Field Trials with Polymer Modified Asphalts in Saudi Arabia

The bonding strength provided by the tack coat between asphalt concrete layers at the interface is considered as an essential issue in the performance of the flexible pavement throughout its service life. However, the surface texture of the pavement surface exhibits another essential issue in the bond strength. In this investigation, three layers of asphalt concrete (base, binder and wearing) courses with (25, 19, and 12.5) mm of nominal maximum size of aggregates have been prepared using roller compactor. Rapid curing cutback RC-70 and cationic medium setting emulsion CMS have been implemented as tack coats with three application rates. The slab specimens were subjected to mean texture depth determination using sand patch method. Core specimens of 102 mm diameter were obtained from the prepared slab samples and subjected to interface bond strength test with the aid of a special manufactured mold. Test results were analyzed and compared. It was concluded that when RC-70 tack coat was implemented, asphalt concrete binder course laid on base course exhibited the highest shear strength of 1600 kPa at an application rate of 0.33 liter/m2 when compared to other application rates. Asphalt concrete wearing course laid on binder course exhibited the highest shear strength of 1515 kPa at an application rate of 0.15 liter/m2 when compared to other application rates. When CMS tack coat was implemented, asphalt concrete binder course laid on base course exhibited the highest shear strength of 1620 kPa at an application rate of 0.23 liter/m2 when compared to other application rates. Finally, the asphalt concrete wearing course laid on binder course exhibited the highest shear strength of 2272 kPa at an application rate of 0.23 liter/m2 when compared to other application rates.

Modification of asphalt binder is a must to enhance the performance of asphalt binder. The objectives of this study are to develop an extensional deformation test method using a Sentmanat Extensional Rheometer (SER) fixture inside a Dynamic Shear Rheometer (DSR) and to investigate the relationship between different percentages of latex polymer and force ductility in polymer (latex) modified asphalt emulsion (PMAE) and polymer modified asphalt binder (PMAB). The sample geometry used in this study is 3 mm × 0.72 mm. Total twenty-four samples are tested by the SER where twelve samples are PMAE and twelve samples are PMAB. One neat binder PG 64-22 and one PMAE are used. 2%, 4% and 6% latex are mixed with PG 64-22 by a mechanical mixer and a high shear mixer for making PMAB. PMAEs are collected from the manufacture with 0%, 2.5%, 4% and 5.5% latex in it. Second peak elongation force, F2 is only obtained from the latex modified binders and emulsions. First peak elongation force, F1 has no linear correlation in case of PMAE and PMAB where F2 has a linear correlation with the percent of the polymer in the PMAE and PMAB with R2 values equal to 0.9934 and 0.9535 respectively indicating extensional deformation test with SER is very promising. Additionally, DSR temperature sweep test results and multiple stress creep recovery (MSCR) test results indicate that F2 is a better indicator of polymer content than rutting factor G*/sinδ and non-recoverable creep compliance, Jnr.

Major distresses such as rutting, fatigue, and thermal cracking are facing asphalt pavement structures due to continuous heavy traffic loading and climate change. The modification of asphalt binders (one of the main components of the asphalt paving mix) has the potential to mitigate distresses through using different additives. Polymer modified asphalt (PMA) binders showed a noticeable resistance to pavement distresses as reported in previous studies. The present study aims to evaluate the effect of polymer modification on the rheological properties of asphalt binders through laboratory tests. The polymers included styrene-butadiene-styrene (SBS) and epolene emulsifiable (EE2) types. The 60/70 binder was used as a control for comparison. The Mechanistic-Empirical Pavement Design Guide (MEPDG) was also utilized to simulate the effect of PMA binders on the rheological properties under different climatic conditions and structural capacities. Additionally, the MEPDG was further utilized to compare the effect of asphalt binders on rheological properties using four different binder input levels. Findings of the study showed that laboratory tests experienced varying outcomes regarding the most efficient asphalt binder by means of distresses resistance. However, the MEPDG evaluation showed that the overall ranking of asphalt binders positively impacting the rheological properties was as following: (1) 4.5% EE2 PMA, (2) 4% EE2 PMA, (3) 60/70 binder, (4) 5% SBS PMA, and (5) 4% SBS PMA binders. Furthermore, statistical analysis illustrated that the effect of using different binder input levels on the performance of pavement varied relatively to the evaluated distresses. The analysis showed that using different binder input levels would affect, to a certain extent, the asphalt binder influence on rheological properties only when evaluating rutting and fatigue distresses. Therefore, it is recommended that precise asphalt binder inputs, that is, shear complex modulus (G*) and phase angle (δ) are used when designing pavement structures in regions with hot and mild climate conditions.

