Performance Evaluation of Hot Mix Plant Recycled

Asphalt Mixtures

Francisco Tavares Aranda de Magalhães Bento

Extended Abstract

Dissertation for obtaining the Master´s Degree in

Civil Engineering

November 2010

1

11 IINNTTRROODDUUCCTT IIOONN

The increase in the incorporat ion of rec la imed asphal t m ixtures in the manufacture

of hot mix asphal t is the main objec t ive in the present disser tat ion and correspond-

ing s tudy. Among the pavement recyc l ing techniques current ly avai lable, the me-

thod of hot mix p lant asphalt recyc l ing with 70% of recla imed asphalt was devel-

oped. Although th is is an economical ly and environmental ly at tract ive technique,

there is st i l l not enough knowledge regarding the performance of these mixtures in-

serv ice, a fac t that has been l im i t ing i ts more widespread use. In th is context , a

prac t ica l case study was developed at the Laboratór io Nac ional de Engenhar ia Civ i l

(LNEC).

In th is way, as s tated previous ly, the present disser tat ion in tends to study the per-

formance of recyc led mixtures with a h igh percentage of rec la imed asphal t m ixtures

incorporat ion, tak ing into account the character is t ics of the mater ials used to pro-

duce the mixture, according to the mix des ign procedure used.

From th is study resul ted three exper imenta l phases developed in laboratory, the

f irs t two being related to the des ign procedure of the recyc led mixture i tse lf and the

th ird one being re lated to i ts character iza t ion and performance evaluat ion. This

th ird phase involved a number of tes ts to analyze water res istance and permanent

deformation res istance.

22 RREECCYYCCLLEEDD MM IIXXTTUURREE DDEESS IIGGNN

In the exper imental s tudies i t was general ly adopted a recyc led mixture des ign me-

thodology wi th a struc ture ident ica l to the one used in the general methodology for

the design procedure of hot mix asphal ts mixtures, adapted according to the avai l-

able laboratory condi t ions and the composi t ion pecul iar i t ies of the rec la imed as-

phalt m ixtures (A. Bat is ta, 2006).

In th is way, i t fo l lows a br ief descr ipt ion of the main s teps that const i tute the mix

des ign procedure used:

In the f irs t p lace the new aggregates and machined mater ia ls are character ized.

The character izat ion of these new aggregates is made through grading analys is and

determinat ion of the phys ical character is t ics that should respect the l im its issued in

the appl icable road works spec if icat ions. The character izat ion of the machined ma-

ter ia l is made through i ts grading analys is as wel l as that of the aggregate of the

machined, af ter the extract ion of the b inder . Bes ides that, th is evaluat ion a lso

2

takes into account the knowledge of the b itumen percentage and the respect ive de-

terminat ion of the needle penetrat ion at 25ºC and the sof tening point ( temperature)

set by the r ing and bal l method.

Af ter the character izat ion of the mater ia ls , i t is then made the study of the mix

compos it ion by the usual way, in which the aggregate of machined mater ia l as-

sumes i ts ro le as another aggregate present in the recyc led mixture, th is t ime with

a recycl ing or incorporat ion rate of 70%, which wi l l have to comply wi th the grading

l im its set in the spec i f icat ions for road works of the Portuguese Road Administ ra-

t ion (CEEP) for the corresponding hot mixture.

Next, an est imate is made of the tota l b i tumen percentage in the recyc led mixture,

pbR , tak ing in to account the results f rom previous studies and cr i ter ia issued in

normat ive nat ional documents . Express ion 1 a l lows to est imate the percentage of

b itumen according to the spec if ic surface of the aggregate mixture.

