SUMMARY OF THE THESIS

INTRODUCTION
	The main problem affecting the life of reinforced concrete structures is reinforcement corrosion. One of the most important risks for corrosion is the carbonation of concrete cover, which produces a reduction of pH of the pore solution and, consequently, the depassivation of reinforcing steels. The other process leading to high risk of reinforcement corrosion is chloride ingress. When a sufficient amount of chlorides reaches the steel surface, a local breakdown of the passive conditions of the steel takes place, and that produces a significative increase in corrosion rate of steels. For these reasons, research on new binders that enhance the corrosion resistance of reinforcements is a matter of interest in civil engineering.
	Catalytic cracking catalyst (FCC) is an aluminosilicate-based material with zeolitic structure that is used in petrol refineries. When FCC losses its pozzolanic activity, it has to be substituted by new catalyst. During last years, some researchers have investigated the properties of this waste as a pozzolanic material, using it as an admixture for mortars and concretes. In these researchs it has been observed that FCC improves mechanical properties of mortars and concretes due to the densification of the cementitious matrix produced by the pozzolanic reaction. However, there is a lack of the knowledge on how the addition of this material can affect the corrosion of steel reinforcements under the classic attacks by carbon dioxide and chlorides.

OBJECTIVE
	In this work it has been studied the role of FCC on the corrosion process of reinforcing steel, when it is used as cement replacement. Mortar and paste specimens have been subjected to aggressive environments (CO2 and Cl-). The experimental work has been divided in different stages depending on the aggressive ambient and its effect on the cementing matrix and on the corrosion of reinforcing steel.

RESULTS
Influence of carbonation on the cementitious matrix of cement/FCC mortars
	Accelerated carbonation tests have been performed in mortars with different level of cement substitution by FCC and different water/binder ratios (w/b). These tests showed that the presence of FCC produces high decrease in the alkaline reserve of mortars due to the pozzolanic reaction, thus producing higher carbonation rates of mortar cover. However, this phenomenon was only observed for mortars with high w/b ratio. For w/b ratios lower than 0.5, the presence of FCC in quantities up to 15% by cement mass, did not offer significative differences in the carbonation rate of mortars. These tests also revealed that cement substitution by FCC produced a densification of the cementing matrix.

Influence of carbonation on the corrosion of reinforcements embedded in cement/FCC mortars
	In corrosion rate tests of steels embedded in mortars under carbonation, it was observed that the incorporation of FCC in quantities up to 15% did not affect significantly the corrosion rate of steels when the w/b ratio of the mortar was lower than 0.5. For higher w/b ratios, the initiation period was shorter for that steels embedded in mortars with FCC. Nevertheless, corrosion rate values obtained for steels embedded in mortars without FCC, once they were depassivated, were similar to that offered by steels embedded in mortars with FCC. This means that the corrosion process would start earlier in mortars with FCC, but the life of structures incorporating FCC will only be slightly shorter (the difference between initiation periods of both concretes, with and without FCC). For low w/b ratio, no differences were observed between steels embedded in mortars with and without FCC.

Influence of chloride ingress on the cementitious matrix of cement/FCC mortars
	The higher proportion of aluminates that FCC contains produces an improvement in the chloride binding capacity of the cementitious matrix of mortars with FCC. Therefore, the non-steady state chloride diffusion coefficient of mortars with FCC is lower than that presented by mortars without FCC. Additionally, the densification of the structure due to the pozzolanic reaction also produces a decrease of steady state chloride diffusion coefficients presented by mortars containing FCC. It is concluded that mortars with FCC offer higher chloride ingress resistance than mortars without FCC.

Influence of chloride ingress on the corrosion rate of steels embedded in cement/FCC mortars
	The higher chloride ingress resistance of mortars with FCC produces lower corrosion rate levels of steels embedded in these mortars. Then, an increase in the chlorides threshold (up to 2% of chloride content by cement mass) is observed for mortars with FCC. This is a significant improvement respect to the maximum level of chlorides allowed by the Spanish Concrete Technical Code, which is fixed at 0.4%.

CONCLUSIONS
	In addition to the enhancement of the mechanical properties that FCC offers, it has been observed that this pozzolan does not worsen the corrosion level of steel reinforcement under carbonation attack for low w/b ratio, and a significant improvement in the corrosion behaviour of reinforcements has been observed under chloride ingress attack for steels embedded in mortars incorporating FCC.