International Concrete Abstracts Portal

Self-compacting concrete, recycled concrete as aggregate, calcium nitrate accelerators—these are just a few of the topics covered in the 47 papers included in ACI SP-200, Fifth CANMET/ACI International Conference on Recent Advances in Concrete Technology. You’ll be able to compare the structural performance of full-scale columns using ordinary and self-compacting concretes and with stirrup configurations representing differing degrees of confinement. You’ll also learn about a procedure that improves the quality of concrete made using aggregate produced from recycled concrete, and about experiments showing that, at 5 °C, calcium nitrate is a much more effective accelerator than calcium chloride. 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. SP200

The results of laboratory and in situ tests of a number of different types of coatings commercially available in Croatia (polymer-cement, epoxy, acrylic, epoxy-acrylic and epoxy-polyurethane), used for reinforced concrete protection of the KRK bridge, are presented. The tests have been carried on throughout the last ten years. Some coatings like epoxy and polymer-cement were found completely unacceptable for the technical reasons. However, epoxy-polyurethane coatings applied on the concrete finished with the thin layer of epoxy-cement mortar are estimated rather effective. They had high adhesion strength (above 2,0 MPa), very low gas permeability, low capillary absorption, satisfactory water vapour diffusion and satisfactory ageing resistance.

In recent years, structures made with anti-washout concrete under marine environment have been increasing. However, the durability of such structures is not yet clarified. Therefore, in order to understand the durability of reinforced concrete made with anti-washout concrete, the exposure tests were carried out under marine environment for ten years. The reinforced concrete specimens prepared with anti-washout concrete containing either silica fume or ternary low heat cement were exposed to marine atmosphere and underwater. Investigations were focused on the variation of concrete quality, concentration chloride ion and corrosion of reinforcement. From test results, the compressive strength of anti-washout concrete is similar to reference concrete in ordinary structures. The carbonation depth of the anti-washout concrete made without admixture silica fume is lower than that of reference concrete. At the distance of 2 cm from the surface of underwater cast concrete of the chloride ion concentration is sufficient to corrode the reinforcement at any concrete. After 10 years of exposure to marine environment, that of reference concrete is from 5 to 10 times that of anti-washout concrete. Therefore, the anti-washout concrete is durable under marine environment and it is possible to design for durability in the same way as for normal concrete.

Biogenic sulphuric acid corrosion is a phenomenon which occurs mainly in sewer pipes. The process consists of four stages: the reduction of sulphate to sulphide; the transition of sulphide to hydrogen sulphide gas in the sewer atmosphere; the re-oxidation of the sulphide gas to sulphuric acid in an oxidizing environment of the sewer pipe and finally concrete attack by sulphuric acid. Different models are developed to predict the sulphide formation and the corrosion rate. The model of Pomeroy, according to which the rate of sulphur production and the rate of corrosion can be calculated, is used in this paper. Different parameters are taken into account and case studies are described. Comparison of the calculated corrosion and the measured corrosion indicates the accuracy of the formula. Additional, a sensitivity study is carried out on the formulae to distinguish the influence of the different parameters. A realistic variation of the different parameters is made, based on measurements at the inlet of purification plants. The most influencing parameters for the model were the temperature, the BOD-content and the pH-value of the waste water, the depth of flow and the detention time.

Serious deterioration of concrete usually occurs under the influence of both sea water and frost action in cold regions. In order to clarify the connection between pore structure and frost behavior of concrete surface as affected by sea water and freezing-thawing action, three series were carried out using small mortar and cement paste specimens. The first one was to investigate the effects of sea water on pore structure by means of mercury-intrusion porosity meter; the second one was to investigate the effects of sea water on products by means of X-ray diffraction; and the last one was to investigate the effects of sea water on freezable water by means of differential scanning calorimetry. Results obtained show that specimens immersed in sea water have many pores ranging in size of several hundred nm to thousand nm, and contain much more freezable water than those immersed in fresh water. When concrete is affected by both sea water and freezing and thawing action, the number of medium-size pores (100 nm to 1000 nm) and the amount of freezable water increase. There is good correlation between the total pore volume and the amount of freezable water. Accordingly, it is considered that marine concrete in cold regions deteriorates because the pore structure near the exposure surface becomes more porous and the amount of freezable water increases.