of air thaw for the unconfined freezing and thawing of aggregates.
An inexpensive solution for the unconfined freezing and thawing of aggregate according
to the AASHTO T 103 specification was achieved by adapting the blast freezer used for the CSA
specification. An industrial timer regulates the cycles of the freezer to provide two 6 hours
periods of freezing each day, and other timers regulate a spacer heater that, combined with high-
powered fans that ensure uniform heating and cooling, thaw the samples. Through several
practice runs and experiments this method has shown the ability to produce consistent and reliable freeze-thaw cycles.
Strength Tests
Aggregate Crushing Value Test (BS 812:110)
Although no AASHTO or ASTM standardized method exists for determining aggregate
strength [1], several simple methods have been used by other countries. Variations of the British
Aggregate Crushing Value (ACV) have been used for some time in Great Britain, Australia, and
New Zealand. This test is thought of favorably and used for qualification purposes in these
countries [35], and the ACV was reported by Hanna et all as being a reasonable approach for
determining aggregate strength [1]. Therefore, the British Aggregate Crushing Value Standard
812:110 [36] has been selected for use in this study.
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The dry method used for the crushing value test follows that which is outlined in the
British Standard BS 812:110, and the wet crushing test method used is adapted from that
described in the Australian Standard AS 1141.22 (Wet/Dry Strength Variation) [37]. The
appropriate equipment was obtained on loan from the Ministry of Transportation of Ontario. The
testing equipment consists of thick, hollow steel cylinder which confines the aggregate, a base
plate on which the cylinder and aggregate sits, and a steel plunger for applying the load. Also
included is a smaller and lighter cylinder to determine the appropriate sample volume.
For the ACV test, the oven dry samples are prepared by filling the provided cylinder with
aggregate and weighing the sample to the nearest gram. The sample is then poured into the steel
cylinder in three lifts, lightly compacting and leveling the aggregate with a metal rod after each
lift. The steel plunger is then inserted into the cylinder. A compressive force is added to the
aggregate at a rate such that 90,000 lbs (soft conversion of the specified 400 kN) is added uniformly over a period of 10 minutes. The sample is then removed and sieved over the No. 12
sieve, and the percent loss is determined as a ratio of loss over original mass.
Wet Aggregate Crushing Value Test (Variation of BS 812:110 and AS 1141.22)
A wet version of the Aggregate Crushing Value, which will be further referred to as the
Wet Crushing Value (WCV) for this research, is used for aggregate qualification purposes in
Australia and in New Zealand. Different crushing strength values can be obtained by testing theaggregate in both oven dry and saturated surface dry conditions. The wet crushing test has been
shown to be useful in evaluating an aggregates strength when evaluating both the strength of the
aggregate and the fines produced. Also of importance is the variation between the ACV results
and WCV results for a given aggregate. Larger variations between the ACV and WCV have been
shown to correlate with aggregate performing poorly due to wetting and drying and freezing and
thawing. This is a relatively quick and easy test, and therefore an adapted version of the WCV
has been adopted for use in this study
The test method for the WCV in this research has been adapted from the Australian AS
1141.22 specification and the British Standard BS 812:110 specifications. The WCV is almost
identical to the oven dry test except that the sample is crushed in the saturated surface dry
condition. Afterwards, the sample is removed and oven dried before sieving. For the purposes of
this research and comparing the oven dry and saturated surface dry aggregate strengths and
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crushing values, a few additions have been made: the load carried by the aggregate at a
deflection of 10% is recorded, and the final deflection of the aggregate at 90,000 lbs is recorded.
Other Tests
Flat and Elongated Test (AASHTO D 4791) and AIMS Test
The flat and elongated test and the Aggregate Imaging System (AIMS) test are included
in the test suite to determine if the shape and surface texture of the aggregate affects micro-Deval
loss. It is believed that a flat or elongated particle will more than likely have more loss than a
round particle in the micro-Deval test, when comparing samples of the same mineralogy, due to
the potential of corners chipping off. It has been shown through research that particle shape can
significantly affect the field performance of aggregates used in hot-mixed asphalt or railroad ballast [2, 38-40].
According to Hanna et al. [1], most state agencies measure the ratio of particle
dimensions rather than measuring the percentage of flat and elongated particles. ICAR 507 is
measuring the thickness to width, thickness to length, and width to length ratios to the nearest
one half of a ratio. These three ratios are then used to come up with a single number that could
be used for comparison purposes.
