INVESTIGATION OF ASPHALT CONCRETE LAYER STRAINS FROM WIDE-BASE TIRES

The application of a continuum-based finite-layer mechanistic model to evaluate pavement strain response under moving traffic loading generated from wide-base tires is presented. The model incorporates important pavement response factors such as the noncircular contact area, complex contact stress distributions (normal and shear), vehicle speed, and viscoelastic material characterization. Results of a parametric study in which two typical thin and thick pavement sections were subjected to traffic loading moving at different speeds are included. The impact of vehicle speed on the strains induced in the asphalt concrete layer is consistent with the results from several field studies. The study reveals that especially in the case of thick pavements, the fatigue failure mechanism resulting from wide-base tires is different from those generated by conventional tires. With thick pavements longitudinal fatigue cracks are expected when the wide-base tires are used

FINITE-LAYER APPROACH TO PAVEMENT RESPONSE EVALUATION

The following aspects of the proposed continuum-based finite-layer model are presented: (1) theoretical basis, (2) applicability in evaluating pavement response, and (3) verification of predictive capability. The model incorporates important pavement response factors such as noncircular contact area, complex contact stress distributions (normal and shear), vehicle speed, and viscoelastic material characterization. The proposed model is much more computationally efficient than the moving-load models based on the finite-element method. A verification study, undertaken to validate the predictive capability of the proposed approach and its ensuing computer program, is also presented. The validation study includes (1) verification using results from ELSYM5, a widely used pavement response model, and (2) laboratory verification using two foam rubber models. Very good agreement was observed in both cases. Applicability of the proposed approach has also been demonstrated using realistic pavement loading. The proposed finite-layer approach is therefore an ideal tool for modeling the behavior of asphalt concrete layer and for studying the effects of vehicle speed and complex tire-pavement interface stresses on pavement response

Monitoring permeability potential of hot mix asphalt via binary aggregate packing principles correlated with Bailey ratios and porosity principles

Asphalt mix designs tend to optimise the load transfer via aggregate skeletons as main mechanism to provide rut resistance, often to the detriment of durability. Permeability, as a significant durability indicator, is more difficult to measure in the field than in the laboratory. Voids in the asphalt mix have a critical zone where an increase in voids is exponentially linked to permeability. This zone is where voids start to become increasingly interconnected. The aggregate grading envelope characteristics can provide an indication of the interconnectedness of the voids to enhance quality control. New rational Bailey Method Ratios (BMRs) were defined with contiguous aggregate fractions in the numerator and denominator. This allows also for porosity calculation using the Dominant Aggregate Size Range (DASR) method. The Binary Aggregate Packing (BAP) triangle porosity diagrams provide insight into the link between porosity and interconnected voids. The wall and the loosening effects create additional porosity (voids) with increased probability of interconnectedness. Clear threshold zones of interconnected voids can be determined with BAP coarse/fine mass ratios. The latter is the inverse of the rational BMRs. It allows for simple spreadsheet calculations of porosity and coarse/fine mass ratio as a screening tool for probable permeability via benchmark analysis. Reworked data sets demonstrated how the inverse of BMRs could show potential for interconnectedness of voids and, therefore, permeability propensity.http://www.journals.co.za/ej/ejour_civileng.htmlam2019Civil Engineerin