felipe halles papertrb13 4177nov15vfinal

8/9/2019 Felipe Halles Papertrb13 4177nov15vfinal

1/15


2/15


3/15

Halles F., Thenoux G. and Gonzalez A. 2

GENERAL DISCUSSION12

Introduction34

Stabilizing or recycling of asphalt concrete pavements using Foamed Bitumen (FB) is a widely5

used rehabilitation technique worldwide. However, there is still no structural design6 methodology fully validated by practitioners and researchers. One reason lies in the fact that it7has not been possible to determine the elastic modulus that FB stabilized layer develops with8

time. Without a reliable modulus or stiffness value, the structural analysis of a FB pavement is9

uncertain. Although there are several laboratory tests for assessing the stiffness of FB mixtures,10none of them allows identifying the observed stiffness evolution with time that has been11

observed in the field.12

There are two trends found in the literature regarding the in-situ stiffness evolution of the13

FB mix. The first comes from studies carried out by Loizos (1) who analyzed back-calculated14stiffness from Falling Weight Deflectometer (FWD) tests from a FB recycled project built in15

Greece (Figure 1). Results indicated that stiffness gradually increases from the day of16

construction until it reaches a constant value after a period of approximately 12 months. A fact17 that explains this behavior is the loss of moisture from the mixture that occurs during the curing18

period. The loss of moisture and increase in strength or stiffness has also been observed by19

Bowering (2), Jones et al. (3) and Fu et al. (4), among others.20

After 12 months the backcalculated stiffness remains constant despite constant traffic of21heavy-weight vehicles (1).22

23

2425

26

27

2829

30

31

32

33

34

FIGURE 1: Elastic modulus back-calculated by Loizos (1 ) for the FB layer.35

Conversely, research studies carried out in South Africa (5) indicated that FB layers36affected to traffic load show a gradual decrease in stiffness. Figure 2 shows results of the37

accelerated pavement testing performed in a recycled pavement with a FB layer using 1.8%38

bitumen and 2.0% cement content. After pavement construction a 40 kN traffic load was applied39using the South African Heavy Vehicle Simulator HVS (6 ,7 ). Multidepth Deflectometer (MDD)40

were installed in the pavement structure to measure deflection and to calculate the effective41

stiffness of each layer.42


4/15


1

2

3

4

5

6

7

8

9

FIGURE 2 Stiffness evolution of the FB layer Stiffness, adapted from (8 ).1011

Stiffness values measured during the period of analysis indicated that FB layer has two12

phases. The first phase corresponds to a decrease in stiffness until a constant stiffness state,13without having a physical manifestation on the pavement layer (cracks or deformations). The14

second phase is represented by a constant stiffness of the FB layer. During the test at15

approximately 1,000,000 load cycles, the traffic was increased to 80 kN. With the 80 kN load,16

the stiffness of the FB layer showed a similar trend to that observed during the first 300,000 load17cycles with 40 kN, with stiffness decreasing gradually until plateaus. Results provided by the18

accelerated pavement test in the long term also indicated that during the second phase the19

material behaves as a granular material, accumulating permanent deformation due to cyclic loads20 applications. The TG2 first 2002 guide (8) proposed that the “constant stiffness state” can be21

comparable to a granular material only in the effective elastic modulus and behavior, but not in22

the physical composition of the materials.2324

25

Influence of the Active Filler in the Mechanical Properties of FB Mixes2627

Active fillers are normally added to FB mixes to improve the mechanical properties of the28

mixture. While some researchers and practitioners have reported mixes without any active filler29

(4,9), others have reported the use of cement (10-13), lime (14-16 ), fly-ash (17,18) and other30

active fillers (18-20). Nevertheless, studies carried out in the last years have demonstrated that31 stiffness of FB mixtures is dependent on both: type of active filler and content. Halles and32

Thenoux (18) reported differences of up to two times between mixes with and without cement,33

for the same FB content, measured using the repeated load triaxial test. The use of lime also34significantly improves the resilient modulus measured in the triaxial test (TxRM) of the FB mix.35

