Influence of spray jet technology on bond strength of asphalt and pavement life

Pienaar, Eugenie (2020-03)

Thesis (MEng)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: Tack coats promote bonding between pavement layers. This allows the pavement structure to behave as a single unit whilst providing adequate strength. The lack of poor bonding leads to a pavement structure comprising of multiple independent (thin) layers. This in turn will be unable to withstand traffic-imposed loading potentially resulting in pavement distress. The occurrence contributes to fatigue distress such as cracking as well rutting significantly reducing pavement life. Various studies have shown that interface bonding between pavement layers (provided by tack coats) has a significant effect on pavement performance. Some of these studies also investigated pavement response due to external factors such as traffic loading, existing road surface conditions and temperature. However, it is also reported that intrinsic factors (e.g. tack coat application method) of the tack coat are found to contribute to the degree of bonding achieved. Various conventional methods are available for application of the tack coat. Alternatively, Spray Jet technology developed by the Wirtgen Group is a more modern method used to apply tack coats. The technology enables the immediate construction of the asphalt surfacing once the tack coat is sprayed onto the surface. Preliminary research shows the economical advantages of the use of the technology but some logistical disadvantages still remain when used in larger projects. Some of the intermediate disadvantages however can be outweighed by the long term benefits provided by the technology. The advantages creates the drive to employ the technology currently in smaller projects such as municipal roads. It also promotes the use of the technology on an international level. The technology is investigated by means of a two-phase project in collaboration with Pisa University. The study includes laboratory work, linear-elastic analysis and mechanistic design as part of the first phase (preliminary research study). The second phase (current study) includes the simulation of the conditions from the first phase through Finite Element Modelling in order understand the results obtained and behaviour observed. The purpose of the analyses is mainly to develop an understanding of the influence of shear strength on the pavement life and which factors influence the shear developed within the tack coat. This will provide insight on the potential advantages or disadvantages of the use of the technology. Both academic institutions considered representative pavement structures and conditions during analyses performed during Phase 1. This phase consists of two components: linear-elastic analysis and laboratory testing. A linear-elastic analysis was completed by Pisa and Stellenbosch University where two types of laboratory experiments were completed by Pisa University. Although, the results vary in terms of degree of stress observed in the pavement, all results favoured the application by means of tack coat compared to other methods. Extended research is required to provide a broader understanding however. The preliminary analysis highlights the influence of material stiffness and layer thickness and its relation with shear generation with certain regions of the pavement structure. The combinations of these two parameters are found to have a significant impact on the pavement life with regards to fatigue and serviceability. From the analyses, the material stiffness was identified as the most critical parameter. For the current research, contradictory results were obtained from the two different simulated models. The conditions of these models were set-up to replicate conditions of the Leutner shear testing device and pavement analysis of national pavement structures with some alterations. The Leutner Shear Test model confirmed the favourable outcome for the use of Spray Jet technology. The simulated FEM model used for the Pavement Analysis showed that tack coat application is unnecessary. The results suggest that pavement performance can be improved by simply adhering to better compaction of granular layers to withstand the same loading conditions. It should be noted that these results were obtained with a structure with poor subgrade conditions which largely influences the outcome of the analysis. Similar as for preliminary research, the Leutner Shear Test model emphasised the influence of material stiffness on the type of bonding achieved under certain conditions. For the Pavement Analysis model, the layer thickness is recognised as the most crucial parameter having a great influence on predicted pavement life (fatigue life). The advantages of the use of Spray Jet Technology and the favourable results recommends the implementation of the technology where additional research would accentuate its use.

