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In this work, the durability performances of mortars made with an ordinary Portland cement and a slag cement, were tested. These mortars were exposed to four different constant temperature and relative humidity during 365 days. The measured properties of both cement types are affected by the environment, but the durability of slag cement mortars is more influenced by temperature and the durability of OPC mortars is more influenced by the relative humidity. The obtained results show that the slag cement mortars hardened under non-optimal environmental conditions have good durability at any hardening age, even better than Portland cement.

Introduction: Juvenile absence epilepsy (JAE) is a generalized form of epilepsy, characterized by absence seizures (AS) initiated in adolescence, with a typical EEG showing generalized spike-wave discharges. Apart from absences, other seizure types may be observed such as myoclonia and generalized tonic-clonic seizures (GTCS). Its long-term prognosis is uncertain. Material and methods: We retrospectively selected all patients who met the 1989 ILAE diagnostic criteria for JAE. We analysed clinical variables, pharmacological treatment, and seizure remission with medical treatment and seizure relapse after stopping medical treatment. Results: We identified 21 patients, 17 women and 4 men, 86% of whom had suffered GTCS and 14% myoclonias. Mean age at AS onset was 17 years old (range 10–44), 4 patients debuted with AS in adulthood. Mean follow up duration was 25 years (range 10–43). Ninety per cent of the patients were treated with valproate and 62% needed polytherapy. Currently 43% have achieved seizure freedom under medical treatment. All attempts to stop treatment failed, in some cases after long periods of seizure remission. Conclusions: Less than fifty per cent of patients with JAE achieve remission, antiepileptic treatment is mandatory during all life, despite having long periods of remission. Resumen: Introducción: La epilepsia ausencia juvenil (EAJ) es un tipo de epilepsia generalizada idiopática que se caracteriza por la presencia de crisis de ausencia (CA) que comienzan en la adolescencia, con un EEG típico de punta-onda generalizada, y que puede acompañarse de mioclonías y crisis tónico-clónicas generalizadas (CTCG). El pronóstico a largo plazo es incierto. Material y métodos: Seleccionamos de manera retrospectiva todos los pacientes que cumplían los criterios diagnósticos de EAJ de la ILAE 1989, analizamos las variables clínicas, el tratamiento farmacológico, el estar libre de crisis y la posibilidad de retirar el tratamiento. Resultados: Encontramos 21 pacientes, 17 mujeres y 4 varones, el 86% presentó también CTCG y el 14% mioclonías. La edad de inicio de las CA fue de 17 años (rango: 10–44). Cuatro pacientes comenzaron con CA en la edad adulta. El seguimiento medio fue de 25 años (intervalo: 10–43). El 90% recibió tratamiento con valproato y el 62% requirió politerapia. El 43% de los pacientes están actualmente libres de crisis, aunque todos ellos en tratamiento farmacológico. Todos los intentos de retirar la medicación fracasaron, pese a largos períodos sin crisis. Conclusiones: Menos de la mitad de los pacientes con EAJ están libres de crisis. El tratamiento antiepiléptico es necesario durante toda la vida a pesar de largos períodos de remisiones. Keywords: Juvenile absence epilepsy, Absences, Prognostic, Treatment, Adulthood, Palabras clave: Epilepsia ausencia juvenil, Ausencias, Pronóstico, Tratamiento, Edad adulta

The results of this research show the viability of using a conductive cement paste anode for the electrochemical extraction of chlorides from reinforced concrete with an efficiency similar to that obtained with a classic Ti–RuO2 anode. The obtained efficiencies are within the typical range of values of overall efficiencies found for such treatments. The thickness of the conductive cement paste anode has a great influence on the capacity of the anode to retain an important part of the extracted chlorides after finishing the electrochemical treatments.

The forced migration test has been used during the last decades as an accelerated and useful method for determining the resistance of concrete to chloride ingress. Furthermore it allows to determine transport parameters of chloride ions through porous materials. The application of electric fields seems to introduce variations in the microstructure of concrete. In this work these variations have been studied using the impedance spectroscopy technique in the high frequency region (1 kHz–1 MHz). The results show that the dielectric response of concrete is also strongly modified during the migration experiments. The variations of the dielectric parameters during the migration tests can be explained in terms of modifications of the microstructure of concrete. The observed modifications are in good agreement with the results of mercury porosimetry analysis.

In this work, it is demonstrated that it is possible to eliminate the filtration step in the determination of the acid-soluble chloride content of cement and concrete by potentiometric titration, irrespective of the method used for detecting the end-point of the titration. Extensive analytical results are presented corresponding to several types of cement and to a broad range of chloride concentrations in concrete. Some requirements to avoid errors in such analytical determinations are discussed.