�� � � � � � √� (1)

in which,

pb – percentage of res idual b itumen;

K – module of b itumen r ichness. For the type of mixtures, K var ies between

2,5 and 3,5;

F – constant equal to 2,65/ρa, in which ρa is the dens ity of the aggregate

m ixture g iven in g/cm3;

Se – specif ic surface est imated by the fol lowing express ion:

� � 0,25 �� � 2,3 �� � 12 �� � 135 ���� (2)

where,

S1 – weight propor t ion of e lements wi th d imens ion greater than 6,3mm;

S2 – weight propor t ion of e lements wi th d imens ion comprised between

0,315mm and 6,3mm;

S3 – weight propor t ion of e lements wi th d imens ion comprised between

0,075mm and 0,315mm;

p2 0 0 – weight propor t ion of elements wi th d imens ion under 0,075mm.

Once the es t imate for the tota l b i tumen percentage in the recyc led mixture is f ixed,

the percentage of new bi tumen to be added to the mixture is determined by expres-

s ion 3.

3

pb� � pb� � pb� � TR (3)

where,

pbN – percentage of new bi tumen in the recycled mixture (%);

pbR – percentage of b i tumen ( f inal binder) in the recycled asphalt m ixture

(%);

pbF – percentage of bi tumen (aged b inder) in the machined mater ia l (%);

TR – recyc l ing rate.

The b i tumen type select ion is made by tak ing in to account the establ ished l im its for

the penetrat ion at 25º C and sof tening point ( temperature) in new bitumens (Char t 1

of Spec if icat ion LNEC E80 – 1997) and resort ing to the express ions f rom Annex 1

of Spec if icat ion E472 – 2006 (4 and 5) or Annex A f rom European Norm EN 13108 –

1:2006 (1) (6 and 7) which establ ishes the re lat ionships between penetrat ion and

sof tening point ( r ing and bal l method) of the b itumen in the recyc led mixture and

the corresponding character is t ics of the aged b itumen and of the new bi tumen.

log"PEN&'�( � )*+�,-.")/�*+(0 )*1�,-.")/�*1(��� (4)

log2T&'�34 5 � )*+�,-.67*+

89 :0 )*1�,-. "7*189 (

��� (5)

in which,

PEN&'� – penetrat ion, in 10- 1

mm, of the b itumen in the recyc led mixture;

PEN&� – penetrat ion, in 10- 1

mm, of the aged b itumen;

PEN&; – penetrat ion, in 10- 1

mm, of the new bitumen;

T&'�34 – sof tening point ( r ing and bal l method), in ºC, of the b itumen in

the recycled mixture;

T&�34 – sof tening point ( r ing and bal l method), in ºC, of the aged b itu-

men;

T&;34 – sof tening point ( r ing and bal l method), in ºC, of the new bi tumen;

P&�– weight percentage of the aged b itumen in the b itumen of the recyc led

m ixture;

P&;– weight percentage of the new bitumen in the b itumen of the recyc led

m ixture;

4

log"pen�( � TRb � log"pen�( � "1 � TRb( � log "pen�( (6)

Tab� � TRb � Tab� � "1 � TRb( � Tab� (7)

where,

penR – penetrat ion of the f inal binder (10- 1

mm);

TRb – recyc l ing rate of the b itumen;

penF – penetrat ion of the old b inder in the machined mater ia l (10- 1

mm);

penN – penetrat ion of the added b i tumen (10- 1

mm);

TabR – sof tening point of the f ina l b inder ( ºC);

TabF – sof tening point of the o ld b inder in the machined mater ia l

( ºC);

TabN – sof tening point of the new bi tumen ( ºC);

(1) I t should be noted that the express ions p resented are s imi lar to those issued in Euro -

pean Norm EN13108-1:2006, but us ing the symbology o f th is s tudy.

Therefore, regarding the selec t ion of the new bitumen type, i t was chosen to select

two types of bitumen , the B70/100 and the B50/70 , creat ing two mix des igns wi th

the same grading composit ion and d if ferent b itumens. The opt ion for b itumen

B70/100 is jus t i f ied by the calculat ions made according to the express ions pre-

sented ear l ier and the opt ion for b i tumen B50/70 took in to account the fact that i t is

a more common bi tumen regarding Por tuguese weather condi t ions ( temperature) .