Hence, in addition to determining the test that better characterizes the mechanical properties of36

the FB mixture, it is necessary to quantify the relative contribution of the active filler used, in37 particular type and percentage added to the FB mix.38


5/15


Analysis of the In-Situ Stiffness FB Mixtures12

Stiffness evolution observed in pavement structures using FB layers can be explained by3studying the microstructure of the FB mixture. The tiny bitumen particles as well as cement4

particles disperse throughout the aggregate by adhering to the finer particles (fine sand and5

smaller) forming a mastic that bonds the large aggregates. The bonds formed by the stabilizing6 agents (bitumen and active filler) are not continuous throughout the microstructure of the7aggregates matrix; the physical bond may be described as “spot welded” (21). When traffic loads8

are applied into the pavement structure, the FB layer is deformed producing strains and stresses9

in the microstructure. These stresses could break some of the bonds upon depending on the10magnitude of the stresses, orientation and concentration, producing a decrease in cohesion and11

therefore a decrease in stiffness. If the stresses or strains are smaller than the limiting stress of12

the mastic, then the FB mix will maintain its original cohesion and therefore its stiffness.13

It is well known that FB mixes can bear tensile stress, but also could be stated that they14are not able to withstand fatigue cracks. Most of the literature have indicated that failure mode15

observed in the field is plastic deformation instead of fatigue cracking (8,22); i.e. when high16

stresses are produced in the bottom of the layer, then bonds in that area are broken and the mix17 continues behaving as an untreated material in that specific area.18

Based on these observations it is possible to state that the different trends of the stiffness19

evolution could be explained by the stress state of the FB layer. To support this assumption, a20

simple multi layered linear elastic model was used to calculate stresses and strains in the FB21layer in the Greek and South African projects. Dual truck tires were modeled with two 20 kN22

loads using a separated by 350 mm and contact pressure of 700 kPa. In both projects, stresses23

and strains were calculated at one quarter of the thickness of the FB layer, measured from the24 bottom of the FB layer. Table 1 shows details of the materials elastic properties and thicknesses25

for each pavement structure evaluated as well as stresses and strains calculated at one quarter of26

the FB layer thickness. The indirect tensile strength (ITS) of the FB mix was assumed to be 30027

kPa in both projects, which is considered a representative ITS of a mix with a 1.0% cement28content.29

30

TABLE 1 Pavement structure characteristics and stresses/strains found in projects from31Greece and South Africa32

LayerElastic Modulus

(MPa)Greece South Africa

T (cm) (kPa) (m) SR T (cm) (kPa) (m) SR

Surface Layer 4000 9 3 3

FB Layer 1200 25 60 45 0.2 25 165 100 0.55

Other Layer 1000 (*) 10 --- ---

Subbase 250 15 25 25

Subgrade 90 (**) --- --- ---(*) Cemented treated layer, (**) Estimated by the authors, SR= Stress divided by the Indirect Tensile Strength, T =33Thickness of the layer, = stress, = strain34

35

Based on the results obtained from the pavement structural analysis, it can be seen that36the FB layer of the pavement structure in Greece was subjected to a SR of 0.20 while the FB37

layer of the pavement structure in South Africa to a SR of 0.55. Both values are very different38and could explain the behavior observed using the concepts for the thickness design of perpetual39


6/15


pavements (23). The perpetual pavements concept states that if the deformations that occur at1

critical points are below a specific value (endurance limit), then the asphalt layer will not suffer2

fatigue and therefore its structural lifetime could be extended to periods of even 50 years. Under3this scenario, only functional maintenance actions should be conducted for keeping the standard4

expected. Results of studies carried out to validate this affirmation have suggested that the5

limiting tensile strain at the bottom of the asphalt concrete layers should be no greater than 606 and that at the top of the subgrade the vertical strain should be limited to 200 .7

Using a similar approach to FB layers, it may be assumed that if SR is lower than the8

endurance limit, then the FB will maintain its stiffness.9

Based on the above discussion, it is expected that after a period the FB stiffness plateaus,10

which will depend of the stress/strain levels applied to the layer depending on the traffic loads11applied in the road, similarly to the behavior observed in the pavements analyzed in this article.12

