Miguel-Ángel Climent

Chloride Penetration Prediction in Concrete through an Empirical Model Based on Constant Flux Diffusion

The authors thank the Ministerio de Economia y Competitividad of Spain and Fondo Europeo de Desarrollo Regional (FEDER) for the funding received for this research through project BIA2010-20548. M. P. Lopez is grateful for a fellowship with the Formacion Personal Investigador (FPI) program (reference BES-2011-046401).

Shape Effect of Electrochemical Chloride Extraction in Structural Reinforced Concrete Elements Using a New Cement-Based Anodic System

This article shows the research carried out by the authors focused on how the shape of structural reinforced concrete elements treated with electrochemical chloride extraction can affect the efficiency of this process. Assuming the current use of different anode systems, the present study considers the comparison of results between conventional anodes based on Ti-RuO2 wire mesh and a cement-based anodic system such as a paste of graphite-cement. Reinforced concrete elements of a meter length were molded to serve as laboratory specimens, to closely represent authentic structural supports, with circular and rectangular sections. Results confirm almost equal performances for both types of anode systems when electrochemical chloride extraction is applied to isotropic structural elements. In the case of anisotropic ones, such as rectangular sections with no uniformly distributed rebar, differences in electrical flow density were detected during the treatment. Those differences were more extreme for Ti-RuO2 mesh anode system. This particular shape effect is evidenced by obtaining the efficiencies of electrochemical chloride extraction in different points of specimens.

Influence of curing conditions on the mechanical properties and durability of cement mortars

Real structures are hardened in conditions different from the optimum laboratory conditions, where materials are usually tested. The different temperature, and especially the different relative humidity present in the environment, may cause a different microstructure and, as a consequence, different service properties. In this work mortars made with two different cement types are tested in laboratory conditions and at a lower relative humidity. These new environmental conditions cause a slower microstructural development and different durability and mechanical properties at early hardening ages.

Short-Term Behavior of Slag Concretes Exposed to a Real In Situ Mediterranean Climate Environment

At present, one of the most suitable ways to get a more sustainable cement industry is to reduce the CO2 emissions generated during cement production. In order to reach that goal, the use of ground granulated blast-furnace slag as clinker replacement is becoming increasingly popular. Although the effects of this addition in the properties of cementitious materials are influenced by their hardening conditions, there are not too many experimental studies in which slag concretes have been exposed to real in situ environments. Then, the main objective of this research is to study the short-term effects of exposure to real Mediterranean climate environment of an urban site, where the action of airborne chlorides from sea water and the presence of CO2 are combined, in the microstructure and service properties of a commercial slag cement concrete, compared to ordinary Portland cement (OPC). The microstructure was studied with mercury intrusion porosimetry. The effective porosity, capillary suction coefficient, chloride migration coefficient, carbonation front depth, and compressive strength were also analyzed. Considering the results obtained, slag concretes exposed to a real in situ Mediterranean climate environment show good service properties in the short-term (180 days), in comparison with OPC.

Impedance Spectroscopy Study of the Effect of Environmental Conditions on the Microstructure Development of Sustainable Fly Ash Cement Mortars

Today, the characterisation of the microstructure of cement-based materials using non-destructive techniques has become an important topic of study, and among them, the impedance spectroscopy has recently experienced great progress. In this research, mortars with two different contents of fly ash were exposed to four different constant temperature and relative humidity environments during a 180-day period. The evolution of their microstructure was studied using impedance spectroscopy, whose results were contrasted with mercury intrusion porosimetry. The hardening environment has an influence on the microstructure of fly ash cement mortars. On one hand, the impedance resistances R1 and R2 are more influenced by the drying of the materials than by microstructure development, so they are not suitable for following the evolution of the porous network under non-optimum conditions. On the other hand, the impedance spectroscopy capacitances C1 and C2 allow studying the microstructure development of fly ash cement mortars exposed to those conditions, and their results are in accordance with mercury intrusion porosimetry ones. Finally, it has been observed that the combined analysis of the abovementioned capacitances could be very useful for studying shrinkage processes in cement-based materials kept in low relative humidity environments.

