Wear and deformation characteristics of fibre reinforced asphalt pavements

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P Peltonen* Abstract The effects of cellulose, glass, mineral and synthetic polyester fibres on the wear and deformation of asphalt pavements are shown. C~'ll,,!osef i b r e s U ~ found to be good because they stabillse greater amounts of bitumen in the asphalt pauernents. A synthetic polyester fibre was found to be a real reinforcing fibre in bitumen. If high stIffnesses are needed for pavement layers a harder, elastic synthetic styrene.butadiene.rubber bitumen together with suitable fibres can also be used. This binder in asphalt mixtures produces high resistance to deformation at high temperatures.

The investigation of fibre.reinforced asphalt pavements originates from Germany 1 and from the USA. 2 The German work concerns the development of 'splittmastic' asphalt, where both short cellulose and mineral fibres have been used as stabilising additives for bitumen. The USA research included a large laboratory investigation where, among others, synthetic polyester fibres were studied as reinforcing additives with good results. Research on the use of fibre-reinforced asphalt paving mixtures 3 began in Finland in 1985 and the results from these experiments were presented at the 1989 bitumen conference. 4 The results shown in this paper are based on the fibre asphalt pavement research carded out in the Finnish Asphalt Pavement Research Programme, ~STO in 1989-1990.

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Sieving curves for the aggregate of the splittmasUc asphalt cement concrete 3MACC 16. Aggregate (1) was used in laboratory investigations and aggregate (2) in field experiments

*~ Road and Traffic Laboratory (Material Section), PO Box 110, 02151 Espoo, Finland. 18

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0618/91/010018 -

0 5 © 1991 B u t t e r w o r t h - H e i n e m a n n Ltd

Table I Composition by weight of aggregate mixes 1 and 2 Fraction, mm Lime filler 0.2 2-5 5-8 8-12 12.16

Stone mixture, weight % (1) (2) 13 10 7 5 4 61

11 11 8 5 20 45

Experimental details Consistency of the test pauements

The optimum binder content of an asphalt pavement is traditionally established on the Marshall mix design2 In this method test samples are pressed in a laboratory compactor from stone aggregates with different bitumen contents. The Marshall stabilities, densities and void contents of these compacted samples are tested. The Finnish splittmastic asphalt, Shv~CC16, is based on the aggregate composition curves presented in Figure 1. Aggregate corresponding to curve 1, in Fig 1, was used in laboratory investigations and an improved composition (curve 2) in field experiments. Table 1 shows the composition of the aggregates used in the curves presented in Fig 1. Without fibres, the aggregate mixtures of the s/~cc 16 as compacted have an open structure which can contain only low bitumen contents, for example 5.2 weight percent. When 0 . 3 - 0 . 5 weight percent of different fibres like cellulose, mineral, glass and polyester are mixed into these paving mixtures as stabilising additives, the bitumen contents can be increased to 6 . 5 - 6 . 8 weight percent. In this kind of mixture the calculated void content of the mineral aggregate (VMA) is about 16 percent and the void content filled with bitumen (VFB) about 84 percent. In the SMACCthe rather open stone mixture, containing a high amount of coarse aggregate, is thus stabilised and reinforced by fibres with an increased bitumen content. The higher bitumen content means that the surface of the pavement is more resistant to water damage, deformation and wear. Special characteristics of the Sh~CC are especially important in those Nordic and other countries where CONSTRUCTION & BUILDING MATERIALS Vol. 5 No. 1 MARCH 1991

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F~g2 Sieving curves for the aggregate used in field experiments on ACC 20 (curve 3) and GACC20 (curve 4) pavements

Table 2

Fraction

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Pavement wear tester used for the asphalt pavement material

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Static creep device used for deformation measurements of asphalt pavement material

Composition by weight of aggregate mix in the ACC and GACC.pavements Stone mixture, weight % ACC 20 (3) GACC 20 (4)

