Key Engineering Materials Vol. 711

Abstract: This work is part of the DURACON Ibero-American project, which seeks to characterize concrete durability under environmental conditions, based on reinforced concrete sample exposure in at least two different atmospheres (marine and urban), for each of the 11 countries in the project. Specimens were exposed to the environmental conditions of 13 Mexican sites (8 urban and 5 marine atmospheres). Concrete specimens were 15 x 15 x 30 cm, with 6 rebars each, and three concrete covers (15, 20 and 30 cm). Two concrete mixtures were used with water/cement ratios of 0.45 and 0.65, respectively. Six reinforced and six plain concrete specimens were placed on each exposure site. Environmental data was collected on each exposure site, including rainfall, relative humidity, time of wetness, temperature, wind velocity, and carbon dioxide/chloride concentrations. Corrosion rates and potentials, as well as concrete resistivity were measured in the reinforced samples. Carbonation depths were measured on the plain ones. The present work focused on the measurements of environmental parameters during the first two years of exposure to analyze the potentiality and the probability of carbonation-induced corrosion, and the evaluation of the corrosion initiation period for the reinforcing steel on the 13 Mexican exposure sites.

Abstract: The performance with regard to chloride penetration of specimens made with three base compositions (supplementary cementitious materials: 20% fly ash, 20% fly ash + 8% silica fume, and 50% slag replacement by weight of cement), and water-to-cementitious ratios of 0.35, 0.41, or 0.47 were investigated here. In this investigation, laboratory experiments were carried out to study the correlation between electrical resistivity and non-steady state chloride ion migration coefficients (D_nssm) of concrete. NT Build 492 was used to determine chloride migration coefficients. Rapid migration tests and resistivity measurements were performed several times over two years, and the non-steady state migration coefficient (D_nssm) vs. resistivity values were correlated. Experimental results show that a good correlation was found between electrical resistivity and D_nssm. Based on the relationships developed from this investigation, it appears that the correlations are age and composition dependent.

Abstract: Within the scope of assessment of deteriorating R/C structures, the paper proposes analytical models for the strength of corroded reinforced concrete beams: bending, shear, and bond are considered. Strut and tie models are adapted to include the corrosion effects on geometry, material properties and the load-resisting mechanism; uniform corrosion and pitting are considered. The Model Code 2010 provisions for bond and its deterioration due to low and medium corrosion levels are used for the verification of the models against experimental data of simply supported beams under 3 or 4-point flexure, showing different modes of failure. The innovative contributions are the consideration of bond deterioration effects in the models, with different shear span-to-depth ratios, and the comparison with tests from different campaigns in the literature, using either natural corrosion, environmental corrosion under load or slow artificial corrosion.

Abstract: The prevention of reinforcement corrosion is primarily achieved by using high quality concrete, adequate concrete cover and suitable casting and curing. Additional prevention methods are adopted when severe environmental conditions occur on structures requiring very long service life. While existing standards, EN 206 or Eurocode 2, adopt prescriptive approach, performance based methods can improve the evaluation of the service life and enable the comparison of available design options. The reliability of the prediction is very important and even widely used models (e.g. fib Model Code) still have open questions. In this paper different additional protection are evaluated: corrosion inhibitors, stainless steel rebars, concrete coatings. A simplified approach is used, considering that the serviceability limit state, i.e. initiation of corrosion in chloride containing environments, can be modeled through the analytical solution of the 2^nd Fick’s law of diffusion. The main factors influencing corrosion initiation (critical chlorides concentration, chlorides diffusion coefficient, surface chloride concentration, concrete cover) are represented by distribution of values and the probability distribution of service life is evaluated by Monte Carlo simulation.

Abstract: A concrete durability site in the Eastern Province of Saudi Arabia that exposes Saudi concrete to harsh marine conditions on the Arabian Gulf and salty air conditions was constructed. The site contains 32 concrete blocks formed from eight different mixtures made with Cement Type I, Cement Type V, Cement Type I with 6% silica Fumes, 25% fly Ash, 70% Ground-granulated blast-furnace slag (GGBFS), Migrate Corrosion Inhibitors (MCI), Calcium Nitrite based inhibitors (CNI) and Caltite. Each mixture formed 4 blocks; 2 were reinforced with black steel and two were plain concrete. The concrete blocks were 1200 mm high, 460 mm wide and 230 mm thick placed vertically. The concrete blocks were placed at three zones to achieve different exposure conditions which are atmospheric, splash or spray zone and tidal zone. Samples will be taken periodically to measure the rate of chloride ingress in each concrete mixture under the different exposure conditions. Embedded steel reinforcement in specimens in atmospheric zone have not recorded corrosion activities at six months of exposure. The steel bars in three zones will be monitored for corrosion activity through linear polarization test. The measured chloride profiles in the exposure site will be compared to the measured concrete transport properties from the companion laboratory specimens. Standard compressive test and bulk diffusion test were conducted for 150x300 mm and 75x150 standard cylinders, respectively. All of the cylinders’ strength exceeded the designed compressive strength of 28 MPa. Whereas for 35 days standard bulk diffusion test, mix contained 100% cement type I had the least chloride concentration, and mix 5 that had 70% GGBFS and 30% cement type I had the highest surface chloride concentration. Overall chloride profiles for all the mixes were within ranges reported in literature. Further tests of chloride binding capacity and bulk diffusion for different intervals will be undertaken.

