1,721,020 research outputs found
Service life of reinforced concrete structures made with blended cements and exposed in urban environment
Full text linkCarbonation-induced corrosion is one of the main causes of degradation of reinforced concrete (RC) structures exposed outdoor in urban environment. To prevent steel corrosion, a durability design, that considers both the initiation and the propagation time, is of fundamental importance. At this aim, the resistance to carbonation of concrete and the steel corrosion rate in the exposure environment need to be known. This paper reports the carbonation coefficient and the corrosion rate of 7-day cured RC specimens made with different binders and exposed outdoor in Milan in unsheltered conditions. Corrosion rates in laboratory conditions with different temperatures and relative humidities are also reported. Experimental data were used to evaluate the service life in unsheltered condition. RC specimens made with Portland cement exhibited the lowest carbonation coefficient and corrosion rate, while specimens with 30% limestone and with 70% ground granulated blast furnace slag the highest
Corrosion rate of carbon steel in carbonated concrete made with different supplementary cementitious materials
No full textCarbonation-induced corrosion limits the durability of reinforced concrete structures exposed in urban environments. In these exposure conditions, the propagation phase of corrosion can be an important part of the service life and, hence the knowledge of the corrosion rate is essential for the design. However, data regarding the corrosion rate in carbonated concrete are scarce and mainly refer to Portland cement concrete. This paper reports the corrosion rate and corrosion potential of steel bars embedded in concretes with different binders and water/binder ratios, exposed both outdoor in unsheltered conditions and in laboratory conditions characterised by different temperatures and relative humidities. Concrete resistivity at different depths is also reported and correlations among these parameters are discussed. Corrosion potential, corrosion rate and concrete resistivity were strongly influenced by the relative humidity, while temperature played an important role only at high relative humidity. Steel in Portland cement concrete showed the lowest corrosion rate
Effects of a hydrophobic treatment on corrosion propagation in carbonated reinforced concrete structures
No full textOn reinforcement in carbonated concrete, corrosion can propagate and lead, even after few years, to cracking and spalling of the concrete cover. Thus, costly repairs both economically and considering the impact on the environment are needed. The use of a hydrophobic treatment allows to control the propagation of corrosion in carbonated concrete, delaying concrete cracking and spalling and removing only cracked concrete. This paper reports the results of experimental tests carried out to study a new type of hydrophobic treatment. The capability of this coating to penetrate through the concrete, not to cause corrosion problems to the reinforcements still in a passive condition (in alkaline concrete) and to control the propagation of reinforcements corrosion in carbonated concrete was analysed. The effectiveness of this coating under different exposure conditions was assessed
Carbonation of blended cement concretes after 12 years of natural exposure
Full text linkIn urban environments, the durability of reinforced concrete structures is limited by carbonation-induced corrosion. To prevent steel corrosion, the selection of a proper concrete in terms of type of binder, water/binder ratio and curing time, is of fundamental importance. At this aim the knowledge of the resistance to carbonation in the exposure environment is required. Usually carbonation is evaluated from accelerated tests, however natural exposure tests are needed to validate short-term tests and make reliable predictions of the behaviour in a real environment. This paper reports the carbonation of concretes with different binders, water/binder ratios and curing, exposed for more than twelve years outdoor in Milan in sheltered conditions. Concretes with Portland cement exhibited a higher carbonation in comparison with concretes with limestone and pozzolanic cements. Curing seemed to be less effective than the type of binder and the water/binder ratio
Long-term corrosion behavior of carbon steel in carbonated concrete made with different binders|Corrosione a lungo termine di armature di acciaio in calcestruzzi carbonatati con diverse composizioni
No full textTo properly predict the service life of a reinforced concrete structure subjected to carbonation-induced corrosion, a correct estimation of the propagation period is needed. The propagation period is related to the rate at which the corrosive attack propagates, and mainly depends on the exposure conditions and the concrete quality. This paper reports the preliminary results of a research aimed at investigating the corrosion conditions of steel in carbonated concrete, made with different compositions and exposed for more than 15 years to an unsheltered outdoor environment. Preliminary results showed the fundamental role of concrete composition in determining the corrosion behavior of steel bars, leading to significant different damage conditions, from the absence of cracking to the complete concrete cover detachment. Moreover, the correlations between the corrosion rate and concrete resistivity as well as corrosion potential were investigated
Effect of carbonated recycled coarse aggregates on the mechanical and durability properties of concrete
Full text linkThe carbonation treatment seems to be an efficient process to increase the quality of recycled concrete aggregate (RCA) and to improve the hardened properties of concrete, especially the mechanical ones, as already demonstrated in several studies. However, research on durability properties of concrete obtained with carbonated RCA is still limited and do not allow to properly optimize the concrete mix design to effectively gain environmental advantages. In this work, mechanical and durability tests were performed on three different concretes, made with a water/cement ratio equal to 0.5, and either fully natural aggregates, or with a partial replacement with RCA or carbonated RCA (cRCA). RCA and cRCA were obtained by crushing respectively old alkaline and old carbonated concretes, and a further carbonation treatment was also performed on a fraction of cRCA. From results, a limited improvement in compressive strength, electrical resistivity, water absorption and sorptivity was observed in concrete made with cRCA with respect to concrete with RCA, whilst a significant decrease of the chloride diffusion coefficient was obtained. Despite the improvements obtained with respect to concrete with untreated RCA, the mechanical and durability performances of cRCA concrete remained on average lower than concrete made with natural aggregate
Preliminary Characterization of Concrete Made with RAP Aggregate
No full textThe use of recycled aggregates allows to reduce the environmental impact of concrete materials, by reducing the amount of waste and limiting the consumption of natural resources. Recycled asphalt pavement (RAP) is a granular material that comes from the milling of road pavements whose size and distribution make it suitable as aggregate for concrete. The environmental benefits of the replacement of natural aggregate with RAP need to be assessed with a better understanding of the long-term behavior of RAP concrete, considering the evolution of its performance in time and its ability to guarantee an adequate service life when exposed in operating conditions. This note presents the preliminary results of a research on the effect of RAP on concrete properties. The addition of RAP aggregate affects concrete properties at fresh and hardened state. Some parameters showed clear trends with the percentage of RAP, however also other factors (e.g. w/c ratio and curing time) seem to play a role. Compressive strength and dynamic modulus of elasticity of RAP concrete were always lower compared to reference concrete, while the electrical resistivity did not show a clear trend. Further investigations will be carried out to clarify the role of RAP aggregate
Preliminary results on corrosion products characterization in reinforced concrete subject to chloride-induced corrosion over more than 20 years
No full textFor reinforced concrete structures subject to chloride-induced corrosion, the assessment of service life at the design stage is often limited to the corrosion initiation phase, whereas in practice many structures are in the corrosion propagation phase. In these cases, for a proper assessment of the residual service life, it is necessary to better understand the processes leading to the detachment of the concrete cover, usually associated with the end of the service life, by studying the development of corrosion at the microscopic level over time. This note reports some preliminary results obtained during a research program aimed at characterising corrosion in reinforced concrete specimens cast in 1998, subjected to accelerated penetration of chlorides, and subjected to natural corrosion propagation over more than 20 years. Corrosion products and the steel-concrete interface were characterised through a combination of optical microscopy, SEM, Raman spectroscopy and computed tomography
- …
