1

Feasibility for the Use of Non-contact Ultrasound for Application in Asphalt Concrete Materials

Michael R. Dunning 1, Moses Karakouzian2, Robert L. Dunning3

Abstract

A rapid quality control test method of hot mix asphalt (HMA) during the production and placement phase of roadway construction can be extremely valuable for the successful completion of roadway construction project to keep it on schedule and under budget. Non-contact ultrasound technique has been used to characterize properties of ceramic and metallic materials. Prior to this study, the non-contact ultrasound technique was not used for constructions materials such as HMA. Until recently, the transmission of non-contact ultrasound through the air prior to propagation into a material such as the highly attenuating HMA was not possible. This study was conducted using a newly-developed low frequency ultrasound non-contact transducers in order to investigate the feasibility of correlating the bulk specific gravity of HMA to non-contact ultrasound measurements. HMA specimens were prepared with varying gradation and asphalt cement proportions. The data revealed that it was indeed possible to correlate non-contact ultrasound measurements to the of the bulk specific gravity of HMA. This work provides the foundation for future research for the utilization of the non-contact ultrasound technique as a viable, cost saving tool for quality control application in asphalt concrete plant production and construction of asphalt concrete pavements. It may very well be possible to reduce significantly the conventional testing by developing ultrasound equipment for density, gradation, and binder content with one signal transmission.

1 Quality Assurance Supervisor, Clark County Department of Public Works Construction Management Division, Las Vegas Nevada 2 Professor, Civil and Environmental Engineering Department, University of Nevada, Las Vegas, Nevada mkar@nevada.edu 3 President Petroleum Sciences, Petroleum Sciences, Inc. P. O. Box 6304 4817 N. Freya, Spokane, WA 99217

Oral presentation made by Dr. Dunning

2

Key Words: Ultrasound, non-destructive testing, quality control, dense grade mixtures

Introduction

The quality control of the production of asphalt concrete and the subsequent placement for roadway pavement requires the extensive use of laboratory and field-testing. These tests determine the mix properties and the field compaction such as gradation, binder content, air void content and percent compaction. The amount of time it takes to perform these tests generates time delays in the information transfer from the laboratory to the construction and plant inspectors. The lack of timeliness of a test result could allow for an inferior product being placed. Thus, there would be a great benefit for the application of a rapid test method during the production and placement phase of the construction. The use of non-destructive testing (NDT) is the means to this end. It is presently possible to determine material properties rapidly with contact ultrasound transducer using a contact gel for good transmission into a specimen. The problem with the contact application is that the measurement requires a stationary position. A non-contact transducer allows for an air or other medium gap distance between the transducer and the material to be measured which makes it more versatility for field and laboratory testing. The transmission of ultrasound through the air prior to propagation into a material such as the highly attenuating asphalt concrete has not been previously performed. The purpose of this study was to answer the question of the possibility of correlating the ultrasound measurement with a common asphalt concrete material property of bulk specific gravity. If confirmed that a value can be obtained using a non-contact transducer and correlated, this would set in motion further research for application in other rapid material property determination such as, but not limited to, dynamic modulus, thickness, and homogeneity.

Background

High frequency sound waves can be used to identify some basic properties of solids. Ultrasonic material analysis is based on the motion of a wave, which will be affected by the material through which it travels. Thus, changes in one or more of the four measurable parameters associated with the passage of a high frequency sound wave through a material such as time, attenuation, scattering, and frequency content will relate to the material characteristics. These can often be correlated with changes in physical properties such as hardness, elastic modulus, density, homogeneity, or grain structure (1).

3

Uses in Construction Contact ultrasound, which is defined as the transducer having physical contact with the

material to be measured, has been used for the inspection of Portland Cement Concrete (PCC) for many years. During the literature search, it was found that the use in the inspection of asphaltic concrete is limited to mainly laboratory based experimental studies, which have shown promising results. The coupling of ultrasonic testing with laboratory-based performance testing of HMA would provide a vital link to rapid quality control testing and quality assurance verification. The application of contact ultrasound in construction materials has grown substantially to include but not limited to: Characterization of elastic and mechanical properties; such as concrete strength (2)

(3) (4) (5) Delaminating in multi-layered systems; such as for pavement integrity and surface

profile (6) (7) Imaging of surface and internal features of materials; (8) Liquids (9)

Previous Work related to this research In a study by Sztukiewicz (10), two contact ultrasound techniques were employed,

through transmission and pulse-echo method which has the transmitter and receiver on the same side, for the testing of asphalt concrete. The through transmission method was used on laboratory-fabricated samples with contact transducers on either side of the samples while the thickness was manually measured between the transducers. For the field application, the only feasible method was the pulse-echo. The asphalt concrete layer was about 50mm thick and the distance of the transducers was measured manually. The author utilized the Abram’s fractional grading coefficient, which is common to Europe, and is similar to the aggregate fineness modulus, to characterize the mineral mix aggregate grading. It was found that the condition of the pavement could be defined with ultrasound, which correlated directly with weather and traffic patterns. Another work was completed Dunning (11) that utilized a single frequency contact transducers and an oscilloscope for the detection of a single frequency pulse through asphalt concrete. The ultrasound velocities were obtained for different asphalt concrete mix design types that were produced from an asphalt concrete plant at test temperatures of ambient and 600 C. It was found that material characteristic correlate with ultrasound velocity, which would allow for a quality control detection of the design or construction of the asphalt concrete.