Af ter the selec t ion of the new bi tumen, the f ina l bi tumen percentage was def ined by

us ing the Marshal l method according to European Norm EN 12697-34+A1:2007. I t is

impor tant to point out that by carrying out two Marshal l s tudies and in case that

both studies show reasonable resul ts tak ing in to account the parameters and l im its

def ined for th is type of methodology, i t is in tended to evaluate the performance of

the asphalt m ixture that conta ins the more usual b i tumen (B50/70). Therefore, i t is

only made the performance evaluat ion of the asphalt m ixture that inc ludes b itumen

70/100, i f the mixture contain ing more ord inary b itumen reveals i tse lf to have a

negat ive performance evaluat ion.

Fol lowing the usual procedure, af ter determinat ion of bulk dens i ty of the b ituminous

spec imens, complying with European Norm EN 12697-6+A1:2007 (Method B: Satu-

rated surface dry) , two compress ib i l i t y tests according to Marshal l method were

carr ied out, a l lowing the determinat ion of the cor responding break ing s trengths and

f lows. Af terwards, wi th the use of a vacuum picnometer i t was determined the theo-

5

ret ica l maximum dens ity of the mixture, according to European Norm EN 12697-

5+A1:2007 (Procedure A: Volumetr ic procedure)

Final ly, the analys is of the results f rom the tes ts produced the values conta ined in

tables 1 and 2, which a l low the drawing of curves that represent the var iat ion of the

character is t ics of mixtures wi th the b itumen percentage.

Table 1 – Results f rom the Marshal l tes t (B50/70) - LNEC.

pbR

(%) pbN (%)

Bm (g/cm

3)

Bt (g/cm

3)

n (%)

TVB (%)

VMA (%)

Sb (%)

Frot (N)

Def.

(mm)

3,5 0,6 2,284 2,487 8,1 7,8 15,9 49,1 25500 2,80

4,0 1,1 2,369 2,471 4,1 9,2 13,3 69,2 32200 2,82

4,5 1,6 2,395 2,466 2,9 10,5 13,4 78,4 25400 2,84

5,0 2,1 2,351 2,421 2,9 11,4 14,3 79,7 20400 3,62

5,5 2,6 2,317 2,413 4,0 12,4 16,4 75,6 16600 4,45

Table 2 – Results f rom the Marshal l tes t (B70/100) - LNEC.

pbR

(%) pbN (%)

Bm (g/cm

3)

Bt (g/cm

3)

n (%)

TVB (%)

VMA (%)

Sb (%)

Frot (N)

Def.

(mm)

3,5 0,6 2,352 2,499 5,9 8,0 13,9 57,6 24500 2,87

4,0 1,1 2,364 2,492 5,1 9,2 14,3 64,3 25800 3,20

4,5 1,6 2,390 2,486 3,9 10,5 14,4 72,9 28100 4,12

5,0 2,1 2,417 2,477 2,4 11,8 14,2 83,1 17800 2,65

5,5 2,6 2,397 2,471 3,0 12,8 15,8 81,0 18000 2,71

pbR (Percentage of b i tumen ( tota l b inder)o f the recyc led mix ture)

pbN (Percentage of new bitumen in the recycled mix ture)

Bm (Densi ty o f the mix ture)

Bt (Maximum theoret ica l densi ty )

n (void conten t )

TVB (Bi tumen volumetric content or b i tumen volumetr ic percentage)

VMA (Voids in Minera l Aggrega te)

Sb (Bitumen sa turat ion rate )

Fro t (Break ing st renght )

Def (Flow)

6

Figure 1 – Curves for the determinat ion of opt imum bitumen percentage, obtained

by Marshal l method in two mixtures wi th the same grading compos i t ion and d if fer-

ent b itumens (B50/70 and B70/100) - LNEC.

