Performance of Foamed Asphalt under Repeated Load Axial Test · 2017. 1. 24. · 4. Repeated Load Axial Test [RLAT] Under the Nottingham Asphalt Tester (NAT) procedure, the RLAT protocol

Procedia Engineering 54 ( 2013 ) 698 – 710

1877-7058 © 2013 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license.Selection and peer-review under responsibility of Department of Civil Engineering, Sebelas Maret Universitydoi: 10.1016/j.proeng.2013.03.064

The 2nd International Conference on Rehabilitation and Maintenance in Civil Engineering

Performance of Foamed Asphalt under Repeated Load Axial Test Sri Sunarjonoa*

aUniversitas Muhammadiyah Surakarta, Indonesia

Abstract

Foamed asphalt is a sustainable road material mixture in which the aggregates are normally mixed at ambient temperature, and the bitumen is created as a form of foam. In laboratory scale, the resistance to permanent deformation of road materials can be measured using Repeated Load Axial Test [RLAT]. This paper reports the results of laboratory testing using RLAT to evaluate the effect of foamed bitumen properties on the measured axial strain. Two types of aggregate gradation were evaluated using different testing modes. The specimens generated using 20 mm graded aggregate and using a 10 mm graded aggregate. The test results can be concluded that the effect of foam properties on the resistance to permanent deformation of a foamed asphalt material is less important than the effect of compaction characteristics (density or energy) or other parameters, e.g. aggregate skeleton.

© 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Department of Civil Engineering, Sebelas Maret University

Keywords: foamed asphalt; repeated load axial test; axial strain; permanent deformati-on.

1. Introduction In an ideal pavement the important mechanical properties related to the materials

used for bound material layers are stiffness, fatigue strength and resistance to permanent deformation (Brown 1994). Stiffness is required to ensure good load spreading ability, fatigue strength will prevent cracking due to traffic loading and resistance to permanent deformation eliminates rutting. It is therefore all bound materials would be required to understand their mechanical properties characteristics. In laboratory scale, the resistance

* Corresponding author. E-mail address: [email protected]

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© 2013 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license.Selection and peer-review under responsibility of Department of Civil Engineering, Sebelas Maret University

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699 Sri Sunarjono / Procedia Engineering 54 ( 2013 ) 698 – 710

to permanent deformation of road materials can be measured using Repeated Load Axial Test (RLAT).

Study on foamed asphalt performance included resistance to permanent deformation is very demanding due to its unique characteristics. Foamed asphalt is a sustainable road material mixture in which the aggregates is normally mixed at ambient temperature, and the bitumen is created as a form of foam. This mixture is commonly applied in road recycling construction. The formation of bitumen-aggregate bonds in foamed asphalt mixture is different from that of other common bituminous mixtures. Based upon laboratory investigation (Sunarjono 2007), the coated particles only comprise around 15% by mass or volume, but they are about 55% in terms of particle surface area. The smaller the particle size the higher the proportion coated by binder, and thus the filler size fraction is the best coated. The maximum size of coated aggregate is 6.3mm, for

This paper presents a laboratory scale experiment of foamed asphalt mixture in the RLAT. The purpose of this experiment was to evaluate the effect of foamed bitumen properties on the measured axial strain and to understand the resistance to permanent deformation of foamed asphalt materials.

2. Foamed Asphalt As a foamed asphalt binder, foamed bitumen can be produced by injecting air and

water droplets under high pressure into a pre-heated penetration grade bitumen. As the water turns into steam, bitumen changes from the liquid state into foam. The life of the foam at ambient temperature is very short, measured in seconds. Soon after production, the foam bubbles quickly collapse thus reverting the bitumen back to its liquid state and gradually regaining its viscous condition. Figure 1 show the Wirtgen WLB-10 laboratory foaming plant in which both air and water are injected into the hot bitumen in an expansion chamber.

