International Concrete Abstracts Portal

These proceedings of the Sixth CANMET/ACI International Conference on Durability of Concrete held in June of 2003 in Greece contain 69 papers on topics that include large girders subjected to alkali-silica reaction, effects of the moisture condition of concrete on steel corrosion, effect of mixing different sizes of synthetic fibers in concrete, durability of porous concrete, low cement-content shotcrete, and the risk of steel corrosion in recycled aggregate concrete. 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. SP212

The purpose of this paper is to study the production of crack-free massive con- crete structures manufactured by using flowing mixtures characterized by low heat development and the following performances of the mixtures: - compressive strength in the range of 30-40 MPa at 28-90 days; - slump level of about 200 mm. The main ingredients of these mixes were: - normal portland Cement (not more than (150 kg/m3); - fly ash as pozzolanic mineral addition (up to 150 kg/m3); - ground limestone as filler (70-250 kg/m3) - superplasticizers based on acrylic or sulfonated napthalene polymers; - natural aggregates with a maximum size of 20 mm.

Modelling chloride transport is usually an integral part of demonstrating that a concrete structure in a chloride-rich environments will have the required service life. Ideally this should take account of spacial and temporal variations in exposure environment and concrete properties. This paper describes how this may be approached through a combination of simulated natural exposure and numerical modelling. This approach helps to reduce the errors associated with coupling different transport processes. The example taken is a reinforced concrete tunnel exposed to chloride-contami-nated groundwater. In a laboratory experiment, opposite faces of specimens of tunnel lining concrete were exposed to the maximum hydrostatic head (30m) of groundwater and the minimum relative humidity (35%) expected inside the tunnel and water outflow and chloride accumulation were monitored over a 3 year period. Water vapourdiffusion, chloride binding and porosity measurements were made on parallel specimens. The measurements were used as inputs to a numerical model of water and chloride transport to extrapolate from the measured chloride profiles to predict future chloride profiles. The results were very sensitive to ground water chloride concentration and chloride threshold level, but relatively insensitive to hydrostatic head.

Polymeric surface protection systems can he a durable and potent method to lower the moisture content of the concrete and to improve its durability by inhibiting the penetration of aggressive substances through the surface as well as by limiting the corrosion rates. At the Institute for Building Materials Research in Aachen, ibac, in cooperation with BAM in Berlin comparative tests have been carried out on the long-term durability of selected classes of surface protection systems financed by the German Ministry of Transport. These systems were weathered naturally at two different locations in Germany as well as artificially in different climatic test facilities. Afterwards the mass and dimension changes of the polymeric films, adhesion strength, diffusion of chlorides and carbon dioxide, cross-cut and crack bridging behaviour have been investigated.

Several factors regarding sustainability of marine concrete structures are dis- cussed based on detailed laboratory and several long-term exposure tests. The factors include voids at the steel-concrete intarface, crack widths and autogeneous healing, blended cements, chemical admixtures, type of bars, and joints. Long-term exposure investigations were carried out utilizing the specimens exposed to the marine environment over 10 years. The following conclusions are drawn: 1. To enhance long-term durability, the steel-concrete interface should be free from voids; 2. Narrower cracks and joint surfaces are healed in the marine tidal environment with alkaline deposits, and thereby control the corrosion of steel bars at these locations; 3. Blended cement with high slag content shows the best performance for long- term durability compared to the normal ponland cement and other investi- gated blended cements; 4. The napthalene group of chemical admixture shows the best performance for long-term durability compared to other investigated chemical admixtures; 5. Deformed bars are more prone to corrosion compared t oplain bars; 6. Brushing-off the laitance and application of a mortar coat at the joint plane is very effective in enhancing long-term durability.