Ultrasound Overview Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations

and to record measurements. It can be used for, but not limited to, flaw detection/evaluation, dimensional measurements, and material characterization. A typical Ultrasound Testing inspection system consists of several units, such as the pulser-receiver,

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transducer, and display equipment (12). A pulser-receiver is an electronic device that can produce high voltage electrical pulse, which causes the transducer to generate high frequency ultrasonic energy. The sound energy is transmitted through the material in the form of waves. The basic transmission mode used in this study is the through transmission which transmits a signal from one transducer through a material to be received by another transducer on the opposite side.

Basics of Non-contact Ultrasound and Material Characteristics

History: A non-contact transducer is used without touching the material to be tested. Unlike the contact transducer, which transmits the signal directly into the material, the non-contact transducer signal passes first through air or water. In the materials industry, one of the early applications of non-contact ultrasound was the testing of Styrofoam blocks by utilizing a 25 kHz frequency (13). Similar transducers were also produced at Stanford University by utilizing silicone rubber as the front acoustic impedance matching layer (14). By using such a transducer at 1MHz, the distance in air could be measured from 20mm to 400mm with an accuracy of 0.5mm. Air coupled transducers based upon capacitance have also undergone substantial developments in recent years. These transducers, which are available in the general market, are characterized by high bandwidths, have been used to evaluate composites and other materials (15). The main tool for the focus for this research was with the new Gas Matrix Piezoelectric (GMP) transducer and the Chirp pulse that was able to penetrate heterogeneous materials, such as asphalt concrete, for large depths for a clear and discernable signal (16).

Velocity of Material: This value is based on the amount time for the sound to travel through a material of a known thickness.

Chirp Pulse: The Chirp signal is related to the Doppler effect in that the motion of the source yields a differential frequency of the transmitted frequency at a given point as illustrated in Figure 1, which is summarized as a “Chirp” due to the similarity to a bird or bat sound. This effect is created using a signal generator which will create a high frequency to low over a given period.

Decibels: Decibels provide a relative measure of sound intensity. The unit is based on powers of 10 to encompass the wide range of the human hearing response, from the standard threshold of hearing at 1000 Hz to the threshold of pain. The Chirp signal will yield higher measurement resolution in the material.

5

Figure 1 Example of the Chirp signal

Attenuation: Ultrasound attenuation is the decay rate of mechanical energy as it propagates through material. The ultrasound attenuation response in the material is affected by the material property. Thus, the ultrasound measurement for the research is the attenuation value which is termed the integrated or fundamental response with units of decibels. Attenuation often serves as a measurement tool that can explain physical or chemical characteristics, which decreases the ultrasonic intensity.

Acoustic Impedance: Sound travels through materials under the influence of sound pressure. Because molecules or atoms of a solid are bound to one another, the excess pressure results in a wave propagating through the solid (1). Acoustic impedance is a ratio of acoustic pressure to flow and is somewhat similar to electric impedance (19). An analogy is the comparison with electrical resistance, which is often explained with the flow of water. However, impedance is used instead of resistance because it is more complex than resistance. In electricity with direct current, resistance is used. However, with high frequency alternating current, impedance is used because more than the resistance in the wire is involved. When using hydraulic resistance, it would be the ratio of the pressure difference between the ends of a pipe to the flow in the pipe thus electrical resistance is the ratio of the voltage applied to the electrical current it produces. A good word picture of this is a swing. To get the best energy transfer, you have to push at the same frequency as the swing, and at the correct phase. When the swing is at the top of the cycle when in effect the swing is shortly at rest, this has the lowest impedance. When you push the swing in phase and at the correct frequency, the least amount of energy will be needed to keep the swing going. If you try to push against the swing at the bottom where it is going the fastest, much greater energy is needed to reverse its direction and the swing offers the greatest impedance. The acoustic impedance Z of a material is defined as the product of density ρ and acoustic velocity V of that material (1).

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ρVZ = [1]

Z = acoustic impedance

ρ = density V = velocity of the material

seccmg =Unit 2 −

Figure 2 Example of Non-contact transmission (13)

Acoustic impedance is used for the determination of acoustic transmission and reflection at the boundary of two materials having different acoustic impedance, which in turn generates the Integrated Response (IR) attenuation value which will be explained later. The reflected energy is that percentage not absorbed by the material and reflected back to the transducer while the transmission energy is what percentage is passing through the material. Both are expressed in decibels. In the case of non-contact transmission, the acoustic impedance of both the air and specimen are to be considered as displayed in Figure 2.

