Manuela M. Salta

EFFECT OF FLY ASH ON CONCRETE REINFORCEMENT CORROSION STUDIED BY EIS

Abstract The corrosion process of steel embedded in concrete with various amounts of fly ash (up to 50% of the total binder) was tested under complete and partial immersion, in sodium chloride solution. The corrosion process was followed by monitoring of open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS). Fly ash addition has led to a raise of concrete resistivity and of the time for corrosion initiation and to a decrease of corrosion rate.

The assessment of the electrochemical behaviour of flyash-containing concrete by impedance spectroscopy

Abstract The effect of flyash addition to concrete on the reinforcement corrosion is studied by electrochemical impedance spectroscopy (EIS) and potential monitoring, leading to the interpretation of the phenomena on the surface of the steel under different exposure conditions. A relationship is established between the flyash content and the concrete resistivity.

Characterisation of Roman Mortars from the Archaeological Site of Tróia (Portugal)

Roman mortars from the industrial archaeological site of Tróia (Portugal) have been studied by means of chemical, mineralogical and microstructural analysis. The mortars are calcitic aerial lime mortars differing in the type and proportion of aggregates used, including crushed carbonaceous rocks (limestone and dolomite), siliceous sand and crushed ceramics. The results show that although these mortars have been subjected to a very aggressive environment they are still in a very good state of conservation.

Long-Term Efficiency of Two Organic Corrosion Inhibitors for Reinforced Concrete

In this paper the efficiency of two organic corrosion inhibitors, a migratory and an admixture inhibitor, was evaluated by electrochemical techniques in solutions simulating the interstitial electrolyte of concrete and on concrete slabs exposed to natural environmental conditions over a five-year period. From obtained results, the usefulness of the two products is discussed aiming its application in new structures to prevent chlorides induced corrosion and as a curative method for repairing reinforced concrete structures contaminated with chlorides and affected by reinforcement corrosion.

Accounting for variability and uncertainties in NDT condition assessment of corroded RC-structures

ABSTRACT The quantitative forecasting of corrosion development remains difficult, limiting the development of validated preventive maintenance strategies. Difficulties come from the spatial variability of material properties, the temporal variability of the environment and the sensitivity of non destructive measurements to changing environmental conditions. The reinforced concrete Barra Bridge, Portugal, has been thoroughly investigated, and on site data have been used for modelling the development of corrosion and its variability. A model has been derived from additional laboratory experiments, which enables to account for the influence of environment and to support the decision process regarding the corrosion state and the forecasting of its evolution.

Embedded Sensors for Corrosion Monitoring of Existing Reinforced Concrete Structures

In this work the performance of two surface treatments and the efficiency of a corrosion inhibitor were evaluated, in the control of steel corrosion in concrete induced by chlorides, through measurements of galvanic current and polarization resistance applied to embedded sensors fixed in existing concrete using different methodologies. From the results obtained the use of the different embedded sensors in the measurement of corrosion rate is discussed aiming the development of new systems for permanent evaluation of the on site performance of products for repairing reinforced concrete structures affected by reinforcement corrosion.

Influence of Mineral Additions in the Inhibition of Delayed Ettringite Formation in Cement Based Materials – A Microstructural Characterization

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.

Chloride profiles in a coastal bridge

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.

Sources of uncertainties for total chloride profile measurements in concrete: quantization and impact on probability assessment of corrosion initiation

Abstract 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.

Reinforced Concrete Durability in Marine Environments DURACON Project: Long-Term Exposure

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...