Hot bitumencirculation

Expansionchamber

Air & waterinjection

Foamed bitumen Figure 1. Foamed bitumen produced in an expansion chamber

Foamed bitumen is commonly characterised in terms of its Expansion ratio (ER) and Half-life (HL). ER is defined as the ratio between maximum volume achieved in the foam state and the volume of bitumen after the foam has completely dissipated. HL is the time that the foam takes to collapse to half of its maximum volume. The ER and HL


parameters were affected significantly by Foaming Water Content (FWC). FWC is an added water (by mass of bitumen) at foam production. Discussion and an example of foaming characteristics related to the relationship between FWC, ER, and HL (Jenkins et al. 1999).

As is common for cold-mix asphalts, the strength of foamed asphalt at early life develops with loss of moisture (Jetareekul et al. 2007). In a pilot scale project (Nunn and Thom 2002), foamed asphalt at very early life exhibited stiffness typical of unbound material when their moduli were investigated using a Dynamic Plate tool. Based on Falling Weight Deflectometer (FWD) data, the stiffness at 20oC of the foamed asphalt layer was found to increase from < 1000MPa (at early life) to 3500MPa (at one year). The mixture developed to gain satisfactorily high stiffness levels within 6 months.(Merill et al. 2004), suggested that the choice of bitumen grade is a compromise between foaming ability and stiffness; higher grade bitumen foams easily but has lower viscosity. Additionally, discussion of foamed asphalt properties in terms of rutting performance under pilot scale project can be seen Sunarjono (2009).

3. Permanent Deformation Rutting is a common failure form for flexible pavements in which material under the

wheel path flows and densifies to form a depression or rut. (Brown 2000) stated, rutting is the sum of permanent deformations in various pavement layers. A single wheel load applied to a pavement material results in deformation or strain. Most of this are recoverable when the load goes away, but a small part may remain. Over time, with a large number of load applications, these small irrecoverable strains accumulate to form permanent deformation, which manifests as rutting in the pavement. This phenomenon is illustrated in Figure 2. Rutting may be the result of permanent deformation from various layers, and is often divided into structural rutting (granular and base layers) and non-structural rutting (surfacing). It is well understood that rutting is influenced by mixture properties i.e volumetric composition and material properties.

Two major mechanisms of rutting are densification (compaction) due to the repeated loading and plastic shear deformation due to the repeated action of shear and tensile stress. If a pavement has been well compacted during construction, further densification during rutting is unlikely, and permanent deformation is principally due to shear flow (Eisenmann and Hilmer 1987).


Figure 2. Idealised response of a bituminous mixture

4. Repeated Load Axial Test [RLAT] Under the Nottingham Asphalt Tester (NAT) procedure, the RLAT protocol can be

seen in BS DD 185: 1994and BS DD 226: 1996. As with all NAT based tests, the RLAT uses a cylindrical specimen with a diameter of 100mm or 150mm and thickness preferably between 40mm and 100mm. In the test, the specimen is positioned vertically between the upper and lower steel loading platens, which are slightly wider than the specimen. The repeated load is applied axially, while the vertical deformation of the specimen is measured by two LVDTs mounted on the upper loading platen as shown in Figure 3. The pulsating load consists of a square wave form with a frequency of 0.5 Hz, i.e. a pulse of one second duration followed by a rest period of one second duration. This simulates the slow moving traffic that leads to the most deformation in a real road.

The input parameters for testing are temperature, specimen thickness and diameter, and stress and number of load pulses including these for the conditioning stage. The standard test uses a vertical stress of 100 kPa at temperature of 30oC for 1800 pulses. Testing is initiated by a stress of 10 kPa for a duration of 10 minutes (the conditioning stage) to ensure that the loading platens are properly seated onto the specimen prior to running the testing. If desired, testing can be continued up to 3600 pulses. During testing, if the specimen deforms more than 8 mm before reaching the specified number of pulses, the test is then terminated. The test output consists of vertical deformations of the specimen plotted against number of load cycles.

Stre

ssSt

rain Elastic

Visco-elastic

Viscous+plastic

Elastic+plastic

Time

Time


Figure 3. RLAT test configuration using NAT apparatus

5. Materials Used and Specimen Preparation

5.1 Materials Used

The aggregate used in this study was virgin crushed limestone. Particle gradation (shown in Figure 4) was designed to be within the ideal grading envelope for foamed asphalt as recommended by Akeroyd and Hicks (Akeroyd and Hicks 1988). This study used bitumen grade of Pen 50/70 and Pen 70/100 which has properties as shown in Table 1. Foamed bitumen was generated using a laboratory mobile foaming plant type Wirtgen WLB 10 in which the bitumen was foamed at a water pressure of 6 bars and an air pressure of 5 bars. The characteristics of foamed bitumen were varied by applying different foaming water contents (FWC) and temperatures.

