Browsing by Author "Pienaar, Eugenie"

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    Influence of spray jet technology on bond strength of asphalt and pavement life
    (Stellenbosch : Stellenbosch University, 2020-03) Pienaar, Eugenie; Rudman, Chantal; Jenkins, K. J.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    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.