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studded tyres are used. In Finland the maximum gravel size for this reason is increased to 16-20mm. In Germany where studded tyres are not used the normal gravel size in Sh~ACCis only 8 or 11mm. This gives better resistance in the warmer countries against deformation and other damages. The traditional asphalt cement concrete in Finland, ACC2O, is based on a sieving curve of the stone mix as presented in Fig 2. The third pavement type used in Finland side by side with ACC and SMA¢Cis gap-graded asphalt cement concrete, GACC20, also shown in Fig 2. The amounts by weight of the aggregate fractions presented in Fig 2 are given in Table 2. The normal ACC2O pavement is tight structured with a low void content of 1 . 0 - 5 . 0 volume percent. For this reason fibres are not used in this kind of paving mixture. Bitumen content of the ACC 2O is also low, 5 . 5 - 5 . 9 weight percent. Because the gap.graded pavement type, GACC20, in Fig 2 contains a high proportion of coarse gravel (12-20ram), the mixture can be stabilised with fibres. The bitumen content of the GACCshown in Fig 2 is 5.5 weight percent without fibres. This is increased to about 6.3 weight percent when using 0.3 weight percent of fibres. The void content of a pavement layer is normally adjusted by using different fillers - rock dust, rock CONSTRUCTION & BUILDING MATERIALS Vol. 5 No. 1 MARCH 1991

powder and an inert lime filler, CaCO3. The asphalt pavement is thus comprised of crushed rock and sand material, lime filler and bitumen. In the deformation studies presented in this article a more reactive hydrated lime filler, Ca(OH)2 was also investigated as a filler material in the asphalt mixtures. The third component, bitumen, was normal quality road bitumen on a penetration level B-120. One modified rubber bitumen was also tested. This was based on the use of a synthetic styrene-butadiene block co.polymer (SBS). Te~dng methods Wear studies

The wear resistance of the asphalt pavements in Finland is measured in the laboratory by using the PWR device shown in Fig 3. The equipment consists of three small 19

studded tyres which run against test samples of diameter lOOmm and height 40mm. Wear tests can be carded out within a temperature range from + 2 0 to - 3 5 ° C in the refrigerating box. Normally the samples are tested for two hours at + 5 oC so that the surface of the samples is wetted with water. The results are given as wear values which are the volumes of the worn ruts in cm 3. Experiments have shown that the equipment is also suitable for the wear testing of different pure stone materials, cement concretes, thermoplastic road markings and epoxy based materials.

Creep.deformationstudies The equipment for characterising the deformation of the asphalt pavements based on the use of static Ioadings is shown in P"~g4. In the creep-device shown, three sped. mens can be tested simultaneously. Each specimen is loaded uniaxially using stress of lOOkPa. Temperature in the water bath during testing is normally +40°C and the deformation curve (Fig 5) is recorded in mm. The deformation is measured as a function of loading time. At first the loading t~ne of the specimens is one hour. During the f'cst ten minutes of the preliminary loading, two percent of the whole stress is applied. After a one hour relaxation period, the permanent deformation is recorded. In the ASTO-programme, it has also been possible to test II - =

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F g5 Deformation characteristics of asphalt pave. merits as measured by the static creep tester: (1) asphalt concrete with standard bitumen; (2) asphalt concrete with polymer bitumen; (A) elastic recovery; (B) permanent deformation

the dynamic creep and stiffness of the asphalt mixtures. These results are not presented in this paper. Results of wear analysis

