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The goal of this project was to develop a chemical admixture that would reduce the need for wintertime thermal protection of freshly placed concrete. Chemicals were investigated for their ability to promote strength gain in concrete cured below 0 deg C. The project was carried out in five phases. Phase 1 evaluated existing and new admixtures. Phase 2 measured the effect of promising chemicals on concrete properties. Phases 3 and 4 tested the practicality of using the new technology/admixture in the field. Phase 5 disseminated the findings through an Army conference and through the development of this report, in addition to normal W.R. Grace advertising channels. Laboratory strength tests established that two prototype admixtures were capable of protecting concrete down to -5 deg C. Results from other laboratory tests show that the chemicals pose no harm to the concrete or embedded ferrous metals. Concrete containing the prototype admixtures passes standard freeze-thaw tests, does not shrink unusually, does not contain harmful alkalis, and does not produce irregular hydration products. Field tests clearly demonstrated that working with these new admixtures requires no new skills. The concrete can be mixed at lower temperatures, saving energy. The admixtures are easily dosed into the mixing trucks, as is normal practice today, and concrete is finished in the usual manner. Estimates show that the two prototype admixtures can extend the construction season by as much as three months in the contiguous United States. The prototype has proved that low-temperature admixtures are possible. The industry partner sees the need to develop admixtures that will work to -10 deg C before going commercial with this technology.
The thermal protection requirements for cold weather masonry, as established in current industry specifications, were evaluated. Experiments were conducted to define the most relevant factors in the process of freezing of newly placed mortar. The effect of unit absorption on the moisture content of mortar during the first hours after assembly was assessed. Correlations of moisture content with time were developed for mortar in contact with masonry units. Frost immunity thresholds in terms of mortar moisture content and in terms of maturity were determined. The test results provided the basis for new proposed guidance on when fresh mortar can be safely exposed to freezing temperatures. Test methods for evaluation of the freeze thaw resistance of masonry units were evaluated. A new test was proposed and adopted by ASTM as a new standard test for the freeze thaw testing of masonry units. In addition, several chemicals were evaluated for their potential as antifreeze admixtures for masonry mortar. Antifreeze admixtures were first developed for use in concrete, but the practicality of using antifreeze admixtures in masonry mortars was demonstrated in a field application in Michigan during the winter.
Since the publication of the first edition ten years ago, significant developments have occurred in the use of admixtures in concrete. Eight new chapters and a full update of the preceding ten chapters bring this book up to date; reflecting the relative advances made in the science and technology of different groups of admixtures. The increased role and development of admixtures in concrete technology is evidenced by a number of conferences, publications, and novel admixtures available in the market place. These developments in the field caused the modification of many chapters in the first edition in order to reflect the advances. Although individual chapters refer to standards and specifications of admixtures, those only interested in the standards or techniques used in investigating admixtures will find the second chapter (Research Technologies, Standards, and Specifications) useful. Admixtures are not as inert as may be presumed. They may chemically interact with the constituents of concrete and affect the properties of the fresh and hardened concrete and its durability. The third chapter deals with these aspects. It was important to devote a chapter to recent attempts in developing new admixtures.
"Held October 20-23, 2003, in Berlin, Germany"--P. [4] of cover.