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Corrosion propagation in carbonated reinforced concrete structures

Corrosion propagation in carbonated reinforced concrete structures
INTRODUCTION: the carbonation and corrosion mechanisms
In reinforced concrete structures exposed in chloride-free environments, the corrosion of the reinforcement induced by the carbonation of the concrete is the main cause of degradation.

This causes cracking and detachment of the concrete cover (produced by the expansion caused by rust) and, because of this, often the need to carry out extraordinary maintenance operations.

Carbonation corrosion is characterized by a trigger period (ti) and a corrosion propagation period (tp). The triggering period is the time required for carbonation (which causes the neutralization of the alkalinity that protects the reinforcement from corrosion) to penetrate into the concrete until it reaches the depth to which the reinforcement is located. The period of corrosion propagation is the time necessary for a condition of degree to be produced such as to reach a limit condition (limit state) for which the structure no longer satisfies the requirements for which it was designed and built and therefore it is necessary to intervene .

When the limit condition is reached, there is the end of the service life (or nominal life) of the structure. The ignition time can be estimated by measuring the depth of carbonation, by the phenol-lymph test, and comparing it with the thickness of the cover. As regards the propagation time, an estimate of it can be made only if the speed with which the reinforcement is corroded is known (Bertoli-ni et al. 2013). This parameter is not easy to determine on the structures (Nygaard et al. 2009), unless specific probes have already been included in the construction phase, and to date no methodology is available to estimate the propagation of corrosion. in existing structures.

The corrosion speed can vary greatly, in particular when the humidity of the concrete changes (Fig. 1); the more a concrete is wet, the higher the corrosion speed and therefore the shorter the propagation time, on the other hand, if the concrete is dry, the corrosion speed becomes negligible and the life of the structure increases considerably.

In the case of existing structures in which the carbonation has already affected the concrete cover, the knowledge of the propagation period can therefore be crucial for deciding the intervention strategy; in areas where the speed remains negligible it may not be necessary to intervene even if the carbonation has already reached the reinforcement, while in the areas where the process advances rapidly it will be possible to program the intervention, and choose the most suitable one, before cracking the concrete cover.

This type of approach, called proactive, allows to reduce the huge costs (not only direct, but also indirect) linked to maintenance interventions (Polder et al. 2013). For example you can decide to intervene by applying a coating (a paint) that tends to keep the concrete dry, so as to slow down the corrosion of the reinforcements, thus avoiding the removal of the carbonated concrete.

The corrosion conditions of the carbonated concrete reinforcements are generally evaluated using electrochemical measurements, such as the mapping of the corrosion potential of the reinforcement, the electrical resistivity of the concrete and the corrosion rate (Bertolini et al. 2013).

They are often made using electrodes placed on the concrete surface. This makes it impossible to use them if an insulating coating has been used on the concrete and, in addition to this, the measurements are influenced by the humidity conditions of the concrete surface, so often no indications are obtained that are representative of the actual conditions of the reinforcements (Gastaldi et al. 2015).

A correct estimate of the corrosion rate of the reinforcement can only be obtained by probes capable of measuring the parameters related to corrosion and placed in the concrete at the level of the reinforcement. Frequently the existing structures present a considerable variability of the concrete cover; therefore it will be necessary to use probes capable of measuring these parameters at different depths in the concrete (Messina et al. 2017).

Furthermore, a reliable estimate of the corrosion rate can only be obtained by monitoring; in fact occasional measurements can provide misleading indications (for example, if the measurement is carried out in a dry period, results will be obtained which show that the reinforcement is not corroding; conversely, in a very rainy period, indications of rapid propagation can be obtained of corrosion).

This note reports the results of experimental tests carried out in the laboratory and in the field to evaluate the effectiveness of the use of the measurement of the electrical resistivity of concrete in the concrete cover for the estimation of corrosion propagation of carbonated concrete reinforcement.

Special specimens were made of reinforced concrete, with reinforcements with different concrete covers, in which different types of probes were inserted, before casting and in hardened concrete, to measure the level of reinforcement of the concrete electric resistance. of the potential and corrosion rate of the reinforcement. The specimens were carbonated and, subsequently, exposed to the atmosphere of Milan, in a position not sheltered from the rain. The correlation between the corrosion rate and the resistivity of the concrete and its validity to vary the cover and atmospheric conditions was analyzed. The probes for monitoring the resistivity of the concrete and the corrosion potential of the reinforcements have therefore been installed in some reinforced concrete structural elements of the “G.

The two speeds of the concrete sector

On the one hand the list of products that his friend Luigi Coppola recalled on Radio 24, such as “eat pollution ” concrete, “draining ” concrete , ” Ultra High Performance Fiber Renforced Concrete “, “self-repairing ” concrete , the concrete “transparent “, the concrete “floating ” the concrete “photoluminescent ” the concrete “3D printing “, … and the presence of some of these materials to the latest editions of the Milan Design Week, of the Italy pavilions in the last two Expo, and on the other a productive sector where plants continue to exist – and unfortunately not in a limited number – with average productions that approach the thousand monthly cubic meters, without internal technical control, little maintenance, with probes now set and disconnected from automation, automations often “modifiable”, non-selected aggregates, FPC certificates expired or obtained from short-sighted organisms in inspections, truck mixers with barrels in which there are blade residues.