Through the analys is of the curves shown in Figure 1 i t is poss ib le to determine the

b itumen percentages per tain ing to the maximum break ing s trength, maximum densi-

ty and medium void content (5%) and respect ive medium values, according with

Table 3. Once the opt imum percentage of new bi tumen is determined, us ing F igures

1 and 2, the corresponding values for break ing s trength, vo id content, VMA and

f low, as shown in Table 4, can be obta ined in order to ver i f y the condit ions issued

in the spec if icat ions for road works of the Portuguese Road Adminis trat ion (CEEP)

per tain ing to b i tuminous macadam type A.

7

Figure 2 – Curves for determin ing f low and VMA, obta ined by Marshal l method in

two mixtures wi th the same grading compos i t ion and d if ferent b itumens (B50/70 and

B70/100) - LNEC.

Table 3 – Bitumen percentages (%) concerning maximum break ing strength, maxi-

mum dens ity, medium void content (5%) and respect ive opt imal percentage, ob-

ta ined by Marshal l method - LNEC.

Determined bitumen percentage B50/70 B70/100

Maximum breaking strength 4,0 4,4

Maximum density 4,4 5,0

Void content of 5,0 (CEEP limits of 4% and 6%) 3,8 4,1

Medium value (optimum bitumen percentage) 4,1 4,5

Table 4 – Summary of mixtures character is t ics re lat ive to opt imum bitumen

percentage - LNEC.

Determined bitumen percentage Limits B50/70 B70/100

Breaking strength (N) 8000 a 15000 31800 28100

Maximum flow (mm) 4 mm 2,80 4,12

Minimal VMA (%) 13% 13,1 14,4

Void content (%) 4% a 6% 3,6 3,9

Optimum percentage of new bitumen (%) 1,2 1,6

Optimum percentage of total bitumen (%) 4,1 4,5

Weight proportion filler/bitumen 1,1 a 1,5 1,71 1,56

8

The analys is of table 4 a l lows us to conc lude that resul ts are sat is factory tak ing in-

to account that we are deal ing with an asphal t m ixture that incorporates 70% of

rec la imed asphal t . Nevertheless, some of the indicated parameters do not comply

wi th the l im its def ined by the spec if icat ions for road works of the Portuguese Road

Administrat ion (CEEP), e.g. the weight proport ion f i l ler /b i tumen, which in case of

the f irs t m ixture (B50/70) exceeds the maximum l im it imposed by the CEEP.

Therefore, a br ief comment is shown regarding the parameters and obta ined values

that do not comply wi th the l im its imposed by CEEP concerning b ituminous maca-

dam type A:

The values of the break ing s trength of both mixtures are much h igher than the l im-

its imposed by the CEEP, which can be just i f ied by the fac t that th is is an asphal t

m ixture that incorporates a h igh propor t ion of recyc led aggregates (70%). I t should

be noted that the values est imated for penetrat ion at 25ºC and sof tening point

( temperature) of the b itumen in the f ina l mixture are typ ical of a B20/30 b i tumen.

Final ly, i t should a lso be noted that in h igh-modulus mixtures CEEP only def ines a

minimum l im it of 16000N for break ing s trength;

Regarding the f irs t m ixture (B50/70) , the void content shows a value of 3,6%, that

is 0,4% below the min imum l im it , as wel l as a weight proport ion f i l ler /bi tumen with

a value of 1,71, that is 0,21 above the maximum l im it imposed by the CEEP.

Regarding the second mixture (B70/100), the maximum f low shows a value that ex-

ceeds the l im it imposed by the CEEP in just 0,12mm (3%), whi le the void content ,

l ike in the f irs t m ixture, presents a value below the min imum l im it , even i f just

0,1%. F inal ly, the weight proport ion f i l ler /b i tumen obta ined shows a value of 1,56,

that is , jus t 0,06 above the l im it imposed by the CEEP.

As far as the curves shown in F igure 2, i t is impor tant to note that the f low curve

for the second mixture (B70/100) , obta ined through Marshal l methodology, presents

a behaviour unl ike what is usual ly expected.