Transmission Coefficient: One of the relationships involved is the transmission coefficient of the material. As ultrasound waves travel from a material with low acoustic impedance to one of high acoustic impedance, only a fraction of the energy is transmitted. The fraction of ultrasound transmission and energy transferred at the air-material interface is given by (20):

Zair

Zair

Zmaterial

Air-Material Interface

Material-Air Interface

Transmit

Receive

7

( )221

21

0 ZZZZ

IIT

+== [2]

I = energy transmitted into the material from the air I0 = energy input m = Material attenuation coefficient r = Density x = thickness of the material Z1=Acoustic impedance of Air Z2=Acoustic impedance of the specimen

Integrated Response (IR): The IR is one of the measured values used in this research,

which is directly related to the transmission coefficient of the material. The IR is the calculated attenuation as measured, in decibels, of the tested material using a Chirp signal (13). The basic equation for how the IR is determined in the pulser-receiver is using the amplitude spectra of the two signals, the initial, and the exiting. The signal is converted to a decibel value, which is the unit of the IR, which is a function of the sound pressure. The IR is related to the acoustic impedance of the material Z. If the material is homogeneous, then the measurement of IRm is related to the transmission coefficient expressed as (13):

20logTIRm = [3]

T = Transmission coefficient (equation 5 above) Given the theory above applied to the practical pulser-receiver measurement, the

transmission co-efficient is derived as the ratio of transmitted acoustical energy V, volts, and the input energy V0 of a plane wave when refracted with 0° incidence on the interface between the two materials as given in:

20

2

VVT ∝ [4]

The equation and relationships can also be described in the decibel scale as (13):

Tlog20VVlog20T

0

=

= [5]

8

The transmission coefficient is assumed independent of ultrasonic attenuation and thickness of the test medium (13). If the transmission co-efficient can be measured with a very high degree of certainty and precision, then it is possible to measure the absolute density of the test material by first determining the acoustic impedance, Zm of the test material using (13):

material ofVelocity = Vmaterial of impedence Acoustic = Z

material of Density =

VZ

m

m

m

m

mm

r

=r

[6]

The IRm, which is the IR of the material, is determined from the IRc and IRa, which are

the material plus air and the air column only, respectively as illustrated in Figure 3. These values are determined using a pulser-receiver. Each of these values is represented on the pulser-receiver display either the peak value or the area under the processed signal curve and for this research, the peak value was used (13). The pulser-receiver has a Quality Control (QC) module which records and generates statistical means and standard deviations of the measurements. The determination of the IRm is simply the subtracting of the recorded signal in air, IRa, from IRc (Equation 7).

acm IRIRIR −= [7]

)(Z columnair =IRmaterial of sides both columnsair and material =IR

)(Z material =IR

aa

c

mm

9

Figure 3 IRa and IRc Display

Methodology

The purpose of this study was to determine if a bulk density change could be detected using the value of IR. The purpose was to compact the same mix type with four different compaction efforts. In other words, the aggregate and binder ratio were the same for four points and the only change was the sample volume, which is directly related to the air voids. The samples were ultrasound measured using the IR value. The measurements were then analyzed with the HMA properties of Bulk Specific Gravity. The correlations were determined with the use of the excel® spreadsheet data analysis module.

Mix Designs Used for Research A design was selected that was already being used for Clark County Department of

Public Works (CCPW) (21). Table 1 displays the material type for the baseline design. The gradations were varied by increasing and decreasing the 2.36 mm sieve fraction by plus and minus eight percent. This will be described in more detail later. Additionally, the percent binder for the baseline and varying gradations were also varied in order to bracket the four percent mix design target air voids with enough spread in order to detect a change

Transmit

Receive Receive

Transmit

IRa IRc

Integrated Response of

Air

Integrated Response of Air

plus sample

10

in the ultrasound attenuation. The design gradation on Table 2 represents the baseline gradation for the mix. Table 4 lists the target binder and air void design values.

In order to generate more designs the 2.36 mm sieve was varied by plus eight percent and minus eight percent. This also forced the previous (0.075 mm through 2.36 mm) and subsequent material sizes (4.75 mm through 25 mm) to vary by some percentage above or below eight percent. These actual gradations are on Table 3 and all of the gradations are displayed on Figure 4.

Table 1 Aggregate and Asphalt Cement Source Nomenclature

Source Type Location Material Type

Aggregate Blue Diamond 25 miles south of Las Vegas Limestone and basalt

Asphalt Cement Santa Maria, CA AC-30

Table 2 Design Baseline Gradation Values

Sieve (mm) % Pass

25 100 19 93

12.5 80 9.5 70

4.75 46 2.36 31 1.18 21 0.6 15 0.3 11

0.15 8 0.075 5.3

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Table 3 Design Gradation Values for +8 and -8

Sieve (mm)

% Pass for +8

% Pass for -8

25 100 100 19 95 91

12.5 85 75 9.5 77 63

4.75 56 35 2.36 39 23 1.18 26 16 0.6 18 11 0.3 14 9

0.15 10 6 0.075 6.3 4.1

Table 4 Target Binder and Air Voids

Target Binder Content

Target Air Voids

4.7% 4.0%

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Gradation Curves for Gradation Type -8, +0, and +8

0

10

20

30

40

50

60

70

80

90

100

Sieve mm

Perc

ent P

assi

ng

+0 Gradation (Baseline) -8 Gradation +8 Gradation

251912.59.54.752.361.180.60.30.15

0.75

Figure 4 All Gradation Curves

Specimen Preparation The aggregate and the asphalt cement binder for the various specimens were prepared

in batch sizes that would allow for a constant height, as best as possible, for the cylinder molds. The constant height was needed only for the convenience of setting the transducers at a constant distance from the top of the specimen. The hammer was automatically dropped as many times or as required per the testing matrix; after which the cylinder with the material is flipped upside down and compacted again. For this study, the compaction process is called a blow count.

