The parameters that are relevant for prediction of service lifetime with respect to chloride ingress, are associated with large uncertainties. The present paper summarizes statistical distributions for relevant parameters based on full-scale measurements from the Gimsoystraumen bridge in Norway. A large. number of chloride profiles are available, and for each of these the diffusion coefficient and surface concentration are estimated. Extensive measurements of concrete cover are also performed. These probability distributions are subsequently employed as input to a prediction model for chloride concentration at the steel reinforcement. Since the input parameters are represented in probabilistic terms, the chloride concentration is also a stochastic quantity. The probability of exceeding the critical threshold can accordingly be determined as a function of time. A design format which reflects the statistical properties of the relevant parameters is considered.

Management of concrete structures affected by alkali-aggregate reactivity is quite complex, particularly in relation to prognosis more than that of diagnosis of the damaged structures. Until now a valid method to determine the potential for further deterioration is not available. Fifteen concrete structures showing typical signs of alkali-aggregate reactivity (AAR) were studied. Cores were taken from the structures and subjected to mechanical investigations and scanning electron microscopy observations in order to identify the cause of concrete deterioration. The observation on only one of these fifteen structures is reported on in this paper as an example of the adopted methodology. Once AAR was diagnosed, part of these cores were used to carry out laboratory tests performed for prognosis purposes. The cores were immerged in 1N sodium hydroxide solution at 40°C and their change in weight and dynamic elastic modulus was monitored up to six months of exposure in order to determine the potential for further reaction. Data related to dynamic modulus fluctuations in time were suitably worked out for each element of the monitored structure. Taking into account both the degree of structural integrity at the time of coring, evaluated through mechanical characterization, and the potential for future deterioration, valuable by means of the dynamic modulus fluctuation under an accelerated laboratory test, a ranking of concrete structures could be suggested in terms of priority of intervention for restoration.

An experimental study is being carried out at the Laboratoire Central des Ponts et Chaussees (LCPC), with Electricite de France (EDF) as a partner, to validate a methodology of mechanical reassessment of real structures damaged by Alkali-Silica Reaction (ASR) based on residual expansion tests on cores, and thus to answer to the needs of owners of civil engineering structures (bridges, dams, pavements). One major purpose of this study on structures is to point out the water driving effect on the swellings. The structures (3 m-long girders) were submitted to a unidirectional moisture gradient (bottom in water and upper face exposed to a 30% Relative Humidity environment), which causes a deformation gradient. Many tests on companion cylinders and prisms were carried out to determine the material expansion and mechanical characteristics. The paper focuses on numerous measurements obtained during the first year of drying: variation of water content, followed by precise weighing and gammadensitometry, relative humidity measurements; local and global deformations and deflection of the beams. Thus, the water effects on the behavior of structures damaged by ASR is documented and emphasized; and the methodology of computing structural deformations due to ASR using strains measured on prisms and cylinders can be validated.

Performance-based specifications for concrete exposed to chlorides may involve the determination of long-term material parameters by relatively short-term laboratory tests. The first generation of chloride environment durability models are likely to be based on diffusion theory, despite the fact that chloride ingress is both by absorption and diffusion. This paper compares chloride resistance values from laboratory experiments and from field trials, derived solely on diffusion-based modelling. Concrete prisms were exposed to sodium chloride solutions in laboratory tests for a period of 12 months. The trials included both continuous immersion and cyclical wetting and drying cycles. Chloride values were determined at 3, 6 and 12 months. Material variables included normal portland cement, fly ash, crushed limestone aggregate, natural sand, and natural gravels. Diffusion coefficients were derived through best-fit curves based on Crank’s error function solution of Fick’s second law of diffusion. It was found that the laboratory test diffusion coefficients diminished significantly with increase in test duration and stabilised between 6 and 12 months, by which time they yielded values of a similar order of magnitude to those from the structures in service. The coefficients for gravel aggregate con- crete specimens were more variable than those for crushed rock aggregate concretes and could exceed the in-service values by a factor of at least two. The beneficial influence of fly ash was reflected in the results.

This investigation was undertaken to examine the performance characteristics of concrete pavements made with high volumes of Class F and Class C fly ash. Three mixture proportions with Class C fly ash up to 70% cement replacement, and three mixtures with Class F fly ash up to 67% cement replacement, were used in this study. Tests were conducted for compressive strength, resistance to chloride-ion penetration, and density using specimens from in-situ pavements. Test results indicate better pozzolanic strength contribution and higher resistance to chloride-ion penetration for concrete mixtures made with Class F fly ash relative to that made with Class C fly ash. Compressive strengths of core specimens taken from in-situ pavements ranged between 45 to 57 MPa. The maximum compressive strength 57 MPa was achieved after 7 years, for the mixture containing 67% Class F fly ash. Field observations made in the year 2000, and continuing observations through April 2002 revealed that pavement sections made with high-volume of Class F fly ash (35 to 67%) performed well in the field, with only minor surface scaling. All other pavement sections have experienced very little surface damage due to the scaling. Field performance data versus laboratory evaluation data for scaling are presented.