International Concrete Abstracts Portal

Corrosion of steel reinforcements in concrete structures is the most important cause of premature failure. To improve service life of concrete structures, corrosion inhibitors are often proposed and used to prevent chloride induced corrosion and carbonation corrosion. This paper deals with a laboratory investigation both in concrete and in a synthetic pore solution on the effectiveness of mixed-in commercial corrosion inhibitors to hinder corrosion initiation and propagation of reinforcements in concrete structures. The results of a laboratory research aimed at studying the effect of inhibitors added to the concrete mixture are discussed. Three organic commercial corrosion inhibitors and, by comparison, nitrite based inhibitors were added to fresh concrete in concentration suggested by the manufacturers. Experimental tests were carried out on reinforced concrete specimens with carbon steel reinforcement in chloride contaminated concrete (both adding chlorides directly in the mixture and penetrating the hardened concrete by means of ponding cycles). In order to study the inhibitors effect, the results, in terms of two electrochemical parameters, i.e. free corrosion potential and polarisation resistance, are compared with those obtained considering concrete specimens without inhibitors. For comparison purposes, results on some pure organic substances are reported, confirming data obtained on the commercial products. Some positive effects are achieved when both commercial products and pure substances were used at dosage rates higher than that recommended.

As part of a U.S. Navy program for the Modular Hybrid Pier to predict long-term behavior of lightweight concrete in marine environments, the condition of a series of concrete samples taken from a floating boat dock exposed to the Pacific Ocean since 1978 were assessed. Samples originating form the top deck, tidal and submerged zones were tested. Microstructural alterations were investigated by petrographic examinations using optical and scanning electron microscopy. Chloride profiles were measured by chemical analyses. The hulk properties of each series of concrete samples were also determined by porosity measurements, pore solution extraction, chloride migration tests and moisture transmission measurements. The actual state of deterioration of each series of samples was compared to the results yielded by a numerical model. This numer- ical model accounts for the coupled transport of moisture and eight different ionic species (such as chloride and sulfate ions) within unsaturated concrete structures. The software also takes into consideration the chemical equilibrium of ten different solid phases (e.g. ettringite, gypsum and Friedel's salts). Parameters affecting the long-term performance of concrete in seawater are discussed.

It was investigated whether normal ecocement manufactured using as raw materials large amounts of urban wastes such as incinerator ash and sewage sludge, could he used for reinforced concrete. It was confirmed that the fresh properties, strength properties, durability, steel corrosion protecting performance, leaching of heavy metals and workability of the concrete using normal ecocement that contains a reduced amount of chloride ions of around 0.05% were equal to those of concrete using normal portland cement. The results of test executions in several field also confirmed that concrete using ecocement demonstrated Workability equal to that of general concrete. Based on these results, it was concluded that normal ecocement can he used for reinforced concrete.

The work reported in the paper is planned to investigate the air-void system and the frost resistance of self-compacting concrete with slag fine aggregates, produced in refining process of metals, such as blast furnace slag (BFS) fine aggregates, ferronickel slag (FNS) fine aggregates and copper slag (CUS) fine aggregates, which were standardized in JIS A 5011 (Japanese Industrial Standard) as slag aggregates for concrete, The positive use of these slag fine aggregates is being enhanced from the view point of utilization and recycling of industrial by-products. Test results are summarized as follows: (1) The air-void system of self-compacting concrete with slag fine aggregates varied depending on the type of slag fine aggregates used in this investigation. Especially, self-compacting concrete with BFS fine aggregates showed much larger air-voids. This was due to the entrapment of large air bubbles in the course of the mixing process of concretes. (2) The highly durable concrete to frost action can he produced by making the proper air void system with the spacing factor of not more than 300-um.

The built environment of the early 20" century, constructed mainly with rein- forced concrete present serious damage problems. Thus, the establishment for an appropriate damage assessment methodology, that evaluates the concrete durability and service life, is a neccessity. In this study, two buildings of the early 20th century, exposed to an aggressive marine environment are examined: the first is the spa at Kallithea in Rhodes, constructed mainly with reinforced concrete, and the other is the Bell tower of the Church of Saint John Prodromos in Simi, where reinforced concrete was used for repairs. A series of non-destructive Techniques (Fiber Optics Microscopy, ultrasound technique, determination of corrosion potential at the reinforcement and determination of concrete carbonation depth) along with Laboratory Techniques (Grain size distribution, Mercury Intrusion Porosimetry, X-Ray Diffraction, Thermal Analyses) were used. The obtained results revealed that the concrete is carbonated up to the reinforcement bars. The reinforcement has lost the bearing capacity after its 7th lifetime decade. In addition, the nondestructive techniques methodology gave satisfactory results and could be undertaken, for the damage assessment of the modern built environment exposed to aggressive environments (marine or urban).