Material Sample Labeling: As described above, the gradation was adjusted to a

maximum and a minimum gradation difference of eight percent on the 2.36 mm sieve. For the ease of clarity, the nomenclature used to represent the gradation type throughout the research was as detailed in Table 5. The mid-range is the original design gradation target identified by “+0”, the plus and minus is the percent increase or decrease from the 2.36 mm sieve.

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Table 5 Gradation Identification Legend

Gradation Type Label Original Design +0

Eight percent above the 2.36 mm Sieve +8 Eight percent below the 2.36 mm Sieve -8

The specimens were labeled in such a fashion to identify the various Marshall blow

counts as displayed in Table 6. As an example, 10A+8 represents specimen 10, with the letter “A” representing 120 Marshall blow count and a gradation type of eight percent above the design optimum of the 2.36 mm sieve size.

Table 6 Specimen Labeling Legend for Design One

Specimen Sequence

Marshall Blow Count Number Gradation Type

Numerical

A = 120 blow B = 112 blow C = 90 blow D = 80 blow

+8 = +8% deviation +0 = 0% optimum -8 = -8% deviation

10 A +8

Data Acquired

Bulk Specific Gravity There were two procedures used for Bulk Specific Gravity, the CoreLok and

Saturated Surface Dry. The Bulk Specific Gravity (BSG) with the use of the CoreLok was determined for this research per the ASTM D 6752 and the Saturated Surface Dry (SSD) method as ASTM D 2726. There is a potential problem with the use of the CoreLok when used on large stone mixes as the bag material used for this process may bridge across a large surface void which could create a bias value (22). Thus, both methods were used in order to check for an obvious error in unit weight determination.

Ultrasound Integrated Response measurement The ultrasound testing system includes a pulser-receiver and a scan table. The

equipment was a NCA-1000-2 pulser-receiver for the transmission of a chirp signal, processing, analysis, imaging, and storage (23). A special tabletop was fabricated to allow the transducers to function in the through-transmission mode without hindrance from the table surface as demonstrated in the schematic on Figure 5 and photo with a sample

14

positioned for ultrasound measurement on Figure 6 Stop bar positions were installed to assure a constant shot location. The transducers were checked for a parallel face with the use of a round bubble level and plumb line for the relative orientation. The signal was set for the transducer parameters and visually checked on the computer screen for maximum peak amplitude by slightly adjusting the transducers per the operation procedure.

Figure 5 Section View of Ultrasound Scan Table and Typical Setup

Figure 6 Example of Specimen Setup

Transducer Positioning: A precise ultrasound measurement is more likely in

homogenous materials. Thus, with homogeneous materials, it is possible to position the transducer anywhere on the material (barring sidewall influences) and have confidence that the measurement will closely represent the material as a whole. This is not the case for heterogeneous materials such as asphalt concrete that is a composite of aggregate, asphalt cement (binder) and air. It would make sense to acquire several measurements, and then average them in order to represent the material.

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The scan table cannot rotate a sample and due to the round nature of the sample, thus, the scan process had to be manual. During a separate sensitivity study, it was found that four dead center shots were the best for repeatability. The center shots were rotated 90º around marks on top of the specimen (Figure 7 and Figure 8).

Figure 7 Example of Sample Rotation Marks, Eight Each on Top

Figure 8 Example of Sample Rotation for Measurement

Detecting Density Change

The purpose of this phase was to determine if a density change could be detected for one sample point. These specimens were purposely compacted with four different compaction efforts. In other words, the aggregate and binder ratio was the same for four points and the only change was the sample volume as indicated visually in Figure 9. These were fabricated in replicates of four per design point however, each of the replicate samples were compacted at different blow counts, thus, only one specimen per point. As a reminder, the Marshall Design method for 150mm diameter molds uses a blow count per side of 112 each. Each set of four were compacted at different blows per side of 120, 112, 90 and 80. This in effect changes the density of the sample thereby giving a density spread to check for correlation to the IR.

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Air

Binder

Aggregate

120 Blow 112 Blow 90 Blow 80 Blow

Figure 9 Design 1 Volumetrics Illustration

Description of Data Acquired There were two components of the data acquired consisting of HMA Material Testing

and Ultrasound Measurement. The testing and measurement matrix is given by Table 7.

Table 7 Specimen Fabrication and Testing Matrix

Gradation Used -8 +0 +8 Non-Contact Ultrasound

(NCU) Measurements

Integrated Response

HMA Testing CoreLok SSD

Other measurements were acquired relative to the related calculations for the IR value

such as air temperature, humidity, and barometric pressure. These data were needed in order to correct the IR value due to the noted environmental items (24). While the air temperature could not be fixed, all specimens were set in an oven at 25o C for four hours prior to ultrasound measuring.

