This research evaluation consisted of a detailed statistical analysis of the recorded data in 72 reinforced concrete specimens, from 12 natural test sites (in nine countries) located in chloride-laden environments (marine airborne-exposure test sites located between 50 m and 250 m from seashore), during a natural exposure period of 10 y. The parameters evaluated included the concrete physical-mechanical characteristics; meteorochemical information; natural reinforcing steel’s instantaneous corrosion current density (icorr) and cumulative icorr; and concrete chloride concentration; surface crack width and rebar cross-section loss correlations. This statistical analysis resulted in empirical instantaneous icorr predictions as a function of the exposure microclimates, through linear multiple regressions. These models showed a high linear dependence of the cumulative icorr with the concrete capillary absorption as well as with the meteorochemical parameters. Results obtained in this investigation showed higher corrosion aggressiveness in tropical environments when compared to nontropical ones. The cumulative icorr proved to be an effective tool to indicate the corrosive likelihood and differentiate the stages of Tuutti’s service life model.

Reliability methods have proved in the past that they were rational aid-tools for the safety assessment of existing structures, within which some uncertainties occurred. Condition assessment is usually carried out using on-site measurements, which are assumed perfect. However, it is now accepted that some significant uncertainties may affect the assessment of material properties using semi-destructive methods. The purpose of this paper is to present a method for the identification and evaluation of measurement uncertainties using a bias and a zero mean error modelled by a random variable. These uncertainties obtained are then modelled using a probabilistic model. In a marine environment, the main cause of reinforced concrete structure degradation is the corrosion due to chloride ingress. The chloride profiles are determined using a destructive method involving many steps where the experimenter plays a key role. In order to identify sources of errors, four researchers have performed repeatability tests. The total chloride content is expected to be the same for all the samples. The heterogeneity has been studied using statistical analysis. A value of the bias is provided and the model results are consistent with the original results. Finally, the impact of measurement errors on reliability and life-cycle assessment is discussed.

This paper presents the results, after a long-term evaluation in marine environments, from an Ibero-American project called “Effect of the environment on reinforcement durability” (DURACON). This p...

Concrete carbonation data from 16 test sites in 9 countries (Bolivia, Chile, Colombia, Costa Rica, Mexico, Spain, Uruguay, Portugal, and Venezuela) were compared to identify concrete performance due to carbonation at natural exposure conditions after almost six years of exposure. This research is part of the DURACON project ("Effect of the environment on reinforcement durability"), a long-term Ibero-American project intended to correlate the influence of urban and marine meteorochemical parameters on the performance of reinforced concrete structures. Environmental parameters were measured following the ISO 9223 standard. Concrete was physically characterized by the results of compressive strength, elastic modulus, total and effective porosity, and water absorption resistance (Fagerlund method) laboratory tests. Concrete specimens (with and without steel reinforcement bars-rebars) were prepared for electrochemical and physical/mechanical/chemical tests using materials available in each country. Concrete composition was kept similar between specimens by following strict preparation protocols. Two water/cement (w/c) ratios were used: 0.45 w/c ratio concrete had a minimum cement content of 400 kg/m(3); and 0.65 w/c ratio concrete had a minimum 28-day compressive strength of 210 kg/cm(2). Materials were type I Portland cement, siliceous sand, and crushed rock as coarse aggregates (13-mm maximum nominal size). After six years of exposure, corrosion potentiality and probability analysis of the reinforcement at the different sites indicated the concrete prepared in Venezuela to have the highest probability of experiencing carbonation-induced reinforcement corrosion. The concrete prepared at the Cali, Colombia, site had the lowest probability. Carbonation aggressiveness was found to be highest at tropical sites, with the Venezuela sites exhibiting the most aggressive conditions among the participating countries.

Organic-inorganic hybrid (OIH) matrices were synthesized by sol-gel method and deposited on hot-dip galvanized steel (HDGS) using a dip-coating process. These OIHs, generally called amino-alcohol-silicates, were synthesized using a functionalized siloxane, 3-glycidoxypropyltrimethoxysilane, and five oligopolymers (Jeffamine) with different molecular weights: 230, 400, 600, 900 and 2000. Besides the five different pure OIH matrix coatings, a similar set of HDGS samples were coated with the OIH matrices doped with Cr(III), which was tested as a corrosion inhibitor. The OIH coatings were assessed using electrochemical studies, namely electrochemical impedance spectroscopy, macrocell current density, open circuit potential monitoring and polarization resistance. The studies were carried out in mortar. Analysis of the results obtained by optical and scanning electronic microscopy methods were consistent with the data obtained by electrochemical techniques. The HDGS samples coated with OIH matrices showed better performance when compared with HDGS uncoated samples. (C) The Author(s) 2014. Published by ECS. All rights reserved.

