A diffusion-reaction model for the carbonation process of oilwell cement exposed to carbonated brine under CO2 geological storage conditions is presented. The formulation consists of two main diffusion/reaction field equations for the concentrations of aqueous calcium and carbon species in the pore solution of the hardened cement paste, complemented by two diffusion-only field equations for chloride and alkalis concentrations, and by a number of chemical kinetics and chemical equilibrium equations. The volume fraction distribution of the solid constituents of the hardened cement paste and the reaction products evolve with the progress of the reaction, determining the diffusivity properties of the material. The model is used to simulate experimental tests performed by Duguid and Scherer (2010), leading to promising results indicating that the fundamental aspects of the phenomenon are captured.
Liaudat, J.; Martinez, A.; Lopez, C.; Carol, I. International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability p. 445-454 DOI: 10.1061/9780784479346.054 Data de presentació: 2015-09 Presentació treball a congrés
In the context of a project to characterize and model the Alkali-Silica Reaction in concrete, the results of a series of tests on specimens with a single interface between aggregate and cement paste, and the comparison to the numerical results of a simplified diffusion-reaction Finite Element model are presented. The tests are conceived as the simplest test to characterize the basic constituent reactions of the process. The model implemented is a first operational version of a more general three-species diffusion-reaction model already formulated and in the process of implementation. In spite of its relative simplicity, the model described seems capable of reproducing the experimental observations with specimens tested under different diffusion boundary conditions, and provides a satisfactory basis for further development.
Liaudat, J.; Garolera, D.; Martinez, A.; Carol, I.; Lakshmikantha, R.M.; Alvarellos, J. International Conference on Computational Plasticity p. 974-981 Data de presentació: 2015-09 Presentació treball a congrés
The purpose of the Wedge Splitting Test (WST) is to generate stable mode I fracture crack along a pre-established path, and be able to measure the specific fracture energy parameter of the material GFI. The test is performed on standard cylindrical notched specimens. In order to make decision on the optimal notch geometry for a specific rock test, a number of WST experiments were simulated numerically via FEM. Continuum elements with isotropic elastic behavior were used to represent the rock, the steel loading plates and an “equivalent spring” to the testing machine compliance. The notch and the fracture path on the rock were represented via zero-thickness interface elements. The notch elements were assumed linear elastic with very low elastic stiffness parameters Kn and Kt, so that they do not oppose any significant resistance to opening. The constitutive model used for the interface elements along the fracture path was the elastoplastic constitutive formulation with fracture energy-based evolution laws. The model results match very realistically the curves obtained in the experimental WST, allowing us to estimate indirectly, not only the specific fracture energy but also other basic mechanical parameters of the rock, such as the elastic modulus and the tensile strength.
Liaudat, J.; Garolera, D.; Martinez, A.; Carol, I.; Lakshmikantha, R.M.; Alvarellos, J. International Conference on Computational Modeling of Fracture and Failure of Materials and Structures p. 265 Data de presentació: 2015-06 Presentació treball a congrés
Wedge Splitting Tests (WST) is a method to perform stable fracture mechanics tests on quasi-fragile materials which provides a relatively simple manner to obtain the specific fracture energy parameter GFIusing simple specimens like cubes or cylinders . The stability of the fracture propagation depends on the interaction between of the control parameter chosen (displacement or deformation control), the stiffness of the testing machine, the specimen stiffness and the specimen geometry, as well as the material properties . In this paper, experimental results performed in-house of an unstable WST were simulated by means of the FEM and fracture-based zero-thickness interface elements. Standard elastic continuum elements were used to represent the rock, the steel loading plates and an “equivalent spring” to the testing machine compliance, while interface elements were used for the notch and along the potential crack path. The interface elements representing the notch were equipped with linear elastic constitutive law, with very low elastic stiffness Knand Kt, so that they do not oppose any significant resistance to opening. The constitutive model used for the interface elements along the fracture path was the elastoplastic constitutive model with fracture energy-based evolution laws described in detail in . In order to obtain a specimen geometry suitable fora stable WST without modifying the remaining significant parameters (machine stiffness and control parameter), a number of additional simulations were performed varying the notch length, until a load-COD curve without snap-back was obtained. Finally, a new experimental WST with the modified geometry was performed leading to a stable load-COD curve, which turned out in very good agreement with the predicted one.