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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.

The purpose of this paper is to determine the effect of mechanical loading on the transport properties of concrete. The test specimen (B 1CL) used for chloride measurement, was a three-meter long reinforced beam kept in a loading state, in a confined salt fog (35 g/l of NaCl) for fourteen years. Because of corrosion of reinforcement, the characterisation of mechanical loading was made on an other old beam (BlT) cast at the same time but stored in a non-aggressive environment. The measurement of tensile concrete strains using strain gauges showed two parts in the bottom of the beam : the first one is characterised by an elastic behaviour and the second one by non elastic one which is still controlled by the steel reinforcement. Total chloride profiles in relation to the depth were measured in different locations of the tensile zone of reinforced beam B 1CL. Until 15 mm depth, the chloride content is constant and corresponds to the maximum chloride content available, taking into account both concrete porosity (where free chloride content corresponds to 35 g/l of NaCl) and concrete binding capacity. Beyond 15 mm depth, total chloride profiles appear to be pure diffusion profiles allowing to calculate the effective diffusion coefficient by using a saturated model of chloride motion taking into account the non-linear binding capacity of concrete. The evolution of effective diffusion coefficient in the beam field (B 1CL) is strongly correlated with the field of non elastic strains in concrete (BlT) and can increase up to 40% in the part of the beam where the non elastic damage is the more important.

In recent years, increasing efforts have been geared toward enhancing the axial load-carrying capacity of wall-like (i.e. high aspect ratio) RC columns commonly used in building estates in Singapore. Although it has been proven through experimental results that composite fiber wraps are effective in strengthening round and square columns by providing passive confinement pressure to the core concrete, wall-like columns experience less effect from confinement, which is limited to the comers. In addition, published research work on wall-like column strengthening did not consider the effects of sustained loading during the application of the FRP. Consequently, the present study explores an alternative strengthening scheme that employs other materials in addition to composite sheets and will investigate the effects of sustained loading on the strengthening efficiency.

Unlike circular columns, jacketing of oblong or wall-type columns produces only marginal improvement in strength and ductility because of inadequate confinement and premature debonding of the wrap. Some possible ways to overcome this problem, at least partially, are to round the corners, to add a semi-circular segment at each of its shorter sides or to produce an elliptical shape enclosing the oblong column. A total of 13 specimens of these cross sectional shapes were tested in direct compression to assess the enhancement afforded by external fiber wraps. It has been found that the modification of a rectangular section by including a semi-circular segment on each of its shorter side or transforming the section to an ellipse before applying fiber wrap leads to a substantial improvement in strength as well as ductility. Of the two fibers used, the glass fiber composite proved to be more cost effective in terms of strength and ductility enhancement.