Gypsum Seting Time

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Faculty of engineering
Civil engineering department

ENCS 314
Building material lab

Experiment No. 15&16
"Determination of water content used to prepare gypsum samples and the determination of the final setting for gypsum"

Prepared by: Rasha Abed 1031107

Partners:
Hazem No'man 1060155
Mohammed Hashlamoun 1060173
Ehab Alawi 1051449

Instructor: Ms. Randa Al- Asmar

Date of experiment: 25-03-2008
Date of submitting: 01-04-2008

"Determination of water content used to prepare standardized gypsum samples and the determination of the final setting for gypsum"

Introduction:

In civil engineering, gypsum plays a role as a building material that contributes to many products such as cement and plaster. In this experiment, we investigated some properties considering hardening of gypsum, such as the standard water content and setting time.

Aim of the experiment:

- Determination of the proper water content to prepare gypsum paste samples

- Determination of the final setting time for gypsum paste.

Theory:

Standard water content: amount of water added to gypsum to form a paste that'd allow the pointer of Vicat's apparatus to descend to a point (30-32) mm above the base of the mold.

Setting time of Gypsum: the amount of time that passes from the moment of adding water to the gypsum paste (would be already determined); to the moment that Vicat's needle would descend to reach 3 mm above the base of the mold.

Apparatus:

• Determination of the water content:

- Vicat apparatus
- Balance
- Metal tray
- Graduated cylinder

• Determination of the setting time for gypsum:

- Vicat's apparatus (the pointer is replaced by Vicat's needle of 10 mm diameter. - Stop watch

Procedure:

• Determination of the water content:

1. A 200 gm sample of gypsum is prepared, and put over a plate, to be added with a specified amount of water.

2. The gypsum is mixed thoroughly with water for 3 minutes, to form a moist paste.

3. A part of the paste is poured in the Vicat's mold, until the mold is filled completely with the paste and the surface of the mold is rimmed.

4. Vicat's mold is applied on the base of Vicat's device. The pointer of the device is adjusted to just touch the surface of the mold, then left to fall freely under the influence of its weight.

5. The reading of Vicat's pointer is taken. This reading indicates the depth that the pointer has reached above the base of the mold.

6. The experiment is repeated using a new sample each time; until the standard water content is reached (Vicat's needle would reach a height of (30-32) mm above the base of the mold.

• Determination of the setting time for gypsum:

1. A 200 gm sample of gypsum is prepared. The amount of water determined in the previous experiment is added to the sample.

2. The gypsum is mixed thoroughly with water for 3 minutes, to form a moist paste, and then part of the paste is poured in the Vicat's mold, until the mold is filled completely with the paste and the surface of the mold is rimmed.

3. Vicat's mold is applied on the base of Vicat's device. The needle of the device is adjusted to just touch the surface of the mold, then left to fall freely under the influence of its weight.

4. The reading of the device's pointer is taken, until we reach a reading of 3mm. 5. The time needed for the needle of the device would descend to a height of 3mm above the base of the mold is recorded using a stop watch.

Data and calculations:

|measured depth |The amount |Trial no. | |from the base (mm) |of added water (%) | | |39...
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