While the flat and elongated test only measures particle shape, the AIMS test was
included due to its ability to measure surface texture. The project proposes to send micro-Deval
test samples for analysis on the AIMS machine before testing in the micro-Deval apparatus.
These samples will be returned, tested according to the micro-Deval specification, and then
reanalyzed on the AIMS machine. Correlations will be developed with the micro-Deval test
results with the before and after surface textures and particle shape. This procedure looks to
determine the effect of particle shape and surface texture on micro-Deval limits.
Percent Fractured Particles Test (ASTM D 5821)
Similar to the particle shape, the angularity of the aggregate has an effect on attrition.
Ekse and Morris [41] have shown angularity to affect the abrasion loss of particles. They found
that for a given source, the more angular the aggregate particle is, the higher the loss is. Boucher
and Selig [39] also found the same result, noting previously worn particles had much less
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attrition than freshly crushed particles. While angularity is not as critical in dense graded hot-
mixed asphalt mixtures as it is in open graded mixtures [2] its effect on micro-Deval loss is
sought. Due to the highly subjective nature of the test, Benson and Ames (507.128) found the
both inter-laboratory precision to be poor. For comparison purposes, ICAR 507 plans to have the
same person perform all of the percent fractured analysis.
Petrographic Examination (ASTM C 295)
Knowing the mineralogy of an aggregate can tell a lot about the probable test results
through comparison with aggregates of similar mineralogical backgrounds. Studies have been
done comparing the petrographic examination to field performance of aggregates with
contradicting results. Rhoades and Mielenz [42] found that the quality of natural aggregates can
be determined by petrographic analysis. Similarly, Cooper et al. [43] established that a detailed
field examination, consisting in large part of a mineralogical determination, was able to predict
the overall quality of a potential aggregate source rock with an 86 percent success rate. When
this field examination was combined with the micro-Deval test, the success rate jumped to 94
percent.
Mielenz (1946) [44] and Boucher and Selig [39] concluded that the petrographic
examination aids in the evaluation of other test results and that the information obtained can be
used for comparison with unknown aggregates for evaluation purposes. However, both authorssay the test results are not sufficient to be used alone in the prediction of performance. Use of the
petrographic examination as a supplement to other tests is recommended; therefore, petrographic
examination is included in this study.
Side Studies
AIMS Test vs. Flat and Elongated Test
The Aggregate Imaging System (AIMS) test and flat and elongated particle test are being
performed on the aggregate samples acquired for the study. As mentioned previously in the
Testing Methodology chapter, the AIMS test is being utilized to develop a correlation between
the surface texture of aggregate and micro-Deval loss while the flat and elongated particle test is
looking to determine a correlation between particle shape and micro-Deval loss.
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While the AIMS test shows promise as a surface texture analyzer, its capabilities also
include particle shape analysis. The particle shape analysis will be performed with no additional
effort while the surface texture is analyzed. According to researchers at Texas A&M University,
the AIMS test has a very strong correlation with the flat and elongated particle test. The flat and
elongated particle test is being used due to its accepted use in industry but it is a very tedious
test. The AIMS test is considerably faster and more objective, but lacks widespread use. If a
strong correlation can be found between the results of the two tests, a more efficient means of
determining particle shape can be utilized with a side benefit of receiving information on the
surface texture of the aggregate as well.
Particle Shape Factor
Research has shown that particle size and shape can play a significant role in wet attrition
tests [41, 45]. Intuition would lead one to believe that all else being equal, the rougher or more
angular an aggregate, the more easily the aggregate will be abraded. Knowing this, a method is
needed to normalize micro-Deval loss to eliminate the bias introduced by particle shape.
Theoretically, an angular, rough aggregate with an exactly identical field performance as a
smooth, rounded aggregate should have identical micro-Deval losses. Intuitively, however, this
is not the case. In the authors opinion, no good proven method of numerically quantifying
aggregate shape for correlation purposes exists. Therefore, as a part of this research two studiesare being conducted to determine the effect of aggregate shape and texture on micro-Deval loss
and its relation to field performance.
Using an adaptation of the AASHTO Flat and Elongated test method, an attempt can be
made to numerically quantify aggregate shape [46]. By adopting the standard flat and elongated
caliper the thickness vs. width, width vs. length, and thickness vs. length ratios can be
determined to the nearest half of a ratio for a specified number of particles of a source. The
average ratio for the source can then be determined. This provides numerical information that
can be used for correlation purposes.