In the case of the pavement structure of Greece, it is probable that a SR of 20% is lower than the13

SR required for generating some damage to the bonds or mastic produced by the bitumen and14

cement particles.15This paper presents results of a research work carried out to represent and quantify the16

stiffness evolution of FB mixes subjected to different SR levels. This information was used for17 two purposes:18

For establishing the effect of the different bitumen and cement content on the long term19

performance of the FB mixtures, in order to determine the appropriate content of each20

one.21

Define the maximum stress level that must be accepted in the FB layer in order to22

maintain constant its stiffness.23

24

25LABORATORY TESTING PROGRAM26

27

Materials2829 Reclaimed Asphalt Pavement and Granular Materials (RAG) Properties30

31

The RAP (Recycled Asphalt Pavement) used was collected from the “Huequén - Los Sauces”32recycling project, located south of Chile (IX Region). Only the RAP was pulverized by the33

recycler machine, (without the addition of foamed bitumen or active fillers). The RAP was then34

mixed with reclaimed granular materials in the laboratory, simulating the same conditions found35

in recycled projects in Chile. The RAP and reclaimed granular materials are the Recycled36Asphalt Granular (RAG) material used in this study. One gradation was constituted from the37

original material by sieving the RAP into three fractions and recombining them with reclaimed38

granular base materials for laboratory testing. Also, inert baghouse dust collected from an asphalt39 concrete plant was used for correcting the final RAG mix. The main properties of the RAG40materials were:41

42

Maximum aggregate size: 19 mm43

Material Passing #200 sieve (0.075 mm): 6%44




7/15


Crushed/Fractured Particles: 100%1

Plasticity Index: Non Plastic2

Optimum Moisture Content: 6.0%3

Maximum Density: 2190 kg/m3 4

5

Stabilizing Agents Properties67

Bitumen properties were: Absolute Viscosity at 60 °C: 3210 poises, Ductility at 25 °C higher8

than 150 cm at 5 cm/min, Penetration Index: -0.9 and the Flash Point: 360 °C using the9Cleveland Open Cup. Also, Viscosity at 60 °C on residual bitumen from TFOT: 9180 poises and10

ductility at 25 °C higher than 150 cm at 5 cm/min. Portland cement type II was used in the11

preparation of all the mixes.12

13

Mixing Preparation, Compaction and Curing1415

The RAG material was foamed using the Wirtgen WLB-10 laboratory at 165 °C with 2.5% of16

foaming water by mass. The expansion ratio was approximately between 12 and 15 and the half-17life was 10 to 12 seconds. RAG was preconditioned placing buckets with 20 Kg of material at18

uncontrolled laboratory temperature (between 18° C and 25 °C) and relative humidity (between1935% and 55%).20

Previously to mixing, the optimum moisture content (OMC) of the RAG material was21

strictly controlled and in average was near to 75% of the optimum moisture content (OMC) of22the RAG mix. Several Proctor tests were conducted to define the OMC value.23

RAG materials and stabilizing agents were mixed using a twin shaft pugmill mixer.24

During mix production, RAG materials were mixed in dry with the active filler, followed by the25

addition of water. After one minute of mixing, FB was injected while the RAG material was26

being agitated.27

150 mm diameter and 60 mm in high ITS specimens were prepared and compacted using28gyratory compaction. The compaction procedure was adjusted to obtain the same density in each29

specimen. Specimens were extruded from the molds immediately after compaction and cured in30a forced air oven at 40 °C during 72 hrs.31

32

Laboratory Tests3334

The stress controlled Indirect Tensile Fatigue test (ITFT) was used to evaluate the stiffness35

evolution of the FB mixes. This test uses the same setup of the Indirect Tensile Strength (ITS)36

test with cyclic loads. LVDTs were installed diametrically in order to measure the horizontal37tensile strains (Figure 3), which is used to calculate the dynamic/elastic modulus, as well as the38

fatigue performance of the mix. The stress level applied in the ITFT was represented using the39Stress-Ratio concept (SR) which is defined as the quotient between the tensile stress (x) and the40