Wear test at + 5 ° C Thirteen different fibre-reinforced asphalt paving mixtures, S/~ACC 16, were tested with the PWR-tester. These wear results are shown in Fig 6. The compositions of the mixtures researched are also shown in Fig 6. Results are presented for pavements both with and without fibres (reference). Mean values of wear and standard deviations are plotted. The following fibres were used as stablilising additives (numbers relate to composition columns of Fig 6): 1 Reference without any fibre (see low bitumen content). 2 Commercial cellulose fibre based on selected spruce fibres; maximum length 5ram, average length 1.1ram (see raised bitumen content). 3 National cellulose fibre modificate. 5 National mineral fibre modificate. 6 Synthetic, commercial polyester; fibre length 6ram. 7 Commercial mineral fibre based on limestone and diabase; fibre length 0.2.2ram. 8 Commercial glass fibre based on C.glass; common fibre length 1 or 2.Smm. Compared to the reference, the three best fibre modi. fled pavements in Fig 6 were modified with Polyester, cellulose or glass fibres. However, only with Polyester fibre were the wear results signficantly better than the reference. With other fibres, the variation of the wear results was large. This m e a n s that cellulose fibres a m o n g others gave rather different wear results between wear tests, though the stone material was not changed. The reason for this was that exactly equivalent crushed stone material was not available for all wear measurements. Wear test at - 20 °C The results of wear tests carried out under cold circumstances are presented in Fig 7. In this comparison

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Wear of SMACC16 at - 2 0 ° C S t a n d a r d d e v i a t i o n o f wear

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Lime filler, wt ~ F i b r e , wt % Fibre type Bitumen;wt % PmB1,wt % Wear M . V , c m "

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13 13 1 3 : 3 4 13 13 13 13 14 13 ILl 13 13 0.3 - 3 3 . 0 3 0 3 ) 3 0 ~ - 03 30303 Fibre type ; 7 :~ 6 2 8 6 6 Bitumen, w ~ 3 6 8 5 ~ @.2 ~ 7 6 . 2 6 9 , 1 B . 5 6.7 5 3 6.2 B.7 6.0 6.0 Near MV, cm 3 I =12_.; 12.7 ~0.~ 40.; .~ 14,818.~36.;35J~12~32 22 Near S T D , cm - q.0 - 6.2 LI.~ -- 3.7 0.3

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Resul~ of wear tests at + 5 ° C on d~:ferent SMACC p a v e m e n t s using b i t u m e n B . 1 2 0 a s binder. Fibre n u m b e r s s h o w n are defined in the text

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Results o f w e a r tests at - 2 0 ° C on different SMACC p a u e m e n t s . Binder was sBs.modified bitumen (PrnB1) or normal b i t u m e n (B.I20).

CONSTRUCTION & BUILDING MATERIALS Vol. 5 No. 1 MARCH 1991

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Comparisonof wear resistance at +5°C of different pavement types

SMACC 16 GACC 20 SMACC 16 ACC 20 ACC 20 SMACC 16 SMACC 16 GACC 20

Compar~on of wear of the different pavement types Figs 8 and 9 show the differences in wear between pavement types ACC20, GACC2Oand Sh~CC 16 at +5°C and - 2 0 ° C respectively. The three best asphalt pavements (Fig 8) obtained in wear investigations were GACC with rubber bitumen and two sh~cc-types reinforced with a cellulose or a polyester fibre. Also in these pavements a synthetic rubber bitumen based on SBS-polymer was used as a binder. The results presented in Fig 9 show that the same pavements were also best at - 2 0 ° C . It could be especially noticed that both at wet and cold conditions the pavements reinforced with synthetic rubber or fibres were better than the traditional pavements without any additives. CONSTRUCTION & BUILDING MATERIALS Vol. 5 No. 1 MARCH 1991

Bitumen Pm B1 Pm B1 Pm B1 Pm B1 B-120AH B-120AH B-120AH B-120AH

Fibre type 6"

2 6 2

*Lime + hydrated lime (8 + 5°/o)

Fig 9 the best wear resistances were obtained with polyester fibre.reinforced pavements beth with a synthetic rubber bitumen or with a normal road bitumen. Other fibres 2, 3 (cellulose), 5 (mineral), 8 (glass) and 7 (mineral), also gave a somewhat better wear resistance than the reference. This is due to the elasticity of the bitumen. enriched pavement surfaces when using fibres.

