Research on components, mechanical properties and the applicability of epoxybitumen binder for asphalt mixtures in Vietnam

and curatives (hardener). The technical characteristics of each component and mixing ratios shown in Table 2-3. 2.1.2. Selecting type of bitumen used in research Bitumen 60/70 of Shell, Singapore was used to manufacture BE binder. 6 2.1.2.1. Content of epoxy in epoxy - bitumen The technical properties of BE binder vary with different contents of epoxy in binders. In this study, the properties of BE binders were be tested with epoxy contents of 15%, 20%, 30%, 35%, 40%, 50% by weight. They were abbreviated respectively: BE15, BE20, BE30, BE35, BE40, BE50. 2.1.2.1. Steps of mixing epoxy-bitumen - Step 1: Producing epoxy resin: Blending main resin with curatives in proportion of 56:44 during one minute in order to produce epoxy resin for the research. - Step 2: Producing BE binder: Mixing bitumen 60/70 with epoxy resin made from step 1 in a paricular proportion during 4 minutes. BE binder obtained from this process will be poured into a mold and dried at 1500C for 1 hour. - Step 3: Maintaining BE sample (As shown in section 2.1.4) 2.1.3. Setting out a time interval and temperature level of epoxy-bitumen sample curing before testing In this study, BE binder was cured at two different temperature levels: 60 0 C (corresponding to the temperature of pavement surfaces in very hot summer areas and on steel plate bridges); 25 0 C (corresponding to average temperature in Vietnam). For the cured samples at room temperature of 25 0 C, tests for them were carried out at different curing time intervals: 2h, 4h, 24h, 48h, 72h, 96h and 168h., tests for them was conducted after curing during 96h for cured sample at 60 0 C. 2.2. Selecting technical specifications and testing methods for BE binders In Vietnam, TCVN 7493: 2005 "Bitumen-technical requirements" are used to assess the quality of bitumens. All 7 technical characteristics to evaluate bitumens according to this specification were applied to BE binders. In addition, viscosity and dynamic shear modulus (DSR) of BE binders were al so performed in this study. Testing methods comply with current standards. Using Minitab software to design general experiments. The number of common repetitions is 3. ANOVA analysis and post-editing analysis used to detect differences according to Tuckey standard. Carrying out the evaluation to remove outliers according to ASTM E178; evaluating the precision according to ASTM C670 with the acceptable limits specified by the respective standard tests. 2.3. Penetration of BE binder with diffirent percentages of epoxy Penetration tested in accordance with TCVN 7495: 2005. The total number of experimental sample groups was 49. By precision analysis in accordance with ASTM D5-2013, it could be confirmed that penetration test results met the precision requirements. 7 Fig. 2-1. Relationship between penetration and epoxy content and different curing conditions Fig. 2-2. Penetration values of epoxy bitumen - Penetration (Pe) decreases with increasing epoxy content. In the case of epoxy content less than 30%, the reduction rate of Pe is about 6,5 ÷ 15 (1/10mm) corresponding to increasing by 15% epox. The average decrease is 3,64 (1/10mm)/5% increase of epoxy content). The rate of reduction in Pe is significant (average reduction of 6.7 (1/10mm)/5%) if the epoxy content increases from 30% to 35%. In the case of epoxy content greater than 35%, the rate of reduction returned to the original level with an average of 3,64 (1/10mm)/5% [see fig. 2-5 and fig. 2-6]. - PE of BE binders in all types of content decreases with increasing curing time, but for the epoxy content below 35% this reduction is negligible and almost stable at 96h; At 35%, 40% and 50%, this reduction is obvious with increasing curing time (see fig. 2-6). - PE of samples cured at 60 0 C for 96h were lower than those of samples cured at 25 0 C for 168h. For samples with 50% epoxy content and