Abstract

This thesis is a contribution to knowledge and research on the durability of recycled aggregate concrete in a marine environment as a scientific contribution to the development of recommendations on the use of this material. 
The construction industry is currently using natural resources and disposing construction and demolition wastes in very large quantities; these practices have environmental and economic implications that are not longer considered sustainable. 
Interest in the use of recycled aggregates from construction and demolition waste (C&D) is continuously growing worldwide due to its potential against a variety of uses, including its use as an aggregate in new concrete manufacturing, being environmentally responsible, technologically available and economically feasible. Although it is environmentally beneficial to use recycled aggregates, the current specifications and experience in many parts of the world are not able to support and encourage the recycling of C&D waste. However, many governments are now promoting policies aimed at reducing the use of primary resources and increasing reuse and recycling.
The use of recycled concrete aggregate on the production of structural concrete may decrease its performance respect to mechanical properties and durability due to its particular characteristics, such as, the high water absorption of this aggregate.
Durability is an important property; and recycled aggregates need to be widely tested to prove its efficiency, in order to gain confidence of its use within the industry. It is generally accepted that corrosion is the most common cause of concrete deterioration and this work shows further possibilities in this field. 
The approach adopted in this research includes a large substitution of natural coarse aggregates by recycled concrete aggregates and its suitability in a reinforced concrete application. The mechanical behaviour and durability against a marine environment for structural concrete made with 0%, 20%, 50% and 100% of recycled coarse aggregates and two effective water cement ratio (wef/c) 0,45 and 0,50 have been assessed and evaluated. Taking into account that corrosion is the principal problem of durability in reinforced concrete, the deterioration mechanisms of concrete permeation properties, such as, permeability, sorptivity, and diffusion for chloride ingress, were analysed. 
Commercially produced coarse recycled aggregate manufactured in Spain were used in the development of this thesis. Throughout the preliminary studies, the characteristics of five different sources of recycled aggregates, the concrete recycling rate (ArH) and its influence on the variability of the compressive strength of concrete were determined.  Furthermore, a recycled aggregate concrete mixed type (ARMH) was analyzed to evaluate the resistance to penetration of chlorides. The manufacturing method and the influence of moisture states of recycled aggregates on the slump and compressive strength of concrete were also evaluated considering its great influence on the properties of recycled concrete. 
Subsequently, characterization tests of concrete were carried out to determine its physical and mechanical properties. All aggregates were used at air-dried condition. The compressive and splitting tensile strength and Modulus of elasticity of the concrete were tested, and the microstructure of the concrete was analysed by Scanning electron microscopy (SEM) to examine the Influence of recycled aggregate on interfacial transition zone (ITZ). The durability properties such as porosity, permeability, capillary absorption and chloride ion penetration for the concrete mixtures were also determined.  
The durability of concrete against corrosion of reinforcement in a marine environment was evaluated through the transport mechanisms for aggressive agents through the concrete. Tests of porosity, permeability, capillary suction and diffusion were carried out to analyse the chloride penetration into concrete recycled aggregates. The penetration of chloride was analysed by migration and natural diffusion, determining in both cases the diffusion coefficient "D".
In the analysis of natural diffusion, the chloride profile at different depths on the concrete specimens exposed to marine environment of artificial seawater for over a year was obtained. While for the migration tests, the diffusion coefficient "D" at steady state (Ds) and non-steady state (Dns), at different ages (7, 30 and 365 days) was determined. The concrete was kept in a moist chamber (20 ¡ C and 100% humidity on) until the test was carried out. The steel corrosion tests were carried out on concrete specimens exposed to a marine environment throughout the investigation. To establish the corrosion rate (Icorr), the GERCOR utilizes the polarization resistance technique. This is a quantitative measure of the amount of steel oxidizing at the time of measurement. Relative to half-cell potentials (Ecorr) and concrete resistivity also were measured. Half-cell potential tests were implemented to evaluate the probability of steel corrosion.
Test results reveal that with proper design, materials and construction, it is safe and feasible to apply recycled aggregate concrete as a structural material in civil engineering. The type of recycled aggregate has a great influence on the properties of concrete, and the amount and type of cement also have an important role. Using cement resistant to seawater, acceptable results were obtained for recycled concrete; therefore, effectively recycled aggregate concrete with the matrix of the cement paste is critical, the ratio w/c and the type of cement are significant factors in their durability properties and therefore on the type of application.
It has been found that concrete containing thick recycled aggregates made out of concrete is feasible for use against mechanical stresses and structural durability. And that currently, on the Spanish market, it is possible to find recycled concrete aggregates with the quality required for the manufacture of concrete of up to 40 MPa.