The Influence of Water-Reducing Admixtures on the Curing of Concrete

The use of water-reducing admixtures in concrete has grown continuously since their introduction over 25 years ago, with a present estimated usage in the production of 25 million cubic yards of concrete annually in the United States alone. Opposition to anything added to concrete, other than cement, aggregates, and water, is gradually disappearing, and considerable recognition is being given to the value of using other ingredients. The research contained in this study may be divided into two portions: tests to determine the rate of volume change of cement paste and compressive strength tests to indicate the effect of moist curing on rate of strength gain. Both portions were carried out with plain (no water reducer added) and treated (containing water reducer) mixes. The results indicate that a much greater volume change occurs in admixture-treated cement pastes than in plain pastes. The theory is advanced that this greater volume change, when a water-reducing ad~ixture is used, represents a more rapid combination of cement and water. This supports the strength test results showing that water reducers lead to high early compressive strength of concrete

UNCITRAL Considers Electronic Reverse Auctions, as Comparative Public Procurement Comes of Age in the U.S.

This article reports on the United Nations Commission on International Trade Law (UNCITRAL) review of electronic reverse auctions in procurement systems around the world. The article describes the U.S. experience, including the stalled regulatory initiative regarding reverse auctions. Drawing on the literature and on UNCITRAL studies from procurement systems in Asia, Europe and Latin America, the article cites lessons from other nations\u27 use of reverse auctions. In particular, the article discusses the European Union\u27s new rule on reverse auctions, which is probably the best example, worldwide, of a careful attempt to regulate reverse auctions. The article discusses traditional questions in reverse auctions - when is it appropriate to use reverse auctions - and also addresses the more difficult question of when it is probably inappropriate to use reverse auctions. Given these recurring problems, and the pitfalls inherent in reverse auctions, the authors argue that, on balance, reverse auctions should be regulated, and should not be left to proliferate without guidance and structure. Finally, they suggest that the reverse auctions debate itself marks a watershed in U.S. procurement policy: perhaps for the first time, thanks to advances in communications and comparative study, U.S. policymakers will be able to draw directly on other nations\u27 successes and failures in addressing a complex and difficult issue of procurement policy