curing at 60 0 C for 96h, Pe was lower than 20 (1/10mm) (see fig. 2-5). The reduction of PE or the increased hardness of the BE binder compared with conventional bitumen is due to epoxy resin as a thermoset component. In BE binders, epoxy is a three-dimensional continuous phase that is hard and becomes harder when heated. As epoxy content increases, the mixtures with more hard components reduce their Pe, while BE binder cured at higher temperature makes it harden faster. Long curing time makes BE continue to complete dispersion phase of epoxy and increase the hardness of BE binder. Setting up the second regression equation showing the relationship between Pe and variables (BE and T) in research limit as follows: Pe = 79,62 – 1,0153 BE – 0,06700 T + 0,00990 BE*BE + 0,000283 T*T – 0,003223 BE*T (2-1) The equation ensures reliability with the adjustment coefficient R 2 đc = 97,68%, p-value of all parameters is less than 0,05. 2.4. Softening point (ring-and-ball apparatus) This test was carried out according to TCVN 7497:2005 - ring-and-ball apparatus. Total number of sample groups was 49. 8 Precision analysis of softening point test results according to ASTM D36 -2014 showed that their precision was satisfactory. Fig. 2-9. Relationship between softening point and epoxy content and different curing conditions Fig. 2-3. Softening point values of epoxy bitumen - SP (Softening point) increases with increasing epoxy content. SP increases slowly (average of 1.3 0 C/5% increase in epoxy content) with an increase from 15% to 30%. An increase of SP is significant when the epoxy content is more than 30%. In the range of epoxy content from 30% to 50%, SP increases from 10 ÷ 60 0 C, corresponding to an average of approximately 7 0 C for every 5% increase in epoxy content. This is shown in the slope of the straight lines in the graph of the relationship between SP and epoxy content which increases significantly at 30% epoxy content (See Fig. 2-10 and Fig. 2-9). - As sample curing time at room temperature increased, SP of all epoxy- bitumen with different epoxy contents increased. However, when the epoxy content was below 35%, the increase was negligible and almost no longer increased after 96 hours. With epoxy contents of 35%, 40% and 50%, the increase is noticeable as sample curing time increases. Of the three types of BE (with expoy contents as above), the growth rate of 50% epoxy sample is the largest, 35% epoxy sample is the smallest (see Fig. 2-10). - SP of curing samples at 60°C for 96 hours is higher than that of curing samples at 25 0 C for 168 hours. With 50% epoxy content and curing at 60 0 C for 96h, BE does not soften even at 120 o C (see Fig. 2-9) - Samples are cured at 25 0 C and 168h after mixing, SP of BE35 is equivalent to PMB-II, of BE40 is equivalent to PMB-III and of BE50 is up to 117 0 C. The theoretical basis for change of SP is similar to that for Pe. Thermoset epoxy component included in BE binder increases temperature resistance, maintains hardness of BE in high temperature. A higher epoxy content expands thermosetting continuous phase which increases the stiffness of BE rapidly under high temperature. As with Pe, curing samples at high temperatures rapidly increases the hardness of BE. Long service time has the effect of developing a dispersed thermoset phase, thereby increasing SP of BE binder. The longer curing time is, the more dispersed thermoset phase develops, thereby increasing SP of BE binder. 9 Setting up the second regression equation showing the correlation between SP and BE and T variables within the study limits as follows : SP = 70,33 – 1,319 BE – 0,1590 T + 0,02371 BE*BE + 0,008356 BE*T (2-2) The correlation equation ensures the reliability with the adjusted determination R 2 đc = 94,61% and the p-value of the parameters are less than 0,05. 