SHORT-TERM AND LONG-TERM AGEING INFLUENCE ON MODIFIED BITUMENS RESISTANCE TO LOW TEMPERATURE CRACKING AND FATIGUE CRACKING

Transcription

1 SHORTTERM AND LONGTERM AGEING INFLUENCE ON MODIFIED BITUMENS RESISTANCE TO LOW TEMPERATURE CRACKING AND FATIGUE CRACKING P. Radziszewski 1, J. Pilat 2, R. Ziolkowski 1 (1) Technical University of Bialystok, Bialystok, Poland (2) Technical University of Warsaw, Warsaw, Poland Abstract Paper presents investigation of viscoelastic properties of unmodified and modified with elastomer, plastomer and scrap rubber bitumen produced in Poland. Bitumens properties were determined before ageing, after shortterm ( Thin Film Oven Test) and long term ( Pressure Ageing Vessel) ageing. Efforts evaluating the low temperature and fatigue cracking resistance on the basis of laboratory bitumen and mineralbitumen mixes tests were taken. The following tests were planned: softening point R&B, penetration in different temperature, force ductility test at different temperature with different elongation speed (deformation work, maximum tensile force), Fraass breaking point, elastic recovery, bending beam rheometer test, Marshall test, indirect tensile test, the fatigue test. On the basis of the first stage carried out research it was stated that there exists an significant correlation between parameters determining bitumen s properties in different stages of ageing (i.e. deformation work determined in force ductility test) and asphalt mixes fatigue life and stiffness modulus in function of temperature. Influence of modification stage on the change of bitumens ageing and bitumens resistance to low temperature and fatigue cracking resistance were estimated. 1. Introduction Bitumen asphalt s physicmechanical properties depend on temperature and time of loading. Three basic states of bitumen performance, viscous, viscoelastic and elastic are depending on type of bitumen and its way of loading. The range of temperatures in which bitumens properties should be determined consists of pavement performance and mixing and construction temperatures. In Poland

2 the range of exploitation temperature is assumed from about 40 o C (the lowest pavement surface s temperature in winter period) to about 70 o C. Bitumen is subjected to high temperatures during mineralasphalt mixes mixing and construction. Technological temperatures range varies from about 90 o C (the lowest temperature of mix compaction) to about 220 o C (the highest temperature of some kind of mineralasphalt mixes). Hence the estimation range of temperatures in which bitumen s properties should be determined is 220 o C [1, 2]. During asphalt mix production processes and road pavement exploitation bitumen is subjected to ageing and it happens because of: oxidation volatilizing of volatile components little significant for longterm ageing, polymerization no scientific explanation for justification of essentiality of this influences on ageing process, thixotropy, separation selective absorption of lighter components by aggregate s grains of higher porosity. In results of ageing effected by lower penetration, higher softening point and penetration index bitumen undergo hardening process. Shortterm ageing takes place during bitumen storing and mixing as well as storing, transport and construction of the mixture. Longterm use in road pavement leads to longterm asphalt ageing process. Increase of road traffic in Poland within the last decade and severe climate conditions determine the wider application of modified bitumens (elastomer SBS, plastomer EVA, scrap rubber of used car tires) in highway engineering. Improvement of viscoelastic properties of modified bitumen comparing to unmodified ones has been proved many times but lack of research works on modified bitumen resistance to ageing process is still noticeable. The main aim of the research was to estimate the ageing influence on modified bitumen resistance to low temperature and fatigue cracking. The paper presents the research results of the first stage of investigations. 2. Materials and research methodology of bitumen modified with elastomer SBS Bitumen of 70 pen produced in Gdansk Refinery was used as a base asphalt in a modification process. As modifiers, the following additives were used: Kraton D 1101 thermoplastic elastomer, polymer type: clear SBS, block styrene content 31 %, Kraton D 1116 thermoplastic elastomer, polymer type: SBS radial, block styrene content 23 %, Kraton D 1184 thermoplastic elastomer, polymer type: SBS radial, block styrene content 30 %, Kraton D 1192 thermoplastic elastomer, polymer type: SBS linear, block styrene content 30 %, EVA thermoplastic plastomer, vinylethyl acetate, Fine and course scrap rubber of used car tires.