Abstract: The massive use of natural resources such as fresh water or virgin rock for aggregates in the construction industry originates the need for possible alternative solutions aimed at the environmental sustainability, as, for instance, the use of chloride-contaminated raw materials for the production of concrete. In the framework of a research project financed by the Infravation Program (Advanced systems, materials and techniques for next generation infrastructure), an experimental study is undertaken aiming at demonstrating the safe utilization of seawater and salt-contaminated aggregates (natural or recycled) for a sustainable concrete production when combined with non-corrosive reinforcement to construct durable and economical concrete infrastructures. Considering the lack of sufficient fresh water in many regions of the world, this paper focuses on a preliminary evaluation of the possibility of replacing fresh water used to mix/cure concrete with seawater, combined with different types of stainless steel reinforcement. Based on literature data and the performance-based approach of “Model Code for Service Life Design” published by the International Federation for Structural Concrete (fib), risks associated with the use of using seawater in relation to the service life a reinforced concrete element in a marine environment are investigated. During the development of the project, laboratory and field tests will allow for the collection of experimental data to better define the durability evaluation and analyse advantages of the proposed approach in terms of life cycle assessment.

Abstract: The service life of reinforced concrete (RC) structures exposed to marine environments or the action of de-icing salts is limited by the corrosion of steel bars. To predict the service life of a RC structure, and especially the initiation time, a reliable estimation of the critical chloride threshold is required. This parameter is strongly influenced by many factors related to the environment and the concrete. This paper presents the results of chloride penetration tests carried out on concrete specimens made with different types of binder, with bars in free corrosion conditions, in order to detect the critical corrosion threshold. During the exposure period of two and a half years, the corrosion behaviour of bars was monitored through measurements of corrosion potential and corrosion rate. Afterwards, potentiostatic polarization tests, during which the potential was increased by step +50 mV per hour and the circulating current was monitored, were carried out on selected specimens. Results of the tests allowed the investigation of the relationship between the potential at which corrosion occurred, during ponding or potentiostatic polarization tests, and the critical chloride content. Considering a range of potential of -100/+100 mV vs SCE, some effect of pozzolanic additions in leading to higher values of the chloride threshold could be observed in this work

Abstract: Corrosion of reinforcement steel bars is a major threat to the durability of concrete structures exposed to chloride contaminated environment. Patch repairing is widely practiced in affected structures to avoid further damage due to corrosion. Macrocell formation within the patch repair is identified as one main reason for the failure of patch repairs. In the present study, a group of patch repairing materials is tested for their potential to form macrocell corrosion after repaired in a chloride contaminated environment. The influence of parameters such as level of chloride contamination, type of repair materials and the area of steel bar receiving repair are presented based on macrocell current measurements. The selected repair materials for study were cement based, GGBS based and polymer based in its composition. It is found that the severity of macrocell depends on the driving potential existing between the repair and substrate concrete. The quality of substrate concrete and repair material influences the macrocell formation. The surface area of the steel bar that receives the repair also affects the macrocell current. The study will be used for the evaluation of repair materials for macrocell corrosion formation potential before their field application in a chloride contaminated environment.

Abstract: The durability of concrete structures in severe environments is not only related to design and materials but also to construction. Thus, much of the observed durability problems can be ascribed due to lack of proper quality control and quality assurance during concrete construction resulting in poorly achieved construction quality. Upon completion of new concrete structures, the achieved construction quality typically shows a high scatter and variability, and during operation of the structures, any weaknesses and deficiencies will soon be revealed whatever durability specifications and materials have been applied. To a certain extent, a probability approach to the durability design can accommodate the high scatter and variability. However, a numerical approach alone is insufficient for ensuring the durability; greater control and improvements in durability also require the specification of performance-based durability requirements which can be verified and controlled during concrete construction in order to achieve quality assurance. For new major concrete infrastructure, documentation of achieved construction quality and compliance to the durability specification should be essential parts of any rational approach to controlling and increasing the durability. In the present paper, a case study is presented which provides comparisons of work performed under performance and prescriptive durability specifications.