2.5. Proposal for selection of BE components From the test results for penetration and softening point of BE binders, the following conclusions are drawn: - Epoxy content ≤ 30%: The rate of reduction of Pe and increase of SP is not significant; PE of BE binders with all tested curing conditions ranges from 40-65 (1/10mm), only equivalent to PMB-II and PMB-III; when expoy content is lower than 30%, SP of BE binders in all curing conditions is lower than 60 0 C which is lower than PMB-I; With an epoxy content of 30%, if cured at room temperature (25 0 C), SP only reaches 60,25 0 C with curing samples for 168h and if cured at 60 0 C for 96h, SP reaches 61,55 0 C, which is equivalent to PMB I. - With epoxy content of 35% or more, Pe and SP of BE are superior to those of bitumen 60/70. With 50% epoxy content, these two properties are still superior to those of PMB-III. Details are as follows: + With BE35: if curing samples at 25 0 C for 168h or curing at 60 0 C for 96h, SP of them is equivalent to PMB-II (higher than 70 0 C); + With BE4: if cured at 25 0 C from 72h to 96h, SP is equivalent to that of PMB-II (higher than 70 0 C); if curing samples for 168h or curing at 60 0 C for 96h, SP is equivalent to that of PMB-III (higher than 80 0 C); + With BE50: if cured at 25 0 C for 96h, its SP is equivalent to PMB III; Especially, if curing time reaches 168h or curing at 60 0 C for 96h, its SP can be up to 120 0 C - superior to PMB-III. + Pe is lower than that of PMB-III (below 40 1/10mm) when cured above 96h at 25 0 C with BE35 and BE40, over 72h at 25 0 C with BE50. From the above conclusions, choosing 02 types of BE binders (BE35 and BE50) corresponding to 35% and 50% epoxy by total weight of BE mixing to conduct further studies in the thesis. 2.6. Experiment on basic properties of BE binder Experimental results of other basic properties of BE35 and BE50 according to TCVN 7493:2005 in table 2-13 show that properties of both tested BE35 and BE50 meet the requirements for 60/70 bitumen. 10 2.7. Dynamic shear modulus of BE binder - DSR test results of original BE15, BE35 and BE50 binders are equivalent to PG70, PG76 and PG82. - PG of BE35 and of BE50 after RTFO remain the same as the original BE resin, respectively PG76 and PG82. - PG of BE15 after the RTFO decreases by one level compared to PG of corresponding original BE, from PG70 to PG64, which is equivalent to PG of ordinary bitumen 60/70 (BE0). 2.8. Conclusion for chapter 2  BE binders using epoxy supplied by TAIYU, Japan meet the requirements for bitumen used in construction according to TCVN 7493:2005. With an epoxy content of 35% or more, SP of BE binder is significantly higher than that of conventional bitumen. With epoxy content up to 50%, this property is also superior to that of PMB III. It is recommended to use BE type with a minimum epoxy content of 35% by weight of BE.  SP and Pe of BE binders are affected by curing time and temperature. The higher the epoxy content is, the greater the influence of these factors on SP and Pe.  At an air temperature of 250C, after mixing for 4 hours, there is any significant difference between properties of BE binder and of bitumen 60/70, so the use of BE as a binder for asphalt mixtures will not meet difficulties in the process of blending in asphalt mixing plant and in construction.  The decline of Pe to approximately 20-25 (1/10mm) during the use of pavements is a risk for cracking by hardening of bitumen. Therefore, it is necessary to study the effect of increasing hardness of bitumen on crack resistance by fatigue testing for asphalt concrete using BE binder.  PG of BE15, BE35 and BE50 are based on |G*|/sin of original BE and after RTFO are PG64, PG76 and PG82 respectively. CHAPTER 3 EXPERIMENTAL RESEARCH ON MECHANICAL AND PHYSICAL PROPERTIES OF BTNE USING BE BINDER Chapter 3 focuses on the study of technical properties of BTNE to assess the quality of them, analyze pavement structures with BTNE surface layers in Vietnam. In addition to common mechanical properties (Marshall stability and flow, static elastic modulus,...), other properties (fatigue life, dynamic modulus...) of BTNE were also analyzed and evaluated. 