Damage model for concrete reinforced with sliding metallic fibers

This contribution presents an effective and practical three dimensional (3D) numerical model to predict the behaviour of concrete matrix reinforced with sliding metallic fibers. Considering fiber-reinforced concrete (FRC) as two-phase composite, constitutive behaviour laws of plain concrete and sliding metallic fibers were described first and then they were combined according to anisotropic damage theory to predict the mechanical behaviour of FRC. The behaviour law used for the plain concrete is based on damage and plasticity theories able to manage localized crack opening in 3D. The constitutive law of the action of sliding metallic fibers in the matrix is based on the effective stress carried by the fibers. This effective stress depends on a damage parameter related to on one hand, on the content and mechanical properties of fibers and on the other hand, on the fiber–matrix bond which itself depends on the localized crack opening. The proposed model for FRC is easy to implement in most of the finite element codes based on displacement formulation; it uses only measurable parameters like Young’s modulus, tensile and compressive strengths, fracture energies and strains at peak stress in tension and compression. A comparison between the experimental data and model results has been also provided in this paper.     

Rubberised concrete: from laboratory findings to field experiment validation

Cement-based materials suffer from low tensile strength and limited strain capacity. They are brittle and highly sensitive to cracking, and such characteristics are the cause of the main distresses that limit the sustainability of their applications. Laboratory findings showed that the use of rubber aggregates obtained by grinding end-of-life tyres was effective in reducing the tendency of concrete cracking. This paper focuses on validating these findings in actual field conditions. For this purpose, control and rubberised concretes were produced using an industrial concrete plant and then used for the construction of prototype pavements. In equivalent conditions of construction, including length, the monitoring of the field experiment over a period of more than one year showed that the pavement constructed using control concrete tended to crack more due to shrinkage than the pavement constructed using rubberised concrete. Such experimental findings show that the use of a concrete incorporating rubber aggregates from used tyres may be an appropriate solution for sustainability, for economy and for saving non-renewable natural resources.     

Finite element modelling of hardening concrete: application to the prediction of early age cracking for massive reinforced structures

This article presents finite element modelling to predict the early age cracking risk of concrete structures. It is a tool to help practitioners choose materials and construction techniques to reduce the risk of cracking. The proposed model uses original hydration modelling (allowing composed binder to be modelled and hydric consumption to be controlled) followed by a non-linear mechanical model of concrete at early ages involving creep and damage coupling. The article considers hydration effects on this mechanical model, which is based on a non-linear viscoelastic formulation combined with an anisotropic, regularized damage model. Details of the numerical implementation are given in the article and the model is applied successively to a laboratory structure and to a massive structure in situ (experimental wall of a nuclear power plant studied in the framework of the French national research project CEOS.fr).     

Simultaneous formation of nitrogen and sulfur-doped carbon nanotubes-mesoporous carbon and its electrocatalytic activity for oxygen reduction reaction

Nitrogen and sulfur dual doped-carbon nanotubes-mesoporous carbon (D-CNTs-MPC) composite is prepared simultaneously and is used in alkaline media as an electrocatalyst for oxygen reduction reaction (ORR). D-CNTs-MPC is synthesized by casting method using nano-CaCO₃ as a template, and binuclear cobalt phthalocyanine hexasulfonate as a carbon, nitrogen and sulfur precursor as well as the catalyst for growth of CNTs. D-CNTs-MPC possesses short CNTs adhering to loosely packed carbon with mesopores. Moreover, nitrogen and sulfur are doped into the carbon framework without addition of other heteroatom-containing precursor. The electrochemical behavior shows that D-CNTs-MPC is an active, methanol-tolerant and stable electrocatalyst for ORR.