Figure 4. Gradation of aggregate used

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10mm 6mm

Fines Filler

Ideal envelope Design


Table 1. Properties of Bitumen Pen 50/70 and Pen 70/100

Test Property Bitumen Pen 50/70 70/100 Specific gravity 1.024 1.03 Penetration (0.1 mm) 54 - 56 85 - 93 Softening Point (oC) 52 - 53 45 - 49 Viscosity at 20oC (kPa.s) 899 257 Viscosity at 40oC (kPa.s) 21.90 5.54 Viscosity at 140oC(mPa.s) 362 262 Viscosity at 160oC(mPa.s) 153 114 Viscosity at 180oC(mPa.s) 77 57

Table 2. Specimen Preparation

Property Specimen Type 20mmgraded

limestone 10mm graded limestone

Bitumen pen

70/100

50/70

Bit temperature 180oC 180oC FWC 1,2,4,5,6,8, and 10 % 1,2,4,5, and 10 % Bitumen content 4% 6,8% Aggregate water 4,6% 6,4% Compaction setting F= 600 kPa,

Angle= 1.25o gyration number= 200

F= 600 kPa, Angle= 1.25o Wet density= 2275 Kg/m3

Specimen dia 100 mm 100 mm Curing period 3 days at 40oC 3 days at 40oC

5.2 Specimen Preparation This study used two types of specimens, i.e. specimen using 20 mm and 10 mm

graded limestone. Characteristics of the specimens preparation is presented in Table 2.

6. Results and Discussion The gradation of limestone aggregate used was designed to be within the ideal

grading envelope for foamed asphalt. The maximum aggregate size was 20 mm with 51.20% fines (< 6 mm) and 8.60% filler. This aggregate has a low Plasticity Index (PI) i.e. 2.7%. The maximum dry density (MDD) and optimum moisture content (OMC) were found to be 2.242 Mg/m3 and 6.4% respectively, determined in accordance with BS EN 13286-2: 2004.

6.1 Compaction and Stiffness Characteristics In the previous section, it has been described that properties of foamed bitumen are

affected by FWC (foaming water content). The effect of foam properties on the resistance to permanent deformation can be evaluated by differing FWC. In this study, there is two type of specimens, i.e. the 20 mm graded limestone and the 10 mm graded limestone. All specimens were compacted using Gyratory compactor and tested their


stiffness using Indirect Tensile Stiffness Modulus (ITSM) before their resistance to permanent deformation are evaluated.

Figure 5 and 6 demonstrate the effect of foaming water content (FWC) on the bulk density and the ITSM values for those of two type specimens. For the 20 mm graded specimens, foamed bitumen was produced using bitumen Pen 70/100 at a temperature of 180oC, whereas for the 10 mm graded specimens, foamed bitumen was produced using bitumen Pen 50/70 at a temperature of 180oC.

The effect of the FWC on either wet density or dry density appears unclear. As shown in Figure 5 and 6, the data reveals no significant trends and the effect of FWC on the mixture density cannot be observed. It appears that FWC is not important in its effect on the density of a mixture compared to other factors such as the aggregate particles and water since the differences in amount of water in the foam are very small, i.e. about 0.04 (at FWC of 1%) to 0.4% (at FWC of 10%) of the aggregate mass. In general correlation, it can be observed that, based on the linear trend line, the density of specimens increases slightly with the applied FWC. In Figure 6, the effect of FWC on the gyration number required to achieve the target wet density (2275 kg/m3). It can be seen that at FWC of 2% and 4% the specimens needed more gyration than at other FWC values. It means the specimens at those two FWC values are less compactable than at others.

