(Received 21 November 2005; accepted 23 May 2006)
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This paper describes the steps taken from development to full implementation, of the three most used concrete mixes, replacing 20% of the cement with ASTM-618 class C fly ash. A testing program was developed to identify the most critical variables that affect the performance against cement replacement, the variables were type of high range water reducer admixture and two types of fly ash. The second part of the program consisted of pouring a significant volume of concrete, using actual production practices, in order to obtain a history of 30 consecutive compressive strength tests per mix. A key factor on the success of this program was the use of a new generation of polycarboxylate admixtures, high early strength-high range water reducers, necessary to provide the required fluidity while reducing the watercement ratio without retarding the setting time. With the incorporation of a non-chloride accelerator, early compressive strengths up to 4200 psi (29 MPa) at 12 h were obtained. Since implementation, 6 months ago, the use of cement has been reduced by 4 600 000 lbs (2 100 000 kg) for the same volume of concrete.
Director of Research and Development, Rocky Mountain Prestress, Denver, CO
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