Corrosion-Inhibitor Efficiency Control: Comparison by Means of Different Portable Corrosion Rate Meters

Corrosion-inhibiting substances have been applied to suppress corrosion mainly on bare steel, but when corrosion is progressing, suppression can be achieved if anodic and cathodic reactions are avoided, which is not an easy objective, particularly if the bare metal is surrounded by concrete. In the present article, several corrosion inhibitors are studied to identify their inhibition efficiency in concrete. The percentage of reduction of the corrosion rate without and with inhibitor is named “inhibition efficiency.” This definition calls for the measurement of the corrosion rate and makes its measurement a must when studying corrosion-inhibiting substances. The most extended technique used for the corrosion rate quantification is based on the calculation of the polarization resistance, Rp. For the study presented in this article, several portable corrosion rate meters based on the Rp technique have been used. These equipment are needed for the evaluation of large structures and are able to confine the current in small areas or to determine the steel area affected by the signal for a correct corrosion rate calculation. A comparison among the different corrosion rate meters used for the inhibitor's efficiency has been done. This comparison has indicated that the corrosion rate meter with nonefficient confinement of the current is not able to detect clearly the passivation state

Relation between fibre distribution and post-cracking behaviour in steel fibre reinforced self-compacting concrete panels

In this research, the influence of the fibre distribution and orientation on the post-cracking behaviour of steel fibre 14 reinforced self-compacting concrete (SFRSCC) panels was studied. To perform this evaluation, SFRSCC panels 15 were cast from their centre point. For each SFRSCC panel, cylindrical specimens were extracted and notched either 16 parallel or perpendicular to the concrete flow direction, in order to evaluate the influence of fibre dispersion and 17 orientation on the tensile performance. The post-cracking behaviour was assessed by both splitting tensile tests and 18 uniaxial tensile tests. To assess the fibre density and orientation through the panels, an image analysis technique was 19 employed across cut planes on each tested specimen. It is found that the splitting tensile test overestimates the post20 cracking parameters. Specimens with notched plane parallel to the concrete flow direction show considerable higher 21 post-cracking strength than specimens with notched plane perpendicular to the flow direction.The studies reported in this paper are part of the research project LEGOUSE (QREN, project no 5387). This project is co-supported by FEDER through COMPETE programme ("Programa Operacional Factores de Competitividade"). The materials were supplied by Radmix and Maccaferri (fibres), SECIL (cement), SIKA and BASF (superplasticizers), Omya Comital (limestone filler), and Pegop (Fly ash)

Fibrous roller-compacted concrete with recycled materials - Feasibility study

This paper presents fundamental work done to enable fibre reinforcement of roller-compacted concrete (RCC). Procedures for mixing and casting two types of steel fibres in RCC were developed. Fresh properties, uniaxial compressive and bending behaviour were examined in a pilot study dealing with cement content, fibre type and dosage. It was found that different fibre types and dosages require different moisture contents. It is concluded that low cement content (less than 300 kg/m3) steel-fibre-reinforced roller-compacted concrete (SFR-RCC) mixes do not have sufficient paste and are prone to fibre agglomeration, hence SFR-RCC mixes richer in paste and at optimum moisture content are recommended. Mixes with cement content of 300 kg/m3 coped better with fibre reinforcement. Despite causing some loss in compressive strength, fibres help enhance the flexural performance and even SFR-RCC mixes with recycled masonry and concrete aggregates performed equally well as natural aggregate mixes. A fullscale trial has been conducted to confirm the findings. This paper is followed by a companion paper dealing with a comprehensive parametric study leading to the development of σ-ε models for SFR-RCC

Current knowledge of external sulfate attack

This paper offers an update of the current understanding of sulfate attack, with emphasis on the sulfates present in an external water source percolating through, and potentially reacting with, the cement matrix. The paper considers the explanations put forward to explain sulfate attack, both from a chemical and microstructural perspective. Similarly, this paper reviews work on the physical damage caused by the precipitation of sulfate salts in porous materials. With the increased use of binary and ternary blends, this paper also considers the impact of binder composition on sulfate resistance, and similarly reviews how the nature of the sulfate species can affect the nature and extent of any deterioration. This then leads on to the important consideration of differences between field- and lab-based studies; reviewing the effect of various experimental parameters on sulfate resistance. This latter topic is of great importance to anyone who wishes to carry out such experiments

