Limiting oxygen index reduction in bitumen modified with nanoclays

Journal Pre-proof Limiting oxygen index reduction in bitumen modified with nanoclays Sara Filippi, Miriam Cappello, Giovanni Polacco PII:

S0379-7112(19)30315-7

DOI:

https://doi.org/10.1016/j.firesaf.2019.102929

Reference:

FISJ 102929

To appear in:

Fire Safety Journal

Received Date: 25 June 2019 Revised Date:

21 November 2019

Accepted Date: 29 November 2019

Please cite this article as: S. Filippi, M. Cappello, G. Polacco, Limiting oxygen index reduction in bitumen modified with nanoclays, Fire Safety Journal (2019), doi: https://doi.org/10.1016/j.firesaf.2019.102929. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

Authors statement Conceptualization Methodology Software Validation Formal analysis Investigation Resources Data Curation Writing - Original Draft Writing - Review & Editing Visualization Supervision Project administration Funding acquisition

Filippi, Cappello, Polacco Filippi, Cappello Polacco Filippi, Cappello, Polacco Polacco Filippi Cappello Filippi, Cappello Polacco Filippi, Cappello, Polacco Cappello, Filippi Filippi Polacco

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Limiting Oxygen Index reduction in bitumen modified with nanoclays

2

Sara Filippi*, Miriam Cappello, Giovanni Polacco

3 4 5 6 7

Department of Civil and Industrial Engineering, University of Pisa, Largo Lucio Lazzarino 2, 56122 Pisa, Italy. * Corresponding author. E-mail address: [email protected] Abstract

8

Organo-modified nanoclays may improve the fire resistance of polymers and bitumen. However, in

9

some cases the nanoclay determines a reduction in the limiting oxygen index (LOI). In polymers,

10

this effect is attributed to an increase of viscosity that limits the dripping of the molten samples

11

during combustion. However, in the case of bitumen this explanation is not sufficient because the

12

reduction is not always associated to high viscosities. In contrast, the mass losses recorded by

13

thermogravimetry in well-defined temperature regions seems to correlate with LOI. Both viscosity

14

and decomposition kinetic of the binders suggest that the nanoclays establish a high degree of

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interaction with the bitumen, thus determining a significant re-arrangement of its colloidal structure.

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Keywords

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Bitumen; flame retardant; nanoclay; limiting oxygen index; thermogravimetry; aluminium

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hydroxide.

20 21

1 Introduction

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When fire develops in tunnels, the asphaltic pavement may burn and release heat, smoke and toxic

23

gases 1. This led to the need of flame retardants (FR) for bituminous materials and the research

24

started from the products already developed for polymers 2. The first FR were based on halogen-

25

functionalized organic compounds and showed to be very efficient, but they also had disadvantages

26

like a complicate mixing technology, the formation of toxic fire effluents and the pollution of the

27

natural environment. These problems driven the search for “halogen-free” FR, such as metal

28

hydroxides, carbonates, phosphorus compounds, clay nanoparticles, carbon nanotubes, etc. These

29

FR works through several mechanisms, including the formation of a physical barrier that that could

30

either slow or completely eliminate the propagation of flame. For this reason, even conventional

31

fillers may act as FR in asphalt mixtures 3. Due to their low costs, toxicity and corrosivity, inorganic

32

hydroxides represent the most important mineral FR 4. In the case of polymers, aluminium

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hydroxide Al(OH)3, commonly referred to as alumina trihydrate (ATH), is used for processing

34

below 200°C, while magnesium hydroxide Mg(OH)2 (MH) is preferred at higher temperatures.

35

Both ATH and MH are compatible with processing of bituminous materials and can endure the

1

temperature range required for processing of bituminous materials. Furthermore, they are

2

responsible for an increase of temperature range where untreated binder would undergo thermal

3

decomposition.. Therefore, ATH and MH

4

conventional FR for bituminous binders 13,19–24.

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Layered silicates (LS) represent a possible alternative to metal hydroxides. Again, the interest for

6

these materials was derived from the polymer science. As it is well known, LS have been used to

7

prepare polymeric nanocomposites (PNC) that attracted great interest as alternative to conventional

8

micro-composites

9

polymers needs to be improved by producing the so-called organo-modified layered silicates (OLS).

