In 1997, CANMET in association with the American Concrete Institute and several other organizations in Australia sponsored the Fourth International Conference on the subject. The conference was held in Sydney, Australia. More than 120 papers from 30 countries were received and peer reviewed in accordance with the policies of the American Concrete Institute; 81 were accepted for publication. The accepted papers deal with all aspects of durability of concrete, including chloride and sulphate attack, freezing and thawing cycling, alkali-aggregate reactions, cathodic protection, and the role of supplementary cementing materials to enhance durability of fiber-reinforced concrete and performance of repaired concrete structures. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP170

Electrochemical tests on mortar electrodes in alkaline chloride solutions were carried out to determine the critical chloride content depending on the mortar composition (type of cement, cement content, water-cement ratio and concrete additions). Sodium chloride, with varying chloride concentrations (between c(NaC1) = 14 and 508 mmol*L-1), was used to initiate corrosion. Depassivation times of the mortar electrodes as well as corresponding total and free chloride contents were determined. By means of macrocell corrosion tests without polarisation and at a constant concentration of the test-solution of c(NaC1) = 282 mmol*L-1, the diffusion process of the chloride and the chloride binding (dependent on the age of the test amples) were investigated in order to obtain reference values for the depassivation time of the steel. Potentiostatic tests with constant polarisation at USHE = +500 mV in alkaline chloride solutions of different concentrations were carried out for 11 different mortar mixtures to determine the critical corrosion-initiating chloride content. A linear relation between corrosion-initiating free and total chloride content was found. A minimum critical chloride content of 0.25 wt.-% relative to cement was determined.

Nine bridges under the control of the Roads and Traffic Authority (RTA), in New South Wales (NSW), were inspected in two different regions of the State, and seven with various degrees of cracking and/or repair were selected for examination, particularly with respect to alkali-aggregate reaction (AAR). Twenty-eight cores were drilled from four bridges in the north-east coastal area and 14 cores from three bridges in the same area but 250 km inland. Detailed petrographic examination and scanning electron microscopy of the cores has shown that of the three inland bridges, definite signs of AAR are present in two bridges but the third bridge has a less clear diagnosis, although the aggregate is the same. For the bridges in the coastal area the glassy basalt may have reacted, although typical visual signs of AAR products were not evident. Clay alteration products in the basalt used for two of the bridges may have caused some dimensional instability. For one of the bridges, signs of alkali-carbonate reaction (ACR) were seen in some cores, but the contribution of this reaction to cracking of the bridge is not clear. This is the first report of ACR in Australia. The expansive behavior of cores and alkali levels are also discussed. subjected to elevated temperature, humidity,

This paper presents results from the OFU Bridge Repair Project on the Gimsarystraumen bridge near Svolvaer, Norway. The results are mainly of laboratory measurements on concrete samples taken undisturbed from the bridge to determine: 1) the relative humidity exerted by the pore water, 2) the pore water content and degree of capillary saturation of the concrete, and 3) the electrical resistivity of the concrete at two temperatures. The laboratory results are related to field monitoring of relative humidity, electrical resistance and temperature at various positions in the bridge over a 2 year period. The results show that the moisture state of the concrete a few mm from the surface and to 40 mm depth vary very little over both time and position on the bridge. The relative humidity is in the range 70 - 80% RH, while the degree of capillary saturation is in the range 80 - 90%. The electrical resistivity of the concrete is a very strong function of both the degree of capillary saturation (about 5% change in resistivity per 1% change in saturation at 3.5’ C and 85% degree of capillary saturation) and the temperature. Interpretation of electrical resistance measurements in the field is difficult with present techniques, but the method is considered promising for routine monitoring of moisture state in the field. It is concluded that any field monitoring method of moisture state must be supplemented by laboratory measurements on undisturbed concrete samples taken from the structure.

air-entrained concretes were made using a silica fume blended cement and six lightweight aggregates having a wide range of absorption values. The properties of the fresh concrete, including the autogenous temperature rise were determined. Concrete specimens were subjected to the determination of the compressive, flexural and splitting-tensile strengths, Young’s modulus of elasticity and drying shrinkage; the resistance to the freezing and thawing cycling, chloride-ion penetration and carbonation were also determined. The tests for the freezing and thawing resistance were performed on concretes made using dry and saturated lightweight aggregates. Small reinforced concrete beams made using three of the lightweight aggregates, and some incorporating polypropylene fibres, were tested for hydrocarbon-fire resistance. The target compressive strength at 28 days (60 to 65 MPa) was generally reached with five of the lightweight aggregates used. As expected the mechanical properties of the concrete were somewhat related to the degree of absorption of the lightweight aggregates. All the concretes investigated demonstrated excellent resistance to chloride-ion penetration at 28 days, negligible depth of carbonation after 448 days of air drying, and excellent performance in the freezing and thawing cycling. Based on the visual evaluation, the use of the polypropylene fibres improved considerably the performance of the high-strength semi-lightweight concrete in hydrocarbon fire.