The importance of wetting in healing of bitumen

Asphalt concrete has the advantageous ability to heal autonomously, however the mechanisms behind this are not fully understood. To increase insight in the healing mecha-nism, the healing model used in polymer science is adopted. It interprets healing as the sum of wetting and intrinsic healing. The presented work introduces a new test set-up, which is de-signed to investigate the relative contribution of wetting and intrinsic healing by measuring the strength gain when two pieces of binder are brought into contact. Results obtained show that for a soft, pure binder, wetting is the dominant process. This can be concluded from the fact that at least 50% of the observed healing can be attributed to wetting. Wetting is highly de-pendent on both the load level and the duration of load application. Consequently, it is shown that the level of healing observed in asphalt concrete is very dependent on the boundary condi-tions

Het healingmechanisme van bitumen nader verklaard

Asfalt heeft de aantrekkelijke eigenschap dat het zichzelf kan herstellen na schade. Er is echter tot op heden geen betrouwbare methode om de healingcapaciteit van een asfaltmengsel te bepalen. Bij het healingproces van een discrete scheur spelen twee processen een rol, namelijk het in contact komen van de oppervlakken van de scheur; het zogenaamde bevochtigen, en het vermogen van deze oppervlakken in contact om kracht over te dragen; de intrinsieke healing. In dit artikel wordt een testmethode gepresenteerd welke in staat is om de verschillende parameters die een rol spelen gedurende de healing te variëren om zo het belang van de processen in healing bloot te leggen. Met behulp van deze testmethode is de mate van healing van bitumen in de tijd onderzocht en de invloed van normaalkracht gedurende healing. Op basis van de gepresenteerde resultaten kan worden geconcludeerd dat bevochtiging van het scheuroppervlak tenminste 50% van de macroscopisch geobserveerde healing bepaalt voor pure bitumen. Dit inzicht kan worden gebruikt om een materiaalmodel voor healing van asfalt te formuleren, op basis waarvan een relatief eenvoudige healingtest kan worden ontworpen waarmee de healingcapaciteit van asfaltmaterialen onderling kan worden vergeleken

Direct tensile test to assess healing in asphalt

Asphalt concrete has the advantageous ability to heal. During rest periods, damage present in the material is restored to a certain extent. Healing of the material can be observed in its regaining of strength and stiffness after rest periods. In this paper, a new test method is presented. It was developed to increase the understanding of the healing phenomenon. The test method focused on asphalt as it was assumed to be the driver of the healing performance. The test method assessed the healing performance of asphalt in stiffness and strength by testing the bond strength in tensile mode of two pieces of asphalt that were assembled under controlled temperature and stress conditions. With the test method, healing tests were performed on one type of binder; the load level during healing and the healing time were varied. The test results showed that after a short healing time of only 6 min, a significant amount of healing could be detected. That finding indicates the importance of adhesion between two crack surfaces when the healing capacity is assessed. It was also found that the maximum tensile stress reached a plateau value after 24 h of healing; the finding indicates that full healing can be realized in short time periods for pure, unaged, soft binders. It was also shown that the load level perpendicular to the damage during healing had a significant effect on the observed healing

The importance of wetting in healing of bitumen

Asphalt concrete has the advantageous ability to heal autonomously, however the mechanisms behind this are not fully understood. To increase insight in the healing mechanism, the healing model used in polymer science is adopted. It interprets healing as the sum of wetting and intrinsic healing. The presented work introduces a new test set-up, which is designed to investigate the relative contribution of wetting and intrinsic healing by measuring the strength gain when two pieces of binder are brought into contact. Results obtained show that for a soft, pure binder, wetting is the dominant process. This can be concluded from the fact that at least 50% of the observed healing can be attributed to wetting. Wetting is highly dependent on both the load level and the duration of load application. Consequently, it is shown that the level of healing observed in asphalt concrete is very dependent on the boundary conditions.Pavement Engineerin

Het healingmechanisme van bitumen nader verklaard

Asfalt heeft de aantrekkelijke eigenschap dat het zichzelf kan herstellen na schade. Er is echter tot op heden geen betrouwbare methode om de healingcapaciteit van een asfaltmengsel te bepalen. Bij het healingproces van een discrete scheur spelen twee processen een rol, namelijk het in contact komen van de oppervlakken van de scheur; het zogenaamde bevochtigen, en het vermogen van deze oppervlakken in contact om kracht over te dragen; de intrinsieke healing. In dit artikel wordt een testmethode gepresenteerd welke in staat is om de verschillende parameters die een rol spelen gedurende de healing te variëren om zo het belang van de processen in healing bloot te leggen. Met behulp van deze testmethode is de mate van healing van bitumen in de tijd onderzocht en de invloed van normaalkracht gedurende healing. Op basis van de gepresenteerde resultaten kan worden geconcludeerd dat bevochtiging van het scheuroppervlak tenminste 50% van de macroscopisch geobserveerde healing bepaalt voor pure bitumen. Dit inzicht kan worden gebruikt om een materiaalmodel voor healing van asfalt te formuleren, op basis waarvan een relatief eenvoudige healingtest kan worden ontworpen waarmee de healingcapaciteit van asfaltmaterialen onderling kan worden vergeleken.Pavement Engineerin

