The deterioration of concrete structures due to age, particularly in marine environments, has recently become a subject of great concern. In this study, the properties of 60-year-old concrete in a marine environment were examined. Taking the opportunity of the demolition of the northern breakwater of a port in Japan, samples were taken from the reinforced concrete caissons, from the upper concrete, and from the foot protection blocks. Tests for concrete strength, porosity, salt content, carbonation, and the corrosion status of the reinforcing bars were performed. The concrete seemed to have retained its strength even after sixty years of exposure to sea water environment. The pore sizes were generally smaller than those of ordinary concrete while the total porosity was the same. The salt content was high at approximately 0.3 to 0.6 percent near the surface of concrete. It reduced, however, to a constant value of about 0.1 percent at a depth of approximately 8 cm. As a result of the study, it was found that the concrete, which was made from blast furnace slag and volcanic ash and appeared to contain sea sand, had scarcely deteriorated at all even though it had been exposed to sea water environment for sixty years.

Coastal defenses in the United Kingdom have often been constructed using natural stone armor or plain concrete armor. This paper reports on the novel use of slender section reinforced concrete units in the marine splash zone. A program of monitoring the durability performance of the coastal defenses was commenced by the University of Liverpool in 1985. A visual survey together with electrical potential and resistivity monitoring of a sample of 51 units is conducted annually. Overall, the slender reinforced concrete units are performing very well both hydraulically and structurally. Some minor impact damage soon after construction has been easily repaired using the steel reinforcement as a bonding key. The results of three years of potential monitoring have shown that the steel reinforcement has been passivated in all but one of the sample units. The resistivity monitoring has shown that the fly ash concrete has a significantly higher resistivity than the ordinary concrete and hence; its use should lead to lower rates of corrosion. Further studies on the durability of reinforced concrete in the splash zone are in progress.

To meet the development in structural design and construction methods, a continuous effort has been made to advance the concrete mix design process. Paper gives a survey of the research work in this process. The mix design has to take care of several contradictory requirements, such as high strength and low permeability on one side and moderate heat development and extraordinary workability on the other. From 1972 to 1986, the concrete grade has been increased from C45 to C70 while the workability (slump) has been increased from 120 to 240 mm mainly due to extreme dense reinforcement (above 1000 kg/m3 in local areas). The chemical composition of the cement is aimed at an optimized 28 day compressive strength with moderate heat development. The fine aggregates are produced through a hydraulic process to obtain the desired particle distribution. Minor changes in the finer part of the grading have resulted in remarkable improvements in the workability and pumpability by stabilizing the paste-aggregate matrix. The practical use of very high strength normal density concrete (C80-C100) and high-strength concrete with lightweight aggregates are new challenges for the concrete mix design so as to satisfy new advancements in construction methods.

Starting in 1984, steel fibre reinforced concrete (SFRC) jackets have been placed around distressed hollow core octagonal concrete piles at the Rodney Terminal wharf, Saint John, New Brunswick. The placement has been by pumping the SFRC into steel forms around the piles. The pumping and pipeline equipment, steel fibres and concrete admixtures have evolved over the years to solve problems, initially with the placement by pumping over a long pipeline and subsequently with the control of air to provide acceptable strength and air void parameters for freeze thaw resistance. This paper describes the experience with this unique method of repairing piles and concludes that, in spite of requiring constant attention to quality control, this is a simple method of repair.

Several projects in the "Concrete in the Oceans" program have measured electrical potentials and resistivities on reinforced concrete specimens exposed to a marine environment. A state of the art survey was also undertaken on corrosion monitoring techniques which led to experimental work to improve the use of these techniques, particularly on marine structures. The main conclusions from this test program are discussed. Two independent sets of electropotential and resistivity measurements taken on beam specimens exposed to a splash zone environment for periods up to five years have been compared with the actual corrosion found after the reinforcement was broken out of the specimens. The comparison of these two sets of data and the ability of these monitoring techniques to predict likely corrosion are discussed and related to the various parameters such as the disposition of the cracks, the depth of cover and the type of concrete. Based on the work described in this paper, the limitations of corrosion monitoring methods are also highlighted.