International Concrete Abstracts Portal

Marine durability of 23-year old reinforced concrete beams (cracked and uncracked) of size 15 by 30 by 180 cm exposed to marine tidal and atmospheric environments is presented here. The study mainly focused on corrosion of steel bars with respect to orientation in concrete, carbonation and chloride-ion induced corrosion of steel bars, quantitative evaluation of corrosion based on the electrochemical data, the influence of stirrups on macrocell formation. The experimental works covered electrochemical investigations (half cell potential, polarization resistance, solution resistance), chloride ion profile and carbonation depth measurements, microscopic observation of steel-concrete interfaces, visual observation of steel bars corrosion, etc. The study concluded that chloride-ion induced corrosion significantly influenced by the orientation of steel bars in concrete. Cracks as well as interfacial gaps between steel and concrete should be taken into account in order to predict the corrosion of steel bars in concrete, I.e. the durability of reinforced concrete structures, especially under tidal environment. Conversely, microcell corrosion was a governing process of corrosion in atmospheric environment. The depth of corrosion can be estimated roughly by using polarization resistance data, provided a suitable pit concentration factor is used.

Previous works on service-life prediction have concluded that concrete structures reinforced with stainless steel bars are several times more resistant to corrosion than structures reinforced with carbon steel bars. The commercial utilization of stainless steel reinforcement is a recent fact, therefore long-term field experiences are not available. Life Cycle Cost analysis has been used as criterion for selecting the type of steel in the reinforcement, estimating the service-life of structures with stainless steel bars with a serviceability of at least 120 years, without maintenance cost. An objective of service-life methodology is to develop a technical basis for predicting the useful life of reinforced concrete structures. The present work makes use of the potenciodynamic polarization curves to study electrochemical behavior of ASTM 316L stainless steel reinforcement. Common carbon steel rebars were included for comparison. The bars were studied n non-carbonated concretes with different chloride contents. Other part of the study also included the mechanical consequences of the corrosion development process: the bond (by pull-out) and tensile strength reduction. Integrating both parts of the study made it possible to develop an approach to the service-life prediction of structures reinforced with stainless steel rebars.

The durability of concrete has become one of the main parameters used in the design requirements of concrete structures. The prediction of the long-term behavior (> 100 years) of concrete structures exposed to severe chemical environments must take into account the evolution of the chemical composition of the material and its microstructure. One of the aims of on-going researches on the long-term durability of cement-based materials is to know, the evolution of concentration profiles of different aggressive ions in the pore solution and solid phase, for a concrete placed in a given environment. A predictive model which leas to a better understanding of this evolution has been developed t LERM. This model has been applied to the concrete of the Vasco da Gama Bridge built in the Tagus bay in Lisbon. In this case, the service life, defined as the initiation period of steel corrosion, of this bridge has to be evaluated using the predictive model, taking into account a critical concentration of chloride at the level of the reinforcement. The coupling of numerical calculations and different experimental measurements and observations realized on the cores of concrete drilled at different times has allowed to a first validation of numerical predictions and realistic prediction the durability of the concrete with regard to the corrosion of reinforcements which is the main risk.

Controlling and mitigating cracks in concrete is one of the most serious and inherent problems. In this research, improvement of crack resistance against thermal stress and shrinkage of the mass concrete at an early age were investigated using the hybrid fiber reinforced concrete. The fibers used were steel and polypropylene fibers with the lengths of 6,12, and 30mm. The physical properties as well as crack resistance capabilities of the hybrid fiber-reinforced concrete were evaluated. As for the evaluation of crack resistant property, strain energy release rate, calculated by the fracture mechanics, has been proposed as a result of this research.

The research dealt with the durability of multilayer sandwich panels cast in situ with shotcrete technology. The research analysed the behaviour of different shotcrete mixtures towards actions caused by the climatic variations changes. A standard shotcrete mixture (traditional), normally used by panel producers, and three differently modified and optimized shotcretes (with silica fume, expansive agent, plastic fibres) were compared. Two accelerated tests were carried out: an accelerated cracking test for the short term degradation and an accelerated aging test for the long term degradation. The test procedures and the climatic chamber used in the aging test are illustrated. This report present the results of investigation on the superficial cracking density of panel specimens. The data obtained obtained at the end of the accelerated tests (total length of cracks per area unit-cm/m2) were compared. The results point out a cracking density of the optimized and modified shotcretes lower than that of the standard shotcrete. In particular the study proved the efficiency of plastic fibre-reinforced shotcrete towards the climatic variations changes both at short and long term.