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.

Supplementary hydrophobic treatments of the concrete surface can be a durable and potent method to lower the moisture content of the concrete and to improve its durability by inhibiting the migration of aggressive substances as well as slowing down the corrosion process. At the Institute for Building Materials Research in Aachen, ibac, comparative tests have been carried out on the efficiency and long-term durability of different hydrophobic agents on different types of concrete. The effectiveness and durability of the hydrophobic treatment was monitored using a sensor called multiring-electrode, which indicates the variation of humidity of the concrete in different depths by measurement of its electrolytic resistivity. The results hsow that the applied dosage on the specimens influenced the durability and efficiency of the hydrophobic treatment most significant. Other factors like active content, type of active agent or penetration depth have only a subordinate influence. The results showed also that a drying tendency of the specimen was only ob- served on the specimens weathered artificially in the VENUS test facility. Short rain periods of some minutes per day as simulated in the VENUS testing facility do not result in a high moisture content of the specimens. In contrast, a drying behaviour was observed also under a relative humidity of 95%. Long rain periods of several hours per day and a typical autumn weather with drizzle lead to a rising moisture content of the naturally weathered specimens even with an applied hydrophobic treatment.