Effect of Last Generation Additives on the Concrete Durability

The influence of carbonation on corrosion of reinforcement depends on the degree of ease of diffusion of CO2 through the concrete from its surface, also on environmental conditions, on the pore structure of concrete (cement, aggregates, and water (without additives)) and on the W / C, where a high ratio generates porous and permeable mortar and concrete (Duran C., 2003; Troconis O. et al., 2006). Permeability is not necessarily related to porosity, but depends on the geometry of the pores and the distribution of pore sizes: two porous bodies can have similar porosities but different permeability, so it is important to consider the penetration of CO2 into the concrete. If the concrete is not permeable, the attack will be relatively superficial and limited to the surface. The attack in concrete is governed by molecular diffusion, which is much slower than convection processes. The use of concrete with low permeability is the primary means to prevent or minimize the effects of external attack (Morin et al., 2001; Papadakis et al., 1992). A well-proportioned mix of aggregate, which follows a continuous grading curve will produce concrete of good workability, high cohesion and a reduced tendency to segregation. At the same time it will be slightly porous and therefore possess a prolonged durability. Superplasticizer additives added to the mix, filling the interstitial space between large particles, which can cause a high density, high strength and resilient material, with a smaller amount of mixing water (Erdogdu S., 2000; Morin et al., 2001). The main mechanism for CO2 transport in concrete is difusion, and with moisture, carbonation leads, a phenomenon to be considered from the viewpoint of durability of reinforced concrete (Carvajal et al., 2006). There are expressions that relate the diffusion coefficient of concrete with compressive strength, where increase of resistance, decrease of diffusion coefficient. Because the phenomenon of diffusion of gases is of long-term, resistance in ancient age must to be taken into account and not the resistance usually specified at 28 days.