Microstructural characterisation of rubber modified asphalt mixtures

Research to improve the performance of asphalt mixtures through the addition of crumb rubber using the dry process has continued worldwide because of its potential as a recycling option for used tires. For decades, dry mixed rubberised asphalt mixtures have performed inconsistently in field trials and laboratory evaluations. However, current research has revealed that the performance of asphalt mixtures is highly dependent on the characteristics of its internal structure or phase constituents. A comprehensive methodology has been developed in this study to characterise the microstructural properties of dry mixed rubberised asphalt mixtures and correlate them with the mixtures' macroscopic response to compression and fatigue. The proposed methodology combines a non-destructive imaging technique; X-ray Computed Tomography (CT) and image processing and image analysis procedures to quantify the properties of air voids and cracks as well as the rubber distributions within the rubberised asphalt specimen. A gap graded mixture of Hot Rolled Asphalt (HRA60/20) containing different percentages and gradings of crumb rubber particles was compared to a conventional mixture (unmodified or control mix). The results showed that the addition of crumb rubber affects the formation and distribution of air voids in an asphalt mixture. Correlations between the internal structural damage parameters and the mechanical behaviour of the asphalt mixtures were unanimous in concurring that adding rubber improves a mixture resistance to fatigue failure. The modulus of the asphalt mixtures at peak stress under compression reduced when the rubber was introduced into the mixture although in contrast, the image analysis showed less fracture within the tested specimen in comparison to the control mix. The imaging procedures developed in this text are recommended as a guide to characterise the internal structure of rubberised asphalt mixtures

Microstructural characterisation of rubber modified asphalt mixtures

Research to improve the performance of asphalt mixtures through the addition of crumb rubber using the dry process has continued worldwide because of its potential as a recycling option for used tires. For decades, dry mixed rubberised asphalt mixtures have performed inconsistently in field trials and laboratory evaluations. However, current research has revealed that the performance of asphalt mixtures is highly dependent on the characteristics of its internal structure or phase constituents. A comprehensive methodology has been developed in this study to characterise the microstructural properties of dry mixed rubberised asphalt mixtures and correlate them with the mixtures' macroscopic response to compression and fatigue. The proposed methodology combines a non-destructive imaging technique; X-ray Computed Tomography (CT) and image processing and image analysis procedures to quantify the properties of air voids and cracks as well as the rubber distributions within the rubberised asphalt specimen. A gap graded mixture of Hot Rolled Asphalt (HRA60/20) containing different percentages and gradings of crumb rubber particles was compared to a conventional mixture (unmodified or control mix). The results showed that the addition of crumb rubber affects the formation and distribution of air voids in an asphalt mixture. Correlations between the internal structural damage parameters and the mechanical behaviour of the asphalt mixtures were unanimous in concurring that adding rubber improves a mixture resistance to fatigue failure. The modulus of the asphalt mixtures at peak stress under compression reduced when the rubber was introduced into the mixture although in contrast, the image analysis showed less fracture within the tested specimen in comparison to the control mix. The imaging procedures developed in this text are recommended as a guide to characterise the internal structure of rubberised asphalt mixtures

Evaluating the cooling rate of hot mix asphalt in tropical climate

This paper aims to investigate the environmental effect on cooling rate and to determine the appropriate time available for compaction (TAC) using laboratory tests. This includes the study parameters, namely solar flux, base and ambient temperatures (daytime and night-time paving) and wind velocity, focusing on hot mix asphalt (HMA) asphalt concrete wearing with 14 mm nominal maximum aggregate size (ACW14) mix type for the wearing course and ACB28 mix type for the binder course. Samples were prepared in slab moulds 30.5 cm × 30.5 cm × 5 cm and compacted using a manually operated steel-roller. Readings were taken by averaging the temperature measurements at the middle and surface of the slabs and a temperature of 160 ºC was used as the mixing temperature. A control sample was prepared for each mix type and tested in the laboratory without the influence of wind velocity and solar flux. It was found that the cooling rate of HMA is significantly affected by environmental factors, thus influencing the TAC. The TAC tends to decrease by 15-50% during windy and night conditions but increases by up to 100% during daytime conditions compared to the control samples

Extension of dynamic source routing protocol in mobile ad hoc network

In a large dynamic network, data can be copied anywhere to make it fault tolerant and easy accessed but there must be an efficient protocol to manage the replicas and make sure the data is consistent and high in availability with a low communication cost. In this paper, we introduced a new protocol, named Diagonal Replication in Mesh (DRM) for data replica control protocol for a large dynamic network by using quorum and voting techniques to improve the availability and the communication cost because quorum techniques reduce the number of copies involved in reading or writing data.The protocol of DRM replicates data for large dynamic network by putting the protocol in a logical mesh structure and access consistent data by ensuring the quorum not to have a nonempty intersection quorum.To evaluate our protocol, we developed a simulation model in Java.Our results proved that DRM improves the performance of the response time compare to Three Dimensional Grid structure Protocol (TDGS)

