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The durability of different types of cement to ammonium nitrate attack was studied. The tests were conducted on mortar prisms kept in ammonium nitrate solutions at different concentrations, ranging from 0.0 to 50.0 percent. Five types of cement were used: ordinary portland, pozzolanic, blast furnace, aluminous, and supersiliceous. Changes in length and weight were registered during 14 years; also determined were the mechanical strength and changes in composition. Initially, the most concentrated solution was the most aggressive, but due to crystallization of the ammonium nitrate in the pores of the mortar, its relative aggressivity diminished with time, so that it was the 0.5 and 5.0 percent solutions that showed the greatest aggressivity. The aluminous cement showed the best resistance to ammonium nitrate attack. Of the other cements, blast furnace cement was the one which best resisted attack.

Long-term durability of structural lightweight concrete used in bridges, ships, and buildings is reviewed. Particular attention is given to mature structures located throughout the world that have been subjected to severe weather conditions. Ongoing testing programs carried out on structures subjected to several decades of exposure are reported. The nature of both the vesicular lightweight aggregate itself as well as the interfacial contact zone between aggregate and cement paste matrix are analyzed, as the microstructure of lightweight concrete reveals factors that contribute to long-term durability. The information gained on the microlevel is used to explain observed performance, and provides a basis for predicting behavior. To facilitate the practical design of durable structures, long-term field exposure studies of normal weight and lightweight concretes are being conducted to assess their relative performance in a severe environment. The results obtained from ongoing testing programs conducted by the Canadian Concrete Technology Section of CANMET at the U.S. Corps of Engineers Treat Island Severe Weather Exposure Station are discussed in relation to the design process.

With special attention to durability of concrete, the author reviewed the proceedings of the cement chemistry congresses as well as other symposia held during the last 50 years by ACI, ASTM, and RILEM. What is presented here is not a comprehensive progress report on the subject of concrete durability but rather a state-of-the-art report from the author's perspective. It seems that, in spite of some important discoveries valuable from the standpoint of durability enhancement, today more concrete structures seem to suffer from lack of durability than was the case 50 years ago. In order of decreasing importance, the major causes concrete deterioration today are as follows: corrosion of reinforcing steel, frost action in cold climates, and physico-chemical effects in aggressive environments. There is a general agreement that the permeability of concrete, rather than normal variations in the composition of portland cement, is the key to all durability problems. There is also a general agreement that rapid growth of the concrete construction industry after the 1940s led to the production and use of wet concrete mixtures, which are able to meet the strength requirement via a change in the composition of portland cement, but were unsatisfactory from the standpoint of corrosion of reinforcing steel, resistance to freezing and thawing cycles, and chemical attacks. A rise in chemical aggressivity of the environment through the increasing use of deicer salts, and an increase in land, water, and air pollution, has also contributed to concrete durability problems. Although significant advancements have been made in regard to understanding and controlling various physical and chemical phenomena responsible for concrete deterioration, the trend towards less durable concrete structures has yet to be reversed. One of the reasons is that most of the information from tests on durability is in fragmentary form and cannot be easily synthesized into a complete understanding of actual, long-term, effects on field concrete. An over-reliance on test methods and specifications dealing with different aspects of durability has therefore become a part of the problem since accelerated laboratory tests do not correlate well with behavior of concrete structures in practice.

The durability of concrete is generally regarded as its ability to resist the effects and influences of the environment while performing its desired function. In an offshore or marine environment, the concrete can be subjected to the influences of wetting and drying, freezing and thawing, abrasion by ice and other debris, chemical attack or mineral depletion by water it is in, salt accumulations, and attack by marine organisms. The paper reviews these dteriorating mechanisms and also reviews the recent trends in strength development for concretes made with modern materials. Chloride ion penetration into concrete information from 33-year old Gulf of Mexico offshore concrete platforms is presented. The advantages of supplementary cementing materials in offshore and marine concretes are discussed along with recommendations for producing durable marine concretes.

Compared to portland cements, pozzolanic cements can better resist various aggressive agents, such as pre and acidic waters, chlorides, and sulfates. Furthermore, they can also prevent expansion caused by alkali-aggregate reactions. Provided that concretes of the same strength are compared, the carbonation depth of pozzolanic cements is similar to that of portland cements. In Italy, where they have extensively been used for the construction of buildings and civil engineering works, pozzolanic cements accounted for over 15,000,000 t of cement production in 1989. This is, however, indirect evidence of the durability associated with this type of cement. Direct evidence is actually provided by many Italian dams built over 40 years ago, which, despite the heavy and manifold environmental conditions that they have been subjected to yearly, still show good serviceability.