International Concrete Abstracts Portal

In the last century, lime concrete, portland cement concrete began to be used for breakwaters, quay walls, and lighthouse towers. Now both for inshore and offshore structures, concrete, reinforced or prestressed, is widely accepted as a most economical material. Its durability is no more questioned as the resistance of hydraulic binders to the chemical attack of seawater has been the object of extensive research and long duration tests. In France, public authorities and cement manufacturers, in close collaboration, have established criteria to evaluate cements for works in marine environment, and each year a list of available cements complying with these criteria is published. The results of the research conducted in the maritime laboratories of the Ministry of Public Works, and in the exposure stations of CEBTP and CNEXO are reviewed. Composite Portland cements, now 70 percent of the French production, call for new research if they are to be used at sea. An accelerated test is now proposed to verify their suitability for marine structures. 105-387

The results obtained on the evolution of permeability to air of six slabs for a period of 20 years are described. Measurements were taken at four pressure levels: 0.40, 0.95, 1.35, and 1.90 kp/cmý. The concrete plates of 1 x 1 x 0.20 m were placed in a test chamber. The results from permeability have a qualitative value, as boundary effects are unknown. In the bibliography, the publication includes quantitative results of eight concretes of different dosage. Differences obtained among the slabs, even having the same dosage and being similarly conserved, are pointed out. Twenty years after the concrete was made and in normal preservation conditions of a test chamber, a tendency to stabilization of permeability values is observed, especially in the lower pressure, 0.40 kp/cmý.

Materials Research

A full-scale prospective durability experiment was established in the spring of 1970 at Covenham, Lincolnshire, England, when five different concrete mixes were used to construct portions of the wave wall of a 88 Ha inland reservoir. The reservoir is approximately 1.0 x 0.9 km in plan, and the maximum water depth is 14 m. The concave face unreinforced wave wall at the top of the embankment faces southwest into the prevailing wind and is subject to wave action in winter. Variables tested were a, increased sand proportion, b, air entrainment, c, increased cement content, and d, use of a lignosulfonate-based water-reducing admixture. The standard concrete mix used for the rest of the reservoir was used as a control. The alternate bay method of construction used for the wave wall insured adequate replication for both test and control concretes. To date, all mixes have performed well, although weathering differences began to show at 4 to 6 years when the alkalinity of the concrete surfaces had been reduced sufficiently by carbonation to allow growth of microorganisms, particularly lichens. Yellow lichen species were most prominent at first, but subsequently were overtaken by grey/green lichens. After 10 years of exposure, all the modified concrete mixes showed less weathering effects than the control mix with least improvement given by the air-entrained concrete a and the mix containing a higher sand percentage b. Increasing the cement content c gave a significant improvement, but the best performance has been obtained with the concrete d batched with a lignofulfonate-based water-reducing admixture.

Durability, or service performance, is one of the most important properties of concrete. Unlike strength, however, it is difficult and frequently impossible to evaluate and predict. There are numerous short-term tests that qualitatively compare relative behavior, but none reliably predict ultimate service performance. Laboratory tests attempt to simulate specific destructive mechanisms. However, to produce results quickly, conditions frequently are more severe, and therefore more destructive than service conditions. Overmagnification or poor reproduction of the exposure condition can produce misleading results. More reliable predictions can be made from long-term service records of concretes containing similar materials and proportions and subjected to similar conditions. Frequently, reliable data are either unavailable or incomplete, leaving the engineer no alternative but accelerated laboratory tests. Results from controlled outdoor exposure tests are far more reliable but require long-term planning. While exposure conditions may not be duplicated precisely, they are more closely approximated. This paper reviews Ontario Hydro's experience in predicting the durability of concrete and assessing its service performance. Included are data from 28 years of outdoor exposure studies, with accelerated laboratory tests on companion specimens and constituent materials, on air- and nonair-entrained concretes, concretes with fly ashes of variable quality and different proportions, and concretes containing aggregates of dubious quality. The results are compared with the performance of concrete in actual structures up to 50 years old. 627-387