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Engineering Aspects
Published in Bruno Langlais, David A. Reckhow, Deborah R. Brink, Ozone in Water Treatment, 2019
William D. Bellamy, François Damez, Bruno Langlais, Antoine Montiel, Kerwin L. Rakness, David A. Reckhow, C. Michael Robson
Gas space concrete, gas stops, gas sealing. To date (1990), there have been no identified problems with existing reinforced concrete structures exposed to “wet” ozone in the contactor head space. The gas space concrete of the structure should be of Type 2 or Type 5 Portland cement using a low water/cement ratio mix design. Consideration may be given to the use of galvanized steel reinforcing steel or at least to providing an additional 10 percent reinforcing steel if uncoated carbon steel reinforcing bar is used. A minimum of 3 in. (7.6 cm) of concrete cover for the reinforcing steel should be provided. According to Fonlupt (1979), 4 cm (1.13 in.) of concrete cover is sufficient. Stainless steel or Teflon gas space seals should be used. All fittings and concrete penetrations such as hatchways, vents, and valves should be 316L stainless.
Limiting the Water Content in Concrete as Protection against Corrosion
Published in Christer Sjöström, Durability of Building Materials and Components 7, 2018
Reinforcement corrosion due to carbonation of the concrete is usually the result of insufficient concrete cover and inadequate concrete quality. In spite of numerous efforts to avoid such damage via appropriate design and the use of suitable materials, large funds need to be allocated every year for repair works. For corrosion damages caused by carbonation of concrete, the above mentionned recommendations in the Guidelines for Repair and Protection of Concrete Components [1] include repair principle W - limiting the water content of concrete. This method essentially involves providing the concrete surface with a suitable surface protection system, after cleaning the steel and replacing the damaged areas of concrete. The applied coating is intended to result in reduction and homogenisation of the water content in the concrete to such an extent as to reduce corrosion at the reinforcement to negligibly small levels. Although the effectiveness of this method has been observed in numerous practical applications, no systematic investigations have been carried out to date with the aim of confirming these observations and determining the possibilities and limits of applicability of this method of repair and protection. Primary advantages of the repair principle relate to the fact that only the damaged concrete needs to be replaced, while no further corrosion is to be expected in any areas of carbonated concrete which may remain, due to the reduced water content resulting from the surface coating.
Development and implementation of digital bridge management systems in the Gulf region
Published in Nigel Powers, Dan M. Frangopol, Riadh Al-Mahaidi, Colin Caprani, Maintenance, Safety, Risk, Management and Life-Cycle Performance of Bridges, 2018
Another point to note in the development of asset management systems in the Gulf is that structures in the region typically have to contend with severe exposure conditions. Summer in the Gulf is extremely hot and humid, with temperatures reaching 45 degrees C and a humidity of 90%. Ground investigations have also found that the soil is comprised almost entirely of crushed shells and sea coral, making the groundwater highly saline and the concentrations of chlorides and sulfates extremely high (Sherif, 2011). The extreme environmental conditions in which road assets are constructed means that design standards and details are often different to those used in Europe and other parts of the world. Concrete structures are designed to have very small crack widths to help prevent carbonation and ingress of chloride ions. This often means that steel reinforcement quantities in concrete structures are higher, with an increased concrete cover to reinforcement. Exposed concrete surfaces are also often coated with multi-part coating systems which are designed to help prevent ingress of carbons and chlorides through the concrete surface.
Best practices for measurement, sensing, and quantifying corrosion in existing reinforced concrete structures
Published in Sustainable and Resilient Infrastructure, 2023
The benefits of conducting a non-destructive evaluation of the concrete cover thickness allow for rapid scanning of larger areas that would be impractical for the aforementioned physical measurement techniques. The most predominant methods for the evaluation of the concrete cover include covermeters and ground-penetrating radar (ACI 228.2R-13, 2013). Covermeters are divided into two classes based on their operating principle: magnetic reluctance or eddy currents (Carino, 1992). Magnetic reluctance covermeters apply a low frequency alternating magnetic field on the surface of the structure. The presence of embedded reinforcement alters the response to this field, and the measurement of such change provides information on the reinforcement location. Eddy current covermeters utilize a coil to apply an alternating electrical current which, when in the proximity of an electrical conductor, result in a change of the magnetic field induced by circulating currents known as eddy currents, Because any current gives rise to a magnetic field, eddy currents produce a secondary magnetic field that interacts with the field of the coil. The second class of covermeters is based on monitoring the effects of the eddy currents induced in a reinforcing bar.
Probabilistic modeling of reinforced concrete bond behavior considering failure mode and corrosion
Published in Structure and Infrastructure Engineering, 2022
Concrete cover is shown to be influential in both corroded and un-corroded specimens (Chun-Qing, Melchers, & Jian-Jun, 2006). Concrete cover provides the confinement around the test bars that could help effectively prevent cracking development in the concrete. A larger concrete cover firstly increases the amount of time that requires for cracking initiation and requires more corrosion rust to fill in the pores. Also, even after cover cracking, the specimen retains its tensile strength, which enables it to transmit shear and tensile stress along the cracks. Several studies have shown that large covers could still be a contributing factor in bond strength in highly corroded specimens (Al-Sulaimani et al., 1990; Amleh, Mirza, & Ahwazi, 2000; Xia, 2010). Particularly, Wang (2009) found that the concrete cover to the main rebar diameter ratio contributes significantly to the bond strength when no confinement reinforcement is provided.
Recommendation for concrete mix design to prevent bleed channels on diaphragm walls
Published in European Journal of Environmental and Civil Engineering, 2022
Chafika Djelal, Yannick Vanhove, Amin Azzi, Olivier Madec
These defects may be ascribed to the placement technique associated with insufficient fluidity and a lapse in maintenance over the placement duration, weak cohesion between layers due to an overly rapid setting, inadequate concrete cover of the reinforcements, a concrete cover fouled by sludge resulting from a loss of workability due to bleeding arising during placement (CIA Z17,17, 2012; Beckhaus et al., 2011; Larisch, 2019). Less workability can adversely affect the quality of walls both aesthetically and mechanically (Beckhaus et al., 2011). After earth-moving operations and surface mining, the surfaces of the diaphragm walls show that many chimneys of water upwelling or sandy veins: The bleed water runs into the concrete (case of an impermeable soil). The hydrostatic pressure of fresh concrete in a diaphragm wall may lead to the creation of longitudinal channels along the wall. These channels might tend to follow equally the tremie pipe alignment in the concrete, which would promote the appearance of longitudinal channels at the centre of the wall. During its migration, this water may sweep away the concrete fines (‘washing-off’ of the concrete), thus segregating the concrete granular skeleton. In some cases, honeycombing might also be present (Figure 2). This pathology represents 90% of the disorders observed on site.