Image Analysis of Fly Ash in the Characterization of the Shape of the Grains
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M. BARRIOULET, H. CROS, B. HUSSON, E. RINGOT
LMDC INSA/UPS Gdnie Civil,complexe scientifique de Rangueil 31077 Toulouse FRANCE
ABSTRACT Fly ash from power stations is used as concrete additive to improve strength and durability. Surprisingly, studies of ashes of identical mineralogical composition from two different places have reported different results in terms of the rheological properties of the fresh material. The viscosity of the pastes made from these different fly ashes seems to be linked to the proportion of spherical and smooth-shaped grains found in them. A quantitative image analysis was carried out to characterize the shape of the grains of these two ashes from different geographical origins. The main result proves that the higher the glassy particle content of the fly ash, the more the hydraulic matrix is fluid. INTRODUCTION Construction engineers had planned to use fly ash from the Le Havre (France) thermal power station, as an additive to concrete. However just before getting down to work, the fly ash from Le Havre became unavailable. They were advised to use fly ash from the Cordemais (France) power station since it produced the same type of silico-aluminous ash (class F) [1] [2]. They soon noticed that the consistency of the Cordemais fly ash based concrete was completly different from the Le Havre type. The former concrete proved to be too dry , so they abandoned the fly ash option and decided on another solution. The present researchers decided to find out why this phenomenon occured. The mechanism governing the flow of a powder mixed with water depends mainly on the surface forces resulting from the electric state of the environment. The mineralogical nature of the surfaces and the specific area of the powder are the main parameters inducing the rheological behaviour of the paste. But it was observed that, besides the same mineralogical composition (Figure 1), the grain size distribution (Figure 2), the chemical composition (Table 1) and the specific area (Table 2) were nearly the same. But in point of fact two different rheological behaviors were noticed, when the fresh paste flowed through a nozzle such of the Marsh cone type, the Le Havre fly ash based paste being more fluid (Figure 3). We started a study to define whether the morphology of the grains could be the main cause of the phenomenon. Image analysis was used because a simple microscopic observation cannot determine which one of the two powders contains more glassy grains or smooth-shaped grains which could flow easier than rough-shaped grains. In this paper we present the procedure worked out to obtain binary images of grain boundaries. Subsequently we present the tools we chose from the range of those already known, of shape analysis. Finally we present the limited results of the global investigation that we are carrying out and that is for the present still incomplete.
125 Mat. Res. Soc. Symp. Proc. Vol. 370 01995 Materials Research Society
Table 1: Chemical Analysis Constituents
Table 2: Physical Analysis Test
Le Havre
Co
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