Carlo Rabaiotti

A thermomechanical framework for non-linear hyperviscoelastic materials

Visco-elastic models are commonly used in modeling time dependent behavior of asphalts, polymers, and biomaterials (e.g., soft tissues). In order to ensure that these models are thermomechanically consistent, their stress-strain behavior has to be derived using a strain energy function. For a non-linear viscoelastic behavior, this appears to be a rather subtle problem: some quasi-linear viscoelastic energy formulations presented in the literature do not use the true energy functions for the stress-strain response attributed to these models, making their mechanical interpretation and validation of thermomechanical consistency difficult. This paper represents an attempt to propose an alternative framework, which would retain simplicity and convenience in numerical applications of the quasi-linear viscoelasticity, but would have a straightforward mechanical interpretation and guarantee the thermomechanical consistency. This is achieved by using a thermomechanical approach with internal kinematic variables, w...

Pavement structural health evaluation based on inverse analysis of three dimensional deflection bowl

Pavement structural evaluation is mainly carried out using the falling weight deflectometer. Being widely adopted, this test still suffers uncertainties in the interpretation of the results. An alternative procedure, based on high precision 3D measurements of static deflection bowl under real axle load, is described in this paper. The procedure has been developed initially based on synthetic measurements generated using finite element calculations. Initial findings have shown that inverse analysis of the synthetic 3D deflection bowl allows for at least eight constitutive model parameters to be back-calculated with reasonable precision and accuracy. Based on these findings, a new testing device (ETH Delta) has been designed and built at ETH, Zürich. Field and laboratory tests have been carried out in order to validate this technique. A good correlation between the parameters obtained within inverse analysis of the field and those from laboratory tests is found.

Pavement rehabilitation of runway 14/32 at Zürich International Airport: service life prediction based on updated incremental damage approach

Zurich International Airport operates with three runways: 16/34, 14/32 and 10/28. The pavement of runway 14/32 has reached its end of service life and should be rehabilitated soon. The old pavement structure consists of concrete slabs on a cement treated base. The 30cm thick concrete pavement will be replaced with a 35 cm thick asphalt layer during rehabilitation. The service life of the proposed rehabilitation design has been analyzed adopting a new mechanistic empirical method based on the AASHTO 2008 design guide, although some improvements have been implemented: 1) three dimensional finite element modeling (FE) with an elasto-plastic strain hardening material behavior model for the subgrade and 2) an iterative procedure, that allows application of damage incrementally to asphalt and cement treated material in an updated FE model. The method has been calibrated with results from deflection tests carried out in the 70’s on an asphalt test track and validated through deflection measurements carried out on the runway 16/34 that has been rehabilitated in 2008 with a similar asphalt overlay.

COMPACTION CHARACTERISTICS AND BEARING CAPACITY OF RECYCLED MATERIALS FOR ROAD CONSTRUCTION

Due to the scarcity of virgin materials, the reuse of granular materials in the road construction becomes of growing importance. However, the use of such recycled materials should not lead to a decrease in quality of the bearing capacity and the life cycle of the road. The compaction of recycled materials requires existing techniques to be adapted to achieve this requirement. The classic compaction theory of granular soils, when applied to recycled materials, does not satisfy the demands on the quality because of the different grain strengths. The recycling materials require increased compaction energy. The Swiss standard on compaction of soils is actually based on the classical AASHTO standard method, which has been the worldwide leading protocol in this field of research. Several tests measuring the bearing capacity and the compaction characteristics of two typical recycling materials have been carried out at the ETH (Swiss Federal Institute of Technology). An attempt has been made in order to correlate the degree of compaction and the bearing capacity of the recycled materials. The bearing characteristics have been measured following the standardized CBR test; the compaction test has been performed according to the Swiss standards. These tests two an interesting response from the recycled materials, which do not match the known dependence of compaction, density and bearing capacity.