3 In modification process according to [3], the base asphalt of 70 pen was initially heated to a temperature of 18. that the each of the additives was gradually added to the bitumen (total adding time 1 min) and the whole was subjected to fast rotate mixing for 60 minutes. Bitumens modified with scrap rubber were subjected to slow rotate mixing. There were added amounts of 3% 5% and 7% of polymer modifiers and 15% and 17% of scrap rubber. As a result of modification process the following modified bitumens were obtained: %, %, % (bitumens modified with thermoplastic elastomer Kraton D 1101), %, %, % (bitumens modified with thermoplastic elastomer Kraton D 1116), %, %, % (bitumens modified with thermoplastic elastomer Kraton D 1184), %, %, % (bitumens modified with thermoplastic elastomer Kraton D 1192), EVA 3%, EVA 5%, EVA 7% (bitumens modified with thermoplastic plastomer vinylethyl acetate), G1 15% (bitumen modified with fine scrap rubber) and G2 17% (bitumen modified with course scrap rubber). All of the modified bitumens first were subjected to the short technological ageing process and after that to long term ageing process. The simulation of shortterm ageing in laboratory conditions was carried out with using method (Thin Film Oven test). Part of the research on chosen bitumens during further stage of examinations was carried out on bitumens aged according to R method (Rolling Thin Film Oven Test). ageing processes, all of the samples were stored in a refrigerator at a temperature of. Longterm ageing was carried out in (Pressure Ageing Vassel). Samples of bitumen were heated under pressure (2,1 kpa), at a temperature of 100 o C (temperature used in temperate climate). Heating time was set on 20 hours. heating the pressure was slowly reduce in order to avoid foaming. that, the samples were subjected to reheating at 163 o C to clearate bitumen. The samples before longterm ageing were first subjected to shortterm ageing. All modified bitumens were tested before ageing, after shortterm and longterm ageing. Changes of the following parameters were investigating: softening point R&B, penetration in function of temperature (25, 15 and ), force ductility test in function of temperature (25, 15 and ) and elongation speed (10, 30 and 50 mm/min), Fraass breaking point, dynamic viscosity in Brookfield apparatus. During force ductility test deformation work (P) and maximum tensile force F max were estimated (Figure 1).

4 Figure 1. Graph of force ductility test. Asphalt concrete with 0/12,8 mineral granulation was chosen for testing fatigue cracking resistance. There were prepared asphalt mixes with modified bitumens (6% bitumen with elastomer SBS 5%, 6% bitumen with plastomer EVA 6 %, 7% bitumen with fine granulated scrap rubber of used car tires 15% and 7% bitumen with course granulated scrap rubber of used car tires 17% + 3% of plasticizer), which were produced in special plate. Mixes were compacted by using static and vibratory rollers. Rolling wheel compaction involves the use of weight and volume calculation to determine the amount of material to be compacted within a known volume mold. mixing all mixtures were heated in oven under temperature 13 for four hours, following the shortterm ageing procedure [4]. For asphalt mixes their Marshall stability, stiffness modulus according to indirect tension test (Brazilian method) and fatigue life were estimated. Fatigue life test was carried out in Schenck s apparatus. Beam specimens of asphalt mix (450x25x25 mm) were put in a thermal chamber at a temperature of 10 o C and subjected to bending according to fourpoint test loading procedure with constant strain amplitude. Stiffness modulus (S 0 ) is to be determined in indirect tensile test which is being currently carried out. The temperature of measurement varied from 10 o C to. The stiffness modulus was determined during five repeated displacements after fifth consecutive load impulse. Maximum strength was set at a level to achieve the vertical displacement of at least 5µm.Time of the strength growth from 0 to its maximum value was set on 124 ± 3 m*s [5]. 3. Changes of viscoelastic properties of modified bitumens in ageing process determination Chosen research results and changes of considering properties (penetration, softening point, maximum tensile force, deformation work, ductility and viscosity) taking place as a result of short and long term ageing are presented in Tables 1 4.