Mix design data review: All of the mix designs were fabricated is the same fashion as

any standard design using the Asphalt Institute MS-2 manual (25). Thus, once the data was

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tabulated and graphed, obvious outliers were identified and removed based on the MS-2 standard graphical representations.

Analysis

The analysis of the data focused on three levels. The analysis used the values of Integrated Response, CoreLok specific gravity and saturated surface dry specific gravity:

Level 1: Regression within each sample set Level 2: Regression plotting of the average of all data points within a gradation type -8, +0, and +8. Level 3: Plotting of All Data

Level 1 Regression within each HMA sample set The following Table 8 through Table 10 and Figure 10 through Figure 19 demonstrate

the high correlation of the Integrated Response for both the CoreLok (CL) and saturated surface dry (SSD) specific gravities. The SSD has a noticeable offset from the CL data and in most cases a lower R-square value. Thus, the CoreLok specific gravity values were considered relevant for the review. Each graph represents binder content in the particular gradation type. The purpose of the different blow was to force the air void value results to have a wide spread. Some specimen sets as displayed in Figure 13, Figure 15, and especially Figure 18 were very compaction friendly. Thus, there was only a slight difference in the separation of the data. However, even with these results, the R-square values are high. The plotted data strongly suggest that as the density increases, the attenuation decreases, or in the context of the Integrated Response which represents the transmission of the signal, as the density increases, the Integrated Response increases.

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Table 8 Gradation -8 Data

Sam

ple

ID

% b

inde

r

IRm

Cor

rect

ed

(dbs

)

%vo

ids C

oreL

ok

Spec

ific

Gra

vity

Den

sity

Cor

eLok

(g

/cc)

Den

sity

SSD

(g

/cc)

10A-8 4.70% -87.7 4.73% 2.364 2.40510B-8 4.70% -87.0 4.14% 2.379 2.42310C-8 4.70% -84.7 3.79% 2.388 2.42410D-8 4.70% -89.2 5.37% 2.349 2.39111A-8 5.00% -82.9 4.02% 2.366 2.40911B-8 5.00% -80.2 3.89% 2.369 2.40711D-8 5.00% -91.5 5.46% 2.330 2.38812A-8 4.40% -79.8 3.71% 2.409 2.43812B-8 4.40% -85.7 5.18% 2.373 2.42012C-8 4.40% -86.9 7.67% 2.310 2.37312D-8 4.40% -90.2 7.72% 2.309 2.378

Gradation Type -8 and 4.7% (Set 10) Binder for Integrated Response and CoreLok Specific Gravity

R2 = 0.8979

R2 = 0.7569

2.3402.3502.3602.3702.3802.3902.4002.4102.4202.4302.440

-90.0 -89.0 -88.0 -87.0 -86.0 -85.0 -84.0 -83.0

Integrated Response (dBs)

Cor

eLok

Spe

cific

Gra

vity

(g/c

c)

CorLok SSD

Figure 10 Gradation -8 IRm versus CoreLok Specific Gravity for 4.7% Binder

19

Gradation Type -8 and 5.0% (Set 11) Binder for Integrated Response and CoreLok Specific Gravity

R2 = 0.9774

R2 = 0.9184

2.300

2.320

2.340

2.360

2.380

2.400

2.420

2.440

-93.0 -88.0 -83.0 -78.0

Integrated Response (dBs)

Cor

eLok

Spe

cific

Gra

vity

(g/c

c)

CorLok SSD

Figure 11 Gradation -8 IRm versus CoreLok Specific Gravity for 5.0% Binder

Gradation Type -8 and 4.4% (Set 12) Binder for Integrated Response

and CoreLok Specific Gravity

R2 = 0.8286

R2 = 0.7364

2.28

2.30

2.32

2.34

2.36

2.38

2.40

2.42

2.44

2.46

-91.0 -89.0 -87.0 -85.0 -83.0 -81.0 -79.0 -77.0

Integrated Response (dBs)

Cor

eLok

Spe

cific

Gra

vity

(g/c

c)

CorLok SSD

Figure 12 - Gradation -8 IRm versus CoreLok Specific Gravity for 4.4% Binder

20

Table 9 Gradation +0 Data

Sam

ple

ID

% b

inde

r

IRm

Cor

rect

ed

(dbs

)

%vo

ids C

oreL

ok

Spec

ific

Gra

vity

Den

sity

Cor

eLok

(g

/cc)

Den

sity

SSD

(g

/cc)

01A+0 4.70% -77.71 3.06% 2.403 2.42901B+0 4.70% -78.03 2.78% 2.409 2.43601C+0 4.70% -80.25 3.53% 2.391 2.42802A+0 5.00% -76.43 1.83% 2.433 2.44902B+0 5.00% -81.62 4.28% 2.372 2.39602C+0 5.00% -78.14 3.25% 2.398 2.42403B+0 5.30% -79.49 1.36% 2.429 2.44303C+0 5.29% -81.99 2.09% 2.411 2.43603D+0 5.29% -81.86 1.78% 2.418 2.44304A+0 4.51% -80.68 3.66% 2.400 2.43704B+0 4.50% -76.72 3.10% 2.414 2.43804C+0 4.50% -84.27 4.13% 2.388 2.43904D+0 4.50% -83.76 4.30% 2.384 2.428

