How to Measure Fly Ash in Liquid

Use simple laboratory procedures to measure fly ash.

Fly ash is considered particulate matter that can range from less than one micrometer to about 200 micrometers. Fly ash is formed in the atmosphere by condensation of gases. It is used to improve concrete performance by increasing its strength and durability and resistance to chemical deterioration. Fly ash is added to cement with water and fills the small spaces in concrete. making it more impervious. To add fly ash to cement, there are some necessary laboratory procedures to determine the fly ash carbon content and foam index.

Things You'll Need

• Fly ash sample
• Drying oven
• Muffle furnace
• Electric current source
• Hot foil instrument
• Balance
• Pipette
• 10% air-entraining agent
• Cement
• Cylindrical flask with lid

Instructions

Fly Ash Carbon Content and Loss of Ignition

1. Dry your fly ash sample in a drying oven.

2. Heat the ash to 750 C (1382 F) in a muffle furnace to get a loss of weight to evaluate the carbon content. Carbon decreases air bubbles in the concrete and protects it from freezing.

3. Weigh 100 mg of liquid fly ash on a balance. Make sure to tare the balance before placing the liquid on it. Dry the fly ash sample in a drying oven.

4. Heat the sample using an electric current or hot foil instrument to determine the loss of ignition. This will take about five to 10 minutes. Weigh the remaining sample on the balance.

Determining Foam Index of Fly Ash

1. Weigh 2 g of fly ash on a balance. Place the fly ash in a cylindrical flask that measures 40 mm multiplied by 80 mm. Place the lid on top.

2. Add 25 mL of distilled water to the flask. Wait five minutes and add 8 g of cement. Shake the flask for one minute to soak the cement and fly ash.

3. Pipette 2 mL of 10% air-entraining agent. Shake the solution for 15 seconds. Continue to pipette 2 mL of 10% air-entraining agent. Shake between each addition for 15 seconds, open the lid and observe the surface of the mixture. If foam appears on the liquid surface, the endpoint has been reached. The amount of air-entraining agent needed for the liquid to foam is considered the foam index for the fly ash and cement mixture.

4. Repeat the experiment above using 8 g of cement instead of fly ash to determine a foam index for the cement. Subtract the value of fly ash foam index from the cement foam index to obtain the correct foam index for fly ash. This measurement will serve as the correct amount of foam index for the fly ash.

References

• Idaho Department of Environmental Quality; Measuring Visible Emissions at Your Facility
• The Fly Ash Resource Center; Fly Ash Quality Control
• Headwaters Resources; Fly Ash for Concrete