An Approach to Quantitative Image Analysis for Cement Pastes
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specific features evaluated were (a) pores (in sizes above about 0.8 gim), (b) separately distinguishable calcium hydroxide particles, (c) residual unhydrated cement (normally within composite phenograins), (d) hydrated phenograins, consisting of both hydration shells and fully hydrated cement particles, (e) the combined composite phenograins, i.e. individual features of (c) plus (d), and (f) the C-S-H in the groundmass. In the remainder of this paper we refer to these features as, respectively, "pores", "CH", "UH" (for unhydrated cement), "HP" (for hydrated phenograins), "CP" for the combined composite phenograins and, and "GM" (for the solid constituents in the groundmass). The solid portion of the groundmass is quantitatively evaluated by difference, and not susceptible to geometric analysis. The analyses assayed included area fraction measurement (usual taken as equivalent to volume fraction measurement), and geometrical measurement of the individual features (particles or voids). Finally, we attempted to evaluate the effects of incorporation of superplasticzer on all of the parameters measured.
Fig. I BEI of polished plain cement paste (w:c 0.45, 100days) showing the groundmass and various recognizable phenograins. The encircled area is visibly porous groundmass. A is a partlyhydrated composite phenograin (the bright area is the unhydrated portion, the gray area is the hydrated portion). B is a smaller, fully hydrated phenograi, . C is an irregular CH phenograin. SPECIMEN PREPARATION Cement pastes of two w:c ratios (0.45 and 0.30) each with and without superplasticizer, were prepared following ASTM C 305. The pastes were all made from a single Type I portland cement, and the superplasticizer was naphthalene sulfonate used at a dosage level of 1% (solid superplasticizer) by weight of cement. All of the pastes were cured in saturated lime water at room temperature for 100 days, and then individual slices were cut from the middle of the paste cylinders. These slices were dried using acetone replacement, followed by vacuum drying, and finally by overnight oven drying.
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The dried slices were impregnated with ultralow viscosity epoxy resin under vacuum, and polished with diamond paste of progressively finer particle size, spread over Texmet polishing cloth. The finest diamond particle size used was 1 [tm. IMAGE ANALYSIS PROCEDURES The SEM - image analysis system consisted of a Akashi Beam Technology 55A scanning electron microscope and a Princeton Gamma Tech IMIX Version 7 image analysis system. Backscattered electron images were acquired at 15 KeV, using a 256 point per pixel averaging system. The images were acquired at 512 x 512 pixels, with the usual division into 256 gray levels. A standard magnification of 500x was used for quantifying all of the features except the capillary pores. For these, a higher magnification of 1000x was used, permitting tallying of pores down to approximately 0.8 gtm diameters in the feature analysis. For area fraction measurement, a sufficient number of fields must be measured
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