International Concrete Abstracts Portal

Report presents the results of a multi-year laboratory exposure of more than 150 concrete samples to alternate immersion exposure in flowing sea water and flowing fresh water. Other exposure variables included loading, cracking, and electric currents. The validity of the controlled-exposure samples was determined by comparing the results with the results from selected samples removed from concrete structures throughout the United States. The results from a marine seawall are presented in this report and compared with previously reported results from marine masonry structures, highway bridges, and other structures.

The ultimate test of concrete durability to natural weathering is how it performs in the environment in which it is to serve. Laboratory testing yields valuable indications of service life and durability. However, the potential disrupting influences in nature are so numerous and variable that actual field exposures are highly desirable to assess the durability of concrete exposed to natural weathering The U.S. Army Corps of Engineers, through the Waterways Experiment Station, Structures Laboratory, maintains a natural weathering exposure station. It is located on Treat Island in Cobscook Bay near Eastport, Maine. This station has been in use since 1936 and is an ideal location for exposure tests, providing twice-daily tide reversals and severe winters. The average tidal range is about 18 ft (5.4 m) with a maximum of 28 ft (8.5 m) and a minimum of 13 ft (4 m). In the winter, the combined effect of air and water temperatures creates a condition at meantide where specimens are repeatedly thawed and frozen. There have been 23 completed investigations and many of these have been previously reported. There are currently 40 active investigations. Four of these investigations are briefly discussed in this paper.

The No. 1 ore dock at Great Lakes Steel Division's Zug Island facility was originally constructed in 1909. Damage caused by freeze-thaw cycling, abrasion wear, severe impact loadings, and reinforcing steel corrosion resulted in a need for repair and rehabilitation. Multiple Dynamics Corporation conducted extensive condition surveys and testing to develop repair strategies for this structure. The remaining service life was then predicted to assist in economic planning. This case history provides an excellent example of concrete performance in an aggressive environment.

The air or oxygen permeability of concrete is usually measured by means of techniques that utilize mechanical driving forces. Thus, air or oxygen is forced to pass through a piece of concrete using different mechanical pressures. The flow of gas so measured is used as an indication of concrete permeability and sometimes is also used to predict the durability of concrete reinforcements based on the relationship between anodic corrosion rate and amount of oxygen, which may be reduced in the cathodic areas. However, this extrapolation may lead to erroneous conclusions, because a dry concrete allows a higher amount of oxygen to pass through it than a wet one, although the corrosion rate should be much lower in dry than in wet concrete. In this paper, comparisons between flow of oxygen measured in paste, mortar, and concrete specimens held at different relative humidities using electrochemical driving forces (polarization at about -750 mV SCE), and corrosion rates (measured by means of polarization resistance) are presented to discuss the inherent relationships. The results show that the oxygen permeability is only dependent on the amount of electrolyte inside the pores, but the corrosion rate is also dependent on the concrete resistivity, which is fixed by the amount of pore water content.

A study was made of three commercially available "second-generation" high-range water-reducing admixtures (HRWR) using cement of high and moderate C3 A content and having a cement content of 545k lb/yd3 (323 kg/m3) and a water-cement ratio (w/c) of 0.50. Second-generation HRWR were used to reduce cement and water contents by 15 to 16 percent. Hardened concrete specimens were prepared and tested for freeze-thaw resistance, resistance to deicer scaling, permeability to chloride ions, drying shrinkage, and compressive strength development. In addition, the air-void systems of concretes containing second-generation HRWR and air-entraining admixtures were analyzed by linear transverse. Similar tests were performedon flowing concretes, where cement and water contents were maintained constant and second-generation HRWR were added to increase initial slump levels to 7 to 9 in. (75 to 225 mm). Results indicate that caution must be exercised when using these admixtures to reduce cement contents in concretes subjected to deicing chemicals, as performance may be adversely affected, especially in high-slump "flowing" concretes. Additionally, drying shrinkage may be moderately increased in these concretes.