Indirect Tensile Strength (ITS). The strains measured by the LVDTs were used for calculating41

the elastic modulus/stiffness (S) of the mix. The following equations were used:42

43

(1)44

Where; P is the vertical load, t is the thickness of the specimen and d is the diameter.45


8/15


1

(2)2

Where; S is the elastic modulus, x the effective tensile stress and the measured tensile strain.34

(3)5Where; x is the effective tensile stress and ITS is the maximum tensile stress.6

Figure 3 shows how the stiffness of the mix decreases due to the progressive increase in plastic7

and elastic deformations under cyclic loading.8

910

11

12

1314

1516

1718

19

2021

22

23

2425

FIGURE 3 Example of Indirect Tensile Fatigue Test.26

27

Experimental Design2829

The laboratory test program using the ITFT was designed to study the impact of the bitumen and30

cement contents. In addition, the ITFT results attempt to define the maximum stress-level that31

the FB layer is capable to withstand without significantly reducing the stiffness.32Four stress levels, defined using the Stress-Ratio (SR), were applied to each specimen.33

Five thousand load cycles were applied at each SR, for a total of 20,000 load cycles. ITFT were34

carried out at 25 °C using a temperature controlled cabinet. The experimental design for this35

study is summarized in Table 2.36 From the twelve mixes of the factorial design presented, only five were selected for37

testing. Mixes FB1C1, FB2C1 and FB3C1were tested for evaluating the effect of the FB content38

and mixes FB2C0, FB2C1 and FB2C2 were tested for evaluating the effect of the cement39content.40

41

4243


9/15


TABLE 2 Experimental design for stiffness evolution measurement.1Variable # of levels Values

RAG source 1

Bitumen grade 1 AC-24

Foaming properties 1 165°C, 2.5% foaming water

Foamed bitumen content 4 1%, 2% and 3%Cement content 3 0% - 1% - 2%

Compaction Effort 1 Gyratory compaction

Curing Period 1 72 hrs at 40 °C

Water Conditioning 2 Dry

ITFT replicates 3 Test carried out at 25 °C

Stress-State Levels 4 Stress Ratio equal to (Effective Stress / ITS)

Total number of tests (average) 100 From 9 (3 x 3) scenarios, only 5 were used

Mixes Evaluated in this Research Work FB Content (%) Cement Content (%)

FB1C1 1.0 1.0FB2C1(*) 2.0 1.0

FB3C1 3.0 1.0FB2C0 2.0 0.0

FB2C1(*) 2.0 1.0FB2C2 2.0 2.0

(*) same mixes/samples2

3

ANALYSIS OF RESULTS45

Effect of the Foamed Bitumen Content on the Stiffness Evolution67

Figure 4, shows results of the ITFT carried out on mixes FB1C1, FB2C1 and FB3C1 in order to8

evaluate the effect of the bitumen content on the stiffness evolution. Results correspond to the9

average of two specimens evaluated.10Trend lines were fitted and extrapolated to each mix for each SR with the objective of11

estimating the stiffness for additional load cycles. Examples of the trend lines for FB2C1are12

shown in Figure 4. Table 3, shows details of trend lines of each mix as well as the stiffness13expected at100,000 and 1,000,000 load cycles. In addition, the quotient between the Initial and14

Long Term Stiffness (RSIE) is presented in the same Table 3.15

It must be noted that a couple of test were carried out using more than 100,000 cycles in16

order verify the extrapolation made.171819

20

21

2223

24


10/15


1

2

34

5

678

9

10

11

12

13

1415

161718

19

FIGURE 4 ITFT Stiffness evolution of mixes with different bitumen content.2021

TABLE 3 Details of trend lines for each mix and estimated stiffness.22

Stress y = a*x b R 2 Long Term Stiffness and RSIE for i cycle loads

Ratio A B (%) i = 100,000 (RSIE) i = 1,000,000 (RSIE)

MixFB1C1 20 c -0.013 50.7 1098 (92%) 1066 (89%)