Direct Tensile Test to Assess Healing in Asphalt

Asphalt concrete has the advantageous ability to heal. During restperiods, damage present In the material is restored to a certain extent.Healing of the material can be observed in iis regaining of strengthand stiffness after rest periods. In this paper, a new test method is presented.It was developed to increase the understanding of the healingphenomenon. The test method focused on asphalt as it v/ss assumed tobe the driver of the healing performance. The test method assessedthe heaUng performance of asphalt In stiffness and strength by testingthe bond strength In tensile mode of two pieces of asphalt that wereassembled under controlled temperature and stress conditions. Withthe test method, healing tests ^yere performed on one type of binder;the load level during healing and the healing tune were varied. The tesiresults showed that after a short healing time of only 6 min, a significantamount of healing could be detected. That finding indicates the importanceof adhesion between two crack surfaces v/hen the healing capacityis assessed. It v/as also found that the maximum tensile stress reached aplateau value after 24 h of healing; the finding indicates thatfull healingcan be realized in short time periods for pure, unaged, soft binders. Itv/as also shov/n that the load level perpendicular to the damage duringheaUng had a significant effect on the observed healing.Pavement Engineerin

The influence of boundary conditions on the healing of bitumen

Damage in pavements is known to reduce over time when the material is left to rest, this phenomenon is identified as healing. It has been shown that healing has a large influence on pavement performance. However, as the healing mechanism is not fully understood, there is currently no accepted method available to assess the healing performance of an asphalt binder. Healing of cracks can be seen as the sum of two processes, cracked surfaces coming into contact (wetting) and strength gain of the contact area (intrinsic healing). This paper aims to increase the understanding of the process of two surfaces coming into contact. Healing of bitumen is assessed using a novel test method, which allows for controlled variation of the stress state during healing. This method consists of bringing two pieces of bitumen together and allowing them to heal under controlled conditions. The extent of healing is then assessed by testing the healed specimens in direct tension. The results, presented in this paper, show that the stress state at assembly and during healing has a significant impact on the extent of healing.Pavement Engineerin

Mechanisms in Healing of Bitumen and the Impact of Normal Force

Damage in pavements is known to reduce over time when the material is left to rest, this phenomenon is known as healing. It has been shown that healing is an important influence factor in pavement performance. However, an accepted method to assess the healing capability of a pavement is currently not available. Healing of cracks is assumed to be the sum of two processes, cracked surfaces coming into contact (wetting) and strength gain of surfaces in contact (intrinsic healing). The paper describes influencing parameters of these two processes. The healing potential of bitumen is assessed using a novel test method. In this method two pieces of bitumen are brought together and left to heal under controlled condi-tions. After healing the amount of healing is assessed by testing the specimens us-ing a direct tensile test. From the results it can be seen that normal force has a sig-nificant impact on the observed healing, indicating that the process of two surfaces coming into contact (wetting) has a significant impact on healing behavior of the bitumen.Pavement Engineerin

Carbon footprint comparison of innovative techniques in the construction and maintenance of road infrastructure in The Netherlands

The ambition of European countries to reduce their national greenhouse gas emissions, has been translated in the Netherlands in green procurement policy of the national road administration. An increasing amount of innovative techniques and approaches in road infrastructure construction and maintenance are available, but their contribution to achieving the national goals is often unknown. The aim of this research was to develop insight for policy makers and researchers on the potential impact of existing and nearly operative innovative techniques in road infrastructure. The emissions during the whole life cycle of Dutch road infrastructure forms the baseline of this study. The total greenhouse emissions from Dutch road infrastructure are estimated at 2 Mt CO2-equivalents per year, which are mainly resulting from production and construction of asphalt road, bricks, concrete elements and electricity for lighting. Subsequently, ten currently and nearly operative innovations are inventoried and assessed on their reduction potential for greenhouse gas emissions. Large reductions can be achieved by switching the energy source of lighting installations towards renewable sources. For asphalt roads, low energy asphalt and the application of rejuvenators had the highest carbon reduction potentials. Reducing the amount of new made bricks by using concrete elements instead leads to almost 30% CO2 reduction for the emissions of brick roads. For concrete element roads, the highest reduction potential is in further applying the construction recycling concept called “Kringbouw”. The cumulative greenhouse gas reduction potential is 37% for both the main road network and the asphalt roads in the secondary road network, 28% for both bricks and concrete element roads, and 84% for maintenance and control of the total road infrastructure. This study shows that the reduction potential for carbon emissions in infrastructure is substantial: a cumulative reduction of one third of the Dutch road infrastructure emissions could be achieved. This study as well as similar follow-up studies can serve as a guide for policy makers in early development stages and decision making