Evaluation of Effect of Chemical Admixture and Supplementary Cementitious Materials on Stability of Cement-Based Materials Using In-Situ Conductivity Method

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Title: Evaluation of Effect of Chemical Admixture and Supplementary Cementitious Materials on Stability of Cement-Based Materials Using In-Situ Conductivity Method

Author(s): C. Jolicoeur, K. H. Khayat, T. Pavate, and M. Page

Publication: Special Publication

Volume: 195

Issue:

Appears on pages(s): 461-484

Keywords: admixture; cement; silica fume

Date: 7/1/2000

Abstract:
There is presently a strong drive to minimize the amount of Portland cement used in cementitious systems replacing it to the extent possible with supplementary cementitious materials, such as silica fume, blast furnace slag or fly ash. Such an approach would enable the use of more and more environmentally friendly concrete. With respect to applications, construction practices continue to evolve towards minimum-labor technologies which are more reliable, and usually more cost-effective. Most of these applications require the use of chemical admixtures, such as water reducers, high-range water reducers, and in some cases viscosity-enhancing additives. With the increase in the replacement value of portland cement with supplementary cementitious materials and the growing trend towards using flowing concrete with high workability, it is critical to assess the risk of such mixtures to bleeding and segregation. This paper presents the results focusing the evaluation of the influence of dosage rates of high range water reducer, set retarder, and viscosity-enhancing admixture on the changes in stability of highly flowable cement-based materials. This characterization is undertaken using a newly developed method to quantitatively measure continuously and in-situ changes in the homogeneity of cementitious materials with time during their consolidation period. The method is based on monitoring the variation of electrical conductivity with respect to depth of the test sample and time using electrokinetic probe with multiple electrode pairs embedded at various heights and operating using a low voltage pulsating current at 1 kHz.