(1% FB+1%Cem) 30 c -0.136 83.4 654 (55%) 478 (40%)

40 c -0.755 96.6 131 (11%) 23 (2%)MixFB2C1 20 c -0.031 88.5 1310 (82%) 1220 (76%)

(2% FB+1%Cem) 30 c -0.140 85.3 828 (52%) 600 (38%)

40 c -0.384 94.5 407 (25%) 168 (11%)

MixFB3C1 20 c -0.019 61.2 1220 (87%) 1168 (83%)

(3% FB+1%Cem) 30 c -0.157 90.1 682 (49%) 475 (34%)

40 c -0.581 96.3 228 (16%) 60 (4%)

Mix FB2C0 20 c -0.031 70.2 849 (85%) 791 (79%)

(2% FB+0%Cem) 30 c -0.261 95.1 341 (34%) 187 (19%)

40 Failure

Mix FB2C1 20 c -0.031 88.5 1310 (82%) 1220 (76%)

(2% FB+1%Cem) 30 c -0.140 85.3 828 (52%) 600 (37%)

40 c -0.384 94.5 407 (25%) 168 (10%)

Mix FB2C2 20 c -0.013 61.2 1538 (90%) 1493 (88%)

(2% FB+2%Cem) 30 c -0.139 90.1 844 (50%) 613 (36%)

40 c -0.576 96.3 324 (19%) 86 (5%)

y: Stiffness of the Indirect Tensile Fatigue/Modulus Test; x: Load cycles; c: Constant value not used in23the analysis.24


11/15


1

Based on the results shown on Figure 4 and Table 3, the following observations can be made:2

3

In general, all mixes show similar trends in terms of stiffness evolution at different stress4

ratios. According to results presented in Table 3, curves were fitted to measured values.5

The curves are described by a power relationship with a,b regression coefficients. Table 36 shows that “b” coefficients are very similar. For example, when a SR of 30% was7applied, “b” coefficient for mixes FB1C1, FB2C1 and FB3C1 were -0.136, -0.140 and8

-0.157 respectively. When a SR of 20% and 40% were applied, a larger variability was9

observed, but “b” values were within the same range.10

The stiffness of the FB mixes plateaus after a certain number of load cycles when the11

stress ratio is in the order of 20%. For example, Mix FB2C1 showed a relative constant12

stiffness of 1200 – 1300 MPa for the long term, which represents almost 80% of the13

initial Stiffness (1600 MPa). In the case of SR equal to 30%, the mix showed a good14

evolution of stiffness, with a constant decreasing line with a low slope. In this case the15stiffness of the mix was 600 MPa after 1 million load cycles, which represents the 37.5%16

of the initial stiffness (1600 MPa). This fact showed that after all the load cycles were17 applied, the mix still is able to keep cohesion due the effect of the stabilizing agents.18

Similar results are observed in mixes FB1C1 and FB3C1. In the case of a SR equal to1940%, mixes showed a clear reduction in stiffness with load cycles. All of them showed20

almost null stiffness after 1 million cycle loads.21

When mixes were subjected to a stress ratio of 50%, specimens collapsed in a relative22

short period indicating that stresses and strains applied are much larger than the cohesion23

provided by the FB and cement to the mix.24

Although trends of the stiffness for each mix were very similar, results show that there is25an optimum bitumen content that maximizes the stiffness. In this case, the better results26

in terms of stiffness evolution were observed in Mix FB2C1 with 2% FB and 1% cement.27

Table 4 shows the slope of the trend line for each mix when SR is 50%.It is interesting to28note that when mixes were subjected to a SR of 50%, the stiffness rate of change for each29

mix were very similar, which means that the FB content did not significantly affect the30 behavior of the mix under these stress conditions.31

32

TABLE 4 Slope of the trend lines for SR equal to 50%33

Mix Stress Ratio (%)Slope (m)

(y = m*x + b)