This paper investigates the damage-healing properties of unmodified and polymer modified asphalt binders under different aging levels using newly developed linear amplitude sweep based healing (LASH) test. One neat asphalt 70# and one Styrene-Butadiene-Styrene (SBS) modified asphalt are selected in this study. The original binders are subjected to the Rolling Thin Film Oven (RTFO) and Pressurized Aging Vessel (PAV) tests for stimulating the short- and long-term aging of asphalt binders during the pavement construction and service phases. Through the LASH tests under different aging levels of the two binders, it is found that the damage-healing performance of both neat and modified asphalt binders gradually decrease with the increasing aging levels. It is also observed that the healing performance of 70# neat asphalt is higher than that of SBS binder in pre-failure conditions, however, the healing behaviors of SBS binder is becoming obviously better than that of 70# binder after fatigue failure. Furthermore, a promising relationship is found between the macroscale healing properties of asphalt binders and their microscale chemical composition under various aging levels.

The objective of this research was to investigate the variability of base layer construction in hot-mix asphalt (HMA) pavements and to assess the impact of base layer variability or nonuniformity on pavement performance. Subjective acceptance criteria of base layer construction may lead to variable pavement performance and may result in early pavement distresses and failure. Eleven existing HMA pavement projects with aggregate base course layers constructed in the past few years were selected for falling weight deflectometer (FWD) testing and visual distress surveys. In six of these projects, issues with aggregate base performance (stability and uniformity) had been observed and reported during paving of the HMA surface layer. Later, these pavements exhibited various levels of early distresses, including cracking (longitudinal, transverse, and alligator), aggregate base failure, and pavement surface roughness or irregularities (for ride quality). The remaining five HMA pavement projects, for which no issues related to aggregate base layer behavior were reported during construction, performed well after construction. A test section of approximately 1 mi on each project was subjected to FWD testing. The existing HMA pavements that showed early distresses exhibited high levels of spatial variability and nonuniformity in aggregate base course layers, as demonstrated by FWD testing and backcalculated base layer modulus values and distributions. The existing HMA pavements that performed well exhibited low levels of spatial variability and good uniformity in aggregate base course layers, as shown by the FWD test results and the backcalculated base layer modulus values and distributions.

The paper investigates the improvement of bitumen mixture fatigue resistance and the rutting performance by using a specific low percentage of a styrene–butadiene–styrene (SBS) polymer, which contains polystyrene and polybutadiene compounds. A Fourier transform infrared (IR-FT) spectroscopy of the SBS polymer used in following test was carried out to ascertain the polybutadiene and polystyrene compound ratio, which may affect the modificant properties. Unmodified, low-percentage modified SBS, and common polymer-modified bitumen (PMB) as a reference were tested to ascertain the properties, fatigue resistance, and the rutting performance. The test results of the low-percentage modification with SBS are compared against unmodified mixtures and standard PMB mixtures. Finally, a simulation of the practical application was performed using the HDM-4 software (version 2.0), where the material research findings, with an emphasis on the rutting performance, were translated into the pavement performance with a varying binder course layer under simulated traffic conditions. Lifecycle analysis, with a focus on emissions production (CO2, SO2, and NOx) during pavement operation, was conducted for pavements with unmodified, low-percentage modified SBS, and standard PMB binder courses. The lifecycle analysis showed that a 3% modification of the binder course with the SBS polymer can extend the rutting parameter pavement lifecycle by approximately 34.5%, which is about half of the extension provided by the standard PMB modification. The resulting improvement in the pavement serviceability translated to a 9% reduction in CO2 and SO2 emissions and a 7.2% reduction in NOx emissions over a 20-year period.