Figure 5. Compaction and stiffness characteristics of 20 mm graded specimens

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ITSM

at 2

0o C (M

Pa)

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den

sity

(kg/

m3 )

Average ITSM value (4 specimens) Average wet (gyratory) density Average dry density

42 - 73 kg/m3

Using 20 mm graded crushed limestone aggregateUsing bitumen Pen 70/100Bitumen temperature 180oCBitumen content 4% (% by aggregate mass)Mixer agitator: flat typeCompaction: Force 600 kPa, angle 1.25o, 200 gyrationsCuring 40oC-3 days

95% confident limit


Figure 6. Compaction and stiffness characteristics of 10 mm graded specimens

The effect of FWC on the ITSM values measured at temperature of 20oC can be identified. The optimum ITSM value is obtained with the specimen prepared at FWC of 5%, although, as indicated by the 95% confident limit bars, the ITSM values at FWC of 2%-4% and of 6%-10% were no different. Based upon Figure 5, it seems the density and ITSM values are clearly linked. It is however, as indicated in Figure 6, it is likely that the gyration number do not affect the ITSM value.

6.2 Resistance to Permanent Deformation Performance of foamed asphalt specimens have been investigated using RLAT and

the results are presented in Figure 7, Figure 8, and Figure 9. An example is presented in Figure 7, in which the characteristics of axial strain increase with load cycles during the test can be identified.

All specimens tested were firstly measured for stiffness (ITSM test). Before the RLAT, the top and bottom faces of the tested specimens were smoothed using sand paper. The sand paper was used since the specimen cannot be trimmed by a saw. The weight and dimension (diameter and thickness) of each tested specimen were determined in accordance with section 5 of BS DD 226: 1996. The ends of the specimen were coated with a thin layer of silicone grease and black powder. The specimens were brought to the test temperature at least 2 hours before testing.

Two types of aggregate gradation were evaluated using different testing modes. The specimens generated using 20 mm graded aggregate were tested at a vertical stress of 200 kPa and a temperature of 30oC (see Figure 8), whereas the specimens using a 10 mm graded aggregate were tested at 100 kPa and a temperature of 40oC (see Figure 9).

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Using 10mm graded crushed limestone aggregateUsing Bitumen Pen 50/70WC = 6.4%, FBC = 6.8%, Bit temperature=180oCSelf-time before compaction = 57 daysForce 600 kPa, angle 1.25o, wet density 2275 kg/m3

diameter= 100mm, height= 66-67mmCuring at 40 C - 3 daysEach point represents an average of 3 samples

Dry density (kg/m3)

ITSM at 20oC (MPa)

Gyration number

95% Confident limit


The latter test series was conducted in order to clarify the effect of FWC on themeasured axial strain; this was not clear in the first test series.

Figure 7. Parameters used to evaluate RLAT resultsaa

The evaluation was based upon three parameter values, i.e. strain at 1800 pulses,strain at 3600 pulses and strain rate over the second 1800 load cycles as shown inFigure 7. The strain at 1800 pulse was included because several specimens failed (i.e. exceeded strain limit) before 3600 pulses had been completed. The parameter of strainrate over the second 1800 cycles was used in order to understand the effect of bindertype on the characteristics of permanent deformation at this pulse range.

As shown in Figure 8, the effect of FWC on the permanent deformation of specimens generated using 20 mm graded aggregate is not clearly defined. The only point is that at FWC of 6% the materials exhibit poor resistance to permanentdeformation. This is particularly clear when evaluation is based upon the strain rate overthe second 1800 cycles. The strain curves at 1800 pulses and at 3600 pulses look parallel and these curves show a slightly different trend compared to the strain rate curve. The compaction and stiffness characteristics of these specimens as shown inFigure 5 have no clear correlation with resistance to permanent deformation. Overall, itis likely that the effect of FWC is not important for resistance to permanent deformation ffof foamed asphalt material using 20 mm graded aggregate. It is probable that the effectof the aggregate skeleton and binder type is more important than the effect of foam properties (with different FWC). Testing modes (stress level and test temperature) mayalso affect the test results causing the effect of foam properties not to be observed.

