Using recycled waste brine or recycled seawater as mixing water in concrete manufacturing and the cement production have led to an increase in CO2 emission, and thus, another alternative needs to be sought. This work was the first in incorporating 5 Cl^- by cement weight (2.56 M NaCl) into mixing water blended with four different pozzolanic materials, examining its effect on fresh, 28-day hardened properties and the embedded reinforcing-steel (RS) corrosion. Results indicated that, with 5 Cl^- , the slump flows of Portland cement type I (CemI), 8 Cl^- encouraged the presence of an expansive gel sodium oxide (Na2O) in CemI (0.51

We present an autonomous system that remotely monitors the state of reinforced concrete structures. This system performs real-time follow-up of the corrosion rate of rebars (iCORR), along with other relevant parameters such as temperature, corrosion potential (ECORR), and electrical resistance of concrete (RE), at many of a structure’s control points by using embedded sensors. iCORR is obtained by applying a novel low-stress electrochemical polarization technique to corrosion sensors. The custom electronic system manages the sensor network, consisting of a measurement board per control point connected to a central single-board computer in charge of processing measurement data and uploading results to a server via 4G connection. In this work, we report the results obtained after implementing the sensor system into a reinforced concrete wall, where two well-differentiated representative areas were monitored. The obtained corrosion parameters showed consistent values. Similar conclusions are obtained with ECORR recorded in rebars. With the iCORR follow-up, the corrosion penetration damage diagram is built. This diagram is particularly useful for identifying critical events during the corrosion propagation period and to be able to estimate structures’ service life. Hence, the system is presented as a useful tool for the structural maintenance and service life predictions of new structures.

The excellent high-durability features of ultra-high performance fibre-reinforced concrete (UHPFRC) have been verified in laboratory studies, but its performance under service conditions are being studied. Indeed, structural health monitoring (SHM) can be considered an efficient strategy to assess built structures in which concrete matrix performance differs from that those found when assessing laboratory samples (variable actions, cracking, etc.). This work presents INESSCOM, an automated corrosion rate monitoring system, as an innovative support to SHM strategy to monitor UHPFRC structures in terms of durability. Its innovation lies in its durable and multi-parametric sensor designed to be embedded in multiple parts of a structure. The results from previous laboratory tests and those obtained during real-time monitoring of an offshore UHPFRC raft are presented. Acceptable deviation of 20% was obtained in corrosion rate measurements with the advantageous reference-electrode-free cell of the sensor with respect to the classical three-electrode cell. Furthermore, sensor provided accurate corrosion measurements in UHPFRC despite its extremely high electrical resistivity and large amount of steel fibres. After 17-month monitoring of the UHPFRC raft, excellent performance was evidenced under service conditions with corrosion rate values always <0.1 mu A/cm(2). Conversely, corrosion rate reached 0.4 mu A/cm(2) in a conventional concrete specimen installed for comparison. Corrosion initiation and propagation stages were clearly defined through the corrosion-penetration-damage (mu m) diagram obtained for the specimen. Present work positions INESSCOM as an innovative support to structural health monitoring strategy in UHPFRC structures.

Potential step voltammetry (PSV) was introduced in earlier works as an advantageous alternative to traditional methods for measuring corrosion rate in reinforced concrete. The present study aims to improve PSV to maximize its applicability in corrosion rate monitoring, that is, beyond the narrowly-defined steel–concrete systems in which was initially validated. It was therefore identified necessary to address the most suitable PSV pulse amplitudes to accurately obtain the Tafel lines and, therefore, corrosion rate in steel-mortar systems with well-differentiated ohmic drop. PSV findings were compared to reference methods, i.e. Tafel intersection and linear polarization resistance. As a novelty, we propose a procedure to improve the reliability of the PSV-determined Tafel lines, which is based on three protocols (P1, P2 and P3). P1 consists of a specific pulse sequence to accurately characterize the morphology of the polarization curve without disturbing the system. P2 consists of two short pulses for determining the ohmic drop compensation factor. Finally, P3 consists of a simple calculation procedure to accurately adjust the PSV pulse amplitudes (∆V) to the steel–concrete system assessed, thus obviating the need for preset values and, therefore, ensuring accurate corrosion rate results. The procedure proposed is intended to improve PSV with a view to its consolidation as a reliable tool for the unsupervised monitoring of real structures.

The need for proactive maintenance of reinforced concrete structures with non-destructive testing (NDT) is less disputable today than ever. One of the most promising strategies in this regard is the in-situ measurement of the reinforcement corrosion rate. This study explored the reliability of modulated current confinement method (hereafter MCC) based on a review of in-situ measurements made with that technique in real-life structures over a 13-year period. The most prominent problems detected included defective confinement of the polarization current in low-resistivity environments and over-polarization of passive reinforcement. The findings, which showed enhancement of MCC reliability to depend on improving the electrochemical current regulation and control methodologies presently in place, are being applied to improve the design of the next generation of corrosion meters.