Effect of rainfall on traffic flow characteristics during night time

Understanding traffic behavior for obtaining a smooth, safe and economical traffic operation requires a thorough knowledge of traffic flow parameters and their mutual relationships.Eventhough adverse weather can reduce traffic efficiencies, there are still questions to answer regarding the relationship between weather conditions and traffic flow at night. This paper presents an investigation of the rainfall effects to the traffic flow characteristics on atwo-lane rural highway during night time. The traffic data and corresponding rainfall data for uninterrupted road segment of Federal route 3 at Dungun, Terengganu were collected under road lighting condition during the north-east monsoon season. The effect of good weather condition, light rain, moderate rain and heavy rain conditions on speed, flow and density were quantified and compared. Results from the analysis indicate that mean speed, mean flow and mean density are reduced under various rainfall conditions. In general, the impact of good weather and various rainfall conditions on Greenshield’s fundamental traffic flow relationship have weak correlations except for the relationship between flow and density. The important points in the fundamental diagram derived from flow-density relationships indicated that critical density, maximum flow, critical speed, jam density and free flow speed of roadway all decrease as rainfall intensity increases. It can be concluded that traffic flow characteristics of two-lane rural highway in Terengganu are affected by rainfall conditions

Laboratory mix design of asphalt mixture containing reclaimed material

This paper presents a study on the production of asphalt test specimens in the laboratory containing reclaimed asphalt. The mixtures considered were stone mastic asphalt concrete mixtures containing up to 30% of reclaimed asphalt. Specimens were compacted to the reference density obtained from the Marshall mix design. Gyration compaction method was used for preparing specimens for the experimental programme, while coring and cutting methods and X-ray computed tomography (CT) were used to investigate the change in properties within the specimens and to validate the selected methodology.The study concluded that gyratory compaction is suitable to produce homogeneous test specimens also for mixtures containing high amount of reclaimed asphalt. Nevertheless, preliminary trials for each material are mandatory, as well as final coring and trimming of the specimens due to side effects

Experimental evaluation of anti-stripping additives on porous asphalt mixtures

The open structure of porous asphalt mix influences its strength and durability against air, water and clogging materials. These factors cause loss of adhesion between binder-aggregate interface and loss of cohesion within the binder film. This could lead to stripping problem which contribute to premature failures as well as deterioration in the performance and service life of porous asphalt. Therefore, this study is aimed to evaluate the potential of diatomite as anti-stripping additives in porous asphalt and compared with hydrated lime and Ordinary Portland Cement (OPC). Field Emission Scanning Electron Microscopy (SEM) test and Energy Dispersive X-ray Spectroscopy analysis (EDX) were conducted to investigate the microstructure and chemical composition of the anti-stripping additives. A number of gyratory compacted samples of porous asphalt mixture with Malaysian gradation were prepared. Each sample was incorporated with 2% of anti-stripping additives as filler then mixed with polymer modified bitumen of PG76. The samples were measured for air voids content, permeability rate, resilient modulus and abrasion loss. The results indicate that samples prepared with hydrated lime show higher permeability rate and lower abrasion loss compared to samples with OPC and diatomite. However, the samples prepared with diatomite show enhanced resilient modulus compared to those with hydrated lime and OPC

Editorial: trends and advanced materials for pavement and road infrastructure

A year with the Covid-19 pandemic has caused great impacts on all aspects of society worldwide. With the current challenges, this special issue offers four interesting technical papers comprising research on bitumen modification, pavement noise, waste material, and modeling of concrete bridges

Characterization of the performance of aluminum oxide nanoparticles modified asphalt binder

This study investigates the physical and rheological properties of asphalt binders modified by nano aluminum oxide (AL2O3). Several conventional tests were conducted, including penetration, softening point and ductility, rotational viscosity and dynamic shear rheometer (DSR). Based on the results of the tests, it was found that the hardness of modified asphalt binders increased with the addition of nano AL2O3 up to 5%. As a result of the increased hardness, the softening point of modified asphalt improved compared with base asphalt binders. The rheological property of modified binders was enhanced at low and high temperatures. The results of a DSR test revealed that the G* were improved, whereas the δ decreased slightly. The addition of a different percentage of AL2O3 to base binder had a remarkable influence on resistance to permanent deformation (high temperature rutting and low temperature fatigue). Results recognize 5 wt.% as the optimum content of the modifier. Therefore, nano AL2O3 can be considered as a proper alternative additive to modify the properties of asphalt cement