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l stra

in (%

)Strain rate over second 1800 load cycles

Strain at 1800 cycles

Strain at 3600 cycles


Figure 8. Results of RLAT of specimens using 20 mm graded limestone aggregate with various FWC

It was decided to investigate the effect of binder in several ways, i.e. reduce the nominal size of aggregate (from size of 20 mm to 10 mm), increase the binder content (from 4% to 6.8%) and reduce the stress level (from 200 kPa to 100 kPa). The test temperature was also increased from 30oC to 40oC in order to achieve failure during testing. Therefore the specimens using 10 mm graded limestone were prepared to RLAT with different test mode.

Figure 9 shows the test results for 10 mm graded aggregate specimens. The compaction and stiffness characteristics of these specimens are presented in Figure 6. It is noted that this material was stored almost 2 months before compaction took place. To avoid any differences between specimens due to the storage period, the material was compacted to achieve a target density of 2275 kg/m3 and hence the dry densities were all comparable. It can be seen that at FWC of 2% and 4% the specimens needed more gyration than at other FWC values. The trend of required gyration number did not noticeably influence their ITSM values. However, it appears that the gyration numbers shown in Figure 6 and the characteristics of permanent deformation resistance shown in Figure 9 are clearly linked. The trend of axial strain at 3600 pulses (or when strain limit exceeded) and the strain rate over the second 1800 load cycles are very close to the trend of gyration number. More energy of compaction appears to have resulted in a better resistance to permanent deformation. It is likely that the effect of FWC on the resistance to permanent deformation of a foamed asphalt material is less important than the effect of compaction characteristics (density or energy) or other parameters, e.g. aggregate skeleton.

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Strain rate

Using 20mm well graded crushed limestone aggregateUsing Bitumen Pen 70/100, temperature 180oCWC = 4.6% FBC = 4.0%Specimen size: diameter= 100mm, height= 66-67mmCuring at 40 C - 3 days, dry density= 2273-2359 kg/m3

Test: stress= 200kPa, temperature= 30 C, 3600 pulseEach point represents an average of 3-4 samples

95% Confident limit(a half of error bar)


Figure 9. Results of RLAT of specimens using 10 mm graded limestone aggregate with various FWC.

Due to foamed asphalt not being a fully bound material and its binder not being as

permanent deformation.

As indicated in the pilot project testing (Sunarjono 2009), foamed asphalt materials tend to fail in rutting, which is affected by the binder type, mixture proportion and the presence of cement. In this study, cylindrical specimens of foamed asphalt materials, produced at various FWC values, were evaluated for their resistance to permanent deformation under the RLAT. Two types of mixture were used, i.e. specimens using 20 mm and 10 mm graded aggregates, which resulted in strains at 1800 pulse about 0.4-0.5 % and 2-5% respectively. However these two mixture types were tested at different stress and temperature, and hence these strains can not be compared directly. Actually, the 10 mm graded specimens were selected in order to explore the correlation between foam properties and resistance to permanent deformation, since the relationship was not clear using 20 mm graded specimens. However, it was found that for 10 mm graded specimens, their resistance to permanent deformation was closely related to compaction energy.

7. Concluding Remarks Following the work described in this paper, it can be deduced that the performance

of foamed asphalt under repeated load axial test (RLAT) are as follows:

1. Repeated load axial loading test can be used to evaluate the resistance to permanent deformation of foamed asphalt materials.

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Axi

al s

train

(%)

-1.00E-03

-5.00E-04

0.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

2.50E-03

3.00E-03

Stra

in ra

te o

ver s

econ

d 18

00 lo

ad c

ycle

s (%

stra

in/ c

ycle

)


Strain at 3600 pulse/ failed

Strain rate

Using 10mm graded crushed limestone aggregateUsing Bitumen Pen 50/70WC = 6.4% FBC = 6.8%Self-time before compaction = 57 daysdiameter= 100mm, height= 66-67mmCuring at 40 C - 3 daysTest: stress= 100kPa, temperature= 40 C, 3600 pulseEach point represents an average of 3 samples

Failed95% Confident limit(a half of error bar)


2. The effect of foamed bitumen properties by differentiate the FWC is not important for resistance to permanent deformation of foamed asphalt material using 20 mm graded aggregate.