10

This modification allows the dispersion at a nanoscale level, with benefits in “mechanical

11

properties, heat resistance, gas permeability and biodegradability”

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nanocomposites were very promising; the only industrial application of OLS is for flame-retarded

13

materials.29–33. LS and OLS have been recently studied as additives for bituminous binders and they

14

showed to influence mechanical properties, ageing resistance and, in the case of polymer modified

15

bitumens, also the storage stability 28,34,35. The effect of LS as FR for bituminous binders has been

16

evaluated

17

physical interactions with bitumen and this aspect has not been investigated yet. Therefore, one

18

objective of this study is to provide a first insight in this direction. Four types of layered silicates

19

with different degree of interaction with a base bitumen have been used and evaluated as flame

20

retardant additives, either alone or together with ATH which is supposed to have a synergistic effect

21

31

22

Unfortunately, in the case of bituminous materials, the testing methods to evaluate fire retardancy

23

are not univocally defined. Moreover, the flame response depends on many parameters, for example

24

the binder composition or porosity of the pavement

25

bituminous materials, we refer to the methods already available for polymers. The five main types

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are: 1) ignitability (or UL94); 2) flame spread; 3) limiting oxygen index (LOI); 4) Cone calorimeter

27

and 5) smoke release. Among these tests, ignitability is the simplest and provides a qualitative

28

rating of the flammability. The flame spread test measures the flame growth on the underside of a

29

horizontal test specimen. The LOI is an “ease of extinction” test made in a flowing mixture of

30

oxygen and nitrogen and measures the minimum oxygen concentration to support downward flame

31

propagation. Cone calorimetry is increasingly used, “although it features in few regulatory

32

requirements. The key flammability parameters obtained from cone calorimetry are the time for

33

ignition, and the heat release rate per unit area” 4.

36–42

25–27

5–18

captured the attention as potential alternative to

. Due to the hydrophilic nature of pristine LS, their interactions with

28

. Although OLS

. LS may act as a conventional solid filler, but they also may establish chemical-

. Limestone (CaCO3, referred as C) was used as reference filler.

43

. In the absence of specific standards for

1

Another useful indicator is thermal analysis, such as thermogravimetric analysis (TGA) or

2

differential scanning calorimetry, either under air or nitrogen atmosphere. These analyses are

3

mainly used in the research and development stage and give an idea of both the temperatures at

4

which the materials decompose/ignite and the final char yield.

5

In our study, the bituminous binders were first characterized by X-ray analysis, to quantify the

6

degree of interactions between silicates and bitumen and then LOI and TGA were used to evaluate

7

their flammable properties.

8 9

2 Materials and methods

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2.1 Materials

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All FR were mixed with a 50/70 penetration grade base bitumen, referred as BB and kindly

12

furnished by Eni. The base bitumen was derived from a vacuum refinery process and had

13

Penetration 56 dmm (UNI EN 1426) and softening point 54 °C (UNI EN 1427). Mixes were

14

prepared with three classes of fillers: (i) LS or OLS, (ii) ATH (iii) limestone ).

15

The three OLS were Cloisite 10A, Cloisite 20A and Cloisite 30B, subsequently referred as 10A,

16

20A and 30B respectively. All the clays are from Southern Clay Products (now BYK) and were

17

derived from a sodium montmorillonite (Na+) by treatment with dimethyl-benzyl-hydrogenated

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tallow ammonium chloride (10A), dimethyl-dihydrogenated-tallow ammonium chloride (20A), and

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methyl-tallow-bis-2-hydroxyethyl ammonium chloride (30B). ATH was Martinal OL-111 LE from

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Martinswerk, purity > 99.0%, median particle size d50=1.1 (µm), specific gravity (g/cm3)= 2.42,

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bulk density=200 (kg/m3), specific surface area (BET)= 11 (m2/g) and Rigden voids = 62 (%). As a

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reference, the native sodium montmorillonite (referred as Na+) was used. A limestone, having the

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following properties: d50=3.2 (µm), specific gravity (g/cm3)=2.71, bulk density=600 (kg/m3) and

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Rigden voids = 39 (%) was used as reference.

25 26

2.2 Methods

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Bitumen was modified at 140 °C following the same modification protocol as described in a

28

previous work 1. The mixing time was 30 min with a high shear mixer (Silverson L4R) set at 4000

29

rpm. In a few cases, due to the high viscosity of the binder, a mixing temperature of 160 °C was

30

necessary.