The concrete electrical resistivity is a prominent parameter in structural health monitoring, since, along with corrosion potential, it provides relevant qualitative diagnosis of the reinforcement corrosion. This study proposes a simple expression to reliable determine resistivity from the concrete electrical resistance (R-E) provided by the corrosion sensor of the Integrated Network of Sensors for Smart Corrosion Monitoring (INESSCOM) we have developed. The novelty here is that distinct from common resistivity sensors, the cell constants obtained by the proposed expression are intended to be valid for any sensor implementation scenario. This was ensured by studying most significant geometrical features of the sensor in a wide set of calibration solutions. This embedded-sensor approach is intended to be applicable for R-E measurements obtained both using potential step voltammetry (PSV, used in the INESSCOM sensor for corrosion rate measurement) and alternating current methods. In this regard, we present a simple protocol to reliably determine R-E, and therefore resistivity, from PSV measurements. It consists in adding a very short potentiostatic pulse to the original technique. In this way, we are able to easy monitor resistivity along with corrosion rate through a single sensor, an advantage which is not usual in structural health monitoring.

There are few techniques available to calculate the corrosion rate (i(corr)) of reinforcing steel in concrete structures. This is due not only to a lack of instrumentation but also because it is necessary to take into account that polarization can irreversibly modify the metal surface and can affect the results or the future state of the metal. This is the reason some researchers prefer to test reinforcing steel with reversible techniques. The main objective of this study is to predict the corrosion rate of reinforced concrete using electrochemical methods combined with statistical tools such as multivariate analysis. Using reinforcements embedded in mortar samples, the corrosion rates were determined at different ages using the Tafel method, and values obtained were compared with other techniques: linear polarization resistance (LPR), potentiostatic pulse testing (PPT), and AC electrochemical impedance spectroscopy (EIS). In addition, these values were compared to those obtained using a mixed technique based on partial least squares (PLS). With this technique, we were able to automatically analyze the current data obtained from LPR, PPT, and EIS and to predict the i(corr) value. The study allows us to conclude that it is possible to obtain reliable i(corr) values, very close to those obtained with the Tafel method by using PLS combined with PPT or LPR. Furthermore, it presents several advantages, such as being able to directly treat data without requiring an established Stern-Geary constant (B) for LPR and not having to use an equivalent circuit (EC) in EIS to calculate i(corr) because only the impedance spectra are necessary.

Corrosion is one of the main triggering factors affecting the service life and durability of structures. Several methods are used for corrosion studies but electrochemical techniques are the most commonly applied. Corrosion processes monitoring and control by means of non-destructive techniques, such as the implementation of embedded sensors, has been the target of many works. It is possible to obtain relevant information of structural corrosion processes in real time. This document describes a system including specific equipment and which allows obtaining relevant information about these corrosion processes. This system is formed by a sensor network. There are several types of electrodes, which are distributed throughout the structure under study and a specific equipment developed by the research group, which is used to determine pertinent parameters such as the corrosion potential (E-corr) and the corrosion density (i(corr)) by applying sequences of potentiostatic pulses. The system allows to reliably determine the corrosion rate in different areas of the structure. The sensor, due to its configuration, provides information of a specific area of the structure, but on the other hand it is involved in the galvanic events that can occur along the structure by differential aeration, galvanic cells, etc. because the sensor is not isolated from the structure. This system also procures information of buried and submerged elements. Besides, it is possible to obtain information related to temperature, concrete resistance. The system includes specific potentiometric sensors to monitor chloride access and carbonatation processes

Concrete durability performance can be assessed by a number of parameters, among which permeability properties are key. In this experimental work, the permeability to water and the diffusion of chlorides in Ultra High Performance Concrete (UHPC) are studied. To this end, three types of concrete were made: two Ultra High Performance (one with fibers and one without fibers) and a Conventional Concrete (CC) of w/c ratio equal to 0.5. The compressive strength of Ultra High Performance Concretes was 130 MPa, and that of conventional concrete was 50 MPa. All of them were cured at a temperature of 20°C and RH greater than 95% until the age of 28 days. In the case of UHPCs with fibers, some of the specimens were not placed in the curing chamber but were allowed to air dry in a laboratory environment in order to study the influence of curing on this type of concrete. The results show that UHPCs have remarkably lower water permeability than CC, with the water absorption and water porosity being in the order of 8 times lower, the water absorption by capillarity being in the order of 30 times lower, and the non-steady-state chloride migration coefficient more than 100 times inferior. The values recorded of absorption and capillarity in UHPCs with and without fibers were very similar. However, the permeability to chlorides was somewhat higher in concretes with steel fibres. With regard to the influence of curing, in air-dried UHPCs there was a significant increase in permeability to both water and chlorides. Despite this, the chloride migration coefficient registered remained very close to the values proposed by some recommendations for very high durability concrete.