Recommendation of RILEM TC 269-IAM: damage assessment in consideration of repair/retrofit-recovery in concrete and masonry structures by means of innovative NDT Methods for damage assessment of concrete members utilizing active elastic wave measurements

This recommendation specifies a method for measuring active elastic waves and assessing damage to concrete members such as decks and girders. The method uses elastic waves propagating inside the concrete member. Elastic waves generated near a surface of the concrete member are detected by acoustic emission sensors installed on the opposite side of the member. Elastic waves propagating in concrete are attenuated or diffracted by damage such as cracks and voids, resulting in fewer AE sources than that of intact areas. Thus, it is possible to distinguish a damaged region from others with density of the observed AE source distribution

Handmade clay bricks: chemical, physical and mechanical properties

The clay brick masonry that is much used in historical structures often is in a rather poor state of conservation. In order to intervene correctly in these buildings, it is convenient to characterize the old material. For this purpose, a large sample of clay brick specimens from the 12th to 19th century were collected from six Portuguese monasteries, and were characterized chemically, physically and mechanically. A large variability of the properties was found. Additionally, a sample of handmade new bricks, which are commonly used as replacing material, was also analysed. The results were compared to the old bricks and could be possibly adequate as substitution bricks. Still, significant differences were found in chemical composition, and in water absorption and porosity, which are much lower in modern handmade bricks. With respect to mechanical properties, the range of values found in old bricks was rather high and the degree of deterioration exhibited a large scatter, meaning that a conclusion is hardly possible.The authors gratefully acknowledge the Instituto de Gestao do Patrimonio Arquitectonico e Arqueologico (IGESPAR) for providing the old clay bricks used in the present work. The first author acknowledges the partial funding of this work by the FCT through the following scholarships POCTI SFRH/BD/6409/2001 and POCTI SFRH/BPD/26706/2005

The feasibility of using electromagnetic waves in determining membrane failure through concrete

Concrete flat roof defects such as water leakage present a significant and common problem in large buildings, particularly in tropical countries, where rainfall is high. To monitor this condition, effective non-destructive test methods are required to detect problems at an early stage, especially hidden defects within the concrete roof, which are critical. This paper presents the potential use of electromagnetic (EM) waves for determining possible leakage of the concrete flat roof as a result of failure of the waterproof membrane layer. This study was assessed, experimentally by investigation of the propagation of EM waves through the roof and their interaction with water. Novel Microwave sensors described in the paper operate in the 6 GHz to 12 GHz frequency range using a Marconi 6200A microwave test set. A range of existing methods was reviewed and analysed. Results of experimental tests confirmed that microwaves could be used as an alternative non-destructive method for identifying water ingress caused by membrane failure into the concrete roof surface

Steel fibre reinforced concrete for elements failing in bending and in shear

Discrete steel fibres can increase significantly the bending and the shear resistance of concrete structural elements when Steel Fibre Reinforced Concrete (SFRC) is designed in such a way that fibre reinforcing mechanisms are optimized. To assess the fibre reinforcement effectiveness in shallow structural elements failing in bending and in shear, experimental and numerical research were performed. Uniaxial compression and bending tests were executed to derive the constitutive laws of the developed SFRC. Using a cross-section layered model and the material constitutive laws, the deformational behaviour of structural elements failing in bending was predicted from the moment-curvature relationship of the representative cross sections. To evaluate the influence of the percentage of fibres on the shear resistance of shallow structures, three point bending tests with shallow beams were performed. The applicability of the formulation proposed by RILEM TC 162-TDF for the prediction of the shear resistance of SFRC elements was evaluated. Inverse analysis was adopted to determine indirectly the values of the fracture mode I parameters of the developed SFRC. With these values, and using a softening diagram for modelling the crack shear softening behaviour, the response of the SFRC beams failing in shear was predicted.Fundação para a Ciência e a Tecnologia (FCT