While manipulating these ratios, the authors discovered that a single number can be
determined to quantify aggregate shape. The three ratios of a given source can be normalized by
the lowest of the three ratios for that source, and then all three normalized ratios can be
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multiplied to determine a particle shape factor. Observations made while relating this factor to
the shape of the aggregate it described were very promising. Rounded particles have the lowest
number, elongated particles have slightly higher numbers, and flat and elongated particles have
the highest number. It would be expected that particles would be more susceptible to degradation
in this order. One would expect rounded particles to be the least susceptible to micro-Deval
degradation and flat and elongated particles to be the most susceptible to degradation.
The number could further be manipulated by multiplying the particle shape factor by
factors relating to the angularity and roughness to increase or decrease the particle shape factor
according to the suspected potential for resulting abrasion loss. Although these values need to be
further evaluated experimentally for accuracy, tentative factors have been assigned. Factors of
0.9 and 1.2 can be used for smooth and rough particles respectively, and factors of 0.9 and 1.2can be used for rounded and angular particles respectively.
This factor has shown promise in limited correlations with micro-Deval thus far. It is the
hopes of the authors that this factor, or some variation thereof, will at the very least provide a
better means of quantifying aggregate shape, or, more desirably, normalize micro-Deval values
to eliminate the bias introduced by particle shape and texture.
Canadian Freeze-Thaw Test vs. AASHTO Freeze-Thaw Test
Recognizing that the CSA version of unconfined freeze-thaw testing is not well known
among U.S. departments of transportation, a side study of the present micro-Deval research is
being conducted to determine if a correlation exists between AASHTO T 103 and the CSA
standard. Attention will also be given to the importance of each test concerning representing
field performance. Fifty aggregates will be selected from the aggregates obtained for this
research. These aggregates will be selected so that a wide variety of field performances,
mineralogical types, and CSA freeze-thaw losses will be represented. A version of Procedure C
will be conducted.
Aggregate Crushing Value Test vs. Wet Aggregate Crushing Value Test
Some feel that the crushing value tests are an indication of potential field performance.
Noting that aggregate properties can be different between a wet and a dry aggregate [47], it
should be of interest to determine the difference in strength between oven dry and saturated
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surface dry aggregates as measured by the Aggregate Crushing Value Test. This has been shown
to be very significant in the determination of potential field performance according to a contact
at Metso Minerals. The results obtained during this research will show how the strength
characteristics of aggregates change. The relationship of each to field performance might yield
valuable information, and the difference between the wet and dry values may be important.
TESTING OPERATIONS
Precision Statements
For all but three test methods, a precision requirement similar to the British Aggregate
Crushing Value test was adopted (BS 812 110). The ACV requirement states that, provided
two test results for a given source fall within 7 % of the mean of the two results, the mean isfound to be acceptable. If this is not the case, then two additional tests must be conducted and the
mean of the four will then become the result. Provided this requirement is met and the control
samples where applicable are also within 7% of the mean, then the results are deemed
acceptable. This was concluded to be an acceptable method of ensuring precise results in an
efficient manner.
This method is not being applied to the Magnesium Sulfate Soundness test, the micro-
Deval test, or the Absorption and Specific Gravity test. For the Absorption test only one sample
is tested as this is all that is required per the specification. For the micro-Deval test, three
samples of each source are tested and the mean is accepted unless an obvious outlier exists.
Control samples from the Brownwood quarry in Texas have been calibrated with Brechin II
samples obtained from MTO and are tested every ten tests or every week a sample is tested. The
control sample results are monitored to ensure that they remain within the acceptable limits set
for in the specification. The micro-Deval testing is being conducted in this manner to match that
which is specified in AASHTO TP 58 [15].The variability of the sulfate tests in general, as shown by previous work [23-25], was too
great to apply the method used in the British Standard. Three samples of each source are tested
by magnesium sulfate with no more than two of the three being tested in the same run. Two
control samples of Brechin II from Ontario are included with each run. If the control samples
yield values outside the acceptable limits provided in the AASHTO test specification [28], then a
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careful examination is given and additional samples are tested if necessary. One Brechin II
control sample and one control sample from the Brownwood quarry in Texas are also used in the
Canadian and AASHTO freeze-thaw tests; however, the precision requirements of these tests are
subject to those outlined in the British Standard. Over 12 practice freezing and thawing tests
have shown that the freezer used for these tests can reliably reproduce freezing and thawing
conditions, and the control samples used thus far have been remarkably consistent.
