A diffusion -reaction numerical model is proposed to simulate the response of concrete exposed to external sulfate attack. Diffusion properties are modified based on the strain reached and the ratio of porosity filled by ettringite. A direct and intuitive approach is proposed for the consideration of the diffusion in a cracked porous media based on the constitutive law of the material. A methodology to compute expansions based on a more realistic consideration of the concrete porosimetry is presented, by which it is possible to distinguish different strain contributions from different pore sizes. The described approach also allows the consideration of different capacities to accommodate expansive product for each pore size considered and the faster filling rate existent in small pores. Critical parameters of the numerical model developed are recognized and
Design codes promote a limitation of permeability (indirectly of porosity) to reduce the sulphate ingress and improve the resistance of concrete and mortar to external sulphate attack (ESA). However, porosity could also have a positive effect on durability by generating additional space to accommodate the expansive phases. The aim of this study is to evaluate the role of porosity in ESA. For that, changes at the macro-scale, phase composition and pore network are monitored for mortar compositions with different pore-size distribution. Results indicate the existence of two mechanisms: the capacity to accommodate expansive phases controls the durability during the initial stages of the attack, while at later stages durability is defined by the permeability. Results from specimens with air-entrainer suggest that the intentional increase of porosity towards maximising the capacity to accommodate expansive products might be a valid approach in order to reduce the expansive forces generated during ESA.
The objective of this paper is to evaluate the influence of sulfate exposure on the pore network development of several Portland cement matrices. MIP, XRD and SEM analysis were performed at different ages in samples exposed to sulfates after 2 days of casting. Results suggest that patterns of precipitation of the expansive products are linked to the degree of refinement of the pore network. During early stages of exposure, large pores concentrate a higher proportion of the expansive product formed. At later stages, precipitation evolves towards finer pore sizes.
14The external sulfate attack is a degradation process that causes expansion and cracking 15 in concrete structures. Due to the absence of simplified methodologies to predict the 16 potential damage, codes specify that sulfate resistant cement should be used whenever
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