International Concrete Abstracts Portal

SP65 The performance of concrete in a marine environment has assumed importance with the discovery of offshore gas and oil deposits. A collection of 33 papers from 12 countries, which opens with a review of durability of concrete in sea water. This is followed by a series of papers dealing with permeability and physio-chemical studies of cement pastes, mortars, and concretes exposed to sea water. Other papers describe the mechanisms of corrosion of reinforcing steel, case histories of performance of concrete in sea water, accelerated tests, and repair techniques. Research reports cover performance of lightweight concrete in sea water and use of corrosion inhibitors.

This paper describes the use of an accelerated test method for durability of mortars using various cements exposed under the combined wetting and drying cycle conditions to seawater, simulating the concrete structures in marine environment. The mortar specimens were prepared using 12 types of cement and various water-cement ratios. The specimens were dried at 30, 60 and 80°C for 6 hours and subjected to wetting at 30°C in substitute seawater with salt concentrations of 0, 3.27 and 6.54 percent. Damage to the specimens exposed to such conditions is classed according to the following three types : scaling, cracking and sound due to attack by seawater and thermal shock.

The seawater resistance of concrete must be considered when it is used for construction on the sea-shore or in the ocean. This paper describes an accelerated test method for assessing durability by subjecting the concrete to repeated cycles of seawater immersion and oven-drying. Test were carried out to evaluate the procedure in which, in addition to visual observation, reduction in dynamic modulus and length changes of the concrete up to 200 cycles were measured. Resistance indicators are proposed which combine these factors. Among the variables included in the test specimens it was found that seawater resistance of concrete is mainly affected by the type of cement, the water-cement ratio, the mixing water (fresh or seawater) and the age at immersion (period of pre-curing) .

The excellent performance of aluminous cement concrete in sea-water is illustrated by a summary of long term exposure tests. Visual examination of laboratory semi-immersed 50 x 100 x 100 mm mortar prisms over 20 years confirms this result. Only rapidly converted (hot cured) specimens at total water/cement ratios >_0.6 show signs of attack after several years. To obtain more up to date information at low water/cement ratios, small (20 x 20 x 100 mm) mortar prisms have been tested for 5 years by semi-immersion in reconstituted sea-water and in tap water. Visual examination at chosen ages is followed by crushing tests on the submerged and exposed halves of each specimen. 16 low ( < 5 % ) C3A portland cements and 7 different aluminous cements have been studied, at constant mortar consistency. Visual examination of small prisms does not provide conclusive comparisons. The crushing strength tests show that the aluminous cements outperform the portland cements, and also enable the relative performance of individual aluminous cements to be established. Complementary data shows that the porosity of converted aluninous cement is similar to and not greater than that of portland cement at the same water/cement ratio. Further work is in progress to distinguish between the role of intrinsic factors (chemical) and physical factors (porosity/permeability) in the relative resistance of portland cements and aluminous cements to sea-water and other corrosive agents.

From the historical records of the operations of the Canada Cement Company, now known as Canada Cement Lafarge Limited, changes in Normal Portland cement composition over the past 75 years are reviewed. Reference is made to the effect on cement composition of improved production technology, and establishment of definite limits i n chemical composition from the standpoint of quality and economy of production. The development of special cements to deal with specific field problems is discussed and essential differences in chemical composition are illustrated. Early attempts to solve the problems of concrete failure in a marine environment by altering the composition of related cements leads to a brief description of a test project conducted in the port of Saint John, New Brunswick, in which several types of cement were used in a pier installation and examined after a ten year period for comparison performance. Major harbour installations, located at Halifax, Nova Scotia, are identified, to illustrate the importance of good concreting techniques in minimizing the effect, of high C3A Normal Portland cement. The effect on cement composition of conformity to environmental requirements is mentioned and the author concludes with a comment on future developments in cement composition arising from the activities of the Canadian Standards Association.