Statistical analysis of unconventional bituminous mixtures performance based on 4PB Tests

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1 Grupo de Investigação em Vias de Comunicação Statistical analysis of unconventional bituminous mixtures performance based on 4PB Tests PORTUGAL Silvino Capitão António Baptista Luís Picado-Santos ISEC ENGINEERING INSTITUTE OF COIMBRA ESTV POLYTECHNIC OF VISEU FCTUC UNIVERSITY OF COIMBRA

2 Unconventional bituminous mixtures tested High Modulus Bituminous Mixtures (HiMBM): 2 Binder Type: 10/20 pen bitumen Content: 4.8% to 5.8% Aggregate Type: granite Max. Size: 20 mm Pavement Layer Base Hot mix Bituminous Recycled in plant (HMR): Binder Type: 35/50 pen + recovered Content: 4.1% to 4.4% Aggregate Type: limestone mainly Max. Size: 25 mm % of recycled mixture 20, 30 and 40% Pavement Layer Base Grupo de Investigação em Vias de Comunicação

3 Mechanical performance evaluation: Stiffness Modulus + Phase Angle σ(t)= σ 0 sin(ωt) Stiffness Modulus ε(t)= ε 0 sin(ωt φ) Controlled displacement S mix = Stress Strain degree φ = t t i p 360 Phase Angle t i time between σ(t) and ε(t) t p - loading cycle time 3 Grupo de Investigação em Vias de Comunicação

4 Mechanical performance evaluation: Fatigue behaviour Fatigue law obtained by the classical approach: specimen fails when required load to keep displacement level has decreased 50 per cent of its initial value. Bituminous Layers ε t = a N b Strain (εt) ε t 4 Number of loading cycles N adm Grupo de Investigação em Vias de Comunicação

5 HiMAM: evaluated parameters A B 5 Grupo de Investigação em Vias de Comunicação

6 HiMAM: stiffness results (example for lab.a2: 5.3% bitumen content) 9.7% 9.6% 10.0% 11.5% 6.2% 4.0% 10.5% 15.3% 5.4% 6.5% 4.8% 4.1% 10.9% 16.1% ε t = 120 μm/m Stiffness Modulus (MPa) 0,1 Hz 1 Hz 10 Hz 5 Hz 6 Temperature ( o C)

7 HiMAM: stiffness results (example for lab.a2: 5.3% bitumen content) 11.5% 15.3% 10.0% 10.5% 4.8% 16.1% 9.6% 4.0% 6.5% 10.9% 9.7% 6.2% 5.4% 4.1% ε t = 120 μm/m Stiffness Modulus (MPa) 25ºC 40ºC 15ºC 45ºC Frequency (Hz)

8 HiMAM: phase angle (example for lab.a2: 5.3% bitumen content) 4.5% 7.2% 8.9% 4.9% 4.1% 3.9% 45ºC 9.6% 6.5% 9.3% 7.5% 9.5% 8.1% 10.8% 8.7% ε t = 120 μm/m 25ºC 40ºC Phase Angle ( o ) 15ºC 8 Frequency (Hz)

9 HiMAM: statistical analysis of stiffness results Specimens from trial sections t test: The difference between the averages of stiffness modulus is not significant, for a 5% significance level. Wilcoxon Signed Rank Test: hypothesis of identical populations is rejected for a 5% significance level. Laboratory Specimens 9 Grupo de Investigação em Vias de Comunicação

10 HiMAM: regression analysis of stiffness results S = x t x T x V x ε x S mix R 2 = 0.89 Example for a typical situation: S mix (MPa) b max b S mix (MPa) mixture s stiffness modulus t (s) loading time T ( o C) mixture temperature V b (%) percentage of bitumen by volume ε max (mm/m) maximum strain S b (MPa) bitumen stiffness. 10 Traffic Speed (Km/h) Grupo de Investigação em Vias de Comunicação

11 HiMAM: regression analysis of fatigue results (examples) Classic Analysis Strain (microns) 1000 Effect of aggregate inter-locking along crack borders R 2 =0.93 ε t =a x N b Lab.A3 (bit=5.8%) Lab.A2 (bit=5.3%) R 2 =0.904 Lab.A1 (bit=4.8%) 70% stiffness reduction R 2 = Load cycles 11 Grupo de Investigação em Vias de Comunicação

12 HiMAM: regression analysis of fatigue results (examples) ε t = a N -b ε 6 strain which induces specimen ruin after 1 million load cycles 1000 Strain (microns) 100 Lab.A2 Vv=1.73% A2.1 Vv=1.79% (bit= 5.3%) A2.2 Vv=1.95 % 1E3 1E4 1E5 1E6 1E7 Number of load cycles ε 6 (microns) A1.1 A1.2 A2.1 A2.2 A3.1 A3.2 Trial sections 12 Grupo de Investigação em Vias de Comunicação

13 HMR: test parameters 13 Grupo de Investigação em Vias de Comunicação

14 HMR: stiffness results (example for mix D: 4.3% bitumen content) ε t = 100 μm/m Higher stiffness values: Better control of the mixing process... Specimens from pavement Specimens from laboratory Stiffness Modulus (MPa) 15 o C 25 o C 40 o C Frequency (Hz) Stiffness Modulus (MPa) 40 o C 25 o C Frequency (Hz) 15 o C 14

15 HMR: regression analysis of fatigue results (example for mix D: 4.3% bitumen content) ε t = 100 μm/m Better performance: Better control of the mixing process... Specimens from pavement Specimens from laboratory Strain (μm/m) 25 o C ε 6 = 205 Strain (μm/m) 25 o C ε 6 = 258 Load cycles Load cycles 15

16 16 CONCLUSIONS HiMBM: The prediction models, bearing in mind their limitations, can be used within the range of characteristics studied for HiMBM, for mixture composition studies and for design purposes (stiffness modulus model) It is adequate assessing fatigue resistance of HiMBM from specimens produced in laboratory instead of building trial sections, particularly for mix design purpose (Parameter ε 6 seems to be adequate for ranking mixtures during the mix design process) HMR: It was found that mixtures produced in laboratory have a better mechanical behaviour than mixtures produced in plant. This underlines the fact that better fabrication and laydown control are significant issues.

17 17 CONCLUSIONS HMR: Hot mix bituminous recycled in plant is possible, in technological terms, with 40% of reclaimed material incorporation by total weight. Finally, it can be affirmed that mechanical behaviour of unconventional mixtures similar to HiMBM and HMR can be evaluated from four point bending tests.

18 18 Grupo de Investigação em Vias de Comunicação Thank You for Your Attention. PORTUGAL Silvino Capitão António Baptista Luís Picado-Santos ISEC ESTV POLYTECHNIC OF VISEU FCTUC UNIVERSITY OF COIMBRA