Steel Corrosion Rate Measurements in FA Concrete Using Three Electrochemical Techniques

Blended cements are today commonly used for concrete structures built near the sea. When reinforced concrete is exposed to the atmospheric marine environment, it is necessary to consider steel corrosion caused by both, chloride ions and carbon dioxide. In this research, reinforced OPC and FA cement concrete samples have been tested in order to evaluate their comparative performance when exposed to chlorides, to CO2 and to both agents acting together. The techniques used to evaluate the steel corrosion rates have been the polarization resistance, intersection method of polarization curves, and electrochemical impedance spectroscopy. The results indicate a similar behavior of FA and OPC concrete for samples exposed to CO2. For the pure chloride exposure and the combined exposure regimes, the behavior depends on the type of binder. The polarization resistance technique appears to show some limitations when there is not enough electrolyte inside the pores.

Comparison Between Dcrit Considering the Abrupt Variation and Inflexion in the Concrete Mercury Intrusion Porosimetry Curve

Mercury intrusion porosimetry (MIP) has been widely used to evaluate the quality of concrete through the pore size distribution parameters. Two of these parameters are the critical pore diameter (Dcrit) and the percentage of the most interconnected net of pores compared to the total volume of pores. Some researchers consider Dcrit as the diameter obtained from the inflexion point of the cumulative mercury intrusion curve while others consider Dcrit as the diameter obtained from the point of abrupt variation in the same curve. This study aims to analyze two groups of concretes of varying w/c ratios, one cast with pozzolanic cement and another with high initial strength cement, in order to determine which of these diameters feature a better correlation with the quality parameters of the concretes. The concrete quality parameters used for the evaluations were (1) the w/c ratios and (2) chloride diffusion coefficients measured at approximately 90 days. MIP cumulative distributions of the same concretes were also measured at about 90 days, and Dcrit values were determined (1) from the point of abrupt variation and alternatively, (2) from the inflexion point of each of these plots. It was found that Dcrit values measured from the point of abrupt variation were useful indicators of the quality of the concrete, but the Dcrit values based on the inflexion points were not. Hence, it is recommended that Dcrit and the percentage of the most interconnected volume of pores should be obtained considering the point of abrupt variation of the cumulative curve of pore size distribution.

Experimental Confirmation Of Some Aspects OfThe Microstructural Model Of The ImpedanceSpectra Of Porous Materials

The use of impedance spectroscopy, IS, has become a useful technique for the microstructural characterisation of cement pastes and mortars. The main advantage is that it is non destructive, but in the other hand the interpretation of the results obtained is not straightforward. A model has been proposed that gives microstructural interpretation of the electrical parameters obtainable from the impedance data. Here is presented a validation of that model, using a model material, which allows controlled changes in the electrolyte conductivity to be monitored by IS. The conductivity of pore solution cannot be controlled in cementitious materials, which makes very difficult to differentiate between changes of pore structure and changes in conductivity. The results presented here show good agreement between predictions of the model, and experimental results.

Impedance Spectroscopy As A Tool To StudyModifications In The Microstructure Of ConcreteIn Ionic Migration Experiments

The study of the penetration of chloride ions in concrete structures is of great interest, because of the pernicious effects that these ions have on the corrosion of steel reinforcements. Accelerated methods have been developed to obtain the diffusion coefficient of chlorides through cement-based materials. One of these methods allows the calculation of both steady and non-steady state diffusion coefficients using a very simple conductivity measurement [1]. The presence of an electric field causes modifications in the microstructure of cement-based materials, and also an acid attack can be produced on the material if the porosity is high enough [2]. As has already been proved, impedance spectroscopy is a powerful technique to study the microstructure of cement-based materials [3]. This technique is used to characterize during the experiment the modifications that are produced in the microstructure of concrete samples during the forced migration tests. The results obtained using impedance spectroscopy have been compared with the results obtained with the mercury intrusion porosimetry, and a very good agreement has been observed.