Tak ing into account the above-ment ioned results , as wel l as earlier mix design

studies , i t was dec ided to def ine the same bitumen percentage (4,5%) for both mix-

tures. In th is way, Table 5 shows a summary of the resul ts obta ined in the curves

that were determined by Marshal l methodology accord ing to the def ined b itumen

percentage.

9

Table 5 – Summary of the character is t ics of the mixtures re lat ive to the def ined b i-

tumen percentage (4,5%).

Defined bitumen percentage Limits B50/70 B70/100

Breaking strength (N) 8000 a 15000 25400 28100

Maximum flow (mm) 4 mm 2,84 4,12

Minimal VMA (%) 13% 13,4 14,4

Void content (%) 4% a 6% 2,9 3,9

Optimum percentage of new bitumen (%) 1,6 1,6

Optimum percentage of total bitumen (%) 4,5 4,5

Weight proportion filler/bitumen 1,1 a 1,5 1,56 1,56

Therefore, by modif ying only the results re lat ive to the f irs t m ixture, according to

Table 5 above i t is possible to obta in:

A weight propor t ion f i l ler / b i tumen of 1,56 that is c loser to the max imum l im it im-

posed by CEEP, a VMA value that deviates fur ther f rom the min imum l im it imposed

by the CEEP, changing f rom 13,1% to 13,4% and, conversely, a void content that

decreases f rom 3,6% to 2,9%, d istanc ing i tse lf f rom the min imum l im it imposed by

the CEEP.

Fol lowing what is previous ly stated, i t should be noted that, in h igh-modulus mix-

tures, CEEP def ines a min imum l im it of 2% for void content s ince, due to the h igh

v iscosi ty of b i tumen, i t is not expected that the mixture wi l l come to present any

stabi l i t y problems. Anyway, permanent deformation res is tance of the mixture shal l

be evaluated and addressed in the thi rd phase of the exper imenta l studies, us ing

the wheel- track ing tes t.

Star t ing f rom the establ ished mix composi t ion (70% of recyc led aggregate and 30%

of 15/25 gravel) , having selected the two types of b i tumen (B50/70 and B70/100)

and once def ined the b itumen percentage of both mixtures (4,5%), the mix des ign

process is conc luded and the las t phase of the exper imenta l s tudies is reached,

which wi l l address the performance evaluat ion of the recycled mix ture.

33 PPEERRFFOORRMMAANNCCEE EEVVAALLUUAATT IIOONN

The performance evaluat ion of the recyc led asphalt m ixture cons ists in evaluat ing

water resis tance through a water sensi t iv i ty test fol lowed by an evaluat ion of the

permanent deformat ions res istance us ing wheel- t rack ing tests . I t should be noted

that both tests are performed in compl iance wi th European Norms EN 12697-

12:2008 and EN 12697-22:2003+A1:2007, respect ive ly.

10

The evaluat ion of water res is tance is based in a comparison of the resul ts of me-

chanical res istance tests performed in two sets of spec imens which are subjec ted

to d iss imi lar condit ions. One is subjected to more favourable condi t ions while the

other is subjected to more severe condit ions, concerning the behaviour of water.

The tes ts to evaluate the res is tance to water were carr ied out in the LNEC labora-

tory according to the above-ment ioned European Norm and Method A, which is

based on the indirec t tens i le st rength of cyl indr ica l spec imens, as stated in Euro-

pean Norm EN 12697-23:2003.

In this way, i t is in tend to ascerta in the ef fect of saturat ion and accelerated condi-

t ion ing in water regarding indirec t tens i le st rength of the cyl indr ica l specimens. Of

the two Marshal l spec imens groups, wi th ident ica l densi t ies and heights , the f irs t

group s tays three days exposed to the a ir a t a 20ºC temperature, whi le the second

is in i t ia l l y kept in vacuum for 30 minutes at 6,7 KPa, immersed in water at 20ºC ( to

insure that water penetrates in the pores) and af terwards is immersed in water at

40º C dur ing 68 to 72 hours .

