Aluminates and Free Lime

Sodium hydroxide—ethyl alcohol solution is prepared with 2.5 g of sodium hydroxide plus 40 mL of water plus 10 mL of ethyl alcohol. If the contact of the polished surface with the solution is more than roughly 20 seconds, a deposit from a reaction between hydroxide and aluminate forms that buffing will not remove. CjA turns blue. If determination of alkali sulfates is desired, stain only one time for approximately 10 seconds, washing with 1 1 ethyl alcohol water solution, followed by isopropyl alcohol. Do not buff. This treatment will darken alkali sulfates slightly and with prolonged treatment (as for CjA) will dissolve the alkali sulfate, producing a dark void. 

Potassium hydroxide solution (0.1 molar aqueous) can be applied in single drop fashion or in a small puddle on a polished surface for 30 seconds. Rinse with an isopropyl alcohol spray and dry with forced warm air. C A and alkali-aluminate stain blue-brown, alkali sulfate darkens, and free lime turns brown. 

Boiling sodium hydroxide solution (10% by mass) will turn calcium aluminate blue or brown in 20 seconds in a high-alumina cement. Etching 30 seconds with a 1% borax solution turns Cj2A gray (Long, 1983). 

Warm distilled water (40°C) in 5 to 10 seconds turns aluminates blue to brown, alite light tan, free lime multicolored, and does not affect belite. 

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Fly ash is composed of tiny spherical and ellipsoidal beads and bubbles of glass, typically containing other phases. Other common constituents are irregular carbon particles, hematite, magnetite, tridymite, cristobalite, quartz, mullite, and spinel. It may contain small amounts of belite, aluminate, and free lime. The RI of the glass is 1.50 to 1.63. 

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