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Wide angle X-ray diffraction (WAXD) was performed in reflection mode by a Siemens D500

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Krystalloflex 810 apparatus, with a wavelength of 0.1542 nm at a scan rate of 2.0 °/min. The clay

33

was analysed as a powder, while the mastics as disks of 1 mm thickness and 10 mm diameter

34

obtained by pouring the samples directly from the cans into cylindrical moulds externally shaped to

1

fit the instrument sample holder. A Brookfield DV-II+ was used for viscosity measurements and a

2

Q500 analyser by TA was used for thermo-Gravimetric Analysis (TGA). For the latter, two high-

3

resolution methods suggested by Masson and Bundalo-Perc were used 44. In the first one, defined as

4

“dynamic rate”, the heating rate was high when small variations in the sample mass were detected

5

and very small when the sample underwent consistent mass loss. In the second one, the sample was

6

subjected to a “constant decomposition rate”. In both cases, the heating rates were tuned through the

7

definition of the maximum heating rate (dT/dt max), a “resolution factor” (R) and a “sensitivity

8

setting” (S) parameter. After a set of preliminary tests, the parameters described in Table 1 were

9

chosen (all scans performed from 50 to 800 °C). Both reproducibility and resolution were improved

10

while always using the same amount of bitumen (about 5 mg). Moreover, before loading into the

11

instrument chamber, the sample was uniformly distributed over the surface of the sample holder

12

through a gentle preheat.

13

The LOI test was performed by LOI-Smoke-230, from Dynisco & Alpha Technologies, USA. This

14

test “determines the minimal oxygen concentration in an oxygen/nitrogen mixture, which allows the

15

sample to burn in a stable way” 1. Unfortunately, the test requires self-sustaining samples, but

16

bituminous binders tend to drip during combustion. The addition of aggregates or mineral powder

17

may reduce the problem 13. Otherwise, the binder can be supported with a porous inert material like

18

e.g. a glass fibres

19

binder as accurately described in Bonati et al. 1. As suggested in ASTM D-2863-10, the LOI was

20

assumed as “the minimum oxygen concentration that allowed a period of burning after ignition

21

equal to 180 s, or an extent of burning equal to 50 mm”.

39

or a synthetic pumice stone 1. Pumice specimens were dipped in preheated

22 23

3 Results and discussion

24

The three OLS were chosen out of a longer list of commercially available silicates, with the criteria

25

of having different degree of interactions with the base bitumen, being the selection mainly based

26

on the XRD analysis. As it is well known, nanocomposites are classified in two main categories: 1)

27

intercalated, where the LS structure still occurs in a crystallographically regular fashion, 2)

28

exfoliated, with LS dispersed as individual layers in the polymeric or bituminous matrix

29

first one, some of the polymer/bitumen molecules diffuse between the lamellae, without changing

30

the original structure of the clay that is dispersed as micron-sized particles. Nevertheless,

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interactions with the dispersing matrix occur at a nanoscale level and the material is a

32

nanocomposite. Of course, the formation of intermediate structures with both intercalation and

33

partial exfoliation is possible, but unfortunately not easily detectable by XRD45. In Figure 1, the

34

XRD patterns of BB, 10A, 20A, 30B and the three corresponding binary BB/OLS blends containing

25

. In the

1

4% by weight of silicate are reported. The XRD pattern of the mix with Na+ is not reported since

2

the clay is not visible, due to its poor dispersion. BB shows the typical halo of amorphous materials,

3

but has a signal in the range 2ϑ=7-11 °. This is quite unusual for bituminous materials and may be

4

due to some asphaltenic aggregate. With regard to the three OLS, their main peak allowed to

5

calculate the interlayer spacing d001 reported in Figure 1, both before and after mixing with the

6

bitumen. In Figure 1 and in what follows, the mixes are indicated as “BB/filler type-filler quantity”.