Gradation Type +0 and 4.7% (Set 01) Binder for Integrated Response and CoreLok Specific Gravity

R2 = 0.773

R2 = 0.2356

2.350

2.370

2.390

2.410

2.430

2.450

-80.50 -80.00 -79.50 -79.00 -78.50 -78.00 -77.50 -77.00

Integrated Response (dBs)

Cor

eLok

Spe

cific

Gra

vity

(g/c

c)

CorLok SSD

Figure 13 Gradation +0 IRm versus CoreLok Specific Gravity for 4.7% Binder

21

Gradation Type +0 and 5.0% (Set 02) Binder for Integrated Response and CoreLok Specific Gravity

R2 = 0.923

R2 = 0.9747

2.362.372.382.392.402.412.422.432.442.452.46

-82.00 -81.00 -80.00 -79.00 -78.00 -77.00 -76.00 -75.00

Integrated Response (dBs)

Cor

eLok

Spe

cific

Gra

vity

(g/c

c)

CorLok SSD

Figure 14 Gradation +0 IRm versus CoreLok Specific Gravity for 5.0% Binder

Gradation Type +0 and 5.3% (Set 03) Binder for Integrated Response

and CoreLok Specific Gravity

1.8% air

R2 = 0.8559

R2 = 0.3087

2.390

2.400

2.410

2.420

2.430

2.440

2.450

2.460

2.470

-83.00 -82.00 -81.00 -80.00 -79.00 -78.00

Integrated Response (dBs)

Cor

eLok

Spe

cific

Gra

vity

(g/c

c)

CorLok SSD

Figure 15 - Gradation +0 IRm versus CoreLok Specific Gravity for 5.3% Binder

22

Gradation Type +0 and 4.5% (Set 04) Binder for Integrated Response and CoreLok Specific Gravity

4.3% airR2 = 0.9635

R2 = 0.1706

2.380

2.390

2.400

2.410

2.420

2.430

2.440

2.450

-85.00 -83.00 -81.00 -79.00 -77.00 -75.00

Integrated Response (dBs)

Cor

eLok

Spe

cific

Gra

vity

(g/c

c)

CorLok SSD

Figure 16 Gradation +0 IRm versus CoreLok Specific Gravity for 4.5% Binder

Table 10 Gradation +8 Data

Sam

ple

ID

% b

inde

r

IRm

Cor

rect

ed

(dbs

)

%vo

ids C

oreL

ok

Spec

ific

Gra

vity

Den

sity

Cor

eLok

(g

/cc)

Den

sity

SSD

(g

/cc)

20A+8 5.00% -75.87 1.82% 2.433 2.43920B+8 5.00% -77.90 1.94% 2.430 2.44720C+8 5.00% -77.38 4.01% 2.37920D+8 5.00% -80.05 2.70% 2.411 2.42721A+8 4.70% -76.18 3.16% 2.409 2.43221C+8 4.70% -76.90 3.36% 2.404 2.43121D+8 4.70% -76.87 3.56% 2.399 2.43621A+8 4.70% -76.24 3.01% 2.413 2.43622A+8 4.40% -76.09 3.14% 2.420 2.44122B+8 4.40% -78.56 4.10% 2.396 2.41622C+8 4.40% -76.56 3.40% 2.413 2.43122D+8 4.41% -77.61 3.46% 2.412 2.432

23

Gradation Type +8 and 5.0% (Set 20) Binder for Integrated Response and CoreLok Specific Gravity

R2 = 0.7956

R2 = 0.3922

2.405

2.410

2.415

2.420

2.425

2.430

2.435

2.440

2.445

2.450

-81.00 -80.00 -79.00 -78.00 -77.00 -76.00 -75.00 -74.00

Integrated Response (dBs)

Cor

eLok

Spe

cific

Gra

vity

(g/c

c)

CorLok SSD

Figure 17 - Gradation +8 IRm versus CoreLok Specific Gravity for 5.0% Binder

Gradation Type +8 and 4.7% (Set 21) Binder for Integrated Response

and CoreLok Specific Gravity

R2 = 0.767

R2 = 0.1685

2.380

2.390

2.400

2.410

2.420

2.430

2.440

2.450

-77.00 -76.80 -76.60 -76.40 -76.20 -76.00 -75.80

Integrated Response (dBs)

Cor

eLok

Spe

cific

Gra

vity

(g/c

c)

CorLok SSD

Figure 18 - Gradation +8 IRm versus CoreLok Specific Gravity for 4.7% Binder

24

Gradation Type +8 and 4.4% (Set 22) Binder for Integrated Response and CoreLok Specific Gravity

R2 = 0.8755

R2 = 0.8096

2.3902.3952.4002.4052.4102.4152.4202.4252.4302.4352.4402.445

-79.00 -78.50 -78.00 -77.50 -77.00 -76.50 -76.00 -75.50 -75.00

Integrated Response (dBs)

Cor

eLok

Spe

cific

Gra

vity

(g/c

c)

CorLok SSD

Figure 19 - Gradation +8 IRm versus CoreLok Specific Gravity for 4.7% Binder

Given the previous data, a general trend graph for the IR can be stated that as the specific gravity of the material increase, so does the IR as displayed in Figure 14.