3.1. Mix design of BTNE mixtures and reference mixtures 11 From the conclusions of Chapter 2, this chapter only conducted experiments in BTNE (BTNE35 and BTNE50) respectively using BE35 binder and BE50 binder. The reference mixture is BTNP using PMB III binder. The study only focused on only one aggregate gradation with a nominal maximum size of 12,5mm (BTNC12,5) with all 3 types of binders: BE35, BE50 and PMB. III (see Fig. 3 - 1). Optimum asphalt content range is determined by Marshall method (see Table 3-6). Choosing optimal asphalt content value corresponding to Va equal to 4,5% ÷ 5,0% (recommended range arcording to Decision 858/QĐ - BGTVT). Selecting optimum asphalt content for BTNP mixture was 5,2% by mixed weight, for both BTNE35 and BTNE50 mixtures were 6,0% by mixed weight. 3.2. Preparation of experimental samples of BTNE  Step 1: Mixing BE binder according to the steps in section Error! Reference source not found.  Step 2: Mixing BTNE mixtures. - After mixing, BE binder as mentioned in Step 1 will be immediately put into the oven to dry at 140 0 C. - Coarse and fine aggregates are dried at approximate 170 0C, mineral powders do not need drying. - Mixing BE binder, coarse and fine aggregates and mineral powders similar to conventional asphalt mixture.  Step 3: Preparing of experimental asphalt samples by gyration or roller compactor. After that, BTNE samples was cured at 25 0 C for 168 hours (7 days) before tesing. In summary, it can be seen that the process of preparing BTNE samples for testing to determine properties of BTNE mixtures is similar to that of conventional AC mixture, except for the production of BE binder. 3.3. Marshall stability, flow and residual stability 3.3.1. Result of Marshall test and analysis An assessment of precision of Marshall stability and flow arcording to ASTM D6927-15 showed that these results were satisfactory. 12 Marshall stability of BTNE50 when immersed in water at 60 0 C for 1h is 51,72 kN, 3,328 times as much as that of BTNP (15,56 kN) and approximately 1,53 times as much as that of BTNE35 (33,86 kN). Marshall stability of BTNE50 when immersed in water at 60 0 C for 24 h is 46,33 kN, 3,319 times as much as that of BTNP (13,96 kN) and approximately 1,59 times as much as that of BTNE35 (29,08 kN). Average value of Marshall stability of BTNE35 is 2,18 times and 2,08 times as much as these of BTNP when immersed in water at 60 0 C for 1h and for 24h respectively. From ANOVA analysis results of Marshall flow, following conclusions can be drawn: - Influence of sample immersion time on Marshall flow is statistically significant; - The type of BTN does not affect Marshall flow. It means Marshall flow of BTNE is similar to that of BTNP. This is an advantage of BTNE, Marshall stability is much higher than that of BTNP but Marshall flow is still in the required range. Marshall flow of the mixes ranges from 3mm - 6mm, meets the requirements of BTNP mixture (see Fig. 3-5). BE binder with epoxy - thermosetting component has played an important role in forming hardness and improve Marshall stability of BTNE. Asphalt component maintains plasticity of BTNE mixtures which is shown by Marshall flow not much different from that of BTNP. 3.4. Static elastic modulus of BTNE Static elastic modulus tested for 3 different temperatures (15 0 C, 30 0 C and 60 0 C) complies with Annex C, 22TCN211-06. 13 3.4.1. Test result and analysis At test temperatures of 15 0 C, 30 0 C, 60 0 C, average static elastic modulus (Eđh) are 64,98%, 35,60% and 24,37% higher than those of BTNP, respectively. At 15 0 C, the difference of Eđh between 3 types of BTN is significant, the degree of difference between them decreases at 30 0 C, and is no longer significant at 60 0 C, especially between BTNE35 and BTNP. 3.4.2. Representative static elastic modulus of BTN At 15 0 C, 30 0 C, 60 0 C, Eđh đt is higher than that of BTNP respectively by 61,56%, 32,43% and 20,04%; Eđh đt of BTNE35 is 30,81%, 9,90% and 4,35% higher