5 Table 1: Changes of bitumen modified with kraton D 1192 properties after shortterm and longterm ageing L. p. Properties 70pen % 70 pen % 70pen % 1 Penetration...0.1mm Softening point [ o C] Fraass breaking point Ductility [mm] Maximum tensile force [N] Table 2: Changes of bitumen modified with kraton D 1116 properties after shortterm and longterm ageing. L. p. Properties 70pen % 70 pen % 70pen % Penetration...0.1m 1 m Softening point [ o C] Fraass breaking point Ductility [mm] Maximum tensile force [N]

6 Table 3: Changes of bitumen modified with kraton D 1184 properties after shortterm and longterm ageing. L. p. Properties 70pen % 70 pen % 70pen % 1 Penetration...0.1mm Softening point [ o C] Fraass breaking point Ductility [mm] Viscosity [Pa*s] 60 o C 90 o C 110 o C Table 4: Changes of the properties of the base bitumen and bitumen modified with fine scrap rubber after shortterm and longterm ageing. L.p. Properties 70 pen 70 pen + 15%G1 Penetration...0.1mm Softening point [ o C] Fraass breaking point Ductility [mm] Maximum tensile force [N] > > > > The results in the tables above indicate that ageing strongly influences on tested bitumens properties for all considered parameters except softening point and viscosity for bitumens with 5% and 7% amount of polymer additives and for asphaltrubber. To investigate ageing influence on modified bitumens Fraass breaking point the variance analyses for obtained results was carried out [6]. As a result of statistical analyses there was stated significant or highly significant ageing influence on following parameters: penetration, deformation work, ductility and softening point and viscosity. The ageing influence of maximum tensile force was stated as insignificant. Moreover, high influence of ageing, type and amount of additive on changes of Fraass breaking point was stated. It is confirmed by results showed on figures 2 and

7 4 12 aging 70 pen % % % 20 Figure 2. Ageing influence on Fraass breaking point of bitumens modified with SBS (5%). Deformation work [N*mm] % % % 70 pen Figure 3. Fraass breaking point versus deformation work for bitumens modified with SBS (5%). On the basis of correlation analyses the highest correlation was confirmed between Fraass breaking point and deformation work, received in force ductility test carried out at and elongation speed of 10 mm/min (P 5C10 ) and between Fraass breaking point and deformation work at with elongation speed of 50 mm/min (P 25C50 ). On the basis of carried out research and statistical analyses it may be said that estimation of deformation work may be used to determine the bitumen low temperature cracking resistance (for first stage of research, Fraass breaking point was used as an estimation criterion). In further examinations there is a prediction for possible using of deformation work estimation in connection with evaluation of low cracking resistance according to BBR (bending beam rheometer) and DTT (direct tension test).