7

As an example: BB/10A-4 contains 4% by weight of Cloisite 10A. It must be underlined that the

8

interlayer distances remain the same irrespective of the clay load. In other words, it depends only on

9

the BB/OLS couple and does not change with the quantity of organo-silicate. In the case of 10A and

10

20A, the increase of interlayer spacing is due to intercalation, but maybe there is also a little bit of

11

exfoliation. The increase of the inter-lamellae distance is considerably higher for 10A (2.5 nm) than

12

20A (1.8 nm) thus suggesting a higher degree of interactions between BB and 10A. The spectrum of

13

the BB/30B mix indicates exfoliation, but the very small shoulder at 2ϑ=2.0 ° may be due to a

14

residual quantity of intercalated lamellae. XRD spectra can be interpreted in terms of compatibility

15

because a high compatibility drives the bitumen molecules into the galleries and allows the

16

substitution of intra-silicate interactions with silicate/bitumen bonds. If a sufficient number of these

17

substitutions is established, the silicate layers can be separated one from each other. Bitumen is a

18

complex mixture of molecules, with different chemical composition, often divided in four groups of

19

increasing polarity: saturates, naphthene aromatics, polar aromatics, and asphaltenes

20

fractions will interact differently with the clay, depending on their chemical and steric

21

characteristics and thus the OLS will selectively “distillate” the more affine molecules among those

22

available in the bitumen matrix. Unfortunately, it is not easy to evaluate how the four fractions

23

change after modification with the clay and it is necessary to proceed through indirect evidences.

24

Since the above-mentioned “distillation” influences the colloidal structure of the bitumen and thus

25

its rheological properties, viscosity is a useful parameter to evaluate the interactions between binder

26

and filler. Starting from the binary mixes, with respect to BB, the addition of calcium carbonate or

27

Na+ determines a moderate increase in viscosity (Table 2). This is not surprising, since these fillers

28

have micron-sized dimensions and scarce interaction with bitumen. Unexpectedly, also 30B has a

29

limited effect on viscosity, even if exfoliated and thus dispersed at a nanoscale level. In contrast,

30

significant increase of viscosity is observed after addition of 10A and 20A that are intercalated (this

31

is why 4% was the maximum possible loading of 10A). This inconsistency between filler loading

32

and viscosity confirms that the silicates interact in a different way with the bitumen. Probably, 10A

33

creates bonds with a higher number of low molecular weight molecules, thus reducing the mobility

34

of the dispersed phase. Otherwise, the high viscosity could be related to the rearrangement of the

46

. The four

1

asphaltenic clusters, due to a variation in the resin composition. Finally, ATH, even if added in

2

much higher quantity, has a moderate impact on viscosity, thus suggesting a low interaction with

3

bitumen.

4

Before commenting the LOI data, it is useful to remind the fire resistance mechanisms involved in

5

polymeric layered silicate nanocomposites (PLSN). The fire resistant character of PLSN has been

6

demonstrated through cone calorimetry and is mainly due to the formation of a residual layered

7

“carbonaceous–silicate structure on the surface that creates a physical barrier to heat, oxygen, and

8

volatiles”

9

ignition may indicate an opposite effect due to the presence of clay. Analogously, a reduction in

10

LOI has been observed for some PLNS 31. A possible explanation is that the organic part of the clay

11

starts decomposing before the polymer, so that combustible volatiles are available at lower

12

temperatures and favour ignition. Therefore, the flame retardant effect of LS sometimes “vanishes

13

when the fire scenario is changed from a developing fire (cone calorimeter) to an ignition scenario”

14

31

15

viscosity and thus dripping tendency become the governing factors” 31. The polymer drippings, in a

16

vertical sample burning from the top, correspond to fuel removal from the fire source. In absence of

17

dripping, the material does not escape from the pyrolysis zone and sustains the flame 47 and because

18

nanocomposites always have high viscosity, they also have a reduced dripping

19

suggested explanation for those cases where LS determine a reduction in the LOI of a polymer.

20

Since all tested OLS reduce the LOI values of our modified binders (Table 2), it is reasonable to

21

check if the same mechanism will apply to bitumen. The base bitumen BB has a low viscosity and

22

LOI value of 28 that becomes 29 if subjected to the same thermal and mechanical stress

23

corresponding to the preparation of the blends (BB processed in Table 2). Similar viscosities and

24

LOI are found with C and Na+ as fillers. Contrary, all OLS increased viscosity and reduced LOI.

25

This is consistent with the hypothesis of dripping governing the LOI test. However, Figure 2 is built

26

from Table2 and clearly shows that LOI does not univocally correlate with viscosity. All mixes with

27

high viscosity have low LOI, but there are also a few mixes with low viscosity and low LOI.

28

Therefore, the absence of dripping cannot explain all the observed decrease in LOI.

29

Analogously, the filler loading, and the intercalated or exfoliated structure of the nanocomposite

30

does not univocally correlate with LOI, however, the TGA analysis helps finding a parameter linked

31

to LOI. Based on their shape, the TGA spectra are divided in four regions, as shown in Figure 3.

