Shadi Saadeh

Investigation of fracture properties of California asphalt mixtures using semicircular bending and beam fatigue tests

Fatigue cracking is a primary distress in asphalt concrete (AC) due to repetitive stresses and strains caused by both traffic loading and environmental factors. The fatigue resistance of AC is investigated by a number of fatigue tests. The main objective of this study is to investigate the use of the semi-circular bending (SCB) test as a quality assurance/quality control (QA/QC) measure for field construction. The comparison of fracture properties of seven AC mixtures from the SCB and beam fatigue test (BFT) is conducted. The J c and K 1c values for the seven mixtures were determined. The BFT was performed on the same mixtures and the initial stiffness, N f and plateau value (PV) were determined. The coefficient of variation (CV) ranged from 0% to 38% for J c and from 0% to 35% for K 1c. The CV ranged from 10% to 93% for the initial stiffness, 2% to 83% for N f and 8% to 167% for PV. The SCB J c and BFT N f and PV indicated lower fracture properties for PG64-10RAP (LIME), AN-HMA and WMA-ADVERA mixtures than other mixtures. The BFT N f and PV achieved similar ranking for all mixtures. There is good correlation between N f and PV with J c, and not a good correlation between the initial stiffness with J c, N f and PV. This has indicated that the initial stiffness is not a good representative for fracture properties of AC while J c, N f and PV are better indicators. The results of this study indicate that the SCB test has a great potential as a QA/QC test of fracture properties of asphalt mixtures.

Mechanistic Properties of Hot-Mix Asphalt Mixtures Containing Hydrated Lime

Permanent deformation and moisture damage are common distresses found in pavements today. The use of hydrated lime is known to decrease moisture susceptibility, and as a mineral filler it increases the stiffness of the mixture. The objectives of this study were (a) to evaluate the fundamental engineering properties of hot-mix asphalt (HMA) mixtures containing hydrated lime compared with conventional mixtures designed to meet the current Louisiana Superpave® specifications and (b) to evaluate the influence of hydrated lime on the mechanical properties of the resulting HMA mixtures. Nine 19.0-mm Level 2 HMA mixtures were designed and examined. Siliceous limestone aggregates that are commonly used in Louisiana were included in this study. The nine mixtures were divided into three sets; each set contained three mixtures. The first set included three mixtures that are conventional, as control mixtures, containing no hydrated lime and an SB polymer-modified asphalt cement meeting Louisiana specifications for PG 76-22M, PG 70-22M, and a neat PG 64-22. The second set included three mixtures that contained hydrated lime that was incorporated into the aggregate and asphalt cement mixture as slurry. The asphalt cements used were identical to the ones used in the first set, namely PG 76-22M, PG 70-22M, and conventional PG 64-22. The third set included three mixtures that contained hydrated lime that was blended dry with the asphalt cements used in the first and second sets, that is, PG 76-22M, PG 70-22M, and PG 64-22. Mechanistic tests were conducted to define the permanent deformation and endurance life of HMA mixtures with and without hydrated lime. The results indicated that the addition of hydrated lime as a mineral filler improved the permanent deformation characteristics of the asphaltic concrete mixtures. This improvement was particularly apparent at higher testing temperatures with mixes containing polymer-modified asphalt and limestone aggregate.

Performance Evaluation of Stabilized Base and Subbase Material

The resilient modulus and permanent deformation are important material properties in the characterization of unbound base materials and subgrade soils and in the design of pavement structures. This study evaluates the effect of stabilizing the base and subbase layers on the performance of a pavement structure. Three test lanes with six sections were constructed at the pavement research facility (PRF) of the Louisiana Transportation Research Center (LTRC). The six sections incorporated six different base course and two sub-base materials. The base materials were crushed limestone, Blended Calcium Sulfate (BCS), BCS stabilized with slag (BCS-Slag), BCS stabilized with flyash (BCS-Flyash), foamed asphalt treated 100% recycled asphalt (RAP) (FA-100RAP), and foamed asphalt treated blend of 50% RAP and 50% soil cement (FA-50RAP-50SC). The subbase materials were lime-treated and cement-treated soils, whereas subgrade was a clay (A-4) soil. The laboratory repeated load triaxial resilient modulus, permanent deformation, and material property tests were performed on these pavement materials. The BCS treated with slag showed the lowest permanent deformation base material followed by BCS treated with flyash, BCS, crushed limestone, and recycled asphalt pavement. Cement-treated soil, among subbase material, showed the lowest permanent deformation followed by lime-treated soil.

On the relationship of microstructure properties of asphalt mixtures to their constitutive behaviour

Asphalt mixtures are composite materials that consist of asphalt binder, air voids and aggregate particles that vary by orders of magnitude in size. Most constitutive models of asphalt mixtures are formulated based on macroscopic measurements. However, little effort has been spent in the past in determining the relevance of these macroscopic measurements to actual material response at the microstructural level. This paper presents an overview of a viscoelastic-viscoplastic model for asphalt mixtures that was developed previously by the authors. The models parameters were obtained in this paper by analysing triaxial repeated creep and recovery tests conducted at different confining and axial stresses. The microstructure characteristics of asphalt mixtures were determined by measuring aggregate physical characteristics, three-dimensional orientations of aggregates and air void distribution. The relationships of models parameters with these microstructure characteristics are discussed in this paper. The results are used to draw conclusions in regard to the influence of microstructure characteristics on asphalt mixture response in terms of hardening, softening and dilation. These results have also provided insight in regard to the suitability of some of the macroscopic measurements in reflecting the actual changes in the material microstructure during deformation.

Correlation of Semi-circular Bending and Beam Fatigue Fracture Properties of Asphalt Concrete Using Non-Contact Camera and Crosshead Movement

Fatigue cracking is a primary distress in asphalt concrete (AC) due to repetitive stresses and strains caused by both traffic loading and environmental factors. The fatigue resistance of AC is investigated by a number of fatigue tests. The main objective of this study is to compare the fracture properties of AC under Beam Fatigue Test (BFT) and the Semi-circular Bending (SCB) test using non-contact camera and crosshead movement. A comprehensive comparison of fracture properties of six AC mixtures from the SCB non-contact camera method, SCB Cross Head Movement (CHM) method and Beam Fatigue test (BFT) was conducted. The critical strain energy (Jc) and K1c values for AC mixtures are determined. BFT was performed on the same mixtures and initial stiffness, Nf and PV are determined. Comparison between the tests parameters was performed, and the Jc and K1c of SCB non-contact camera and CHM methods indicated lower fracture properties for PG64-10RAP (LIME), AN-HMA and WMA-ADVERA and higher fracture properties for 710P4-AR, AN-WMA and PG64-28PM mixtures. Similar results were achieved by BFT Nf and PV parameters. Data analysis showed that there is a linear correlation between Jc and K1c from the both SCB test methods, a good correlation between Nf and PV with Jc, and poor correlation between initial stiffness with Jc, Nf and PV. This has indicated that the initial stiffness is not a good representative for fracture properties of AC while Jc, Nf and PV are better indicators. The results of this study indicate that the SCB test has a great potential as a QA/QC test of fracture properties of asphalt mixtures.