2005-04_update on icar 507_the significance and application of the micro-deval test

7/28/2019 2005-04_update on Icar 507_the Significance and Application of the Micro-Deval Test

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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.

Williams, Hampel, Allen, and Fowler 1


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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



22/28

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.



23/28

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2005-04_update on icar 507_the significance and application of the micro-deval test

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