than that of BTNP (see Table 3-12). The results of static elastic modulus test show that BTNE has higher deformation resistance than conventional asphalt concrete (BTN) and also higher than BTNP using PMB III which are commonly used in Vietnam. Epoxy with the ability to improve hardness and maintain elasticity of BE is a factor that enhances the deformation resistance of BTNE. 3.5. Flexural strength of BTNE Flexural strength of asphalt concrete is determined in accordance with annex C of standard 22 TCN 211-06. The test was performed on beam samples with dimensions of 240x60x60 mm. 3.5.1. Result of flexural strength test and analysis At 15 0 C, Rku of BTNE35 and that of BTNE50 respectively 1,07%, 87,44% higher than that of BTNP. Experimental results are statistically significant at the 95% confidence level. Analysis of fracture cross-section of the sample after the test (see Fig. 3-16) showed that: fracture of BTNE35 and BTNP samples only occurred at position of BE binder. Fractures of the BTNE50 samples were very flat and cut through aggregate particles. It shows that BE50 has very high hardness due to epoxy component in BE binder. 14 a. BTNE50 b. BTNE35 c. BTNP Fig. 3-1. Photos of fractures after bending test 3.5.2. Representative flexural strength of BTN At 15 0 C, Rkuđt of BTNE35 and BTNE50 are respectively 21,95%, 93,96% higher than that of BTNP. Rkuđt of BTNE50 is 59.05% higher than that of BTNE35. Thus, it can be seen that bending resistance of BTNE50 is superior to that of BTNE35 and BTNP. High tensile flexural strength at 15 0 C is quite consistent with the results of a pilot project in Europe. These results indicate that the role of main resin component in epoxy resin ensures flexibility and plasticity of BE binder at low temperature, when conventional asphalt binder is hard-brittle. This feature was further verified by fatigue test for BTNE. 3.6. Wheel rutting depth of BTNE After 40.000 cycles of loading, wheel rutting depth of BTNE50 and of BTNE35 are only approximately 1/3 and 1/2 of that of BTNP respectively. Rutting depth of BTNE50 sample after 40.000 cycles is equivalent to that of BTNP sample after 1.400 cycles and that of BTNE35 sample after 13.000 cycles. Rutting depth of BTNE35 sample after 40.000 cycles of loading is equivalent to the depth of BTNP sample after 3.600 cycles. From the above analysis, it can be seen that Rutting deep of BTNE (especially BTNE50) is very good. Outstanding advantage of BTNE rutting resistance compared to that of BTNP is due to thermoset propertie of epoxy resin, with its hardness and ability to maintain its elasticity at high temperature. This result is completely consistent with many studies in the world. 3.7. Fatigue life of BTNE 15  Principles and parameters of test: 4-point beam bending test, deformation control, sinusoidal continuous load, 10Hz load frequency, test temperature 10 0 C.  Initial stiffness module (S0) of BTNE50 is much higher than that of BTNE35 and of BTNP.  Phase angle of BTNE50 is the lowest and thag of BTNP is the highest. This shows that BTNE50 exhibits the lowest viscosity properties and BTNP has the highest viscosity properties of three tested types of BTN.  Nf50 of BTNE50 is significantly better than that of BTNE35 and of BTNP.  Nf50 of BTNE35 is not significantly higher than that of BTNP at 2 levels of deformation 200 và 300, but much lower than that of BTNP at deformation level of 400. Higher stiffness module and smaller phase angle of BTNE50 show more clearly a role of epoxy resin to ensure higher elasticity of BE in BTNE mixture. Higher fatigue life of BTNE, especially BTNE50 verifies the ability to maintain the toughness of BE binder in the mixture.  Establishing fatigue life equation Fatigue curve of three types of asphalt concrete has been built and shown in Fig. 3-32. Results of establishing fatigue life equation (relationship between fatigue life (N f50) and deformation ()) of three types of asphalt at 10 0 C, 10Hz are shown in equations (3-8), (3-9) and (3-10). 