Spe

cific

Gra

vity

Integrated Response

Figure 20 Trend Graph for CoreLok Bulk Specific Gravity and Integrated Response for Air Void Change

Level 2 Regression Plotting of the Average of each Gradation Type The data in Table 11 contains the average of the data for each gradation type and by the

Marshall Blow count with the Figure 21 through Figure 24 illustrating the plots. As can be

25

seen, there appears to be a very clear distinction between gradation types with the average of the CoreLok bulk specific gravity.

Table 11 Average Data by Blow Count and Gradation Type for CoreLok Specific Gravity

All Gradations 120 Blow

CorLok SG (g/cc)

All Gradations 112 Blow

CorLok SG (g/cc)

All Gradations 90 Blow

CorLok SG (g/cc)

All Gradations 80 Blow

CorLok SG (g/cc)

Grad -8 2.380 2.374 2.349 2.329Grad +0 2.412 2.406 2.397 2.401Grad +8 2.420 2.413 2.399 2.407

Table 12 Average Data by Blow Count and Gradation Type for Integrated Response

All Gradations 120 Blow IRm (dBs)

All Gradations 112 Blow IRm (dBs)

All Gradations 90 Blow

IRm (dBs)

All Gradations 80 Blow

IRm (dBs)

Grad -8 -83.5 -84.3 -85.8 -90.3Grad +0 -77.1 -79.0 -81.2 -82.8Grad +8 -76.0 -78.2 -76.9 -78.2

26

All Gradations Average of 120 Blow Specimen Sets

Integrated Response and CorLok Specific Gravity

Gradation -8

Gradation +0

Gradation +8

R2 = 0.9948

2.375

2.380

2.385

2.390

2.395

2.400

2.405

2.410

2.415

2.420

2.425

-85.0 -83.0 -81.0 -79.0 -77.0 -75.0 -73.0

Integrated Response (dBs)

Cor

eLok

Spe

cific

Gra

vity

(g

/cc)

Figure 21 Plot of Average Gradation Type for 120 Blow Count for Integrated Response, Fineness Modulus, and CoreLok

All Gradations

Average of 112 Blow Specimen Sets Integrated Response and CorLok Specific Gravity

Gradation -8

Gradation +0

Gradation +8R2 = 0.9973

2.370

2.375

2.380

2.385

2.390

2.395

2.400

2.405

2.410

2.415

-85.0 -83.0 -81.0 -79.0 -77.0

Integrated Response (dBs)

Cor

eLok

Spe

cific

Gra

vity

(g

/cc)

Figure 22 Plot of Average Gradation Type for 112 Blow Count for Integrated Response, Fineness Modulus, and CoreLok

27

All Gradations Average of 90 Blow Specimen Sets

Integrated Response and CorLok Specific Gravity

Gradation -8

Gradation +0

Gradation +8R2 = 0.7959

2.340

2.350

2.360

2.370

2.380

2.390

2.400

2.410

-88.0 -86.0 -84.0 -82.0 -80.0 -78.0 -76.0 -74.0

Integrated Response (dBs)

Cor

eLok

Spe

cific

Gra

vity

(g

/cc)

Figure 23 Plot of Average Gradation Type for Integrated Response, Fineness Modulus, and CoreLok

All Gradations

Average of 80 Blow Specimen Sets Integrated Response and CorLok Specific Gravity

Gradation -8

Gradation +0

Gradation +8R2 = 0.9007

2.322.332.342.352.362.372.382.392.402.412.422.43

-94.0 -89.0 -84.0 -79.0 -74.0

Integrated Response (dBs)

Cor

eLok

Spe

cific

Gra

vity

(g

/cc)

Figure 24 Plot of Average Gradation Type for the Integrated Response, Fineness Modulus, and CoreLok

28

The graphs presented valuable illustrations of the discrimination between the gradation types. This level uses the ANOVA to demonstrate that there is a real statistical difference between the Integrated Response and the gradation type. Table 13 and Table 14 contain the data for the ANOVA null hypotheses of:

typegradation = j and it typemeasuremen =x

:H

= :H2

j gradation andx 2

i gradation andx a

2 j gradation andx

2i gradation andx 0

m≠m

mm

The ANOVA reveals that the null hypotheses are rejected for the Integrated Response

with respect to the different gradation types when all of the samples are considered. However, when considering each blow count separately, this is not the case. This could be due to the small sample sets.

This result demonstrates the possible discerning nature of the Integrated Response value for the detection of gradation changes in a mix design production.

