Analytical Investigation for Determining Ressilient Modulus for Interface Layer of Aggregates
Quality road aggregates have become rare and costly in many places in India due to massive construction activities required for the development of new infrastructure facilities. The pavement industry seeks ways of improving lower quality materials that are readily available for use in roadway construction. Cement treatment has become an accepted method for increasing the strength and durability of soils and marginal aggregates. However, cement-stabilized bases can also be the source of shrinkage cracks in the stabilized base layer, which can reflect through the asphalt surface. Introducing “Interface Layer of Aggregates (ILA)” between stabilized base and bituminous concrete (BC) layer appears to be very favorable. The present paper presents the determination of resilient modulus of ILA using FPAVE software. Figures have been developed to determine resilient modulus, varying the CBR value, the thickness of cement treated base and the thickness of interface layer of aggregates which is useful to determine the pavement thickness for cement treated base.
Mechanistic Performance Analyses of the FHWA’s Accelerated Loading Facility Pavements
Mechanistic analyses using available pavement analysis programs-KENPAVE, WINLEA, EVERSTRS, EVERFLEX, and VESYS 5W were conducted for the Federal Highway Administration’s (FHWA’s) Accelerated Loading Facility (ALF) pavements that were constructed using different asphalt binders including highly modified and unmodified ones. The analyses were divided and presented in two parts: (1) the primary response under the ALF pavements, and (2) the performance of the ALF pavements. In the present paper, the discussion is limited to the second part as the first part is available elsewhere. The analyses included pavement performance analysis using VESYS 5W program, performance predictions using existing rutting and fatigue models, and calibration and evaluation of these models. The mechanistic analyses showed that the VESYS-predicted HMA rut depths correlated well with the ALF-measured HMA rut depths for both the ALF 150-mm and 100-mm asphalt pavements, and that the VESYS 5W program seemed to be capable of predicting the HMA layer rutting more effectively than the pavement total (surface) rutting. It was also found that the VESYS 5W program under-predicted the ALF-measured rut depths in the primary phase (at earlier stages) of rutting, and it favorably predicted the measured values in the secondary stage of rutting. None of the existing rutting models used in this study provided good predictions of the ALF-measured rutting performance due to the fact that all of these models assumed that the evaluation of surface rutting was controlled by only the vertical compressive strain on top of the subgrade layer. However, the vertical compressive strain on top of the base layer (or at the surface of the HMA layer) was found to be as significant as the compressive strain on top of the subgrade layer in controlling surface rutting. The new rutting model presented in this paper provided more realistic form for a rutting model based on the fact that surface rutting is the accumulation of the permanent deformations over all of the pavement layers. The correlation between the model-predicted number of load cycles to fatigue failure and the ALF-measured wheel passes at 20- m cracked length (that corresponded to a cracked area of 20 percent) was found to be significant using the AI and the Shell models with a high coefficient of determination (R2) of 0.88 and 0.99, respectively. The AI and the Shell models were calibrated using the ALFmeasured fatigue performance data whereas the IDOT model could not be calibrated using the same data. It was found that a fatigue model form similar to that of the AI model (or the Shell model) provided better fit to the ALF fatigue performance data than a form similar to that of the IDOT model. The dynamic modulus of the HMA layer was found to be as significant as the tensile strain at the bottom of the HMA layer for pavement fatigue performance predictions.
Effect of Different Axle Configurations on Fatigue Life of Asphalt Concrete Mixture
The fatigue life of an asphalt mixture under different truck axle configurations was determined directly from the indirect tensile cyclic load test by using load pulses that were equivalent to the passage of an entire axle group or truck. The dissipated energy approach was adopted in analyzing the results and determining the number of repetitions to failure for each case; a unique fatigue curve that can be used for multiaxle configurations was developed. Trucks consisting of up to 11 axles and axle groups of up to 8 axles were studied. The results indicated that the normalized damage per load carried decreased with an increasing number of axles within an axle group. Additionally, the fatigue lives predicted by using single load pulses were compared with the measured ones from the different axle groups and trucks.