16 The slope of fatigue curves of BTNP, BTNE35 and BTNE50 are 3,615; 4,256 and 3,770. These results are consistent with published results of fatigue research in the world (usually from 2 ÷ 6). Fig. 3-32 shows: fatigue sensitivity of BTNE35 is the greatest, respectively 17,73% and 12,89% higher than that of BTNP and of BTNE50; Fatigue curve of BTNE35 is very close and cuts through fatigue curve of BTNP. 3.8. Dynamic modulus of BTNE 3.8.1. Analyze experimental results on dynamic module of BTN Experimental results ensure the precision and shown in Figure 3 -37, Figure 3- 38 and Figure 3-39. From the results of these experiments, the following conclusions can be drawn:  Temperature and load frequency have a great influence on |E*|, as follows: At the same frequency, when experimental temperature increases, |E*| decrease very fast; At the same temperature, when the frequency decreases then |E*| also drops. This explains viscoelasticity of BTNP and BTNE materials.  At all experimental test temperatures (between 10 – 600C) and experimental frequencies, |E * | of BTNE50 are greater than that of BTNE35 and |E * | of BTNE35 is greater than that of BTNP. At higher temperatures, the greater the gap between |E * | of BTNE and of BTNP is. 3.8.2. Establishing master curve of dynamic modulus 17 Master curve of dynamic modulus (|E * |) is constructed from time- temperature correlation. Master curves of |E * | characterize viscoelastic property of asphalt materials in a wide range of frequencies and temperatures. It is used to predict |E * | at different load frequencies and temperatures. 3.8.3. Modelling master curve of dynamic modulus using 2S2P1D model 2S2P1D model was studied and proposed by Olard, F., & Di Benedetto (2003). This model consists of 7 input parameters (E00, E0, δ, β, τ, k and h) to model master curves of dynamic modulus of both asphalt binder and asphalt concrete. Parameters of 2S2P1D model are determined by Trial and error to minimize the errors between results from experiment and model.  Assessing the fit between 2S2P1D model and experimental results Using statistical model "Goodness of Fit" to assess the fit of 2S2P1D model with experimental results. The results in table 3-25 show that R 2 > 0,90 and Se/Sy < 0,35 for all BTNE35, BTNE50 and BTNP. This proves that this is a suitable model. 3.9. Conclusion for chapter 3  Marshall stability of BTNE50 and BTNE35 are 3 times and 2 times as much as that of BTNP respectively.  Static elastic modulus (Eđh) of BTNE50 is significantly higher (from 64% to 24%) than that of BTNP.  Tensile strength (Rku) of BTNE50 is superior to that of BTNE35 and BTNP. Rku is approximately 2 times as much as that of BTNP, and Rku of BTNE35 is only 1,2 times as much as that of BTNP.  Wheel rutting resistance of both BTNE50 and BTNE35 is very good 18  Fatigue life of BTNE50 is superior to that of BTNE35 and of BTNP. Fatigue life of BTNE50 is from 1,339 times to 3,369 times and from 1,477 times to 2,387 times as much as that of BTNE35 and of BTNP respectively.  Fatigue life of BTNE35 is only equal to or lower than that of BTNP when tested at large deformation (400). Slope of its fatigue curve is also the highest of 3 slopes which characterize three types of tested asphalt concrete.  |E*| của BTNE50 có giá trị lớn nhất ở tất cả các tần số và nhiệt độ, sau đó đến của BTNE35 và nhỏ nhất là của vật liệu đối chứng – BTNP.  2S2P1D model is suitable for modeling for |E*| of all three types of asphalt in the research.  BTNE still has visco-elasticity and thermal sensitivity of conventional asphalt. This is shown by appearance of phase angle between stress and strain in fatigue test and dynamic modulus test, as well as the dependence of dynamic modulus of BTNE on temperature and load frequency. However, heat sensitivity of BTNE is greatly improved compared to conventional asphalt concrete. CHAPTER 4 RESEARCH ON APPLYING EPOXY ASPHALT MIXTURE AS SURFACE LAYER OF HIGH CLASS ROAD PAVEMENTS AN