Demonstration 4

It's Heating Up!

Objective: The purpose of this demonstration is to track the temperature changes that occur during the curing process of concrete.

Materials and Supplies:

• fresh cement-- use at least 100 grams for best results
• thermometer
• insulated container with a cover
• drinking straw
• plastic cup to hold cement

Suggestions:

1. Use 150 grams of cement and 75 mL of water in a 6 ounce yogurt container or other plastic container.
2. Use an insulated 1 quart drinking mug or place the sample in a plastic bottle which is set inside a child's thermos. The thermometer is inserted into a one-holed rubber stopper which fits the thermos. Alternatively, the sample bottle can be placed in a box filled with Styrofoam. Another option would be to use a coffee can. The space inside the can could be packed with insulation, and the outside could be wrapped in pipe insulation. A hole can be cut in the coffee can lid to accommodate the thermometer.

Procedure:

1. Fill the container with fresh concrete, using aggregate is not necessary.
2. Fold over an inch of the drinking straw and tape closed. Insert thermometer into straw.
3. Place the filled container into an insulated container. Insert the drinking straw housing the thermometer into the center of the concrete. Place the lid securely on the container.
4. Record the temperature every 5 minutes for 20 minutes. Most of the change will occur in the first 15 minutes but will continue throughout the whole curing period.

Optional Procedure:

1. Repeat experiment using an admixture, such as calcium chloride, which speeds up the process (Use 2 % of CaCl2 by weight of cement )
2. Attach the apparatus to a computer thermocouple that will record the temperature changes for the class over a day.

Expected Results:

You should see an increase for 4 hours, most of which is observed within the first 15-20 minutes. The larger the mass of concrete the higher the temperature rise. 500 grams of concrete should give a rise of about 10[[ring]]C if well insulated. 150 grams of cement gave a 4 [[ring]]C change.