8 4. Investigation of fatigue cracking resistance of asphalt mixes with modified bitumens Chosen research results, which have been finished are presented in Table 5. Marshall test results show, that modifier additives don t significantly influence on improvement of stability. It is only noticeable increase of stability for asphalt aggregate mix with elastomer SBS modified bitumen. Dynamic stiffness E 60 of asphaltaggregate mixes with standard bitumen and SBS and EVA modified bitumen are more or less equal. The average dynamic stiffness of the course and fine rubber modifications is lower then the other three mixes. Cumulative dissipated energy and fatigue life results significantly differ modified and unmodified mixes. For each mix an N f ε relation was derived by linear regression. For comparison the test results are given in figure 4. These results show that modified asphaltaggregate mixes after shortterm ageing, in the same strain amplitudes, have 5 to 25 times higher fatigue life comparing to asphaltaggregate mix with standard bitumen. Especially the course and fine rubber modifications show better fatigue properties. Table 5: Experimental results of asphalt aggregate mixes with modified bitumen Asphaltaggregate mixes with bitumen Marshall stability Fatigue response 70 pen stanadard bitumen [N] Initial stiffness modulus E th cycle in fatigue test [MPa] pen + 5% SBS pen + 6% EVA pen + 15% G1 (fine scrap rubber) 70 pen + 17% G2 + 3% plasticizer (course scrap rubber) Strain amplitude ε [ì m/m] Fatigue life N f [x10 3 ] Cumulative dissipated energy W f

9 Figure 4. Fatigue life results versus initial strain amplitude. Investigation of fatigue life of asphalt mixes with modified bitumens has already been carried out by coauthor of this paper in [2]. He constructed a number of regression models based on rheological parameters describing modified bitumens and bitumen mastics. One of the models describes asphalt mix s fatigue life using plasticity work determined in force ductility test. Carried out research and obtained results have confirmed adequacy of the assumed model in [2]. There was proved strong correlation dependence between initial stiffness modulus (which parameter is a part of formula describing fatigue life) and elastic stiffness modulus (determined in indirect tensile test at temperature of 10 0 C). The equal dependence was obtained for plasticity work and deformation work (determined in force ductility test). inserting deformation work and stiffness modulus into formula describing regression model [2] the following equation for asphalt mix s fatigue life estimation was received: N = 1,840*10 34 *ξ 6,450 0 S 4,611 1,354 0 P R where: ξ 0 pavement initial strain amplitude, S 0 stiffness modulus from indirect tension test, P R deformation work after R ageing obtained at. (1) For the formula (1) regression coefficient Rsquared is 0,95. This formula shows that fatigue life of mineral asphalt mixes with modified binders depends on the deformation work, which is determined after shortterm ageing. Asphalt mixes with modified binders characterized by higher values of the deformation work show higher fatigue life.

10 Cumulative dissipated energy seems to be promising parameter to predict the resistance to low temperature and fatigue cracking hence in the nearest future the research works on modified asphaltaggregate mixes will be also started. 5. Conclusions Carried out research and investigation lead to the conclusions: Ageing processes significantly influence on the properties of modified bitumens (especially long term ageing). The influence depends on the kind of modifier. Modified bitumens occur to be less sensitive to ageing influence comparing to unmodified ones concerning their low temperature and fatigue cracking. Deformation work determined at (P 5C10 ) and deformation work determined at (P 25C50 ) may be used to estimate bitumens low temperature cracking resistance in aspect of Fraass breaking point (further research works that are going to be carried out will be extended to create new models considering BBR(Bending Beam Rheometer) and DTT (Direct Tension Test) test results). Fatigue life (fatigue cracking resistance) may be adequately estimated on the bases of deformation work after R of modified bitumens. Deformation work strongly influences on fatigue cracking resistance (preferences for bitumens with higher values of deformation work). 6. References 1. Gaweł I., Kalabińska M., Piłat J.: Asfaty drogowe, WKŁ, Warszawa Radziszewski P. Modelowanie trwalosci zmeczeniowej modyfikowanych kompozytow mineralnoasfaltowych, Politechnika Bialostocka, Bialystok Shell Chemicals, The preparation of blends of KRATON D and bitumen, Bulletin, TPE 6.2.3, Strategic Highway Research Program, Contract A003A (SHRP A003A) Performance Related Testing and Measuring of Asphalt Aggregate Interactions and Mixtures, Quarterly Report, University of California, Berkely, Kalabinska M., Pilat J., Radziszewski P.: Technologia materialow i nawierzchni drogowych, Warszawa Ahrens H.: Analiza wariancji. PWN, Warszawa 1970.