Af ter determin ing the Indirec t Tens i le Strength ( ITS) of the immersed spec imens

( ITSW ) and in “dry” condi t ions ( ITSd ) , a value for the ITSR is reached through the

express ion (8).

ITSR � A7BCA7BD

� 100 "%( (8)

The results obtained in the tes ts performed in the two groups of spec imens show

ident ica l va lues of Indirec t Tens i le Strength reaching ITSR=100% . In th is way, i t

can be conc luded that the water sens i t ivi t y test fu l f i ls the min imum l im it issued for

the str ingest category of the Indirect Tensi le Strength Rat io ITSR90 (Min imum

Indirec t Tens i le Strength Rat io = 90%), according to what is stated in European

Norm EN 13108-1:2006.

Among the traf f ic s imulat ion tests , an opt ion was made in this study for the wheel

t rack ing tes ts, in which a number of comparat ive studies are performed, regarding

the behaviour of pavements when subjec ted to repeated passes of a wheel ax le in

control led test condit ions. There are a number of var iants of th is type of tes t where

cons iderat ion is g iven to dif ferent dimensions of the spec imen, type of wheel ax le,

loading f requency, appl ied pressure, temperature, to name but a few. But a l l these

var iants share the same operat ing pr inc ip le (F. A. Bat is ta, 2004).

The tests for evaluat ion of permanent deformation res istance (wheel t rack ing) were

carr ied out in the LNEC laboratory, fu l f i l l ing the above mentioned European Norm.

11

For that purpose, two pr ismat ic spec imens were moulded in laboratory us ing a

small s ize device, using a v ibrat ing compact ion apparatus, in which star t ing f rom

the desired dens i ty, obta ined f rom the Marshal l s tudy, i t is guaranteed the compac-

t ion of the spec imen with the es tabl ished d imensions (Procedure b – condi t ion ing in

a ir ) , according to European Norm EN 12697-33:2003+A1:2007 – Spec imen prepared

by ro l ler compacter.

In th is way, the permanent deformation was measured and recorded in 27 points of

each s lab (Procedure: B ≥ 25 points) resul t ing in the values and respect ive medium

values that are shown in Table 6. I t is a lso presented in Figure 3 the permanent

vert ica l deformat ion evolut ion curves a long 10000 cyc les. For a bet ter understand-

ing of the values shown in Table 6, the express ions used to determine the W heel

Track ing Slope (mm/103cyc les) and the Proport ional Rut Depth (%) according to the

European Norm EN 12697-22:2003+A1:2007:

FG�HIJ � "KLMMMMNKMMM(O (9)

in which,

d5 0 0 0 and d1 0 0 0 0 – Rut depth af ter 5000 load cyc les and 10000 load cyc les , in

m il l imeters (mm).

PQ � 100 � "RL0S0 RT(U�V (10)

In which,

m n – Measured rut depth in measured cross-sect ion, in mi l l imeters (mm);

n – Number of measured cross-sect ions;

h – Specimen th ickness, in mil l imeters (mm).

Table 6 – Summary of resul ts and corresponding medium values obta ined in wheel

t rack ing laboratory tes ts - LNEC.

PARAMETER IDENTIF. RESULT.

Maximum deformation (rut depth at 10000 cycles), mm Specimen 1 0,60

Maximum deformation (rut depth at 10000 cycles), mm Specimen 2 0,65

Mean rut depth at 10000 cycles, mm 0,6

Wheel tracking slope (between cycles 5000 and 10000), mm/103 cycles Specimen 1 0,02

Wheel tracking slope (between cycles 5000 and 10000), mm/103 cycles Specimen 2 0,03

Mean wheel tracking slope (WTSAIR), mm/103 cycles 0,02

Proportional rut depth at 10000 cycles Specimen 1 1,2

Proportional rut depth at 10000 cycles Specimen 2 1,3

Mean proportional rut depth (PRDAIR), % 1,3

12

Figure 3 – Evolut ion of the permanent ver t ica l deformation a long 10000 cyc les -

LNEC.