AFRIKAANSE OPSOMMING: Kleeflae bevorder die binding tussen plaveisellae wat lei tot samehangende gedrag van die plaveiselstruktuur. Dit lei tot genoegsame sterkte van die plaveiselstruktuur. Die gebrek aan behoorlike binding in ʼn plaveiselstruktuur veroorsaak dat die plaveisellae lae as veelvoudige, onafhanklike lae optree. Wanneer hierdie lae blootgestel word aan verkeerslading kan dit lei tot die ewekansige verswakking van die struktuur. Hierdie gedrag dra by tot vermoeidheidverswakking soos kraakvorming en spoorvorming wat plaveisellewe aansienlik verkort. Verskeie studies beklemtoon dat koppelvlak binding tussen die plaveisellae, wat deur die kleeflaag verskaf word, ʼn noemenswaardige impak het op die werkverrigting van die plaveisel. Sommige van hierdie studies het ook ondersoek ingestel op die impak van eksterne faktore soos verkeerslading, bestaande padoppervlak kondisies en temperatuur op plaveiselwerkverrigting. Nogtans, is dit ook bevind dat interne faktore soos die aanwendingsmetode van die kleeflaag, ook bydrae tot die verkrygbare binding onder sekere kondisies. Verskeie tegnologieë word gebruik in hierdie verband, waarvan die spuitbalk tegnologie, ontwikkel deur die Wirtgen Groep, ʼn moderne metode is wat in hierdie hoedanigheid gebruik word. Die tegnologie gee die geleentheid dat onmiddellike konstruksie van die asfaltlaag, nadat die kleeflaag op die oppervlak geplaas is. Voorafgaande navorsing toon die ekonomiese voordele van die gebruik van die tegnologie maar logistiese uitdaging in terme van aanwending van die tegnologie op groter projekte is geïdentifiseer. Ten spyte hiervan, is dit gevind dat die intermediêre uitdagings oorheers word deur die langtermyn voordele wat deur die tegnologie gebied word. Hierdie voordele voorsien die dryfkrag om die implikasies in terme van plaveisel werkverrigting te beklemtoon in munisipaliteit verwante padprojekte. Dit bevorder ook die gebruik van hierdie tegnologie op ʼn internasionale vlak. Die tegnologie is ondersoek deur middel van ʼn twee fase projek in samewerking met Universiteit van Pisa. Die eerste fase van die studie (voorafgaande navorsingsprojek) sluit in laboratoriumwerk, lineêrelastiese analises en meganistiese ontwerp. Die tweede fase (huidige studie) behels die simulasie van kondisies ondersoek gedurende die eerste fase om die resultate verkry en waarnemings wat gemaak is te bekragtig. Die doel van die analises is om die invloed van skuifsterkte op plaveisellewe te verstaan en faktore wat die skuifskeur van die koppelvlak beïnvloed, te identifiseer. Beide akademiese instellings het verteenwoordigende plaveiselstrukture oorweeg vir die analises wat uitgevoer is gedurende Fase 1. Hierdie fase bestaan uit twee komponente: ʼn lineêr-elastiese analise en laboratoriumtoetse. ʼn Lineêr-elastiese analise is uitgevoer deur beide Stellenbosch en Pisa Universiteit waar twee tipes laboratoriumtoetse deur Pisa Universiteit voltooi is. Alhoewel, die resultate vanuit die verskillende analises verkry verskil in terme van ordegrootte, was alle resultate ten gunste van die gepruik van die tegnologie in vergelyking met ander konvensionele metodes wat tans gebruik word. Meer uitgebruide toetse word verlang om genoegsame inligting te verskaf wat hierdie waarneming kan bevestig. Die voorafgaande analises beklemtoon die invloed van materiaalstyfheid en laagdikte en die verwantskap met ontwikkeling van skuifskeur binne sekere gedeeltes van die plaveiselstruktuur. Die kombinasie van hierdie twee faktore toon ʼn groot invloed op die resultate verkry in terme van plaveisellewe (vermoei– en dienslewe). Oor die algemeen, is die materiaalstyfheid as die mees kritiese veranderlike geïdentifiseer. Vir die huidige navorsing, is resultate verkry teenstrydig tussen die twee gesimuleerde modelle. Die modelkondisies is van so aard dat dit werklike kondisies voorstel van die Leutner skuiftoets en plaveisel analise van gekose verteenwoordigende plaveiselstrukture. Sommige aanpassings is aangebring tot die modelle. Die Leutner Skuifskeur Toets bevestig die waarnemings gemaak gedurende die lineêr-elastiese analise(s) waar die resultate ten gunste is vir die gebruik van die spuitbalk tegnologie. Die tweede model, Plaveisel Analise model, toon dat die gebruik van ʼn kleeflaag onnodig is en dat dieselfde sterkte kapasiteit bereik kan word deur genoegsame kompaksie van die granulêre lae in die plaveiselstruktuur onder dieselfde kondisies. Hierdie resultate is verkry vanuit ʼn model wat bestaan uit swak grondlaag kondisies wat aansienlik die resultate kan beïnvloed. Soortgelyk aan die lineêr-elastiese analises, het die Leutner Skuifskeur Toets die invloed van materiaalstyfheid en laagdikte op die tipe binding verkry onder sekere kondisies beklemtoon. Vir die Plaveisel Analise model, is slegs die laagdikte geïdentifiseer as die mees kritiese veranderlike met die grootste invloed op die beraamde plaveisellewe (vermoeilewe spesifiek). Die voordele van die gebruik van die spuitbalk tegnologie en die voordelige resultate beklemtoon die implementering van die tegnologie alhoewel addisionele navorsing verlang word om hierdie bevinding te bevestig.

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