Pavement type

Comparison of wear resistance at - 2 0 °C of different pavement types

Results o f c r e e p - d e f o r m a t i o n analysis Four modifications to splittmatic asphalt cement concrete Sh~C¢ ]6 were produced: (1) (2) (3) (4)

with cellulose fibre 2 with normal bitumen, with cellulose fibre 2 with rubber bitumen, with cellulose fibre and with hydrated lime filler, and with cellulose fibre, hydrated lime filler and rubber bitumen.

Each pavement combination was tested both with creep and wear devices. Results are shown in Fig 10. Another series of modified pavement mixes was produced, similar to those presented in Fig 10, but changing the stabilising fibre to the synthetic polyester type. The results of wear and deformation with these pavements are presented in Fig ] 1. The three lowest creep-deformation values were obtained with the following pavements: 21

l~j~Wear

5

B-120 was 1.42mm. This value was noticeably higher in this test than the corresponding values obtained with polymer or with fibre-modified pavements.

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Conclusions Wear and deformation resistance testing of the different fibre-reinforced asphalt paving types has been carried out. The following ideas are presented on the basis of the results:

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(1) The bitumen content of the fibre-modified asphalt pavement is higher than normal. With cellulose fibres in particular, due to their efficiency in stabilising bitumen, the wear results are positive. Best wear resistances of s/v~cc are achieved with polyester, cellulose and glass fibres.

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(2) Traditional road bitumen alone is not as resistant to studded tyre wear as the fibre.modified bitumen composites or the polymer-modified bitumen. (3) The efficiency of GACCand S/v~CC pavement types in resisting wear was better than that of the traditional ACC, when the pavements were modified with synthetic rubber or with polyester or cellulose fibres. (4) Creep-deformation resistance of SMACC was improved by using polyester fibre as well as cellulose fibre together with hydrated lime filler and synthetic rubber. For warmer countries, the results mean that asphalt pavings made using suitably modified bitumens can be more resistant to deformation. In these circumstances the use of cellulose fibres, polymer.modified bitumen and hydrated lime f'dler material together with a suitable paving combination should be encouraged.

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Acknowledgements I LF PES B-120 A H

ll

2 LF PES PmBI

3 LF/HL PES B-120 AH

4 LF/HL PES PmBI

Wear a n d creep deformation results at + 5 °C for modified S M A C C p a u e m e n t s with polyester fibre (LF - lime filler; HL - hydrated lime)

(4) Synthetic rubber, polyester fibre and with hydrated lime filler; the permanent deformation value in Fig 11 was very low in this test, only 0.18mm. (2) Cellulose fibre, synthetic rubber and pure lime filler; the best deformation value reached in Fig 10 was 0.62mm. (2) Polyester fibre, lime filler and with PmB1; the permanent deformation value reached in Fig 11 was 0.85ram. It is important to notice that the best permanent deformation value obtained with normal bitumen

22

The results presented are based on the fibre asphalt pavement project of the Finnish Asphalt Pavement Research Programme, ASTO. The author thanks this project for supporting the writing of this paper.

References 1 2 3

4 5

K i l t , 0 E. Long-term experience with splittmastix-asphalt in the Federal Republic of Germany. Proc. 3rd Eumbitume Symposium, The Hague, 1985, Vol !. Bu~mt, J W and Huml~r, T G. Synthetic fil:~=s in asphalt paving mixtures. Texas Transportion Research Institute research report 319.1F, 1984. Peltonen, R Modifying of bitumen and asphalt paving mixtures using fibres. Proc. ASTO-Conference, 2 November 1989, Technical Research Centre of Finland, Road and Traffic Laboratory. Peltonen, P. Fibres as additives in bitumen. Proc. 4th Eurobitume Symposium, Madrid, 1989, Vol V! pp 938-942. Standard test method for resistance of plastic flow of bituminous mixtures using Marshall apparatus. Annual book of ASTM standards 1988, Section 4 construction, Vol 04.03 Road and

Paving Materials; Travelled Surface Characteristics. ASTM, Philadelphia, pp 203-207.

CONSTRUCTION & BUILDING MATERIALS Vol. 5 No. 1 MARCH 1901