WATER RATIOS FOR PORTLAND CEMENT SLURRY
To show the effects of varying amounts of mixing water on the physical properties of Portland cement. These properties are Free Water Separation, Normal and Minimum Water Content and Thickening Time.
The Atmospheric Consistometer
The Atmospheric Consistometer consists of a Stainless Steel Water bath that houses the slurry containers. An instrument panel houses components that allow control of the bath at any temperature from ambient to 93°C, and rotation of the slurry containers at 150 RPM. Units of consistency of the cement are directly indicated on the top dials of the slurry containers. The containers are rotated by engaging the pins of the lid in the slots of the rotator. The rotators have timing sprockets, belt driven by a gear-head motor. The belt also drives an impeller, which agitates the bath water. The motor should be turned off while engaging or disengaging the containers. Temperature is indicated and controlled by a Thermocouple actuated Potentiometric Type Temperature Controller. The Controller actuates a relay, controlling a 1,500- watt heater. Switches and Pilot Lights are provided as required by the operation. A dial thermometer indicates bath temperature when the temperature controller indicator is off the scale. The entire instrument has overall dimensions of 15″ (39 cm) wide x 15″ (38 cm) deep x 19″ (48 cm) high.
(A) FREE WATER SEPARATION:
- Weight out 400 grams of cement into each of three quart jars. The dry cement sample should be passed through the sieve in order to remove lumps and foreign materials. The cement temperature should be 80 + °F.
- Prepare 170 cc, 190 cc and 210 cc of sweet water into three 250 graduate cylinders. This amount of water will produce cement slurries with water to cement ratio of 0.425, 0.574, 0.525 by weight.
- The blender to high speed, and mix the slurry for 35 seconds. Add the cement samples to the three water volumes in a metal quarts while the mixer was on low speed. When all cement has been added, turn the blender to high speed, and mix the slurry for 35 seconds.
- Pour 225 c.c. of slurry into 250 c.c.- graduated cylinder. Tightly cover them with aluminum foil. Allow to stand for two hours.
- Carefully decant the free water and measure in a 10 c.c. graduated cylinder. Do this for each slurry. Calculate the per cent (%) free water upon settling.
(B) NORMAL & MINIMUM WATER CONTENT OF CEMENT SLURRY:
- Prepare 4 slurry samples of varying water to cement ratios, as described in part (A) 1 & 2.
- Pour the samples immediately into an Atmospheric Consistometer and stir for a period of 20 minutes, under ambient conditions.
- Record the Consistency immediately after 20 minutes of stirring has elapsed.
- Determine the Normal and Minimum Water Content.
Normal Water Content
This is the water content of slurry yielding a consistency of 11 Bc.
Minimum Water Content
This is the water content of slurry yielding a consistency of 30 Bc.
(C) THICKENING TIME TEST:
This is the amount of time necessary for the cement slurry to reach a consistency of 100 Bc or poises, at different well temperature, depth and pressure conditions. It also represents the length of time the slurry is pumpable.
After the cement slurry (Sample 1 Part (B)) is prepared, pour it immediately into the Atmospheric Consistometer and begin stirring.
Record the consistency after every 4 minutes. Tabulate the results in the appropriate table.
Plot the Consistency in Bc versus time on a log-log paper and extrapolate the straight time to 100 Bc, to determine the thickening time.