3. The effect of foamed bitumen properties by differentiate the FWC value can be fasilitated using smaller nominal size of aggregate, increase the binder content, and reduce the stress level.

4. The resistance to permanent deformation of foamed asphalt materials is closely related to compaction energy.

5. The effect of foamed bitumen properties by differentiate the FWC value on the resistance to permanent deformation of foamed asphalt materials is likely less important than the effect of the aggregate skeleton and binder type.

Acknowlegement The author is very grateful for the assistance and advice of Dr. N.H. Thom and Dr.

S.E. Zoorob, and for many helpful discussions with Dr. M.H. Sutanto. This work was carried out with the financial support of TPSDP program SPMU-UMS unit Civil Engineering.

References Akeroyd, F.M.L. & Hicks, B.J., 1988. Foamed Bitumen Road Recycling. Highways, Volume 56, Number

1933, pp 42, 43, 45.

British Standard, 1994. Method for Assessment of Resistance to Permanent Deformation of Bitumen Aggregate Mixtures Subject to Unconfined Uniaxial Loading. Draft for development, DD 185: 1994.

British Standard, 1996. Method for determining Resistance to Permanent Deformation of Bituminous Mixtures Subject to Unconfined Dynamic Loading. Draft for development, DD 226: 1.

British Standard, 2004. Unbound and Hydraulically Bound Mixtures Part 2: Test Methods for the Determination of The Laboratory Reference Density and Water Content Proctor Compaction. BS EN 13286-2: 2004.

Brown, S.F., 1994. Properties of Road Layers. In: Bituminuous mixtures in road construction, pp 43-63. Edited by Hunter, R.N. Thomas Telford, London.

Brown, S. F., 2000. Introduction to Pavement Design. In the Residential Course on Bituminuous Pavements, Materials, Design and Evaluation. Lecture Notes, University of Nottingham, School of Civil Engineering. 3rd-7th April 2000.

Eisenmann, J. and Hilmer, A., 1987. Influence of Wheel Load and Inflation Pressure on The Rutting Effect at Theoretical Investigations.Proc. 6th Int. Conf. on the Structural Design of Asphalt Pavements, Ann Arbor, Michigan, USA.

Jenkins, K.J., de Ven, M.F.C. and de Groot, J.L.A., 1999. Characterisation of Foamed Bitumen. 7th Conference on Asphalt Pavements for Southern Africa (CAPSA).

Jetareekul, P., Sunarjono, S., Zoorob, S.E., Thom, N.H., 2007. Early life performance of cement and foamed bitumen stabilised reclaimed asphalt pavement under simulated trafficking. The International Conference on Sustainable Construction Materials and Technologies, 11-13 June 2007, Coventry UK.


Merrill, D., Nunn, M. and Carswell, I., 2004. A Guide to The Use and Specification of Cold Recycled Materials for The Maintenance of Road Pavements. Highways Agency, Hanson Environmental Fund (Viridis), Scottish Executive, Tarmac, UKQAA, WS Atkins, Colas, RBA. TRL Report TRL 611. First published 2004, ISSN 0968-4107, Copyright TRL Limited 2004.

Nunn, M.E. and Thom, N.H., 2002. Foamix: Pilot Scale Trials and Design Considerations. Viridis Report VR1, First Publi-shed ISSN 1478-0143, Copyright TRL Limited 2002.

Sunarjono, S., 2007. Quantifying The Effect Of Foam Dispersal On The Permanent Deformation Of Foamed Asphalt. Jurnal Eco Rekayasa, Vol. 3, No. 1, Maret 2007.

Sunarjono, S. 2009. Investigating Rutting Performance of Foam-ed Cold-Mix Asphalt Under Simulated Trafficking, Jurnal Dinamika Teknik Sipil, Vol 9, No. 2, Juli 2009, ISSN: 1411-8904, Terakreditasi BAN DIKTI 55a/DIKTI/Kep/2006.

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Performance of Foamed Asphalt under Repeated Load Axial Test · 2017. 1. 24. · 4. Repeated Load Axial Test [RLAT] Under the Nottingham Asphalt Tester (NAT) procedure, the RLAT protocol