International Concrete Abstracts Portal

The effect of steel fiber volume fraction on the flexural strength flexural rigidity, toughness, and ductility of reinforced concrete beams was evaluated. A total of twenty simply supported reinforced concrete beams were tested. Ten of the twentybeams were cured under controlled laboratory conditions and the other ten were cured under field conditions characterized by intense heat, low relative humidity, and large diurnal variations. Tests were carried out 28 or 90 days after casting. The study shows that the flexural strength flexural rigidity, toughness, and ductility are in direct proportion with the fiber content. It also shows that the enhancements in these engineering properties due to the steel fiber addition are not affected by the above described severe field conditions. Furthermore, inclusion of steel fibers in concrete helps, to some extent, in reducing adverse effects of the severe climatic conditions on the properties of concrete.

This paper discusses the present status of specifying concrete for corrosion durability in the Australian marine environment. A modified diffusion model for approximating time to corrosion in marine concrete structures based on chloride penetration is discussed and calibrated to data acquired from 7 years of monitoring of a reinforced concrete jetty. A method is suggested for applying laboratory chloride diffusion testing to service life prediction in marine structures. The Australian Standard AS3600 Concrete Structures Cod has been reviewed from the viewpoint of adequacy in relation to durability, and the provisions tested against the proposed service life model. A case history of an Australian offshore concrete structure is presented to describe the author’s proposed performance based approach to specifying concrete in a marine environment for corrosion resistance. This approach underlines the need to balance the durability performance criteria with various design and construction constraints.

In this paper, an analytical model to predict the service life of reinforced concrete (RC) structures in marine environment is proposed. For constructing a model, the deterioration process of RC structures was assumed to be divided into two stages: the penetration period of chlorides into concrete and the ensuing cracking stage due to corrosion of reinforcement. Two indices, TO and T1, were introduced in this model: the latent period from the beginning of the chloride penetration until the onset of corrosion, denoted as TO, and the progressive period until the initiation of the longitudinal cracking, denoted as Tl. Since the TO model was already described in the previous report, Proposed durability design for RC marine structures CONSEC ‘95 (4) modeling of Tl and a rational service life prediction using a combination of TO and T1 are discussed in this paper. The T1 model was constructed by a parametric study using Finite Element Method, after investigating the effect of finite element layout. In the analytical study, parameters were determined considering the experimental results obtained from exposure tests. The results of parametric study were combined in the regression analysis. An attempt has also been made to discuss some experimental results in the light of the proposed model. Finally, a program (called MS LIFE), which predicts the service life of RC structures in a marine environment was proposed by combining the model for predicting the T1 with that for TO. Some results of the trial calculation using this model were also introduced for verification.

Changes to the New Zealand concrete design standard incorporate requirements for durability, based on a minimum design life of 50 years for structural elements as required under the New Zealand Building Code. Many New Zealand cities are near the coastline. and concrete quality and reinforcement covers are designed to control chloride induced reinforcing steel corrosion. Four exposure classifications in the Standard require increasing protection from chlorides based on increasing exposure to a marine environment. The paper outlines how these exposure classifications were established. The concrete structures standard specifies minimum concrete strength and reinforcement cover based on the use of normal portland cement concretes for each classification. The enhanced durability performance of some blended cement concretes is recognized along with the role of concrete coatings, and alternative combinations are permitted provided the designer establishes equivalent performance. A BRANZ research program is targetted towards developing an assessment methodology in the laboratory for evaluating the durability performance of blended cement concretes against normal portland cement concretes. The first stage of a laboratory program evaluating the performance of normal Portland, slag, silica fume and flyash cement blend concretes is reported. Evaluation methods used included absorption, rapid chloride ion penetration, chloride diffusion and chloride ponding. Further research using site surveys of concrete structures in the near coastal zones is planned.

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.