Finite element crack width computations with a thermo-hygro-mechanical-hydration model for concrete

The paper presents an overview of a finite element approach for the analysis of the thermo-hygro-mechanical-hydration behaviour of concrete structures. The thermo-hygro component considers the mass balance equation of moisture as well as the enthalpy balance equation, and uses two primary variables, namely the capillary pressure and temperature. Heat of hydration is simulated using the approach of Schlinder and Folliard. The basic mechanical model simulates directional cracking, rough crack closure and crushing using a plastic-damage-contact approach. Hydration dependency is introduced into the mechanical constitutive model. The material data from the Concrack benchmark (CEOS.fr,2013) are considered with the model. This includes data on adiabatic temperature changes during curing, changing elastic properties during curing, shrinkage and creep. The model, as implemented in the finite element program LUSAS, is used to analyse the Concrack benchmark beam RL1. Particular attention is paid to crack openings and the difference between predicted crack openings from analyses with and without time dependent effects. It is concluded that ignoring time dependent effects can result in a significant under-estimate of crack openings in the working load range

A plastic-damage-contact constitutive model for concrete with smoothed evolution functions

A new 3D finite element concrete model is described. The model brings together two recently developed sub-models for simulating cracking and crack contact behaviour, both of which use smoothed evolution functions, with a triaxial plasticity model component. A number of examples are presented that validate the model using a range of plain and reinforced concrete test data. These examples demonstrate that the model is numerically robust, has good equilibrium convergence performance and is objective with respect to mesh grading and increment size. The examples also illustrate the model’s ability to predict peak loads, failure modes and post-peak responses

Co-Mn oxides supported on hierarchical macro-mesoporous silica for CO and VOCs oxidation

The hierarchical macro-mesoporous silica (MMS) was used for a first time as a support for catalysts for oxidation reactions. The macro-mesoporous silica was synthesized by the emulsions templating mechanism and modified separately or simultaneously using cobalt and manganese oxides. The obtained materials were characterized by different physicochemical methods and tested in the oxidation of CO and n-hexane combustion reactions. The modification of the MMS materials does not change significantly the mesopores characteristics; however, its pores are partially blocked by the oxides. For Co-MM sample agglomerates consisting of Co3O4 with average size of 100−150 nm and small spherical aggregates, encapsulated in the mesopores are formed. The amorphous manganese oxide preferentially fills up the mesopores in Mn-MM sample. Mixed oxide Co-Mn phases situated in the mesoporous network are formed in the bi-component Co-Mn samples. No significant change is observed either in the texture, or in the structural features of the catalysts after reaction. The highest catalytic activity for Co-MM sample in CO and n-hexane oxidation is related to the predomination of Co3+ species on the surface of Co3O4 and the more accessible oxide particles located outside the mesopores. The encapsulation of mixed Co-Mn oxides particles in the pores of the macro-mesoporous silica is responsible for a lower catalytic activity in comparison with that of the mono-component cobalt sample