The purpose of this research is to study the moisture induce damage performance of dense graded (AC14) and stone mastic asphalt (SMA14) asphalt pavement using Nanolyacrylate polymer modified asphalt binder. The physical properties of aggregate, volumetric and performance of asphalt mixes were assessed and evaluated with the laboratory tests. The study investigates fourteenth different asphalt mixtures consisting of NP modified asphalt binder formulations at 2%, 4% and 6%. Two types of asphalt binder, penetration grade PEN 80-100 and performance grade PG 76 were added with Nanopolyacrylate as asphalt modifier. The modified asphalt binder was prepared by adding 6 percent of Nanopolyacrylate (NP) to the asphalt binder. Both AC14 and SMA14 mixtures passed the Marshall requirements which indicate that these mixtures were good with respect to durability and flexibility. In terms of moisture induce damage, it was observed that the strength of the asphalt mixes increased with the addition of NP polymer modified asphalt binder. Similar trend could also be seen for SMA14 mixes, where the ITS value of SMA14 showed a significant difference compared to AC14 and all the mixtures exceeded the minimum requirement value as specified in the specification. Thus, addition of nanopolyacrylate polymer to the asphalt binder has significantly improved the cohesion as well as adhesion properties of the asphalt binder, and hence the stripping performance. Therefore, it can be concluded that the nanopolyacylate is suitable to be used as a modifier to the modified asphalt binder in order to enhance the properties of the asphalt binder and thus improving the performance of asphalt in both AC14 and SMA14 mixes.

Recent studies have concluded that measured surface deflections can be used as a low-cost pavement monitoring and condition assessment tool to determine remaining structural life and pavement performance. Moving load devices are being used more often to measure continuous surface deflections. They are considered a faster alternative to falling weight deflectometer–based structural condition evaluation applications. The objective of the study was to compare the analytical dynamic simulation of slow-moving deflection measurements with field data. The surface pavement deflections and the pavement structural responses generated by the Euroconsult Curviametro loading at the Minnesota Department of Transportation’s MnROAD facility near Maplewood, Minnesota, were used in the evaluations. Four geophones were embedded near the pavement surface to measure surface deflections during field trials at each of three tested MnROAD cells. In addition, numerous other sensors, such as strain gauges and thermocouple trees, were available at the MnROAD facility. The 3D-Move program was used in the simulations because it can accommodate moving loads and the viscoelastic properties of pavement layers and produce continuous deflection basins. The viscoelastic properties of pavement layers were estimated on the basis of the actual temperatures at the time of the field trials and the appropriate loading frequency of the Curviametro. The proposed dynamic analytical model provided a good match with a variety of independent pavement responses, which included surface deflection basins (measured by embedded geophone sensors) as well as horizontal strains at the bottom of the asphalt concrete layers (measured by MnROAD sensors).

The interlaminar shear and fatigue performance of pavement structure connected by the nail

The study investigated the effects of laboratory ageing on the fluxed and water-foamed asphalt binders in scope of Fourier transform infrared spectroscopic measurements of ageing indicators and changes in their chemical composition. The investigated binders included two paving grades, two polymer modified asphalt binders, and a highly modified asphalt binder. The bio-flux additive was produced from rapeseed methyl esters in an oxidation reaction in the presence of a metal catalyst and organic peroxide. The use of the bio-origin additive, in particular oil derivatives, was aimed at softening and better foaming of asphalt binders. This modification is possible due to the good mixability of vegetable oils with an asphalt binder, which gives a homogeneous product with reduced stiffness. The study involved the rolling thin film oven, short-term, and the pressure ageing vessel, long term, and ageing to induce oxidation on the evaluated asphalt binders. The addition of the bio-flux additive has significantly decreased the measured content of ketone compounds related to oxidation in both non-aged and aged asphalt binders, although this effect after ageing were far smaller in magnitude. Additionally, both ageing processes decreased significantly the absorbances in the ester spectral bands specific to the bio-flux additive. All mentioned effects were similar in magnitude in all tested asphalt binders.

