The Reactivity of C109 Sand: A Closer Look
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THE REACTIVITY OF C109 SAND: MICHAEL W. GRUTZECK Materials Research Laboratory, Park, PA 16802
A CLOSER LOOK
The Pennsylvania State University, University
ABSTRACT It was observed that standard ASTM C 109 sand (St. Peter Sandstone) from working quarries in the Ottawa area (northeastern Illinois) is nearly always sub-angular to rounded, frosted in appearance, and occasionally covered with localized, relatively large, terminated quartz overgrowths. At higher magnifications the frosted surface of the quartz sand was found to consist of a thin layer of micron-sized, coprecipitated quartz crystals and occasional kaolinite flakes. Upon reaction of the sand with either a saturated Ca(OH) 2 solution or as part of a sand-cement paste, some of these features were preserved, whereas others were lost. Micrographs of sand cured in cement paste at 90'C are presented showing that the kaolinite flakes react and become "puffy" and rounded in appearance. Also, the smooth surfaces of the large, terminated quartz overgrowths are severely etched as a result of dissolution. Sand reacted at 38°C in saturated Ca(OH) 2 solution demonstrated more subtle effects, perhaps obscured by precipitated CaCO 3 and C-S-H on the surfaces of the quartz overgrowths. These results suggest that ASTM C 109 sand is not entirely inert, but exhibits a limited amount of temperature-dependent pozzolanic activity.
INTRODUCTION Standard ASTM C 109 sand (St. Peter Sandstone) from the Ottawa area is a characteristically well rounded, very pure silica sand used by cement technologists in their ASTM test procedures. The sand is quarried from deposits of the St. Peter Sandstone, one of the most widespread formations in the upper Mississippi Valley. The deposits are exposed due to erosion in Illinois, Wisconsin, Iowa, Minnesota and Missouri [1]. The St. Peter is a friable, remarkably pure, moderately to well-sorted sandstone. The sand grains are normally frosted in appearance and have secondary quartz overgrowths (both as superficial crystals, covering the entire surface, and as large, terminated single crystals) [2-4].
EXPERIMENTAL METHODS The sands described in this ýaper were obtained from three working quarries in northeastern Illinois . Samples consisted of water-washed and sieved material that had been processed to remove the majority of the clay from the sand grains. Whenever possible, the requested samples were sized and graded according to ASTM C 109. 10 Specimens were examined using a scanning electron microscope (SEM) equipped with an energy-dispersive x-ray analyzer (EDX). Mineralogies of both the sand and the clay fractions were verified by x-ray diffraction. Microstructures of the three sands were found to be similar, so the 9
The Ottawa Silica Company and the Unimin Corporation (both in Ottawa) the Wedron Silica Corporation (in Wedron). 101SI DS°I30.
Mat. Res. Soc. Symp. Proc. Vol. 85. 1987 Materials Research So
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