Artigo completo publicado na revista Journal of The Electrochemical Society 161:6 (2014) C349-C362 e disponivel no RepositoriUM em: http://hdl.handle.net/1822/33784. Errata disponivel no RepositoriUM em: http://hdl.handle.net/1822/40064. (Publisher’s note: An erratum that addressed the errors in Figure 9 was originally published on Dec. 10, 2014, however the graphs in that erratum were not correct.)

The alkali-aggregate reaction (AAR) in concrete is a group of chemical reactions that involves the reaction of certain minerals present in the aggregates with alkali and hydroxyl ions in the interstitial solution of cement paste in concrete. These reactions form an alkaline hygroscopic gel that absorbs water and expands causing internal stresses with cracking [1].The AAR mitigation measures oblige the correct evaluation of the alkali reactivity of the aggregates. This is normally assessed by petrographic, chemical or expansion test methods.Several studies regarding alkali reactivity of aggregates for concrete structures in Portugal, including bridges and dams, indicated that their field performance does not correspond to the previously performed evaluation.Presently, Portuguese methodology is based on the LNEC Specification E461-2007, which shows some limitations regarding rock types such as granitoids [2]. This situation motivated the development of a research project, involving medium. and long term expansion tests in different conditions, under accelerated and natural exposure conditions, as well as petrographic evaluation of the main Portuguese aggregates used/to be used in concrete. This paper presents the preliminary results of this research.

This study is focused on the electrochemical behavior and surface analysis of an eco-friendly organic inorganic hybrid (OIH) coating for hot dip galvanized steel (HDGS) in contact with cementitious media. This treatment is a proposed alternative to replace toxic Cr(VI)-based pre-treatments used to control reactions between the zinc and wet concrete. HDGS samples were coated with two different sets of OIH gels obtained by a sol-gel process using a dip-coating method. Five distinct OIH matrices were obtained by reaction of functionalized metal-alkoxide (3-isocyanatopropyltriethoxysilane) with five different molecular weight diamine-lkylethers. One set of HDGS samples was coated with each of the five pure OIH matrices and another was coated with similar matrices doped with Cr(III). The morphology of OIH coatings over HDGS surface was characterized by SEM/EDS. Similar films were prepared separately and the respective resistivity was measured by electrochemical impedance spectroscopy. Polarization resistance and macrocell current density were used to evaluate the corrosion protection properties of the HDGS coated samples in contact with cementitious media for a period of 74 days. Results showed that the produced coatings provide barrier properties that withstand the high pH of the electrolyte, protecting the HDGS when it first contacts cementitious media. (C) 2013 The Electrochemical Society. All rights reserved.

The organic-inorganic hybrid sol-gel films have been reported as an effective anti-corrosion and environmentally friendly alternative to Cr(VI) pre-treatment for aluminium alloys. The sol-gel process used to obtain these coatings allows the variation of the different synthesis parameters to achieve coatings with optimized properties. In this work, hybrid films with different Zr/Si ratios were synthesized from glycidoxypropyltrimethoxysilane (GPTMS) and zirconium n-propoxide (TPOZ) precursors. Electrochemical Impedance Spectroscopy (EIS) was used to evaluate the corrosion behaviour of coated aluminium specimens in 0.5 M NaCl solution. The morphology and chemical structure of the hybrid coatings prepared were studied by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), Fourier Transformed Infrared Spectroscopy (FTIR) and Thermo Gravimetric Analysis (TGA). It was found that increasing Zr/Si ratio leads to a more cross linked inorganic network, resulting in higher initial coatings resistance, but may turn coatings more hydrophilic, prone to rapid degradation in water, due to a less connected organic network. Consequently, the best anticorrosive performance derives from the balance between the two opposite trends and it was achieved with Zr/Si molar ratio of 0.25.