A test method is proposed for measuring chloride diffusion coefficients through nonsaturated concrete specimens with controlled water contents. The experimental setup used allows one to supply an initial limited amount of Cl − to the tested concrete surface. The procedure consists of submitting the surface of concrete specimens to interaction with the products of combustion of PVC, which contain mainly gaseous hydrogen chloride. This interaction yields a limited Cl − contamination of the concrete surface. After returning the specimens to their controlled humidity exposure conditions, the kinetics of Cl − transport from the surface inwards may be studied. The experimental Cl − concentration profiles determined at selected time intervals have been adjusted to a diffusion model of “instantaneous plane source,” which takes into account the particular initial and boundary conditions of the experimental procedure, for obtaining the corresponding diffusion coefficients.

A potentiometric titration procedure that makes use of Gran’s method for end-point detection has been developed to analyze acid-soluble chloride in cement, mortar, and concrete, eliminating the filtration steps performed in habitual laboratory reference methods. The accuracy and reliability of the proposed analytical technique has been checked against a standard method, such as Volhard’s, by analyzing duplicate samples of cements, mortars, and concretes with varied chloride contents.

Chloride contamination of concrete by interaction with PVC combustion gases has been studied in a small-scale testing chamber, which allows simulating the conditions probably prevailing in PVC fires of different magnitude through variation of the quotient between mass of burnt PVC and exposed concrete surface (PVC/S). In all cases, a steep gradient of chloride concentration with depth is found after the fire: most chloride is detected in the outermost layer at depths below 5 mm. Surface chloride contents (within 5 mm) for prestressed and reinforced concretes, tested with a high (PVC/S) ratio, are as high as 2.5 and 5% by weight of cement, respectively. Chloride concentrations in concrete near the steels are below the corrosion thresholds after the fire, but they can rise by diffusion to values able to induce rebar corrosion, especially if concrete is exposed to a humid atmosphere.

Carbonation of concrete by atmospheric CO 2 may lead to breakdown of the passivating layer of the steel reinforcements, leading to catastrophic corrosion, if the pH of the electrolyte in the concrete pores decreases below 8. The nature of this carbonation process has been studied by means of potential-modulated reflectance (PMR) spectroscopy, following the changes in the PMR spectrum of air-passivated iron in 1M NaOH produced by sparging the electrolyte with a CO 2 + air mixture. Decreasing the pH from 8.02 to 7.69 produced the disappearance of the Fe 2 O 3 PMR signal and nearly a doubling of the PMR maximum of FeOOH, pointing to a hydration of Fe 2 O 3 to FeOOH preceding the breakdown of the passivating layer. A further decrease of only 0.07 pH units, down to pH 7.62, effected an increase of the corrosion rate of nearly two orders of magnitude and the disappearance of the PMR spectrum of the passivating layer, this being the first spectroscopic proof that depassivation by carbonation is due to a complete electrochemical dissolution of the passivating layer.

The measurement of the free chloride concentration in the pore solution of cement paste or concrete is of interest for assessing the probability of corrosion of the steel reinforcements embedded in concrete. This determination is performed through leaching or pore-pressing methods or through embedded potentiometric sensors into the hardened cementitious material. The potentiometric determination of chloride in cement paste pore solutions is limited by hydroxide ion interference, due to the high alkalinity of such media. The potentiometric selectivity coefficients, k Cl - , OH - , are determined for a chloride ionic selective electrode in alkaline solutions simulating the electrolyte present within the pore network of cement paste and concrete. This is done using a fixed interference methodology, with least-squares non-linear curve fitting for obtaining the selectivity coefficients together with other relevant electrode parameters. The limit of detection of the Cl− ISE, due to OH− interference, varies with pH. For the pore solution corresponding to an ordinary Portland cement paste or concrete, this limit can be set between 3 × 10–3 m, and 7 × 10–3 m, i.e., approximately below a chloride concentration value of 1 × 10–2 molal. Taking into account these limits of detection the free Cl− concentrations able to depassivate the steel, can be adequately determined by potentiometric measurements with calibrated ISEs in the expressed pore solutions of Portland cement concretes, without significant influence of OH− interference. Nevertheless, this effect can prevent the adequate measurement of low free Cl− concentrations, below the corresponding limit of detection value.

A test method is proposed for measuring chloride diffusion coefficients through partially saturated concrete specimens with well characterized water contents. It includes an experimental procedure for supplying a limited amount of Cl- to the tested concrete surface, and two mathematical models for processing the experimental Cl- content profiles obtained at selected diffusion times. The use of the more refined model, taking into account the chloride binding by concrete, allows to increase the reliability of the determined diffusion coefficients. For the two tested Portland cement concretes, (water/cement ratios 0.6 and 0.5), the Cl- diffusion coefficient decreases about two orders of magnitude, from 6 · 10- 12 to 2 · 10- 14 m2/s, when the relative humidity of the atmosphere in equilibrium with concrete is lowered from 95% to 54% approximately. © 2007 Elsevier Ltd. All rights reserved., This work has been financially supported by the Ministerio de Ciencia y Tecnología of Spain and by the Fondo Europeo de Desarrollo Regional (FEDER) through project BQU2001-0837-C02-01. We thank also the funding from the Competitive and Sustainable Growth Programme of the European Community through contract G6RD-CT-2002-00855 (Chlortest project).