Mix FB1C1 50 -0.1116

Mix FB2C1 50 -0.1207

Mix FB3C1 50 -0.1189

Mix FB2C0 40(*) -0.0643

Mix FB2C1 50 -0.1207

Mix FB2C2 50 -0.2183

(*) mixes FB2C0 collapsed for SR equal to 40%3435

3637


12/15


Effect of the Cement Content on the Stiffness Evolution12

Figure 5, shows results of the ITFT carried out on mixes FB2C0, FB2C1 and FB2C2 in order to3evaluate the effect of the cement content on the Stiffness evolution. Results correspond to the4

average of two specimens.5

Trend lines were fitted and extrapolated to the modulus measured for each SR with the6 aim of estimating the stiffness if additional load cycles were applied. Examples of the trend lines7for mix FB2C2 loaded at different SRs are depicted in Figure 5. Table 3 shows details of the8

trend lines of each mix as well as the extrapolated stiffness at100,000 and 1,000,000 load cycles.9

In addition, the RSIE was included in Table 3.1011

12

13

1415

16

1718

19

20

2122

23

2425

26

27

282930

31

32

Figure 5 ITFT Stiffness evolution of mixes with different cement content.3334

Based on results of Figure 5 and Table 3, the following observations are made:3536

It can be observed that there are significant differences between mixes without cement37(Mix FB2C0) and with cement (Mixes FB2C1 and FB2C2) for the same bitumen content.38

Mixes with cement (FB2C1 and FB2C2) have larger stiffness compared to Mix FB2C039

(with FB only). While stiffness of mixes FB2C1 and FB2C2 are 1310 MPa and 153840MPa respectively for 100,000 cycles, stiffness for mix FB2C0is 849 MPa. These results41

indicate that a pavement structure with FB2C1 and FB2C2 layers will have a better42

structural capacity than using mix FB2C0.43

Additionally, Mixes FB2C1 and FB2C2 were able to withstand more cycles than mix44FB2C0 for the same test loading sequence. While Mix FB2C0 collapsed for a SR equal to45

40%, mixes FB2C1 and FB2C2 collapsed for a SR equal to 50%.46


13/15


The stiffness of the FB mixes plateaus after a certain number of load cycles when the1stress ratio is in the order of 20%, providing guarantee that the mix will keep its cohesion2

in the long-term.3

For the case of a SR equal to 30%, mixes with cement (FB2C1 and FB2C2) showed an4

acceptable stiffness evolution. It is interesting to note that although mix FB2C2 initially5

has a greater stiffness than mix FB2C1, when extrapolated to 100,000 cycles, both6stiffnesses tend to be the same. Stiffness of Mix FB2C1 is equal to 828 MPa for 100,0007

extrapolated cycles while stiffness of mix FB2C2 for the same conditions is 844 MPa.8

For the case of a SR equal to 40%, mix FB2C1 showed a better stiffness evolution than9mix FB2C2. In this case the stiffness rate of change for mix FB2C2 was significantly10

higher than mix FB2C1, which gives lower stiffnesses in the long term. When comparing11

trend lines fitted to the data, it can be seen that values of the variable “b” are -0.384 for12

mix FB2C1 and -0.576 for mix FB2C2. If the fitted equations are used to extrapolate the13stiffness, at 1 million load cycles the stiffness of mix FB2C1 is 168 MPa while stiffness14

of mix FB2C2 is 86 MPa. In contrast, mix FB2C0 (only with FB) collapsed for a SR15

equal to 40%.16

For the case of a SR equal to 50% in mixes FB2C1 and FB2C2 as well as SR equal to1740% in mix FB2C0, trend lines were fitted to the data (see Table 4). The slopes for each18

equation (m) indicated that as the cement content increases the rate of change of the19stiffness also increases. This means that when increasing the cement content, mixes with20

the worst behavior are obtained for a SR of 50%.21

Overall, the use of 2.0% cement in a FB layer will be beneficial only if the FB layer is22loaded to a SR equal or lower than 30%. If the FB layer is loaded to a SR equal or higher23than 40%, it is recommended only to use 1.0% cement together with FB.24