These are the two speeds of the concrete sector
and the gap becomes wider and wider between an offer of increasingly smarter, more sustainable, more specialized concretes and a market that tends to everyday construction sites, not those of the changing Milan, not those of designer buildings, to maintain a strong attention to the price and to the discount rather than to the qualification of the supplier, to the evaluation of its ability to supply a concrete capable of satisfying the durability and performance requirements that the work requires.

It is an elastic that stretches, and which is bound on the one hand by a lack of rules, but of real respect for them , not technologies, but a lack of their request.

Unfortunately, we continue to be the country in which concrete is often dosed in the plant but then mixed into a truck mixer which is often not even owned by those who are formally the manufacturer of that material, to be the country where it is not possible. make a list of active concrete producers because it is not clear if the list of FPC certified plants is updated, to be the country in which the choice to close, or rather to seal, the mixer tap water voluntarily remains on top to the concrete supplier and is not imposed by law.

And if you try to put a minimum of filter to this situation you fall into the risks of antitrust sanctions, because in Italy, too often, the control regards not those who drag downwards but those who would like to point upwards.

What are the ways to reduce this gap then?

Quality passes through cultural growth
andrea-dari.gifWhile it is important to continue, on the part of the supply chain, to support technological innovation and its application in construction; on the other hand it is essential to increase the awareness on the part of professionals, or those who design and prepare the specifications.

The choice of products is not enough, we must also focus on the choice of suppliers. And this choice goes through the requirements that a professional can put in the specifications: requirements that can therefore concern not only the mechanical performance and workability, as has been done for years now, but also of special performances, such as waterproofing, or absorption of pollutants, or self-repair, of drainability … but also of controls during the initial qualification phase, and not only of casting … but also of evaluation of the supplier, such as, for example, a preverification of the plant and its characteristics as well of the supplier organization.

It is necessary that the virtuous experience of Italferr and High Speed ​​become in all respects the basis for the prescription of the future. Those who invest in maintenance, those who invest in sustainable plants, those who invest in controls, those who invest in organizations, those who invest in process automation are not afraid of a more selective market, indeed, it is for this market that is focusing on products with a higher rate. of specialization and technology. But these companies, which may be small, medium or large, fear, indeed they suffer, exactly the opposite: not the selection, but the lack of selection, the lack of a widespread culture of quality

The road remains clean not only if we have a municipality that organizes the activities of collection and cleaning as well as possible, but also if there is a system of control and sanction against those who dirty that road, and especially if there is a correct mentality on the part of the citizen, who does not use the sidewalk as a bin for his cigarette butts or his papers.

In the same way our reinforced concrete works will be more reliable and durable not only if the supply chain will be able to study products of increasing technological value, but even if the same supply chain will be able to supply them diffusely and correctly and, above all, if whoever he has the responsibility to prescribe them and to control them will have acquired the attention that is such to make, in fact, a natural upward selection of supply and demand.

How To Plan Your Dining Room’s Design

To many people, the dining room should be designed to be practical meaning it should have the tables and chairs and other complimenting furniture items. Unfortunately, the lack of attention to details can be very frustrating for the homeowner in the long run. Therefore, even if you value substance over style, you should plan how to design your dining room to avoid the building frustration with the dining room layout in the long run.

If you are starting from scratch, one of the first things you should do is to measure the dining area. This would give you a good idea of how large or small the table would have to be to provide enough space around the room for everyone. The measurement would be good information when out in the market for a table for the dining room.

Apart from measuring the dimension of the dining room, you should also consider how many people would be occupying the room in a normal situation. If you have a large family, you should look for space saving tables which would not sacrifice the number of people it can serve. If you have a small family on the other hand but you are also expecting your family to grow in the very near future, you should take this into consideration.

Aside from the table, the chairs also take up too much space in the dining room. If you chose the wrong chairs, you could have a cramped dining area which can be frustrating for everyone involved. Some chairs are too bulky which would not be a good fit for smaller dining areas. Even if they are the most comfortable dining chairs, you should always look into the practical side of things. If they are taking up too much space, they are not the most practical choice.

Whenever in the market for dining room furniture, always consider go for things that you are sure would work well for your home. If you think that the dining room furniture “may” be a good addition to your dining room, it is best to look for another choice.

Although it is best to only buy practical dining room furnishings, you should also try to match these furniture pieces. This way, your dining room would be practical and appealing as well. This could make your dining experience more appealing. It is also not a big problem if you want to mix and match dining room furnishings to match your unique style and preference for home decoration.