International Concrete Abstracts Portal

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

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.

The first reinforced concrete (RC) structure in a marine environment in Norway was built in the early 1890’s. At that time no standard or code existed. The first Norwegian regulations on RC structures were issued in 1926 and since then standards have become available. The standards have been revised several times and requirements on durability have varied. Up to the early 1960’s, the durability requirements were relatively strict. From the early sixties until the mid eighties, the durability requirements were extremely liberal resulting in a rapid increase in deterioration. The main problem has been chlorides, mixed in or penetrated into the concrete, causing corrosion of the reinforcement steel. Development of durability requirements for RC structures in marine environment in the Norwegian Standards, in the Directorate of Public Roads Codes, and in the Regulations from the Norwegian Petroleum Directorate are presented briefly. The correlation between the changing requirements and the degree of deterioration is discussed.

The scaling of concrete and mortar involves sub-parallel de-laminations of material from the surface. To produce this phenomenon, differential stresses parallel to the surface and resulting in differential strain must be active. This research measured the differential strain developed along the surface of specially shaped mortar bars upon their wetting, drying, and osmosis due to application of deicer salts. Mortar bars were made at a w-c ratio of 0.4 and 0.6 with shaley sand and high quality dolomite as aggregate. The sand is known to cause surface scaling. The bars were cast in a ‘half circle’ shape. The normally cured samples were dried, and all but the outer surface of the ‘half circle’ were sealed.. This allowed the ingress of water and solutions from one direction only, such as would occur in an ‘infinite’ concrete surface. Steel pins were secured to the ends of the half circle to facilitate measurement of the strain. The strain of the specimens was measured during the following states: 1. dry samples, 2. saturating in water, 3. drying, 4. saturated, placed in saline solutions, 5. then placed in pure water. The results show that as the water entered or left the surface, stresses developed which were sufficient to deform the ends of the half circle up to 0.6% of the diameter distance. Largest deformations took place upon wetting, followed by those on drying, and the least deformation resulted from osmotic forces. When the samples had equilibrated, i.e., became either fully saturated, dried, or the pore fluid composition equaled that of the saturating medium, the strain was relaxed. Water-cement ratio influenced the time of maximum strain development and aggregate and cement type determined the magnitude of the strain.