The organic-inorganic hybrid sol-gel films, the structure of which comprises interconnected inorganic and organic networks have been reported as an environmentally friendly anti-corrosion pre-treatment for several metals, including aluminium alloys. In this paper, an epoxy-silica-zirconia hybrid sol-gel coating was synthesized from glycidoxypropyltrimethoxysilane (GPTMS) and zirconium n-propoxide (TPOZ) precursors and applied to EN AW-6063 alloy by dip-coating. To promote the organic network formation through the epoxy group polymerization at room temperature, two types of amine crosslinkers were added during synthesis: diethylenetriamine (DETA), in different concentrations, and a tri-functional aminosilane. The evolution of the curing process and the corrosion behaviour of the coated aluminium alloy specimens were evaluated by Electrochemical Impedance Spectroscopy (EIS) in 0.5 M NaCl. The morphology and surface chemistry of the hybrid coatings were characterized by Energy Dispersive Spectroscopy (EDS) coupled with Scanning Electron Microscopy (SEM) and by Fourier Transform Infrared Spectroscopy (FTIR). The results obtained revealed that the sol-gel coatings with lower amine ratios required longer curing times, but showed the best anticorrosive performance with time. The increase in amine concentration has led to a more cross linked organic network, resulting in higher initial coatings resistance; however it has turned coatings more hydrophilic, prone to rapid degradation in water.

This article addresses the results obtained in the field investigation performed on Barra Bridge, on the Portuguese Atlantic coast, to determine the degree of chloride transport into the concrete. A critical analysis is performed to quantify (i) the influence of the degree of exposure to the chloride environment, (ii) the average values of the apparent chloride diffusion coefficients, (iii) the surface chloride content estimated from the chloride profiles and (iv) the uncertainties associated to these concrete variables, which are expressed in terms of their covariance. Considerations are also given to the relevance of these results for (i) corrosion modelling of reinforced concrete, which aims to predict the time to corrosion initiation in concrete structures in marine environments and (ii) improving maintenance planning.

The degradation of concrete structures caused by delayed ettringite formation (DEF) is a problem that affects many concrete structures worldwide [1]. This pathology is due to the formation of expansive ettringite inside the material and is very difficult to deal with, because presently there is no efficient method to repair concrete structures affected by DEF. Hence, there is an urgent need to find preventive methods that may enable the inhibition of DEF in new constructions. This paper presents the findings of a long-term study [2,3] on the expansion rate and microstructure of heat-cured concretes with different amounts of mineral additions, like fly ash, metakaolin, ground granulated blast-furnace slag, silica fume and limestone filler. For this purpose different concrete compositions were produced using the same binder, water/binder (w/b) ratios and aggregate type. The concretes were prepared and subjected to a heat-curing cycle and subsequently to two drying-humidification cycles. After these cycles the concrete specimens were immersed in water for long-term storage at 20 ± 2°C. Length changes of specimens were measured at regular intervals. The microstructures of old heat curing specimens were investigated by optical microscopy and SEM-EDS analysis. The results of the blended-concrete compositions were compared with control compositions, and the conclusions were extracted.

The degradation of concrete structures caused by delayed ettringite formation (DEF) is a problem that nowadays affects many concrete structures worldwide. This pathology is due to the formation of an expansive compound – ettringite - inside the material. This is a hydrated calcium sulphoaluminate produced by the chemical reaction between sulphate ions, calcium hydroxide and alumina present in the Portland cement paste. This product, normally formed during the hydration of cement, presents an acicular morphology (needles) that can be observed by scanning electron microscopy (SEM). However, DEF can also be formed after the setting of the cement causing, in this case, a deleterious expansion of the concrete. This secondary ettringite can also be produced after an excessive heating of the concrete, caused by a high amount of cement or by the use of heat cure. SEM has been used to distinguish between expansive and non expansive ettringite based normally in morphology analysis, since the former is characterized by a compressed or compact nature where the needle shapes disappear or are welded together. Furthermore, the use of other techniques, like X-ray diffraction or micro-XRF, has been limited because the compressed or compact ettringite is badly crystallized or even amorphous and the elemental composition is similar and therefore it is difficult to detect. This article presents a methodology for the diagnosis of DEF using polished concrete thin sections and combining polarised and fluorescence light optical microscopy with SEM-EDS.

Recently some concrete bridges in Portugal have shown premature deterioration due to intensive concrete cracking development mainly attributed to internal expansive reactions. An important experimental program was conducted in order to diagnose the causes and also prognostic the long-term behaviour of the deteriorated concrete bridges. The research conducted has indicated that the concrete cracking was mainly due to the occurrence of internal expansive reactions: alkali-silica reaction (ASR) and/ or delayed ettringite formation (DEF). The ASR was caused by the use of alkali reactive aggregates and the DEF by the high heat-curing temperature obtained during the setting and hardening in combination with the high portland cement content used in the concrete mix designs. Residual expansion tests were done in order to access the residual ASR and DEF reactivity. Most of the bridges show residual capacity to continue the expansion due to ASR or DEF, which has forced remedial measures against these expansive reactions, mainly associated with control of the ingress of water into concrete. To avoid these causes of damage the design and construction of new structures must follow the new Portuguese preventive methodologies.