Idaho Transportation Department (ITD) Mohamed Zubery. Vince Spisak FHWA. By: Fouad Bayomy, PhD, PE. Department of Civil Engineering

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1 Acknowledgement: A Simple Fracture Test For HMA By: Fouad Bayomy, PhD, PE University it of Idaho Department of Civil Engineering 47 th Idaho Asphalt Conference October 25 th, 2007 Idaho Transportation Department (ITD) Mike Santi Mohamed Zubery Monte Tish Vince Spisak FHWA UI, CE Dept and NIATT 3 4

2 Cracks 5 Cracks The Question is? When should we apply the maintenance and rehab activity? How to predict when cracks and how they occur in the pavement?

3 What about the mix design? Fatigue Beam Test Volumetric? Rut-tester? Indirect tensile? Stability? Hveem, Marshall, what else? Fatigue &Fracture Fatigue Beam Test Fatigue Beam Test

4 Beam Fatigue Fracture Test Specimens? Disk-Shaped Compact Tension Test Semi-Circular Notched Bending Fracture Test Samples Field Samples Lab Samples

5 Filed Cores The Goal Evaluate the fracture characteristics of the HMA using Semi-Circular Notched Bending Fracture (SCNBF) Test. Objectives and Scope Development and analysis of a simple fracture test using the gyratory compacted sample. Evaluation of the sensitivity and the variation of the fracture resistance with the properties of the mix constituents. Asphalt Mixes 34 different Hveem Designed Mixes. 2 different Superpave Designed Mixes.

6 Properties of Selected Field and Lab Modified Hveem Mixes Properties of Selected Modified Superpave Mixes Mix PG AC% -1.0% -0.5% Optim um +0.5% +1% % % Preparation of Specimens and Test Setup The HMA samples were compacted using the Superpave pave Gyratory y Compactor (SGC) to achieve a sample with final air voids of 4±1%. Semi-Circular Notched Specimens Sliced from a Standard Gyratory Compacted HMA Sample. Semi-Circular Notched Bending Fracture (SCNBF) Test Setup Constant vertical deformation rate of 0.5 mm/minute. at room temperature of approximately 25 C.

7 What do we measure? J c = d U U da b where, U is the strain energy to failure which equals to the area underneath the load- deformation curve up to the peak load; b is the specimen thickness; and a is the notch depth. How? From Simple Load-deflection diagram J c Calculations J c Calculations J c Determination for three Different Asphalt Mixtures ness, m gy/thickn.mm/mm Energ N y = x Notch, mm

8 Some Results Effects of Asphalt Content J c, kj/m Field mix Lab(-1% AC) Lab mix (4.3 AC%) Mix Group: G29 Lab(+1% AC) Results were found to be sensitive to the variation in the asphalt binder content. Effects of Asphalt Grade 0.80 Effect of Aggregate Structure /m 2 J c, kj PG PG PG PG76-28 Asphalt Binder Grade Mix Group: G20 Results were found to be sensitive to the variation in the asphalt binder Grade. Results were higher for mixes with finer gradations (Class I and II).

9 Effect of Temperatures Results for the tested mixes showed that they follow the same trend at different Temperature. Single Edge Notched Beam (SENB) Test (Comparison) MPa.m 0.5 (24 & 54.4 C C) KIC, M M1(-0.5AC%) M1(Opt-PG64-34) 54.4 C 24 C 4.4 C M1(+0.5AC%) M2(-1AC%) M2(Opt-PG64-28) M2(+1AC%) M2(PG64-22) (4.4 C) C, MPa.m 0 KI.m 0.5 KIC, MPa. SCNBF versus SENB Tests Results 0.3 SENB SCNBF M1(Opt-PG64- M1(-0 0.5AC%) M2(Opt-PG64- M2(+1AC%) M2(PG64-22) 22) 34) 28) Conclusions HMA Fracture Resistance can be measured using the semi-circular notched bending fracture (SCBNF) test. SCBNF is simple, quick and repeatable. Test results were found to be sensitive to the variation in the asphalt binder content and grade. Results for the tested mixes showed that there was no significant difference.

10 Conclusions (cont.) Mixes with finer aggregate g gradations showed higher Fracture Resistance over that with coarser gradations. When comparing SCNBF test and SENB test, there was no significant difference between test results. SCNBF test yielded greater values at low temperature of 4.4 C and low values at high temperature of 54.4 C C. Conclusions (cont.) Furthermore, for the tested mixes results at room temperature (24 C) followed the same trend of results determined at both temperatures 4.4 and 54.4 C. Results by SCNBF test at any temperature ranked the tested mixes in the same pattern. Semi-Circular Notched Bending Fracture test is a simple way to evaluate mix resistance to fracture Pavement Fracture. Is it Is it really bad?