In th is way, i t can be conc luded that the wheel t rack ing test , whose resul ts are pre-

sented in Table 6, fu l f i l ls the l im its stated for the stringest category of the Wheel

Tracking Slope WTSAIR0 , 0 3 and for the second str ingest category of the Propor-

t ional Rut Depth PRDAIR1 , 5 , complying wi th European Norm EN 13108-1:2006.

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Deform

ation (mm)

Number of Cycles (RPM)

Specimen 1 Specimen 2

13

RREEFFEERREENNCCEESS

Bat is ta , António Miguel Costa Bat is ta – “Mis tu ras Betuminosas Rec ic ladas a Quente em

Centra l . Contr ibu ição para o seu estudo e ap l icação” . Disser tação de Doutoramento,

Faculdade de Ciênc ias e Tecnolog ia da Univers idade de Coimbra, Por tugal , Dezembro de

2006. (A. Bapt is ta , 2006).

Bat is ta , Fát ima Alexandra Barata Antunes Bat is ta – “Novas Técnicas de Reabi l i tação de

Pav imentos. Mis turas be tuminosas densas a f r io ” . Disser tação de Douto ramento, Laborató-

r io Nac ional de Engenhar ia Civ i l e Ins t i tu to Super ior Técnico da Univers idade Técnica de

L isboa, Por tugal , 2004. (F. A. Bat is ta , 2004).

CEPSA Betumes – “Manual de Pav imentação”. Por tugal , Novembro de 2007. (CEPSA,

2007).

Est radas de Portugal – “Caderno de Encargos : 03-pav imentação” . Vo lume V, Almada. (EP,

2009).

European Commit tee for Standard izat ion – “Bi tuminous mix tures - Test methods fo r hot mix

asphal t - Par t 12: Dete rminat ion of the wate r sens i t iv i ty o f b i tuminous spec imens”. EN

12697-12. Bruxelas. (CEN, 2008) .

European Commit tee fo r Standard izat ion - “Mis turas Betuminosas - Espec i f icações dos

Mater ia is - Par te 1 : Betão Betuminoso”. EN 13108-1. Bruxelas. (CEN, 2006).

European Commit tee for Standard izat ion – “Bi tuminous mix tures - Test methods fo r hot mix

asphal t - Par t 34: Marshal l Test ”. EN 12697-34+A1:2007. Bruxelas. (CEN, 2004) .

European Commit tee for Standard izat ion – “Bi tuminous mix tures - Test methods fo r hot mix

asphal t - Par t 22: Wheel t rack ing”. EN 12697-22+A1:2007. Bruxelas. (CEN, 2003-a) .

European Commit tee for Standard izat ion – “Bi tuminous mix tures - Test methods fo r hot mix

asphal t - Par t 23 : Dete rminat ion of the ind i rec t tens i le s t rength of b i tuminous spec imens”.

EN 12697-23. Bruxelas. (CEN, 2003-b) .

European Commit tee for Standard izat ion – “Bi tuminous mix tures - Test methods fo r hot mix

asphal t - Par t 33: Spec imen prepared by ro l ler compactor ” . EN 12697-33+A1:2007. Bruxe-

las . (CEN, 2003-c) .

Laboratór io Nac ional de Engenhar ia Civ i l – “Guia Para a Rec ic lagem de Mis turas Betumi-

nosas a Quente em Cent ra l ” . LNEC E472. L isboa. (LNEC, 2006).

Laboratór io Nac ional de Engenhar ia Civ i l – “Be tumes de Pav imentação: Class i f icação, pro-

pr iedades e ex igênc ias de conformidade”. LNEC E80. L isboa. (LNEC, 1997).