In a marine environment the durability of permeable concrete is a function of the chemical resistance of the hydrated cement paste to sea water. Portland cements with various amounts of C3A, blast-furnace slag cements, and pozzolan cements were investigated. The test specimens were stored both in laboratory and natural sea water conditions. The sequence of chemical reactions between the hydrated components and the aggressive ions dissolved in sea water was followed by scanning electron microscopy, electron probe microanalysis and X-ray diffraction. It is concluded that as a result of diffusion of C1- and SO42- ions, degradation of Ca(OH)2 and C-S-H occurs due to the substitution of Mg2+ for Ca2+ and formation of secondary products such as CaS04.2H20, C3A.CaC12.10H20, C3A.3CaS04.32H20, and CaSiO3.CaS04.CaC03.15H20.

This report describes laboratory and field tests on the corrosion preventive effects of resin coating, galvanizing, cathodic protection, concrete surface coating and commercial inhibitors used as a protection measures for steel in concrete. The following conclusions were drawn from the test results: (1) The best in protective performance among the epoxy coatings is the powder epoxy. For protective performance, a coating thickness of 150um or greater is required, but for good bond to concrete, the thickness is preferably less than 150um. Thus the coating thickness of 150um is considered to be optimum. The liquid type tar epoxy coating is not satisfactory in its protective performance or for bond to concrete. (2) Galvanization gives good protective performance but is not always satisfactory at the splash zone. (3) Cathodic protection has an excellent protective effect in the tidal area and in seawater. The voltage to be applied is preferably -1000 to -1200mV. When it is higher than -800mV, the effect is not satisfactory, and when lower than -1500 mV, over-protection may result. (4) Urethane coating over the concrete surface failed to give a satisfactory cutoff effect in the tests and proved to be of no protective value. (5) Sodium sulfite series inhibitors had no protective effect.

This paper explains some of the current programs and future plans for the Treat Island Exposure Station. During the past few years, the U. S. Army Corps of Engineers has been very interested in research and technology transfer, and as such determined to do everything possible to avoid duplication of other research programs. To coordinate all of this research requires knowledge of work being performed by government agencies and private qrganizations around the world. Because the Corps already has the Treat Island facilities, many specimens from other research organizations have been incorporated into the programs, consequently reducing the cost for these other organizations in maintaining a facility of their own. Future plans are to include more specimens. Another area requiring much work is to correlate the Treat Island results with in situ concrete structures. In the past, many of the results reported could be visually determined by inspection; in the future, a greater in-depth analysis will need to be developed so that the contribution of all of the parameters including concrete constituent properties to deterioration may be analyzed.

This report deals with a calculation model for the corrosion of steel in concrete. The aim has been to make a highly complicated durability problem sufficiently simple to obtain a survey of the importance of various factors for the service life of the concrete structure. Some researchers will doublessly regard the model as an excessively rough simplification of the actual process but 90 to 95% of all corrosion problems which occur in practice agree well with this theory. The service life for concrete structures with regard to reinforement corrosion is broken down into a initial stage and a propagation stage. This breakdown is suitable since the primary parameters are different in the two sub-processes. The penetration of various passivation-breaking and activation substances to the steel is studied in the initiation stage, as well as the concentrations which give rise to corrosion or a marked increase in corrosion. The corrosion rate has increased considerably in the propagation stage and the factors which determine the rate of corrosion thus become interesting. In addition, the degree of corrosion which can be permitted with regard to load bearing capacity, esthetic aspects etc, must be determined. The report also presents examples of a number of material coefficients which are necessary for the model.

The ultimate test of the durability of concrete is its performance under the exposure conditions in which it is to serve. Although laboratory tests yield valuable indications of probable durability, the potential disrupting influences in nature are so numerous and variable that actual field exposures are highly desirable to assess the durability of concrete when exposed to natural weathering. The exposure station located at Treat Island in Cobscook Bay near Eastport, Maine, has been in use by the U. S. Army Corps of Engineers since 1936. Its location makes it ideal for exposing concrete and concreting materials to severe natural weathering. Its effect is to provide a natural field laboratory where no size limitation is placed on the exposed specimens. The specimens are installed at mean-tide elevation and the alternating conditions of immersion of the specimens in sea water, then exposure to cold air, provide numerous cycles of freezing-and-thawing of the concrete during the winter. The effect of the relatively cool summers is to lessen, in general, autogenous healing and chemical reactions in the concrete. There are currently 36 active research programs in progress at Treat Island involving the exposure of some 1700 concrete specimens. The annual testing and continuous monitoring of these programs yield valuable data on the durability and performance of concrete and concreting materials.