International Concrete Abstracts Portal

Diffusion and migration are the two major transport ways of chloride ions in concrete. The single-species models were usually used to predict the chloride diffusion and migration behavior. However, the diffusion and migration processes of chloride ions in concrete are more complicated than expected. The single-species models have obvious limitations in predicting the diffusion and migration processes. In this paper, two multi ionic models are introduced to predict the chloride diffusion and migration processes, respectively. In the diffusion model, the ionic actions and multi-phase reactions are both considered in order to simulate the realistic situations. In the migration model, the ionic actions are also considered while the multi-phase reactions are ignored due to the strong electrical field force applied in the migration test. Besides, a pore structure hypothesis is assumed by a simple deduction to distinguish the migration process from the diffusion process. By considering the factors mentioned above, the governing equations of diffusion and migration models are deduced respectively. In order to verify the multi ionic models, two numerical examples and the verification tests are also conducted. The results show that the multi-ionic models are feasible to predict the chloride diffusion and migration in concrete.

Reinforced concrete structures in service may be affected by aging, which may include changes in strength and stiffness beyond the baseline conditions which are assumed in structural design, in particular when the concrete is exposed to an aggressive environment. For reinforced concrete structures, due to the uncertainties in material and geometrical properties, in the magnitude and distribution of the loads, in the physical parameters which define the deterioration process, the structural safety should realistically be considered time-variant. This paper provides a computational probabilistic approach to predict the time-evolution of the mechanical and geometrical properties of a reinforced concrete structural element (i.e., bridge pile) subjected to corrosion-induced deterioration, due to diffusive attack of chlorides, in order to evaluate its service life or, complementarily, residual service life. Adopting appropriate degradation models of the material properties, concrete and reinforcing steel, as well as assuming appropriate probability density functions related to mechanical and deterioration parameters, the proposed model is based on Monte Carlo simulations in order to evaluate time-variant axial force-bending moment resistance domains, with the aim to estimate the time-variant reliability index. Finally, an application to estimate the expected lifetime of a deteriorating reinforced concrete bridge pile is described.

The concrete exposed to freeze-thaw cycles, with or without deicing salts presence, can suffer extensive damage on the cement matrix with a direct impact on the structures durability. The prescriptions to be adopted for preventing this concrete deterioration are described in the European Standard EN 206-1. This standard provides specific exposure classes for Concrete Structures exposed to freeze-thaw cycles (XF) and, for each of them, a series of requirements to ensure the necessary durability. Among these requirements there is the adoption of a minimum volume of entrained air, which avoids the excessive development of internal stresses due to ice formation in the cement matrix. The introduction of air significantly reduces the concrete’s mechanical performance. To take account of this aspect, the mix design must be modified with a higher content of cement to restore the final compressive strength. This aspect becomes more penalizing and not much sustainable for high performance concretes (HPC). The aim of the work is to propose a sustainable use of fly ash in concretes, compatible with the XF exposure classes defined in the European Standard. The solution allows to restrict the cement content to the minimum values required, with technological, economic, and environmental benefits, due to using a by-product from coal combustion power plant.

Metallic soaps are salts from long chain fatty acids and they are popular as waterproofing due to their low cost and effectiveness. A detailed investigation on the mortar specimens made with different chemical additives based on Na oleate, Ca stearate – Na oleate, Al stearate and Ca - Na laurate has been performed. The additives analyzed present a different mechanism of action: Na oleate has a strong effect on the development of mortar microstructure while Al stearate or Ca - Na laurate leaves the microstructure very similar to that of the reference samples. The experimental evidences, by measuring the porosity, the water absorption, the mechanical properties and the morphology, confirm these internal structures in the mortars.

Mix-design of self-consolidating concrete (SCC) with construction and demolition concrete waste (C&DW) as recycled aggregates is investigated. The novelty of this paper consists in the possibility of using both fine and coarse high-grade C&DW for the preparation of new SCC. The effects of recycled aggregates on porosity measurements and mechanical investigations combined with time-dependent properties are investigated. A reference SCC mix, with natural aggregates and the same water/powder ratio as SCC with recycled aggregates, is reported for comparison. Results are correlated in an integrated approach to study the feasibility of structural SCC with medium-high mechanical strength. Finally, this work attempts to strengthen the concept of sustainability in civil constructions.