International Concrete Abstracts Portal

The results of laboratory and in situ tests of a number of different types of coatings commercially available in Croatia (polymer-cement, epoxy, acrylic, epoxy-acrylic and epoxy-polyurethane), used for reinforced concrete protection of the KRK bridge, are presented. The tests have been carried on throughout the last ten years. Some coatings like epoxy and polymer-cement were found completely unacceptable for the technical reasons. However, epoxy-polyurethane coatings applied on the concrete finished with the thin layer of epoxy-cement mortar are estimated rather effective. They had high adhesion strength (above 2,0 MPa), very low gas permeability, low capillary absorption, satisfactory water vapour diffusion and satisfactory ageing resistance.

In recent years, structures made with anti-washout concrete under marine environment have been increasing. However, the durability of such structures is not yet clarified. Therefore, in order to understand the durability of reinforced concrete made with anti-washout concrete, the exposure tests were carried out under marine environment for ten years. The reinforced concrete specimens prepared with anti-washout concrete containing either silica fume or ternary low heat cement were exposed to marine atmosphere and underwater. Investigations were focused on the variation of concrete quality, concentration chloride ion and corrosion of reinforcement. From test results, the compressive strength of anti-washout concrete is similar to reference concrete in ordinary structures. The carbonation depth of the anti-washout concrete made without admixture silica fume is lower than that of reference concrete. At the distance of 2 cm from the surface of underwater cast concrete of the chloride ion concentration is sufficient to corrode the reinforcement at any concrete. After 10 years of exposure to marine environment, that of reference concrete is from 5 to 10 times that of anti-washout concrete. Therefore, the anti-washout concrete is durable under marine environment and it is possible to design for durability in the same way as for normal concrete.

Biogenic sulphuric acid corrosion is a phenomenon which occurs mainly in sewer pipes. The process consists of four stages: the reduction of sulphate to sulphide; the transition of sulphide to hydrogen sulphide gas in the sewer atmosphere; the re-oxidation of the sulphide gas to sulphuric acid in an oxidizing environment of the sewer pipe and finally concrete attack by sulphuric acid. Different models are developed to predict the sulphide formation and the corrosion rate. The model of Pomeroy, according to which the rate of sulphur production and the rate of corrosion can be calculated, is used in this paper. Different parameters are taken into account and case studies are described. Comparison of the calculated corrosion and the measured corrosion indicates the accuracy of the formula. Additional, a sensitivity study is carried out on the formulae to distinguish the influence of the different parameters. A realistic variation of the different parameters is made, based on measurements at the inlet of purification plants. The most influencing parameters for the model were the temperature, the BOD-content and the pH-value of the waste water, the depth of flow and the detention time.

Serious deterioration of concrete usually occurs under the influence of both sea water and frost action in cold regions. In order to clarify the connection between pore structure and frost behavior of concrete surface as affected by sea water and freezing-thawing action, three series were carried out using small mortar and cement paste specimens. The first one was to investigate the effects of sea water on pore structure by means of mercury-intrusion porosity meter; the second one was to investigate the effects of sea water on products by means of X-ray diffraction; and the last one was to investigate the effects of sea water on freezable water by means of differential scanning calorimetry. Results obtained show that specimens immersed in sea water have many pores ranging in size of several hundred nm to thousand nm, and contain much more freezable water than those immersed in fresh water. When concrete is affected by both sea water and freezing and thawing action, the number of medium-size pores (100 nm to 1000 nm) and the amount of freezable water increase. There is good correlation between the total pore volume and the amount of freezable water. Accordingly, it is considered that marine concrete in cold regions deteriorates because the pore structure near the exposure surface becomes more porous and the amount of freezable water increases.

In 1986, as a part of CANMET’s on-going program on the long-term durability ofconcrete in marine environment, twelve concrete panels, each 3.7 meter long, were installed at a site at Nanisivik (Latitude 73’ North), Baffin Island, North West Territories, Canada. Six of the panels were made with normal-weight aggregate concrete, and the other six panels were made with concrete incorporating expanded shale lightweight aggregate. Other variables in the concrete mixtures included steel fibres, and the replacement of portland cement by fly ash, slag, silica fume, or a combination of fly ash and silica fume. The cement replacement levels used ranged from 10 % for silica fume to 50 % for ground granulated blast-furnace slag. The water-to-cementitious materials ratio of all these concretes ranged from 0.37 to 0.42. In 1996, visual examination was made and cores were taken from the concrete panels to determine the chloride content at various depths from the exposure surface. After 10 years of exposure in the Arctic marine environment, the panels made with normal weight aggregate showed very little mass loss on the surface due to ice abrasion, whereas panels made with lightweight aggregate seems to have some mass loss on the surface exposed to the tidal zone. The steel fibre-reinforced panels appear to have less damage and cracking than the corresponding ones without fibres. Concrete incorporating supplementary cementing materials such as fly ash, silica fume, slag, or a combination of fly ash and silica fume generally had better resistance to the penetration of chloride ions compared with corresponding control portland cement concrete of similar water-to- cementitious materials ratio. In general, the concentration of chloride ions in fibre-reinforced concrete was similar to or lower than those of the corresponding non-fibre-reinforced concrete exposed. For the non-fibre- reinforced portland cement concrete, the use of either normal weight limestone aggregate or expanded shale lightweight aggregate did not seem to significantly affect the resistance of the concrete to the chloride-ion penetration. However, fibre-reinforced portland cement concrete made with lightweight aggregate appears to have lower chloride-ion content than that made with normal weight aggregate.