International Concrete Abstracts Portal

Determines the relationship between the cracking in loaded reinforced concrete and the corrosion of embedded steel. The test specimens used in this work are 3 m long beams and their constructive dispositions and loadings are in conformity with French specifications (BAEL 83). A salt fog and gas mixture with the same percentage of carbon dioxide and atmospheric air are the two aggressive environments. The authors use the single-replica technique, which enables crack openings of 0.1 micrometer to be discerned by scanning electronic microscope. The loadless initial state of concrete and the load damage state after bending can also be described. At this resolution, the reinforced concrete beams exhibit an absence of microcracks in both initial and loaded states. The study of the diffusion aggressive ions in concrete allows the microstructural state of cement paste-aggregate interfaces to be defined. The authors conclude that damage of the aureole of transition in the tensile zone of bending beams occurs. The aggressive ions quickly reach the reinforcement through the cracking, whatever their widths, and then progress along the embedded tension steel. The influence of concrete cover is clearly proved, as well as the aggressive difference between conservation environments. The authors follow the corrosion development by using steel electrode potential measurements. Previous results are corroborated; in particular, crack existence appears to be an essential parameter but not crack width. The aggressive environment is an important factor that should be taken into consideration by building regulations. Concrete thickness cover is also important, as well as its permeability, but the latter cannot be studied due to the use of only one concrete composition.

Compared artificial portland cements (CPA type) without mineral addition and blended portland cements (CPJ) containing 15 to 25 percent filler, while attempting to keep the mechanical strength class of both types constant. The properties studied were: binder hydration, strength variations, types of hydrates, porosity, etc.; effect of seasonal temperature variations; and resistance to various aggressive environmental agents (carbonation, freezing and thawing, seawater, diffusion of chlorides). For constant mechanical strength class, the durability of CPJ cements with fillers is identical to that of CPA without mineral addition.

Studies of slag activation by alkalies have been carried out since 1973 at the Institute of Building and Refractory Materials, Academy of Mining and Metallurgy, in Cracow, Poland. Laboratory tests were followed by production of the activated slag on a large scale. It appeared that the new cementing material composed of the granulated blast furnace slag mixed with an alkaline activator showed high strength and corrosion resistance. The present work deals with the problem of reinforcing steel corrosion in the alkali-activated slag mortar exposed to the attack of concentrated chloride solution. The observations of reinforcement in ordinary portland cement (OPC) mortars, OPC plus silica fume (SF) mortar, or OPC plus limestone flour mortar were carried out simultaneously. The resistance of alkali-activated slag mortar to the attack of a solution of high Cl- concentration was proved previously. The effective, protective action of the alkali-activated slag mortar was confirmed by electrochemical measurements and weight loss determination after 365 days' exposure to a chloride solution. A similar effect was found in the case of silica fume or limestone flour addition to the OPC mortar, but the corrosion of the reinforcement was clearly visible, as shown by corrosion pits in the reference standard OPC mortar samples.

SP-126 In August 1991 the Canada Centre for Mineral and Energy Technology (CANMET) in association with the American Concrete Institute; the Institute for Research in Construction/ National Research Council, Ottawa; and the Eastern Ontario and Quebec Chapter of American Concrete Institute sponsored the 2nd CANMET/ACI International Conference on Durability of Concrete. More than 100 papers from 20 countries were received and peer reviewed in accordance with the policies of the American Concrete Institute. Seventy were accepted for publication. The accepted papers are published in two volumes.

A recent report claimed that ASR expansion was suppressed when calcined clay was added to concrete used in hydroelectric dam construction containing reactive aggregates. The authors report a laboratory study on the effectiveness of metakaolin in preventing ASR. Samples of metakaolin were prepared by calcining china clay (relatively pure kaolin) and several ball clays, all collected from Southwest England. Compression cube strength tests were carried out in which part of the cement content of a 1:6 mixture of aggregate and ordinary portland cement (OPC) was replaced by calcined clay. Results showed that some of the mixtures containing calcined clay exhibited no reduction in the 28-day compressive strength, even when 25 percent of the OPC was replaced. Tests for ASR were conducted using prisms produced in accordance with the Draft British Standard 812, Part 123, containing highly reactive natural aggregates that expansion of 0.450 percent at 12 months. Prisms in which up to 25 weight percent of the OPC was replaced by calcined clay have been monitored over a period of 18 months and have shown no expansion or deleterious surface appearance. As a result of these tests, it is concluded that expansion due to ASR is completely suppressed when sufficient metakaolin is added to the concrete formulation. Metakaolin does not reduce the ultimate compressive strength of the concrete, provided that the feed clay is relatively free of impurity minerals.