Six pavement sections were tested using a falling weight deflectometer (FWD). The six pavement sections were all in the Phoenix, AZ area. All six pavements have the same pavement structural cross-section: 3 to 4 in. (76.200–101.60 mm) of hot mix asphalt concrete surface supported by 10 to 13 in. (254.00–330.20 mm) of aggregate base course and underlain by a granular subgrade. Three of the six pavements possess aggregate base courses which have been stabilized with 1 % hydrated lime. The other three pavements incorporate the same aggregate base course but without lime stabilization. Resilient moduli of all pavement layers were back-calculated based on the FWD data. The moduli of all pavement layers are analyzed statistically. The addition of the same percentage of lime is shown to make a substantial difference in the stiffness of the layers and the structural contribution of the base layer to the pavement system. The effect of the stabilization with small percentages of lime on pavement performance and pavement life is discussed.

A high-performance thin asphalt overlay (HPThinOL) is specified as having a thickness of 1 in. or less and is used in applications requiring high levels of rutting and fatigue resistance. HPThinOLs are used as a pavement preservation strategy and are placed on pavements that have remaining structural capacity that is expected to outlive that strategy. Current specifications for HPThinOLs generally call for a polymer-modified asphalt (PMA). However, PMA binders are more expensive than unmodified asphalt binders. This expense, coupled with the higher binder content requirement generally associated with HPThinOL, could lead to an initial higher cost in relation to other pavement preservation strategies. Although the higher initial cost can be offset by incorporating high amounts of reclaimed asphalt pavement (RAP), the use of high amounts of RAP in PMA mixtures might adversely affect the mixture performance (stiffness, cracking, or workability). Warm-mix asphalt (WMA) technology may improve the workability of HPThinOL that incorporates high RAP content and PMA binders. This study evaluated the effect of PMA binders, high RAP content, and WMA technology on the stiffness, resistance to reflective cracking, moisture susceptibility, and workability of HPThinOL mixtures. PMA binders and high RAP content increased the stiffness of HPThinOL significantly; however, the use of WMA technology lowered mixture stiffness and improved workability. PMA may improve the cracking resistance, moisture susceptibility, and rutting resistance of high-RAP HPThinOL mixtures, depending on whether a WMA technology is used.

Bitumen stabilized materials as pavement overlay: Laboratory and field study

The primary objective of this study was to determine the effect of asphalt structure patterns on permanent deformation, and investigate the contribution of pavement structural layers to permanent deformation of asphalt pavement. Three test segments were constructed at the Circular Track in Chongqing. The three segments had a similar HMA wearing course, binder course, and sub-grade. However, the base course and sub-base of the three segments were different, and the total depth of asphalt layers was different. All three segments were tested under the Accelerated Loading Facility to 500 thousand passes. The permanent deformation was evaluated using rutting measurements. The test results showed that the majority of permanent deformation occurred in top 200mm of the asphalt layer and the maximum cumulative deformation rate occurred within 120mm depth, which may indicate that the binder course significantly influenced permanent deformation of asphalt pavements.

Asphalt pavement susceptibility to moisture damage is considered as a major issue in the durability and service life of the roadway. Quick and nondestructive testing of asphalt concrete pavement are the major concern for predicting its suitability for evaluation. In the present investigation, nondestructive test has been implemented to detect the moisture damage issue of asphalt concrete mixture. Asphalt concrete specimens were prepared using Marshall method. Aggregates gradation of wearing, binder and base course was implemented for the preparation of the specimens. Specimens were tested for ultrasonic pulse velocity before and after practicing the moisture damage procedure. The variations of seismic modulus among various gradation before and after the moisture damage were considered as a criterion for moisture damage and related to tensile strength ratio TSR. It was observed that the pulse velocity decline by a range of (11 to 16) for asphalt concrete after moisture damage. It was concluded that the Seismic modulus as calculated from the ultrasonic pulse velocity test was effective in distinguishing the impact of moisture damage. The seismic modulus at optimum asphalt content decline by (34.7, 46.7, and 52.6) % after moisture damage for wearing, binder, and base course mixtures respectively. The ultrasonic pulse velocity test is recommended for assessing the susceptibility of asphalt concrete mixture to moisture damage.