25

26

CONCLUSIONS27

28An analysis of the stiffness degradation of foamed bitumen mixtures was done using the indirect29

tensile fatigue test (ITFT) aiming to identify the evolution of the elastic modulus or stiffness of30the mixture in long term. The experimental study was designed to obtain the maximum stress31

level that the FB layer is capable of withstanding without significantly reducing its stiffness as32

well as to study the effect of the bitumen and cement contents in the long term stiffness.33

34Based on the results presented the main conclusions may be summarized as follow:35

36

The stiffness of FB mixes will evolve according the stress-level applied to the FB layer.37If the stress level is lower than a specific value the stiffness of the mix will remain38

constant at a value very close to the initial stiffness. If the stress level is greater than a39specific value the stiffness of the mix will gradually decrease.40

If the Stress-Ratio of the mix is lower than 20%, then the mix will have a stiffness within41a range of 75% - 90% of the Initial Stiffness after one million load cycles. The value will42keep relatively constant during the life of the pavement.43

If the Stress-Ratio of the FB mix layer is between 20% and 40%, the stiffness will44gradually decrease. The higher the Stress-Ratio, the higher will be the reduction rate of45

stiffness.46


14/15


If the Stress-Ratio is around 50% then the mix will “collapse” and the cohesion provided1 by stabilizing agents will reduce to zero in a relative short period. In that case the2

stiffness will be equivalent to the elastic/resilient modulus of the reclaimed material3

without stabilizing agents.4

Analysis of the bitumen content effect showed very little influence on the stiffness5

evolution, but it was possible to find an optimum content that maximizes the stiffness; in6this case, Mix FB2C1 followed by mixes FB3C1 and FB1C1. Conversely, the effect of7

cement content was significant on the stiffness evolution as well as in the absolute value8of stiffness. In addition, it is possible to state that cement must always be incorporated to9

FB mixes for guaranteeing minimum short and long term stiffness.10

Results showed that the use of 2% of cement in the FB layer will be beneficial only if the11

FB layer is loaded to a SR equal or lower than 30%. If the FB layer is loaded to a SR12

equal or higher than 40%, it is recommended to add only 1% of cement and FB.1314

The data and analysis provided in this research work can be used to estimate an effective elastic15

modulus (EMM) of the FB mix in the long term based on the stress-state expected at the FB16

layer. The EMM may be defined as a percentage of the initial stiffness and a shift factor must be17developed to adapt the elastic modulus provided by the ITFT to the elastic modulus that better18

represents the mechanical properties of the FB mix in the field.19It must be noted that the laboratory work presented in this paper was carried out using20

only one aggregate source, one bitumen source, a single active filler and a single temperature.21

All these factors contribute significantly to the FB mix performance and therefore results22obtained are limited. Conclusions must be validated using a larger experimental design.23

24

REFERENCES2526

1. Loizos A. In-situ characterization of foamed bitumen treated layer mixes for heavy-duty27

pavements. International Journal of Pavement Engineering, Vol. 8, N° 2, June 2007, 123-28 135.29

2. Bowering R.H. Foamed bitumen: Production and application of mixtures, evaluation and30 performance of pavements. In Proceedings of Association of Asphalt Paving31

Technologists, Vol 45: 453 – 73, 1976.32

3. Jones D., Fu P., Harvey J.T., and Halles F. Full-Depth Reclamation with Foamed33 Asphalt: Final Report . Davis and Berkeley, CA. University of California Pavement34

Research Center. (Research Report UCPRC-RR-2008-07), 2008.35

4. Fu P., Jones D., Harvey J.T. and Halles F. Investigation of the Curing Mechanism of36 Foamed Asphalt Mixes Based on Micromechanics Principles. Journal of Materials in37

Civil Engineering, Vol. 22, pp.29-38, 2010.38

5.