32

The four temperature intervals (°C) are: T<350, 350500. “The mass

33

loss in the first region is due to the distillation of low molecular weight components. Then, the other

34

three are attributed to thermal cracking and loss of volatile fragments” 44. For a better comparison of

31

. However, it is important to emphasize that other parameters, like e.g. the time of

. Another explanation is that “in LOI the superficial barrier plays a minor role, while melt

31,48

. This is the

1

the different materials, the first derivative of the mass loss as a function of temperature is shown in

2

Figure 4. For the sake of clarity, the Figure contains only the binary mixes at a single filler loading.

3

The mass losses corresponding to all samples can be found in Table 2.

4

Since it is due to evaporation of the lighter components and oxidation reactions have not occurred

5

yet, region 1 is probably correlated with ignition in the LOI test. This mass loss corresponds to

6

availability of combustible molecules in the gas/vapor phase. It is interesting to observe that the

7

presence of the fillers significantly change the aspect of this peak. The three fillers that do not

8

influence the LOI (Na+, C and 30B-4) show a single sharp peak centred around 290 °C. In contrast,

9

the two blends with lower LOI (10A and 20A) have a smaller peak, shifted to higher temperatures.

10

Therefore, the two clays that determine a reduction in LOI have the smaller (and at higher

11

temperature) release of volatiles. This is not contradictory, because the availability of volatile

12

molecules may favour the lighting, but does not guarantee the full combustion of the sample.

13

The second temperature region is characterized by the presence of more than one peak. In the third

14

region, there is a single signal, whose shape depends on the blend and again clays 10A and 20A

15

determine the higher mass loss. Finally, in the fourth region all samples show a wide peak that is

16

smaller and occurs at higher temperatures for clays 10A and 20A. The TGA spectra of ternary

17

mixes are not reported here, however, they were qualitatively similar to those without ATH. As a

18

general comment, the presence of ATH reduces a little bit the dissimilarities between the different

19

compositions.

20

It is now interesting to plot the LOI as a function of the mass losses in the four regions (Figure 5).

21

The only region where the experimental data are randomly dispersed and mass losses do not

22

correlate with LOI, is the second one. However, region 2 is the one were the decomposition

23

reactions start and is also the less reliable one with respect to reproducibility 44.

24

In contrast, in the other regions a trend appears, suggesting that the lower is the LOI:

25

•

the lower the mass loss in the first and fourth regions

26

•

the higher the mass loss in the third region

27

As already underlined, in the LOI test a flame is directly applied to the sample until ignition occurs

28

and then the test evaluates flame propagation. This procedure bypasses a possible scarce availability

29

of combustible compounds on the sample surface during ignition. After ignition, that mainly

30

involves the lighter bitumen fractions (regions 1 and 2 in TGA), the combustion may stop or

31

proceed depending on the behaviour of the remaining fractions (regions 3 and 4). The

32

decompositions occurring in regions 3 and 4 involve the fractions that are less prone to burning and

33

thus the part of bitumen responsible for flame extinction in LOI experiments with too low oxygen

34

concentration. The TGA data suggest that in samples with low LOI, the viscosity and/or the

1

interactions with the filler, limit the evaporation of the lighter fractions (low mass loss in region 1).

2

Then, these molecules decompose at higher temperatures (high mass loss in region 3) and grant

3

enough combustible to keep the flame alive. Of course, if a high percentage of the material

4

decomposes in region 3, then a lower one remains for region 4.

5 6

4 Conclusions

7

The nano-modification of bitumen with layered silicates has a strong impact on the bitumen

8

properties, included flame resistance. The literature almost unanimously confirms that layered

9

silicates improve the fire resistance of bituminous binders. Nevertheless, the addition of three

10

different organo-modified silicates to a base bitumen led to a reduction in the LOI of the binder.

11

This effect has not been observed with other inorganic fillers tested on the same base bitumen.

