Lattice Modelling Of Chloride Diffusivity Of Cement Paste

Chloride diffusion in concrete is a key problem for durability design. Since the micro-structure of concrete has a great influence on the chloride diffusivity, it is quite important in theory and practice to study the relationship between micro-structure and its chloride diffusivity, especially under load. This article carried a further discussion of this subject and the main research content includes the following several aspects:A 3D irregular lattice analysis platform is generated based on MATLAB. Combined with a cement paste hydration numerical model, this platformcan is applied to build a heterogenous finite element model. By introducing some advanced numerical technique, such as sparse matrix, partitioned matrix and pre-conditioned conjugate-gradient approach, a super- large finite element analysis is achieved.The experiment data obtained from relevant literature is used to study the relationship between randomness of lattice model and chlorid diffusivity of solution in capillary pore. The result shows that a high randomness corresponds to the capillary pore with high chloride diffusivity.Based on an irregular transport lattice approach, the phenomenon that the chlorid diffusivity of solution in capillary porocity is lower by more than an order of magnitude casued by surface absorption effect is studied; The effective chloride diffusivity of cement paste varied with hydration time and Blaine fineness is predicted; The correlation between effective chlorid diffusivity and capillary porosity is studied quantitatively.A simplified fracture lattice model is applied to simulate the distribution of cracks in cement paste caused by uniaxial tension. It is showed that,, a lower water-cement ratio cement paste has a more concentrated cracks distribution which is more likely to form a through crack.A cracked element is introduced to build a fracture-transport lattice system at micro-scale to simulate the chloride diffusivity of a cracked cement paste. In t his system, the fracture model is used to generate the cracked cement paste, of which chloride diffusivity will be predict by the transport lattice model. Results show that the influence of uniaxial tension and crack density on the chloride diffusion presents a threshold effect.