Long F. M. The development of structural design models for foamed bitumen treated39 pavement layers. Contract Report CR-2001/76, Gauteng – CSIR, South Africa, 2001.406. Verhaeghe B, Sadzik E. and Visser A. Three Decades of Development and Achievements:41

The Heavy Vehicle Simulator in Accelerated Pavement Testing. 10th International42

Conference on Asphalt Pavements (ICAP) , 2006. 437. Du Plessis L., Coetzee NF and Burmas N. Heavy vehicle simulator in accelerated44

pavement testing: a historical overview and new developments. 3rd International45

Conference on Accelerated Pavement Testing (APT), Madrid, Spain, October 2008.46


15/15


8. Asphalt Academy Transportek. South African Interim Technical Guidelines. Design and1

Use of Foamed Bitumen Treated Materials - TG2. CSIR Transportek, South Africa, 2002.2

9. Sunarjono Sri. Tensile Strength and Stiffness Modulus of Foamed Asphalt Applied to a3

Grading Representative of Indonesian Road Recycled Pavement Materials.4

DinamikaTeknikSipil, Vol.7, pp 1 – 10, January 2007.5

10.

Thenoux G., Gonzalez A. and Jamet A. Aspectos Constructivos del Primer Proyecto de6 Reciclado en Frío In-Situ con Asfalto Espumado en Chile. Revista Ingeniería en7Construcción Vol. 18, 2003, pp. 148-156, Pontificia Universidad Católica de Chile.8

11. Twagira M.E., Jenkins K.J. and Ebels L.J. Characterization of Fatigue Performance of9

Selected Cold Bituminous Mixes. Proceedings of the 10th

International Conference on10Asphalt Pavements, Quebec, Canada, 2006.11

12. Jenkins K.J.; Long F.M. and Ebels L.J. Foamed Bitumen Mixes = Shear Performance?.12

International Journal of Pavement Engineering, Volume 8, Issue 2, June 2007, pages 85 – 13

98.1413. Long F. M. and Theyse H.L. Mechanistic-Empirical Structural Design Models for15

Foamed and Emulsified Bitumen Treated Materials. Conference on Asphalt Pavements16

for Southern Africa – CAPSA, 2004. South Africa.17 14.

Nataatmadja A. Some Characteristics of Foamed Bitumen Mixes. In Transportation18

Research Record. Journal of the Transportation Research Board, N° 1767, TRB, National19

Research Council, Washington D.C., 2001, pp. 120-125.20

15. Ramanujam J.M. and Jones J.D. Characterization of Foamed-Bitumen Stabilization.21International Journal of Pavement Engineering, Vol. 8, Issue 2, June 2007, pp. 111-122.22

16. Leek C. Insitu Foamed Bitumen Stabilisation – The City of Canning Experience.23

Proceedings from 20th Australian Road Research Board Conference, Melbourne, 2001.2417. Saleh M. Effect of Rheology on the Bitumen Foamability and Mechanical Properties of25

Foam Bitumen Stabilised Mixes. International Journal of Pavement Engineering, Volume26

8, Issue 2, June 2007, pages 99 – 110.27

18. Halles F. and Thenoux F. Degree of influence of active fillers on the properties of28recycled mixes with foamed asphalt . In Transportation Research Record 2095: 127-135,29

2009.30

19. Lancaster J., McArthur L. and Warwick R. Vicroads Experience with Foamed Bitumen31Stabilisation. Proceedings 17th Australian Road Research Board Conference, Volume 16,32

Part 3, pp. 193-211, 1994.33

20. Hodgkinson A. and Visser, A.T. The role of fillers and cementitious binders when34recycling with Foamed Bitumen or Bitumen Emulsion. Proceedings of the 8th Conference35

on Asphalt Pavements for Southern Africa. September, 2004.36

21. Jenkins, K.J. Mix design considerations for cold and half-cold bituminous mixes with37

emphasis on foamed bitumen. Ph.D. Thesis. University of Stellenbosch, South Africa,382000.39

22.

Gonzalez, A, Cubrinovski, M, Pidwerbesky, BD, and Alabaster, D 2009, Full scale40

experiment on foam bitumen pavements in CAPTIF accelerated testing facility,41

Transportation Research Record 2094, Transportation Research Board, Washington,42D.C., 21-29.43

23. Committee on General Issues in Asphalt Technology. Perpetual Bituminous Pavements.44

Circular Number 503. A2D05 Committee, Transportation Research Board, 2001.45

felipe halles papertrb13 4177nov15vfinal

Documents