Influence of Granite Powder on Physico-Mechanical and Durability Properties of Mortar

This study explored the pozzolanic reactivity of granite powder (GP) and its influence on the microstructure of cement paste. An analysis of the physical properties (water demand, setting time, heat of hydration and total shrinkage), compressive strength and durability indicators (water absorption, porosity, acid attack and chloride ions diffusion) was carried out on mortar containing 10%, 15% and 20% of GP as partial substitution to cement (CEM I 42.5 R) in the short and long term. The results showed that the GP does not exhibit pozzolanic reactivity and that it reduces the heat of hydration. Water demand and setting time were not affected by the GP. The compressive strength decreases with increasing the content of GP; but in the long term, the compressive strength was not affected for 10% GP substitution. The presence of granite powder in mortar induces an increase in porosity, which led to an increase in the diffusion properties of fluids (capillary water absorption and chloride ions diffusion).

Multi-term time fractional diffusion equations and novel parameter estimation techniques for chloride ions sub-diffusion in reinforced concrete

In this paper, searching for a better chloride ions sub-diffusion system, a multi-term time-fractional derivative diffusion model is proposed for the description of the time-dependent chloride ions penetration in reinforced concrete structures exposed to chloride environments. We prove the stability and convergence of the model. We use the modified grid approximation method (MGAM) to estimate the fractional orders and chloride ions diffusion coefficients in the reinforced concrete for the multi-term time fractional diffusion system. And then to verify the efficiency and accuracy of the proposed methods in dealing with the fractional inverse problem, two numerical examples with real data are investigated. Meanwhile, we use two methods of fixed chloride ions diffusion coefficient and variable diffusion coefficient with diffusion depth to simulate chloride ions sub-diffusion system. The result shows that with the new fractional orders and parameters, our multi-term fractional order chloride ions sub-diffusion system is capable of providing numerical results that agree better with the real data than other models. On the other hand, it is also noticed from the numerical solution of the chloride ions sub-diffusion system that setting the variable diffusion coefficient with diffusion depth is more reasonable. And it is also found that chloride ions diffusion coefficients in reinforced concrete should be decreased with diffusion depth which is completely consistent with the theory. In addition, the model can be used to predict the chloride profiles with a time-dependent property. This article is part of the theme issue ‘Advanced materials modelling via fractional calculus: challenges and perspectives’.

Investigation on the transport properties of chlorides in concrete II Numerical simulation

The chloride ions diffusion in concrete is an important problem inducing the corrosion of reinforcement under marine environment. Based on a parallel transmission model, the diffusion coefficient of chloride ions in ITZ was determined. Thereafter, the measured parameters of ITZ were integrated into a numerical model to simulate the chloride ions diffusion and the reliability of the model was verified by comparing the numerical simulation with the surface scanning results collected from the electron microprobe. The test results show that if the concrete is taken as a threephase composites, the numerical model can reflect the real transmission process of chloride ion more accurately.

Coupling Effects of Chloride Penetrating and Corrosion Damage Evolving Process in Concrete under Marine Environment

Chloride penetration could lead to the rebar corrosion and cause the durability problem in concrete structure under marine environment. It is a coupling process between chloride penetrating and corrosion damage evolving in concrete. This paper proposed an analysis method to deal with this coupling problem. The corrosion damage degree was considered as an internal variable in coefficients of chloride diffusion. Additionally, the interfacial boundary displacement values varied with chloride concentration and service time of concrete structure. This iterative computing algorithm was tackled as user subroutine packaged into software ABAQUS. The numerical examples were given to confirm the reliability of the developed model. The results show that corrosion expanded damage accelerates chloride ions diffusion and vice versa.

Diffusion of Chloride Ions in Ultra High Performance Concrete

The article is dealing with study of chloride ions diffusion in ultra-high performance concrete UHPC, which might be potentially dangerous. Life of concrete structures, in particular in transport sector is jeopardized by risk of steel reinforcement corrosion with regards to exposure of the concrete surface to direct impact of de-icing salts. Measured data were examined in relation to the depth of penetration of chloride ions into the concrete structure. Experiment results proved that UHPC concretes are more resistant to penetration of chlorides than normal strength concretes.