Table 13 Results for the One-way ANOVA for Integrated Response and Gradation Type for all Blow Counts

All Blow Counts Gradation -8 to +0Source of Variation df F P-value F crit

Between Groups 1 22.02 0.0001 4.32Gradation +0 to +8

Source of Variation df F P-value F critBetween Groups 1 10.88 0.0033 4.30

29

Table 14 Results for the One-way ANOVA for Integrated Response and Gradation Type for Each Blow Count Type

120 blow Gradation -8 to +0Between Groups df F P-value F critWithin Groups 1 1.23 0.3301 7.71

Gradation +0 to +8Between Groups df F P-value F critWithin Groups 1 10.21 0.0331 7.71

112 blow Gradation -8 to +0Source of Variation df F P-value F crit

Between Groups 1 8.72 0.0318 6.61Gradation +0 to +8

Source of Variation df F P-value F critBetween Groups 1 0.00 0.9525 7.71

90 blow Gradation -8 to +0Source of Variation df F P-value F crit

Between Groups 1 13.63 0.0210 7.71Gradation +0 to +8

Source of Variation df F P-value F critBetween Groups 1 4.33 0.0919 6.61

80 blow Gradation -8 to +0Source of Variation df F P-value F crit

Between Groups 1 35.86 0.0093 10.13Gradation +0 to +8

Source of Variation df F P-value F critBetween Groups 1 10.85 0.0459 10.13

Level 3 Plotting of All Data This review level demonstrates the previously presented trend of the data from the

coarse gradation -8 to the fine gradation +8 using the plotting of all data points of the IR against the CoreLok specific gravity. Figure 25 clearly demonstrates this trend and the narrow band that represents the compaction, gradation, and binder content range.

30

The utility of this plot is of great value when considering that if the different blow count (which represent compaction), the gradation type, and the binder variation, were the specified limits of the asphalt concrete placement, then Figure 25 would be the IR specification criteria for acceptance of the placed asphalt concrete

.

Design 1 for All Gradations All Blow Count Specimens

Integrated Response and CoreLok Specific Gravity

y = -0.0002x2 - 0.0281x + 1.4517R2 = 0.6474

2.25

2.30

2.35

2.40

2.45

2.50

-93.0 -88.0 -83.0 -78.0 -73.0

Integrated Response (dBs)

Cor

eLok

Spe

cific

Gra

vity

(g/c

c)

120 Blow 112 Blow 90 Blow 80 Blow

Figure 25 Design 1 Plot of All Gradation Data Points for Integrated Response and CoreLok Specific Gravity

Summary and Conclusions

It is presently possible to determine material properties rapidly with contact ultrasound. However, a non-contact ultrasound device would provide more versatility for field and laboratory testing for construction materials. Thus, this study was conducted using ultrasound non-contact transducers with never before tried testing of the laboratory prepared asphalt specimens. The transmission of ultrasound through the air prior to propagation into a material such as the highly attenuating asphalt concrete has not been previously performed.

The purpose of this study was to determine if a non-contact ultrasound transducer could penetrate asphalt concrete to generate a measurement that would correlate with the

31

specific gravity of the material. It was found that in all cases, the value of IR had a very high correlation with the material bulk specific gravity. It was also found that the IR value was able to discern between gradation types.

The other aspect of the use of Ultrasound was the time involved in testing as compared to the conventional method in this study which was the density using the CoreLok and Saturated Surface Dry (SSD). The point of comparison is after the samples were laboratory fabricated and cooled. The time to test and calculate for CoreLok or SSD is about ½ hour. The time for an ultrasound test is one minute. However, for Ultrasound, there would need to be an initial correlation of the mix design in order to establish graphs so as to use the ultrasound value against the graph for a density. The correlation though represents not just the density, but of the system to include gradation and percent binder using acceptance range charts established at the start of a project such as the plot in Figure 25. Thus, the amount of time saved in an extraction, gradation and percent binder test is an additional 1-1/2 hours.

This work lays the foundation for future research for the use of the non-contact ultrasound technique as a viable tool for quality control application in asphalt concrete plant production and construction of asphalt concrete pavements.

Future Work

This study focused on the material property of bulk specific gravity. There are numerous other material aspects to consider as well as practical application of the equipment. There is a need to establish the laboratory protocols to create a design and field-testing target band. This research used arbitrary variation in the mix design for a comparison of measurements. The actual mix design specification is much narrower. The development of asphalt placement specification tolerances could then be applied to a field project study for pass/fail criteria. Need to compare the same design material fabricated in the laboratory gyratory compactor against samples that are collected from field placement. The asphalt cement material source needs to be variable within a design set to see if the ultrasound can detect this change. Establish if a pulse-echo transmission could be correlated to the laboratory samples then applied to the field placement without the use of cores. Apply other performance and conventional testing material property characteristics versus the Ultrasound Integrated Response and/or material velocity for correlation such as dynamic modulus.

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Acknowledgements

Thankful for the wisdom given generously by my Lord and providing the interaction and help of many. The University of Nevada Las Vegas, which provided the ultrasound equipment and transducers. The Clark County Department of Public Works, Nevada, for the laboratory and Lynette Wojtowicz, Hiram Sedano ,and Barry Stevens which were the team who fabricated the specimen and tested the material properties. Mahesh Bhardwaj, of Ultragroup, for his guidance and insight into the world of ultrasound in dealing with his equipment and transducers.

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