12

These include conventional limestone as well as a common flame retardant (ATH) and the native

13

clay from which the organo-modified ones have been produced. A similar effect on LOI has been

14

previously described for some polymeric nanocomposite. The increase in viscosity associated to

15

clay addition is as possible explanation, because it limits the dripping of the sample during

16

combustion. However, some of the bituminous binders showed very low LOI values while having

17

viscosities comparable with that of the base bitumen. Therefore, some other mechanism must be

18

involved in the case of binders modified with OLS. The key factor, probably is the bitumen/clay

19

interface where the interactions are limited to those bitumen molecules that have a favourable steric

20

hindrance and polarity, likely included in the resin fraction. This drives to a variation in the

21

composition of the “liquid” matrix that regulates the colloidal structure of the bitumen and thus in

22

consistent variation in its viscosity and properties. This hypothesis is corroborated by the TGA

23

spectra that are highly altered with respect to base bitumen even in the presence of small clay

24

quantities. Moreover, it is interesting to observe that the weight losses in different temperature

25

regions correlate quite well with the LOI behaviour, being this correlation observable irrespective of

26

the filler. A similar correlation was not found for other parameters like viscosity, filler loading, or

27

onset of the thermal events recorded with TGA.

28

Finally, it is worth adding a couple of observations. First, a low LOI does not necessarily mean a

29

poor flame resistance. The same materials may show improvement in other aspects related to flame

30

resistance, like i.e. flame propagation rate or smoke release. Second, the operating conditions

31

adopted during the binder modification may affect its final rheological properties and thus some of

32

the above described findings. Nevertheless, the use of low mixing temperature and time should have

33

minimized this problem.

34

1

5 Aknowledgements

2

The authors gratefully acknowledge Filippo Bartoli for performing the LOI test.

3 4

6 Figure legends

5

Figure 1 - XRD spectra of bitumen, OLS and BB/OLS mixes.

6

Figure 2 - LOI as a function of viscosity.

7

Figure 3 – Weight percentage spectra and its first derivative with respect to temperature for BB.

8

Figure 4 – First derivative of the weight percentage with respect to temperature for mixes with 4%

9

of filler loading.

10 11

Figure 5 - Mass losses in the four temperature regions.

12

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1

Table 1 - Parameters adopted in the TGA analysis Temperature Range (°C) 50-310 310-440 440-800

method Constant decomposition rate Constant decomposition rate Dynamic rate

dT/dt max (°C/min) 5

R

S

-4

1

5

-2

3

50

3

1

2 3

4 5 6

Table 2 – LOI, viscosity and TGA. Viscositya Region 1 Blend LOI (mPa · s) (w loss %)b 28 450 15 BB 29 450 18 BB (processed) 24 1471 12 BB/10A-2 24 18000 8 BB/10A-4 28 508 16 BB/20A-1 26 608 14 BB/20A-2 25 2304 12 BB/20A-4 23 2813 10 BB/20A-6 22 17000 10 BB/20A-8 21 20000 11 BB/20A-10 28 471 14 BB/30B-2 29 542 14 BB/30B-4 24 850 14 BB/30B-8 + 29 475 18 BB/Na -4 27 504 11 BB/Na+-8 30 463 16 BB/C-4 30 479 15 BB/C-8 33 646 14 BB/ATH-20 25 1533 12.61 BB/10A-2/ATH-20 25 1675 12.44 BB/20A-4/ATH-20 31 838 13 BB/30B-4/ATH-20 31 696 12 BB/Na+-4/ATH-20 32 683 13 BB/C-4/ATH-20 a – Brookfield viscosity at 135 °C. b – Values normalized with respect to bitumen content.

Region 2 (w loss %)b 22 17 24 14 20 19 23 16 14 23 24 23 21 14 20 17 22 29 20 22 22 19 20

Region 3 (w loss %)b 18 16 25 45 21 26 29 39 43 32 19 16 21 17 25 17 14 22 21 20 17 20 17

Region 4 (w loss %)b 44 47 36 26 41 39 33 31 28 27 42 42 38 45 37 44 40 43 33 32 33 33 36

Conflict of Interest and Authorship Conformation Form Paper: “Limiting Oxygen Index reduction in bitumen modified with nanoclays” Authors: Sara Filippi, Miriam Cappello, Giovanni Polacco Submitted to Construction and Building Materials o

All authors have participated in (a) conception and design, or analysis and interpretation of the data; (b) drafting the article or revising it critically for important intellectual content; and (c) approval of the final version.

o

This manuscript has not been submitted to, nor is under review at, another journal or other publishing venue.

o

The authors have no affiliation with any organization with a direct or indirect financial interest in the subject matter discussed in the manuscript

Author’s name Giovanni Polacco Sara Filippi Miriam Cappello

Affiliation University of Pisa University of Pisa University of Pisa