Monitoring of Fluctuations in the Physical Properties of a Class C Fly Ash
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MONITORING OF FLUCTUATIONS IN THE PHYSICAL PROPERTIES OF A CLASS C FLY ASH SCOTT SCHLORHOLTZ, KEN BERGESON and TURGUT DEMIREL Department of Civil Engineering, Iowa State University, Ames, IA, 50011 Received 1 November,
1986; refereed
ABSTRACT The "quality" of fly ash produced during 1985 at Ottumwa Generation Station, was evaluated by two different experimental programs. The first consisted of the physical tests specified in ASTM C 311; these results are applicable to the use of fly ash as an admixture to portland cement concrete. The second consisted of monitoring the changes in the physical properties of fly ash pastes; these results would be applicable to the use of fly ash as a grout or a soil base stabilization agent. The physical properties monitored during the testing program were compressive strength, volume stability and setting time. In general, the results obtained from the two testing programs were quite different. When using testing procedures defined by ASTM C 311 the fly ash appeared quite uniform, but results obtained from the fly ash pastes were quite erratic. It was found that compressive strengths of the pastes can vary by a factor of five in rather short periods of time. INTRODUCTION An investigation has been made of various physical properties of fly ash produced during 1985 at a coal fired power plant located near Ottumwa, Iowa. The fly ash has a high-calcium content (ASTM Class C) and is self-cementitious. Power plant details and bulk ash properties have been presented in another paper at this volume [1]. The purpose of the investigation was to: (1)measure the physical properties (i.e., strength, volume stability, etc.) as a function of sampling time in an effort to define the variability of the fly ash; (2) assess the potential of the fly ash as a construction material when it is used as the primary cementing agent (i.e., grouts or road base stabilization). EXPERIMENTAL PROGRAM Fly ash samples were obtained from Ottumwa Generating Station (OGS) using a sampling frequency as prescribed in ASTM C 311 [2]. Grab samples were taken from each ash truck exiting the power plant (i.e., each grab sample represented about 20 tons of ash). The trucks were loaded pneumatically from a single silo (3500 ton capacity). After 20 grab samples had accumulated, they were combined to form a composite sample which represented 400 tons of fly ash. The final sample volume was approximately one gallon. Each sample received by the Materials Analysis and Research Laboratory (MARL) was subjected to physical testing as described in ASTM C 311 [2]. The physical tests required by C 311 are moisture content, loss on ignition, pozzolanic activity, specific gravity, fineness and autoclave expansion. As described in an earlier paper at this volume [1], we no longer use the lime pozzolanic activity test (described in ASTM C 311) for monitoring the pozzolanic activity of high-calcium (Class C) fly ashes. Instead, AASHTO specification M 295-841 [3] has been adopted and Type I portland cement is being used to assess the pozzola
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