Standardizing Gradations
The acquired aggregate arrived in a variety of gradations. This created a potential
problem in comparing one sample to another. States specify different gradations for different
uses and not all states specify the same gradation for the same use. The gradation can affect test
results according to Rogers, et al. [48] and Selig and Boucher [49]. This poses the question, how
do we meet the needs of all states and provinces when each performs different tests and uses
different gradations.
Volger has reported that nine of sixteen states responding to a survey standardize
gradations before testing [29]. It was decided to create uniform gradations that each sample
should meet for comparison purposes. These uniform gradations were mostly specified by testing
specifications, but where they were left open according to the specification, a material passing
the 1/2 inch sieve and retained on the 3/8 inch sieve was used. This particle size was chosen for
two reasons: it is a median range for a typical coarse aggregate used in road construction that
should provide a representative test result and the micro-Deval sample most commonly used
(grading A) is comprised of fifty percent of 3/8 inch material. Since the ICAR 507 project is
determining the role of the micro-Deval test, it was determined 3/8 inch material would be a
good representative size for comparison purposes.
All sources are tested according to the specified gradations. However, rare instances are
occurring where not enough material is available for the all testing. In these cases an attempt is
first made to obtain additional material from the same stockpile. If this attempt fails and particles
of a larger size of the same sample are available, the aggregate then is crushed to meet the
specification. If no larger sizes are available, or if this is not practical, the sample sizes of the
soundness, freeze-thaw, and crushing value tests are reduced by no more than 50%. There have
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been a few rare instances where not enough material was available and substitutions were
required. One case resulted in substituting 1/2 inch material for 5/8 inch material for all tests.
Two instances have occurred where an insufficient amount of 3/8 inch material was available
and half inch material was substituted. A few more instances occurred where no #4 material was
present in any appreciable amounts. In this case the soundness tests and freeze-thaw tests were
conducted without this material. In all such cases, the actions taken have been documented and
will be reported.
CURRENT RESULTS
The project is now operating in two laboratories located on the J.J. Pickle Research
Campus, part of The University of Texas at Austin. The Construction Materials Research Group
just opened a new lab which this project was involved with. A new micro-Deval test machine
and a new blast freezer for freeze-thaw testing have been acquired and placed in the laboratory.
A convection type oven was also attained and refurbished for use in the new laboratory and a
magnesium sulfate soundness test setup was also developed and constructed. A thermostat for
the room, independent of the building was installed for better temperature and solubility control
of the sulfate soundness test.
Arrangements have been made for use of TxDOTs L.A. abrasion test machine. TxDOT
has also offered to perform magnesium sulfate soundness testing for comparison purposes. The
Ontario Ministry of Transportation (MTO) has also graciously lent the equipment required for
Aggregate Crushing Value testing. Both TxDOT and MTO have supplied a wealth of
information in setting up and constructing testing equipment. Measures have also been taken to
secure an experienced geologist to perform petrographic examinations.
The two graduate students that started with the project will be graduating in May, 2005. It
was arranged to have another graduate student take over testing and compilation of the finalreport. The succeeding graduate student began with the project in January to provide a transition
time for questions and familiarity with the testing procedures and equipment.
Testing of 47 aggregate sources is completed. The results of these sources will be used
for two theses scheduled to be completed by June, 2005. Earlier this year it was determined that
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testing could be completed by the end of March for 47 of the 117 sources acquired. Most of the
remaining sources have some test results but were not far enough along in testing to be
completed for the theses planned for June, 2005. ICAR 507 is still expecting a few additional
sources to trickle in from agencies that wanted to provide aggregate but were unable to do so
earlier for various reasons.
The test results thus far look promising. The potential of the micro-Deval test to
distinguish the field performance of aggregates used in base, hot-mixed asphalt, and concrete
appears to exist. Finding the optimum application of the micro-Deval test is the key.
CONCLUSIONS
With the pressure to begin constructing longer lasting roads and structures with more
marginal aggregates due to depletion of available resources, accurate and reliable testingmethods and limits need to be developed to identify appropriate aggregate. Researchers have
shown that traditional testing methods are not always suitable alone or even in combination with
other tests. However, several agencies have published reports showing micro-Deval to be an
outstanding indicator of field performance. However, others have shown results that show micro-
Deval as having poor or mixed correlations with field performance. By investigating the
relationship of micro-Deval and other common aggregate tests to field performance, realistic
limits can be determined for the qualification of aggregates. The results of this study should
provide micro-Deval limits that either alone or combined with other test results will be realistic
predictors of field performance.
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